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COMMITTEE ON NUCLEAR SCIENCEL. F . CUR -, Ck a J ~ ROBLEY D. EVANS, Vh Ct in na sNa tion al Bu r ea u of ~a nla Ma ma oh u em a In st it ut e of Te oh u olo gy

J . A. IWUREN , S e c r d u r yWeWl@mue E le ot r lc C or p r a tlo nC. J . BO~M R I* Na d ooa l La b or a t or yR OBE RT G. 00CH RANTexa n &@xh um l a n d Mech an ica l

S AMUE L E P ST EI NC alifo rn ia I ne ti t u w o f T eo hu o lo gyU. F ANONa t i ona l Bureau of StudadaH ER BE RT GO-E D?Nu olea r Deve lop men t Co~r at lon of

Ame r i oa

J . W. IRVINE,J R .M a ea a c h u ee t ca I ll la nw a d T eo hm log yE. D . I UEMANo rt lm eu t em Un t ve ra lWW. WAYNE ~~Un tve r slv of Mk h lga nJ . J . NICKSONM em o r ia l H oE J@t a l, NOW YorkR OBE RT L. P LATE MANIa bm vlt oir e & Ch hn ie P h y81q ueD. M. VAN P A77ERBa r t ol R ea ea ro h F ou d ulon

LIAISON MEMBERSP AU L C . AE BE R&XiO CHAR LE S K. HEE DAtOm io En e r gy Com n lion ion U. S . Air F om eJ . H OWARD MO~EN WIIJJAM E . WR IG HTN at io n al S ole n ce F ou d a tlo n OH lce of Na va l R eoe am b

SUBCOMMITTEE ON RADIOCHEMISTRYW. WAYNE MEINKE , Ch fn w u x HAHOLD NIBBYU n lv er a lly o f M lc h lg an Ma d Uh cm a t or yGR EGOR Y R . CH OP - GEORGE LEDDICOITE F lo rld a S ta te Un lv en 9i~ Oa k R - Na t ion a l La b om tor yGEORGE A. COWAN J ULIAN N IELSENLoa Ak u oa 6Ci~1fi0 La bor a t or y Ha n t b r d La b or a t n r lenARTHUR W. FADLHALL ELLIS P . STE~EHG~n lvem i~ of Wa a h bgt on &gon n e Na t ion a l La b or a t or yJ E HOME H UDIS P ETE R C. STE VE NSONB ro ok h av en Na tio na l L ab or a to ry Un iv er si t y o f C alifo rn ia (L 1v er m or e)E AR L H YDE LE O YAF F EUn lv er n i@ o f Ca lifo rn ia (Be rk ele y) McGUl LIn lvare i lg

CONSULTANTSNATHAN BALL (XJ J AMES D eVO ECe nm a d E tu da d e lE ne r gle Nu cle air e U niv er si t y o f Mich ig auMol-Da & Ba lsIu m

WI LL IAM MAR LowNa tion a l Bu r ea u of Sm u da rd s


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The Radioc hem ist ry of t he Rare Gases

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FOREWORD

Th e Su bcomm it t ee on Ra d loch em ls t r y Is on e of a n umb er ofsu b comm it t e es w or k in g u n d er t h e Comm it t e e on Nu cle a r Sc ien cew it h in t h e Na t ion a l Aca d emy of Sc ien ce s - Na t ion a l Re se a r chcou n cil. I t s m emb er s r ep r esen t gover nm en t , Wdu s t r ia l, a h du n ive r s i t y la b or a t or ie s in t h e a r ea s of n u cle a r ch em ist r y en da n a lyt ica l ch em is t r y

Th e Su bcomm it t ee h a s con ce r n ed it se lf w it h t h ose a r ea s ofn u c lea r sc ien ce wh ich in volve th e ch em is t , su ch a s th e collec-t ion . a n d d is t r ib u t ion of r a d ioch em ica l p r oced u r e s , t h e es t a b -lishm en t of sp ec ifica t ion s for r a d ioch em ica lly p u r e r e a gen t s,a va ila b ili t y of cyclot r on t im e for se r v ice ir r a d ia t ion s , t h ep la ce of r a d ioch em is .t r y in t h e u n d e r gr a d u a t e college p r ogr am ,e tc .

Th is se r ie s of m on ogr a p h s h a s gr ow n ou t of t h e n eed foru p -t o-d a t e comp t la t ion a of r a d ioch em ica l in for m a t ion a n d p r o-c edu r e s . Th e Su bcomm it t e e h a s en d ea vor ed t o p r esen t a se r ieswh ich w ill b e of m a xim um u se t o t h e wor k in g sc ien t is t a n dwh ich con t a in s t h e la t es t a va ila b le in for m a t ion . F@ch m on o-gr a p h colle ct s in on e vo lum et h e p er t in en t in for m a t ion r eq u ir edfor -r a d ioch em ica l w or k w it h en in d ivid u a l e lem en t o r ac lose ly r e la t ed ,e lem en t s ,

An exp er t h t h e r a d ioch em ist r y of t h e p a r t ict ia rh a s w r it t e n t h e m on ogr a p h , follow in g a s t a n d a r d for m a tb y t h e Su bcomm it t e e . Th e At om ic~er gy Comm iss ion h a st h e p r in t in g of t h e se r ie s .

gr ou p of

e l emen tdeve lopedspon so r ed

Th e Su bcomm it t ee is con fid en t t h e se p u b lica t ion s w ill b eu se fu l n o t on ly to t h e r a d ioch em ist bu t a lso t o t h e r ese a r chwor k e r in ot h er fie ld s su ch a s p h ys ics , b ioch em ist r y or m ed icin ew h o w ish e s t o u se r a d loch em ica l t e ch n iq u es to so lve a sp ec ificp rob l em .

W. Wayn e Mein k e , Ch a ir m a nSu bcomm it t ee on Ra d loch em lst r y

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INTRODUCTIONTh is r ep or t d ea lin g w it h t h e r a d ioch em is t r y of t h e r a r e ga se s w a s p r e -

p a r ed a t t h e r eq u e st of t h e Su bcomm it t ee on Ra d ioch em is t r y of t h e Comm it t eeon Nu clea r Sc ien ce of t h e Na t ion a l Rese a r ch Cou n c il a sm on ogr a p h s on t h e r a d ioch em is t r y of a ll t h e e lem en tE .

Th e ea r ly se c t ion s of t h is m on ogr a p h a r e d evo t ed

on e of a se r ie s of

t o gen e r a l r e view s ofr a r e ga s p r op er t ied of in t e r em t t o t h e r a d ioch em im t a n d to som e gen er a l d is -cu ss ion of sep a r a t ion t e ch n iqu es for r a r e ga s e s . Th e la s t t h r e e ch a p t e r s a r er esp e ct ive ly a d iscu ss ion of t h e r em ova l o f r a r e ga se s fr om ta r ge t s , a d is -cu ss ion of t ech n iqu e s u sed for cou n t in g r a d ioa ct ive r a r e ga se s , a n d a co llec -t ion of r a d ioch em ica l p r oced u r e s for r a r e ga se s .

Th e a u t h or wou ld a p p r ec ia t e r e ce iv in g fr om r ea d e r s. a n y a d d it ion a l in -for m a t ion , p u b lish ed or u n p u b lish ed , w h ich sh ou ld b e in clu d ed in su ch a r ep or ton t h e r a d ioch em ist r y of t h e r a r e ga se s .

Th e a u t h or t a k e s t h is op p or t u n it y t o a ck n ow led ge t h e a ,b le a ss is t a n ce ofMr . R . A. d a Ro za in t h e p r ep a r a t ion of t h is m on ogr a p h .

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CONTENTSFor ew or d . . . . . . . . . . . -11In t r od u c t ion . . . . . . . . . . . iv

I . Gen er a l R e fe r en ce s P e r t in en t t o Ra r e Ga s Ra d ioch em ie t r y . 1I I . Ta b le of Iso t op e s of He , Ne , A, Kr , Xe , a n d Rn . . 2I I I . R ev iew of F ea t u r e s of In t e r es t in Ra r e Ga s Ra d ioch em i E t r y . 5IV. Samp le Solu t ion a n d Exch a n ge w it h Ca r r ie r s . . . 27V. Cou n t in g Ra r e Ga s Act iv it ie s . . . . . . 29VI . Collec t ion of Ra d ioch em ica l P r oced u r es for t h e Ra r e Ga se s

P r oced u r e 1 Remova l of Kr a n d Xe fr om Air a n dTh e ir Su b seq u en t Sep a r a t ion . .

P r oced u r e 1 A Remova l a n d Sep a r a t ion of Kr a n d XeF iss ion P r od u c t s fr om U 235 Ta rg e t s

P r oced u r e 2 Th e Ext r a c t ion , P u r ifica t ion a n d85In d u s t r ia l UBee of Kr . . ,

P r oced u r e 3 Ra p id Rem ova l of F iss ion P r odu c tKr fr om U Foil . . . .

P r oced u r e 4 Recove r y of F iss ion P r od u ct Xefr om UMet a l . , . .

P r oced u r e 5 Ra p id Rem ova l of F iss ion P r od u ct Xefr om U03 or U02(N03)2 . 6 H 20 Ta r ge t s

P r oced u r e 6 Sep a r a t ion of Lon g-lived F iss ion Ga se sP r oced u r e 7 Rem ova l of Rn fr om Th Ta r ge t s a n d it s

Collec t ion on t h e Ca t h od e of a Disch a r geTu b e . . . . . .

P r oced u r e 8 De t e r m in a t ion of Act ive Ga s Ha lf-live sby t h e Ch a r ged Wir e Tech n iqu e (I I) .

34

34

40

43

. 46

46

4848

49

51

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The Radiochem istry of the Ra reFLOYD F . MOMYER , J R

L aw r e n c e R ad ia tion La bor at or yUn ive r sit y of CaUfor rd aL iver mor e, Ca lifor n ia

Gases

I . GENERAL REFERENCES P ERTINENT TO RARE GAS RDIOCHEMISTRYH. R emy, Tr e a t ise on Ln or ga n ic Ch em is t r y , VO1. I (t r a n s la t e d by J . S.An d e r son ), E lsev ie r P u b lish in g Co, , New Yor k (1956).S . Du sh m an , Va cu u m Tech n iq u e , J oh n Wiley a n d Son s , New Yor k , 1949.R . T. Sa n d e r son , Va cu um Ma n ip u la t ion of Vola t ile Comp ou n d s , J oh nWiley a n d Son s In c . , New Yor k ( 1948).R . E . Dod d a n d P . L. Rob in son , Exp e r im en t a l In or ~a n ic Ch em is t r yCh a p . 2, E lsev ie r P u b lish in g Co. , New Yor k (1954).S. Br u n a u er , Th e Ad sor p t ion of Ga se s a n d Vap or s , Vq l. .1, I P h ysica lAd sor p t ion , P r in ce t on Un ive r s it y P r ess , P r in ce t on , N, J . (1942),A. I . M. Keu lem a n s , Ga s Ch r om a t ogr a p h y , Re in h o ld P u b lish in g Co. ,New Yor k , 1959, 2n d ed it ion .Law r en ce A. Welle r , llTh e Ad~or p t ion of Kr yp t on a n d Xen on on Act iva t edC h a r c o a l .- A Bib liogr a p h y , I I M ou n d La bor a t or y r ep or t MLM- 1092,Miam isb u r g , Oh io , 1959.A. Gu t h r ie a n d R . K, Wa k er lin g, ed it or s , Va cu u m Equ ipm en t a n d Tech -n iq u es , Na t ion a l Nu c lea r En e r gy Ser ies , Div . I , Vol. 1, McGr aw -HillBook Co. , blC, , New Yor k , 1949.C . D. Cor ye ll a n d N, Su ga r m a n , ed it o r s, R a d ioch em ica l St u d ies : Th eF iss ion P r od u ct s , Na t ion a l Nu c le a r En e r gy Se r ie s , Div . IV, Vol. 9,~ook a 2 a n d 3, McGr aw -H ill Book Co. , In c . , New Yor k , 1951. P a p e r s64-70, 139, 141, 145-50, 154, a n d 311-17.

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I I . TABLE OF ISOTOPES OF HELIUM, NEON, ARGONKRYP TON, XENON AND RADON ,*

Isot op e Ha lf -life Typ e of Deca y Met h od of P r ep a r a t ion

He3

He4He6Ne18Ne9Ne20Ne21Ne22Ne23

Ne24A35A36A37

A38A39A40A41

A42Kr76Kr77Kr78Kr79

Kr80

St ab le (a bu nd an ce( abundance

St ab le (a bu nd an ce-0.8 sec1.6sec-18 se cSt ab le (a bu nd an ceSt ab le (a bu nd an ceSt ab le (a bu nd an ce-40 sec

3.38 m in-1.8 se cSt ab le (a bu nd an ce-35 d a y

St ab le (a bu nd an ce-265 yrSt ab le (a bu nd an ce-110 m in

~3.5yr9.7 h r-1.2hrSt ab le (a bu n da nce34,5hr

St a b le (a bu n d a n t e

1.3 X10-4 ~Oa tm os . ) Na t u r a l1. 7X10-5% we lls)-looyo)

P -P +P +

90. 92%)0.257 ~,)8 . 8 27 )

P -

P -P +

0.337%) EC

O. 063%)P -

99. 60070 )P -

P -EC

Na t u r a lBe9(n , a )F 19(P F 2n )F 19(p , n )Na t u r a lNa t u r a lNa t u r a lNe22(n , y); Ne22(d , p );Na 23(n , p ); Mg26(n , a )Ne22(t , p )S32(a , n ); C135(p , n )Na t u r a lS34(a , n ); C137(d , 2n );C137(p , n ); K39(d , a );Ca 40(n , a )Na t u r a lA38(n #y); K39(n F p)Na tu r a lA40(d , P ); A40(n , Y);K41(n , p )A41(n )~); p a r en t K 42Y89(p , sp an )

EC-20~0, ~+ -80910 Se74(a , n )o . 3 54 7,) Na t u r a l

EC 957, ~+57 Se76(a , n ); Br 79(d , 2n );Br 79 (p , n ); Kr 78(d , p );Kr 78(n , y )

2. 2 7~0 ) Na t u r a l

*Lis t ed a r e t h ose n u clid es h a vin g a n IIAII o r I IBII c la ss ifica t ion in llTa b le ofIso t op e s, D. St r om in ger , J . M, Holla n d er a n d G. T. Sea b or g: Revs . Mod .P h ys . 30, No. 2, P a r t I I , Ap r il 1958. F u r t h e r in fo rm a t ion a n d r e fe r en ces t ot h e or i~n a l li t e r a t u r e m a y be fou n d in sa id a r t icle ,

2


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TABLE OF ISOTOPES OF He, Ne , A, Kr , Xe , a n d Rn , (Cen t d ]

Isot op e Ha lf - life Typ e of Deca y Me th od of P rep a r at ion

Kr81Kr 1Kr82Kr83m

Kr83Kr84Kr85m

Kr85Kr86,Kr 87

Kr88Kr89Kr90Kr9Kr92Kr93Kr94Kr97xe121xe122xe123xe124xe125m

xe125xe126xe127

-10 .se c IT2.1X105 yr ECSt a b le (a bu n d a n ce 11. 56~0)114 m in IT

Sta b le (a bu n d a n ce 11, 557.)St a b le (a bu n d a n ce 56. 90!70)4.36 h r ~-78~0, IT 22~0

10.3 yr P -St a b le (a bu n d a n ce 17. 377.)78 m in

2.8hr3 m in33 a ec9.8 se c3. Osec2.0 se cl,4sec1 se c40 m in20 h r2 h rSt ab le (a bu nd an ce55 a ec

18.0 h rSt ab le (a bu nd an ce75 se c

P-i=P-f3-P-FFP-P-P+ECEC, f3+

O. 096~,)IT (?)

ECo . 0 90 7,)

IT

Br s l(p , n ); d a u gh t e r Rb 81Kr80(n,y)Na t u r a lSe80(a , n ); Kr 82(d , p );Kr 82(n , y); x-r a ys on

. Kr 83; fi ss ion U, d a u gh t e rBr83 ; ~a u gh t e r Rb83Na tu r a l; fis s ion UNa tu r a l; fi ss ion USe82(a , n ); Kr 84(d , p );Kr84 (n , y); Rb 85(n , p );Sr 88(n , a ); fis sion U,d a u gh t e r Br 85Kr 84(n , y); fis s ion UNa t u r a l; fis s ion UKr 86(n , y); Kr 86(d , p );Rb 87(n , p ); fi ss ion UF iss ion U, ThF iss ion U, P uF iss ion U, P uF iss ion U, P uF iss ion U, P u , ThF iss ion U, P uF iss ion UF iss ion U, PU1127 (p , 7n )1127 (p , 6n )1127 (p , 5n )Na t u r a l1127 (a ,6n )Cs 125; d a u gh -t e r Cs125Te122 (a , n ) Xe 124(n , y )Na t u r a l1127 (a ,4n )Cs 127; d a u gh -t e r Cs lz7

(Ta b le Con t in u e s on p a ge 4)

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TABLE OF ISOTOPES OF He, Ne , A, Kr , Xe , a n d Rn . (Cen t d )

Iso tope H alf - life Typ e of Deca y Met h od of P rep a r at ion

~e127

xe128xe129mxe129xe130xe131mX=131~e132xe133mxe133

xe134xe135m

~e135

xe136xe137xe138~e139Xe 140xe141~e143Xe 1448Rn206Rn207Rn208Rn209~n210~n 21 1Rn 21 2~n215

36.41 d a y EC

Sta b le (a bu n d a n ce 1, 919L70)8.0 d a y ITSta b le (a b u n d a n ce 26. 447.)St a b le (a bu n d a n ce 4. 08~0)12.0 d a y ITSt a b le (a bu n d a n ce 21. 18%)St a b le (a bu n d a n ce 26. 89~~)-2.2 d a y IT5.270 d a y 13 -

St a b le (a b u n d a n ce 10. 4470)-15 m in IT

9.13 h r P -

St a b le (a bu n d a n ce 8. 8770)3.9min P -17 m in P -41 se c P --10 se c P --2 se c P -l. Ose c P --1 se c f3 --6 m in a 65~0, EC 35~0-10 m in EC 96~0, a 470-22 m in EC-80~0, a -20~o30 m in EC 83~0, a 17~02.7 h r a -96~0, E C-4~o16 h r EC 74~0, a26%23 m in a-10-6sec (e st . ) a

~e124 (a , n ); 1127( d ,2n )1127 (p , n ); Xe Iz+n,y)Na t u r a lxe128

(njy)Na t u r a lNa t u r a lxe131 (n , n ); fis s ion UNa t u r a l; fi s s ion UNa t u r a l; fis s ion Uxe132 (n , y ); fi s sion Uxe132 (n , y ); Xe 132(d , p );~e134 (n ,2n ); Te130(a , n );ca133 (n , p ); Be 136(n , a );fis s ion UNa t u r a l; fis s ion Uxe136 (n , 2n ); Xe 134(n , y);Ba138 (n , a ); fis s ion Uxe134 (n , y); Xe134(d , p );~e136 (n , 2n ); Ba 138(n , a );fis s ion UNa t u r a l; fis s ion U~e136 (n , y ); fis s ion UF iss ion UF ission U, ThF iss ion U, ThF iss ion UF iss ion UF iss ion U*U197 (N14, 5n )*U197(N14 , 4n )Sp a n Th ; P b (C12, s p a n ).-Sp a ll Th ; P b (C 1, sp a n )

12Sp a n Th ; P b (C , sp a n ). .Sp a n Th ; P b (C l, sp a n )Sp aU Th ; P b (C12, SP 1l)U-227 23 2

ch a in fr om Th(a , %)


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TABLE OF ISOTOP ES OF He, Ne , A, Kr , Xe , a n d Rn , (Cen t d )

I s o tope Ha lf-life Typ e of D eca y Met h od of P rep ar at ion

~n z 16

Rn 2

Rn 2

Rnz17

8

9

Rnzzo

~n zz 1Rnzzz

-10-4s e c (es t . ) a

10-3 se c a

0.019 se c a

3.92 se c a

51.5sec a

25 min ~- -80~, a -20~o3.8229 d a y a

~228 232ch a in fr om Th(a , 8n )~229 23 2ch a in fr om Th(a , 7n )~230 23 2ch a in fr om Th(a , 6n)Membe rcha inMembe rcha in

~235 d e c a y

Th232 d e c a y

Thz32 (p , sp an )Mem b er U238 d eca ycha in

I II . REVIEW OF FEATURES OF INTERESTIN RARE GAS RADIOCHEMLSTRY

Th e r a r e ga se s , Gr ou p O of t h e p e r iod ic t a b le , a r e h e liu m , n eon , a r gon ,k r yp ton , xen on , a n d r a d on ; He liu m a n d n eon p osse ss n o r a d ioa ct ive iso t op e sof h a lf-life lon g en ou gh t o p e rm it r a d io ch em ica l s t u d ie s in t h e or d in a r y sen se .On e ca n con ce ive s it u a t ion s in w h ich t h e sep a r a t ion of t h e r em a in in g fou r r a r ega se s fr om con t am in a n t s a n d fr om on e a n o t h e r m igh t b e n ece ssa r y. How eve r ,t h e m os t comm on p r ob lem by fa r is t h e sep a r a t ion of k r yp t on a n d xen on r e -su lt in g fr om fiss ion of h e a vy e lem en t s fr om ot h er fis s ion p r od u c t s a n d fr omea ch o t h er . Th e lit e r a t u r e on r a r e ga s r a d ioch em is t r y is la r ge ly con cer n edw it h t h is p r ob lem , a n d most d e t a iled d iscu ss ion in t h is m on ogr a p h w ill lik e -w ise cen t e r a r ou n d k r yp t on a n d xen on . As r a r e ga s sep a r a t ion s gen er a llyd ep en d on som e p r op er t y w h ich va r ie s g r ea t ly a n d in a r egu la r m a n n e r a s on ep r oce ed s t h r ou gh t h e gr ou p fr om h e lium t o r a d on , t h e fu r t h e r a p p lica t ion oft h e p r oced u r e to in clu d e o t h e r r a r e ga se s w ill o ft en b e s im p le if r eq u ir ed .

R ev iew s of t h e Ich em ica l p r op er t ie s il o f t h e r a r e g a se s w ill b e fou n d1in m os t t e xt s on in or ga n ic ch em is t r y . In a p r a ct ica l sen se , t h e r a r e ga se s

a r e ch em ica lly in e r t . Th ey w ill r em a in ch em ica lly u n a lt e r ed in a n y r e a c t ion sch osen t o q u a n t it a t ive ly r em ove im p u r it ie s ot h er t h a n r a r e ga s e s fr om t h em .

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Howeve r , r a r e ga s a t om s d o in t e r a ct w it h ot h ert h e ir n e igh b or h ood . Wh e th er t h e se in t e r a ct ion fich em ica l o r Iva n d er Wa a l!sr in n a tu r e is of n o

a tom s,. m olecu les , or ion s ina r e p r ope r ly con s id er edcon ce r n h e r e .+Th e exis t e n ce in d isch a r ges of sp ec ie s su ch a s HeH an d He2 h a s been+

e s t ab l i s h ed . Hyd r a t e s for t h e fou r h e a v ie r m em be r s of t h e gr ou p a r e k n ownt o ex is t , a n d so lu b ili t ie s of r a r e ga se s in a n umb er of so lven t s a r e r e la t ive lyh igh . Volu b ili t y in a g iven so lven t gen e r a lly in cr e a se~ w it h a t om ic n umb er oft h e r a r e ga s . A n umbe r of s t u d ies of r a r e ga s volu b ili t y d ep en d en ce on so l-ven t, t em pe ra tu re , a n d p a r t ia l p r essu r e of t h e r a r e ga s (Hen r yls law is a p -p l icab le over w id e r a n ges ) h a ve a p p ea r ed in t h e lit e r a t u r e . On e of t h e m or ecomp r eh en s ive s t u d ie s a lso ou t lin es a p r op osed sys t em for r ecover in g k r yp t ona n d xen on fr om ga s s t r eam s b y t h e ir a b sor p t ion in a cou n t e r -cu r r en t s t r e am

2of or ga n ic liq u id (k er osen e).in h a n d lin g r a r e ga se s , e sp e cia lly t r a ce r am ou n t s, on e d oes w ell t o

r em em ber th a t con t a ct w it h liq u id s or solid s (in clu d in g sys t em wa lls ) o rcon d en sa t ion fr om t h e ga s p h a se of ot h e r liq u id s or solid s m a y r esu lt in r e -m ova l of r a r e ga se s fr om t h e ga s p h a se t h r ou gh solu t ion , a d sor p t ion or p h ys -ica l occlu s ion . Th u s in qu a n t it a t ive wor k r a r e ga s ca r r ie r s a r e u su a lly a dd edfor essen t ia lly t h e sam e r e a son s th a t ca r r ie r s a r e a d d ed for sp ec ie s t o b esep a r at ed fr om so lu t ion s.

A se r ies of su b s t a n ce s k n own a s cla t h r a t es h a s r ece ived con sid er a b le3,4s t u d y , Cla t h r a t e s of a r gon , k r yp t on a n d xen on h a ve been p r ep a r ed b y

cr ys t a llizin g qu in ol u n d e r a n a tm osp h e r e of t h e r a r e ga s a t h igh p r essu r e .R a r e ga s a t om s a r e con t a in ed in ca ge s w it h in t h e r e ; u lt in g cr yst a l, t h en umbe r of t h ese ca ge s se t t in g a n u p pe r lim it on t h e am ou n t of r a r e ga s in t h ecr ys t a l (on e r a r e ga s a t om for ever y t h r e e qu in ol m olecu les ). Th e a ct u a lcon cen t r a t ion of r a r e ga e in t h e cr yst a l d ep en d s m a r k ed ly on t h e con d it ion s ofc r ys t a lliza t ion a n d is u su a lly con s id er a b ly le ss t h a n t h e t h eor e t ica l lim it .Cla t h r a t e s of fis s ion -p r od u ct k r yp t on h a ve r ecen t ly b een p r ep a r ed for u se a s

85 5sou r ce s of Kr ac t iv i ty . Th e p r ep a r a t ion d e scr ib ed in th e r e fe r en ce r e -su i t s in k r yp ton con cen t r a t ion s equ a l t o 25% of th e t h eor e t ica l lim it . Th i scor r esp on d s t o t h e con cen t r a t ion in t h e ga s p h a se a t a bou t 25 a tm osp h er e s

85 .p r essu r e a n d r esu lt s in 3 cu r ie s of Kr pe r gr am of cla t h r a t e (u s in g fis s ionp r odu ct k r yp ton wh ich is a bou t 5~0 Kr 85). Th e m a te r ia l m a y b e gr ou n d t o ap owd er w it h n o a p p r ecia b le loss of a c t ivit y a n d th e 10Ss on st a n d in g is on ly afew p a r t i p e r .m illion . p er d a y if t h e m a t e r ia l is p r ot ect ed fr om wa te r a n dot h er su b st a n ces wh ich d issolve qu in ol.

Th e ch em ica l op er a t ion s in volved in sep a r a t in g a n d p u r ifyin g r a r e ga se sa r e p er form ed on e lem en t s or compou n d s o th e r t h a n r a r e ga ses . Th e sep a r a -t ion of t h e r a r e ga se s fr om on e a n ot h e r m u st b e a ccomp lish ed on t h e b a s is ofd iffe r en ces in som e p h ys ica l p r op er t y (u su a lly va p or p r essu r e or ext en t of

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ad so rp t i on ) .r a t e som e or

It m a y oft en h a p p en t h a t t h is p h ys ica l sep a r a t ion w ill a lso sep a -a ll of t h e im p u r i t ie s o t h e r t h a n r a r e ga se s fr om a p a r t icu la r

r a r e ga s . Th u s it i s oft e n n e i t h e r n ece ss a r y n or m os t con ven ien t t o p u r ifyt h e r a r e ga se s ch em ica lly a s a gr ou p a s t h e fir s t s t ep or s t e p s in a r a d ioch em -ica l p r oced u r e . Dep en d in g u p on t h e con t am in a t in g sp ec ie s a n d t h e ir am ou n t sit m a y be p oss ib le t h a t n o ch em ica l op e r a t ion s wh a t eve r w ill b e n ece ssa r y .

Su b s t a n ce s w h ich m a y con t am in a t e r a r e ga s e s a r e lim it e d t o t h ose wh ichm a y exis t in a p p r ec ia b le con cen t r a t ion s in t h e ga s p h a se a t t h e t em p er a t u r e oft he exp er im en t . At sa id t em p er a t u r e t h is w ill in clu d e : 1) ga se s , t h e t e r mb e in g u sed h e r e t o d en o t e a p p r e cia b le am ou n t s of su b s t a n ce s a b ove t h e irc r it ica l t em p e r a t u r e or h a v in g va p or p r e ssu r es gr e a t e r t h a n 1 a tm osp h er e ;2) u n sa t u r a t ed va p or s , su b s t a n ce s w h ose va p or p r e ssu r es a r e le ss t h a n on ea tm osp h e r e bu t w h ich a r e p r e sen t in am ou n t s a p p r ec ia b le bu t sm a ll e n ou ght h a t t h e ir p a r t ia l p r e ssu r e s a r e le s s t h a n t h e ir va p or p r e ssu r e s ; a n d 3) sa t u -r a t e d va p or s in equ ilib r ium w it h so lid s or liq u id s h a v in g a p p r ec ia b le va p orp r e s s u r e s . Th e w or d Ia p p r e c ia b le lr in t h e fo r ego in g m u st of cou r se b e d e-fin ed in t h e con t ex t o f t h e exp e r im en t . Alt h ou gh t h e a b ove is a la r ge ca t egor y ,t h e n u mb e r of con t am in a n t s u su a lly en cou n t e r ed is q u it e sm a ll. Th e r a r ega se s m u s t oft e n b e p u r ified fr om t h e con s t it u en t s of a i r , fr om vola t ile sp e c ie sin vo lved in t a r ge t d isso lu t ion su ch a s h yd r ogen , h yd r ogen h a lid e s a n d o t id esof n i t r ogen , a n d occa s ion a lly fr om sm a ll am ou n t s o f h yd r oca r b on s a n d t r a ceam ou n t s o f e lem en t a l h a logen s . Me t h od s of r em ova l a r e lis t e d b e low for e a chof t h e se . Th e lis t i s b y n o m ea n s com p le t e a s r ega r d s m et h od s w h ich h a veb een or cou ld be u sed , bu t it is h op ed t h a t it is r e p r e sen t a t ive en ou gh t o b eusefu l .

1 ) Nit r ogen : Mole am ou n t s m a y be q u a n t it a t ive ly r em oved by r e a c t in gw it h t it a n ium sp on ge , 14-20 m esh a t 1000 -11 OOC. Use of low e r t em p e r a t u r es(e a . 850C) h a s b een r ep or t ed . 6 Oxygen is a lso r em oved qu a n t it a t ive ly .Qu a r t z o r ce r am ic fu r n a ce s a r e n ece ssa r y a s t h e se t em p e r a t u r e s a r e a b ovet h e soft e n in g p oin t o f P yr ex g la e s e s . Th e r ea c t ion is q u it e exot h e rm ic a n dso t h e t em p e r a t u r e m u s t b e m on it o r ed a n d flow r a t e of t h e ga s con t r o lled t op r even t d e st r u c t ion of t h e fu r n a ce . Ca lc ium h a s oft e n b een u sed sa t is fa ct o r ilyt o r em ove n i t r ogen (400 -5.00 C). Ca lc iu m d oe s , h ow eve r , t e n d t o b ecom ep a ss ive t h r ou gh for m a t ion of su r fa ce film s. F or sm a ll am ou n t s of im p u r it ie st h is p r ob lem is som e t im e s c ir cum ven t ed b y con d u ct in g t h e r e a c t ion in t h e ga s

7p h a se w it h Ca va p or . Cle a n u r a n ium t u r n in gs a t 800 C w ill a lso r ea ct w it hn it r ogen (a n d d ecom pose h yd r oca r bon s).

2 ) Oxygen : Will b e r em oved w it h n it r ogen in t h e a b ove r e a c t ion s . Oxy-gen a lso r ea c t s r a p id ly w i t h cop p er t u r n in gs a b ove 350C t o g ive CUO.

3 ) Hyd r ogen , ca r bon m on oxid e , ligh t p a ,r a ffin h yd r oca r bon s : P a ss a ge

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of t h e ga s s t r eam ove r CUO a t 500C w ill oxid ize HZ to H20 9 a n d CO t o C02r a p id ly. Hyd r oca r bon s w ill b e oxid ized in lik e m an n e r t o H20 a n d C02 bu t at em p er a tu r e of 900C is n ece ssa r y to a ch ieve r a p id r ea c t ion . Su b sequ en t r e -m ova l of oxygen m ay b e n ece ssa r y (a n d is ea s ily a ccomp lish ed ), if h igh en ou ght em p er a t u r e s a r e u sed t h a t t h e d issoc ia t ion p r egsu r e of oxygen over CUO becom esapp r e c i ab l e .

4) Wa t e r : In a dd it ion t o con d en sa t ion of wa t e r in cold t r a p s (a m et h odoft en n ot sp e cific en ou gh ), w a t e r m a y be r em oved b y p a ssa ge th r ou gh a n y on eof a n umbe r of d e sicca n t s . P 205, Mg(C104)2; a n d CaC12 a r e r ep r e sen t a t ive ,w it h equ ilib r ium p a r t ia l p r essu r e s of w a t e r ove r t h em a t r oom t em p e r a t u r e

-5Ofzx lo , 5 x 10-4, a n d O. 2 mm Hg r esp ec t ive ly . P 205 a n d CaC12 r ep -r e sen t t h e ext r em es of e ffic ien cy in comm on d es icca n t s . Ma gn e siu m p er -ch lor a t e h a s a ch ieved w id e u s e a s it is e ffic ien t en ou gh for p r a ct ica lly a ll p u r -p ose s a n d is e a s i ly r egen e r a t ed b y d is t illin g t h e w a t e r off in va cu o a t 220-C,Wh er e la r ge am ou n t s of w a t e r a r e in vo lved , ga se s a r e oft e n d r ied fir st w it hCaC12 t o r em ove most of t h e w a t e r a n d t h en w it h Mg(C104)2 t o r em ove r e -m a in in g t r a ces of m oist u r e .

5) Ca r bon d ioxid e : May be r em oved b y p a ss in g t h e ga s t h r ou gh a t r a pcon t a in in g Asca r it e , a gr a n u la r commer cia l p r ep a r a t ion wh ich is essen t ia llya sb e st os im p r egn a t ed w ith sodium hyd ro t i d e . Sofn olit e , or sod a -lim e , am ixt u r e of NaOH an d CaO ma y a lso be u sed . Sweep in g t h e ga s t h r ou gh asolu t ion of a lk a li m et a l h yd r ox id e is a lso e ffe ct ive . Solu t ion s a r e som et im e sle a s con ven ien t in va cu u m sys t em s t h a n solid m a t e r ia ls , h ow ever .

6) Hyd r ogen h a lid es : May be r em oved in th e sam e m an n e r a s ca r bond io t ide .

7) Oxid e s of n it r ogen : Dissolu t ion of t a r ge t s in n it r ic a cid w ill r esu ltin evolu t ion of N O, NO an d NO in va r yin g p r op or t ion s .2 2 N20 u su a lly occu r sin r e la t ive ly sm a ll am ou n t s . I t s r em ova l m a y be a ccomp lish ed by ca t a lyt icr ed u c t ion w it h h yd r ogen or by oxid a t ion t o NO by scr u b b in g t h e ga s w it h asolu t ion of s t r on g ox id izin g a gen t su ch a s p e rm a n ga n a t e . NO an d N02 m a yb e r em oved b y sweep in g th e ga s #t r eam t h r ou gh a so lu t ion of sod ium h yd r ox-ide . P e r fo rm in g t h e so lu t ion u n d er r e flu x w ill in fa ct wa sh a good p or t ion oft h e h igh er oxid es b a ck in t o th e d issolve r fla sk . I f a lt e r n a t e m et h od s of solu -t ion a r e a va ila b le it is oft e n m os t con ven ien t t o a void t h e u se of n it r ic a cid ,

8) Ha logen s : F r e e h a logen s a r e a ll r e la t ive ly vola t i le , a n d a ct ive h a lo -gen s m ay oft en be p r esen t in t r a ce am ou n t s in t a r ge t s fr om wh ich r a r e ga s esa r e t o b e r em oved . I f t h e so lu t ion p r oce ss lea ve s t h em p a r t ly or en t ir e ly int h e zer o ox id a t ion s t a t e , t h e ga s s t r e am w ill b e con t am in a t ed . Sw eep in g t h ega s th r ou gh a solu t ion of sod iu m h yd r oxid e w ill r a p id ly con ver t a ll t h e fr eeh a logen s t o n on -vola t i le sp e cies (h a lid e a n d h yp oh a lit e ). 10 Th e r a p id ex-ch a n ge of t h e h a logen s w it h t h e ir cor r esp on d in g h a lid e s in so lu t ion is a n ot h er

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11, 12u se fu l m ea n s of d econ t am in a t ion fr om t r a cer h a logen s . Iod in e is qu a n -t i t a t ive ly r em oved b y con t a c t w it h s ilve ru sed a s a t r a p p a ck in g for t h is p u r p ose).s o lu t i o n .

(si lve r ed Ra sch ig r in gs h a ve beenIod in e is r ed u ced to iod id e in NaHS03

Wh er e r e a ct ion r a t e s a r e S1OW en ou gh th a t p u r ifica t ion m a y n ot b e com -p le t ed in on e p a ss , it m a y b e n ece ssa r y t o c ir cu la t e t h e off g a se s fr om t a r ge td isso lu t ion t h r ou gh a p u r ifica t ion t r a in . Th e c la ss ic , a n d st ill m os t gen e r a llyu se fu l, d ev ice for cir cu la t ion (or t r a n sfe r ) o f ga s e s is t h e Toep le r p ump ,

13w it h wh ich r a t e s of a bou t a lit e r p er m in u t e m a y be ob t a in ed . Ot h e r cir cu la t -in g p ump s w h ich m ay b e u se fu l in p a r t icu la r in s t a n ces h a ve b een d e s ign ed .Th ese con sist essen t ia lly of a ch am b er d e sign ed t o p er m it on ly u n id ir e ct ion a lflow of ga s a n d a m ea n s of p r od u c in g p er iod ic p r essu r e ch a n ge s w it h in t h ec h amb e r . Alt e r n a t e h ea t in g a n d coolin g of t h e ga s in t h e ch am be r h a s b een

13u sed to a ch ieve flow r a t e s of O. 5 lit e r s p e r h ou r . An ir on p is t on en c losedin gla ss a n d e lec t r om a gn e t ica lly op er a t ed h a s p r od u ced r a t es o f a few lit e r s

14p er m in ut e , P r e ssu r e d iffe r en t ia ls d eve lop ed we r e . n ot n ot ed in t h e r e fe r en cebu t a r e p r oba b ly sm a ll. An o t h er a ch ieves s im ila r ly h igh flow r a t e s b y p u ls in gt h e ch amb er p r essu r e b y m ea n s of a m yla r d ia p h r a gm d r iven b y h igh p r e ssu r e

15ga s .Ult im a t e ly t h e r a d ioch em is t m u st con ce r n h im se lf w it h t h e p h ys ica l

p r op er t ie s of t h e r a r e ga se s . Ta b le 1 su mm a r izes som e d a t a w h ich m ay be16of in t er es t.

Ta b le 1

Atmosphe r i c(Volum e %)

a b u n d a n c e

Boi lin g P oin t ( C)Melt in g P oin t ( C)

At om ic d iam et e r inc r yst al (a ngs t rom s)

He Ne A~ Kr Xe w

5.25 1.82 0.934 1.14 8.7 6 x 10-18x 10 -4 Xlo -3 Xlo -4 Xlo -6

-269 -246 -186 -153 -107 -65-272 -249 -189 -157 -112 -71(25 a tm . )3.57 3.20 3.82 3.94 4.36 ----

Dis t i lla t ion a n d a d sor p t ion t ech n iq u e s a r e t h ose wh ich fir s t com e t o m in dfor sep a r a t ion of t h e r a r e ga se s . Th e p u r e r a r e ga s e s h a ve of cou r se b eensu ccess fu lly p r od u ced commer c ia lly b y t h e fr a ct ion a l d ist i lla t ion of a ir , w it ht h e excep t ion s of h e lium wh ich is ext r a ct ed fr om cer t a in Texa s n a t u r a l ga se sa n d r a d on wh ich is ob t a in ed a s a m emb er of t h e 4n +2 n a t u r a l r a d ioa c t ive d eca y

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s e r i e s . F r a ct ion a l d is t i lla t ion is d iscu ssed in m ost t ex t s on p h ysica l ch em -ist r y a n d t h e fr a c t ion a t ion of r a r e ga se s fr om a ir is d iscu ssed in n u m e r ou 8

17-20p la ce s . Glu eck a u f u sed a p r oced u r e com b in in g fr a ct ion a l d is t i lla t ion ofa ir a n d a d s or p t ion t e ch n iq u e s in t h e d e t e r m in a t ion of k r yp ton a n d xen on con -

21t en t s o f t h e a tm osp h e r e. I t i s ve r y ~lik e ly t h a t t h e r a d ioch em is t w ill h a ven eed to u s e su ch low t em p er a t u r e fr a c t ion a t ion co lum n s in t h e la bor a t or y sot h e r e w ill b e n o d iscu ss ion of t h e m et h od h er e .

On t h e ot h e r h a n d , s im p le d ist i lla t ion a n d con d en sa t ion p r oce sse s w illb e u sed in p r a c t ica lly eve r y exp e r im en t in t r a n sfe r r in g ga se s or e ffec t in gr ou gh se pa r at ion s. Th u s a p lot ( fo r low t ~m p er a t u r e s ) of va p or p r e ssu r e s a sa fu n ct ion of t em p er a t u r e for r a r e ga se s a n d o t h er vola t i le sp e c ie s comm on lyen cou n t e r ed t ill p r ove ve r y h a n d y to t h e r a d io ch em ist . Th e r ea d er is r e fe r -r e d t o t h e gen er a lly a va ila b le Ha n d book of Ch em is t r y a n d P h ys ics 22 for d a t an e cess a r y for su ch a p lot . Du s hman 2 3 (p a ge 781 e t seq . ) a lso t a bu la t e s va p orp r essu r e d a t a for a n um be r of su b s t a n ce s a t low t em p er a t u r e s. In or d e r ofd e cr ea s in g vo la t ili t y (d ecr ea s in g va p or p r essu r e a t a g iven t em p er a t u r e b e lowt h e cr it ica l t em p er a t u r e ) t h e comm on ga se s a r e N2, A a n d 02, Kr , Xe , Rna n d C02,, a n d H20. Ga se s lis t ed in p a ir s h a ve va p or p r es su r e cu r ves a t lowt em p e r a t u r es w h ich a r e ve r y s im ila r .

E fficien c ie s of p r oce sse s su ch a s t h e t r a n s fe r o f a ga seou s sp ec ies con -t a in ed in a sys t em t o a cold t r a p a t t a ch ed t o t h e sys t em a r e d e t e r m in ed by t h er e la t ion of t h e in it ia l p a r t ia l p r e ssu r e of t h e sp e c ie s in t h e sys t em t o t h e va p orp r essu r e of it s solid or liq u id a ft e r con d en sa t ion in t h e cold t r a p . As a n ex-am p le , t h e va p or p r e ssu r e of so lid Kr a t -195C is 2-3 mm Hg, so r ou gh ly99V0 of t h e Kr in a sys t em a t 20 cm Hg p r e ssu r e m a y be colle ct ed in a n a t t a ch edsm a ll cold t r a p a t - 195C . As liqu id n i t r ogen is gen e r a lly t h e co ld es t con -ven ien t ly a va ila b le r e fr ige r a n t , Kr is o ft e n m an ip u la t ed by con d en sa t ion a tt h is t em per a t ur e. Th e r esu lt a n t losse s , d ecr e a se w it h in cr e a s in g in i t ia l k r yp t onp r essu r e a n d m a y b e m in im ized b y u s in g t h e sm a lle s t sys t em s a n d t h e [a r ges tam ou n t s of k r yp t on ca r r ie r p r a c t ica b le -- u su a lly t h ey m a y be m a d e sm a lle n ou gh th a t t h e y a r e a ccep t a b le for t h e sa k e of sp e ed a n d con ven ien ce . I f on em u s t o f n e cess i t y collec t k r yp t on a t p r e ssu r e s comp a r a b le t o 2-3 mm Hg fr oma sys t em , h e m u s t r e sor t t o low e r t em p e r a t u r e r e fr ige r a n t s , r e fr ige r a t eda b sor b en t s su ch a s ch a r coa l, o r Toep le r p ump s . P r e sen ce of sm a ll am ou n t sof n on con d en s ib le ga se s m a y ser iou s ly low e r t h e r a t e s o f t r a n s fe r p r oce s s e asu ch a s t h e a b ove k r yp t on con d en sa t ion , d u e t o t h e r e la t ive s low n e ss of ga s -eou s in te r d iffu sion p roce sses . Th u s on e w ish e s a va cu u m sys t em w it h a b a sep r e s su r e or d e r s of m a gn it u d e lowe r t h a n t h e low es t va p or p r e ssu r e s in volvedin m an ip u la t ion s h e m ay w ish t o p er for m . Syst em s w it h b a se p r e ssu r e s of10-5 to 10 -6 mm Hg a r e e a s ily con st r u ct ed a n d w ill su ffice for t h e , r n am ip u la -

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t ion s in vo lved in m os t r a r e ga s r a d ioch em ist r y (a ssum in g th a t m a cr o r a t h e rt h a n t r a ce r am ou n t s a r e in volved ).

R emova l o f on ly th e le a s t vola t i le sp e cies fr om a ga s s t r e am is fe a s ib lew h en a t em p er a t u r e ca n b e fou n d a t w h ich it s va p or p r e ssu r e is su fficie n t lyle ss t h a n it s p a r t ia l p r essu r e in th e ga s s t r e am t h a t con d en sa t ion is e ssen -t ia lly comp le t e , wh ile t h e va p or p r e ssu r e s of ot h er con s t i t u en t s a r e h igh e rt h a n t h e i r p a r t ia l p r essu r e s over t h e t r a p : Ass um in g equ ilib r ium con d it ion sa n d in solu b ili t y of t h e ot h er sp e c ie e in t h e con d en sed p h a se , p a ssa ge of t h egq s s t r eam t h r ou gh t h e cold t r a p e ffe ct s t h e d e s ir ed sep a r a t ion qu it e s im p ly.Lf con d en sa t ion occu r s u n d er equ ilib r ium con d it ion s , t h e fr a c t ion of sp e cieslost (p a ss in g t h r ou gh t h e t r a p w it h t h e ga s st r eam ) i~ t h e r a t io of it s va p orp r es su r e a t t r a p t em p e r a t u r e t o it s p a r t ia l p r es su r e in t h e in flu en t ga se s . Toim p r ove t h e a p p r oa ch to eq u ilib r ium con d it ion s , flow r a t e s a r e lim it e d a n dcold t r a p s p a ck ed w it h som e m a t e r ia l t o p r ovid e a la r ge con t a ct a r e a a n d t op r even t m ech a n ica l b low -t h r ou gh of con d en sed m a t e r ia ls . Gla ss wool, b e a d sor r in gs a r e m a t e r ia ls common ly u sed for t h is p u r p ose . S t a in less s t ee l b a ils(3/16 in . ) com b in ed w it h su it a b le g la ss wool p lu gs h a ve a lso p r oved ver y sa t -i s fac to ry . Su ch a p a ck in g h a s t h e ,a d va n t a ge th a t t h e s t e e l m a y b e w a r m ed byt h e in d u ct ion of ed d y cu r r en t e in it t o a ch ieve r a p id a n d effic ien t r em ova l ofcon den sed m at er ia ls . T im e for t h e rm a l equ i lib r iu m t o be r e a ch ed in t r a p sm u s t a lw a ys be a llow ed be for e in it ia t in g ga s flow . As coolin g of t r a p p a ck in gsu n d er va cu um m ay b e q u it e s low , t em por a r y in t r od u c t ion of som e ea s ily r e -m ova b le ga s su ch a s h e lium to im p r ove h ea t t r a n s fe r is oft e n u sefu l.

Ln lik e fa sh ion seve r a l con d en sed m a t e r ia ls , of w id e ly d iffe r in g vola t il -i t ie s m a y oft en be sep a r a t ed by w a r m in g t o a su it a b le t em p e r a t u r e a n d d ist i ll in gt h e m or e vola t i le com pon en t s in t o a n o t h e r cold t r a p . I t i s oft en n ece ssa r y t om e lt a n d r e fr e e ze t h e con d en sa t e r em a in in g beh in d seve r a l t im e s , e a ch t im er em ovin g th e vola t i le m a t e r ia l e volved to t h e ot h e r cold t r a p , t o e ffec t com -p le t e r em ova l of occlu d ed or d issolved t r a ce s of t h e vo la t i le m a t e r ia ls (e . g . ,t h e d is t i lla t ion of C02 fr om C02 -ice con d en sa t e a t d r y-ice t em p er a t u r e ).

Th e su b jec t of t r a p r e fr ige r a n t s sh ou ld b e t ou ch ed on b r ie fly . Liqu idn it r ogen (- 195. 8C), d r y ice (-78. 5-C), a n d ice (OC) a r e common ly a va ila b lein m os t la bor a t or ie s. F or t u n a t e ly t em p e r a t u r e s low er t h a n t h a t of liq u idn it r ogen w ill u su a lly n ot b e r equ ir ed in h a n d lin g r a r e ga s e s o t h er t h a n h e liuma n d n eon . I t m igh t b e n ot ed th a t p um p in g on liqu id n it r ogen w ill coo l it b yeva p or a t ion to it s t r ip le p oin t (-2 10, 9*C, 96.4 mm Hg). Tem p e r a t u r es in t e r -m ed ia t e t o t h ose of liq u id n it r ogen , d r y ice , a n d ice a r e oft e n n ecessa r y a n da r e common ly ob t a in ed b y coolin g a su it a b le liq u id w it h liq u id n it r ogen or d r yice t o ob t a in a p a r t ia lly fr ozen I ls lu sh ll a t t h e m elt in g p o in t . S lu sh or liq u idr e fr ige r a n t s p r ov id e bet t e r h ea t t r a n sfe r fr om th e t r a p t h a n solid r e fr ige r a n t s,

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t h u s d r y ice is u su a lly m ixed w it h a ce t on e t o p r ovid e a s lu sh r e fr ige r a n t a t-78. 5C. Discu ss ion of cold ba t h e m ay be fou n d in m os t t ext s wh e r e va cu umt ech n iqu e s a r e d iscu ssed . 24, 25 Th e a u th or h a s fou n d t h e follow in g ba t h s p a r -t i t u la r ly u se fu l in wor k in g w it h r a r e ga se s : a ce t on e , -95 *C, n -p en t a n e , -130 C,a n d isop en t a n e , - 160c.

It is u su a lly m os t con ven ien t t o r e fr ige r a t e t r a p s t h r ou gh wh ich la r gequ a n t it ie s of ga s w ill flow w it h liqu id n it r ogen , d r y ice , or ice s in ce su cht r a p s a r e ea s ily r ep len ish ed in p la ce on th e lin e . Slu sh - cooled l t r a p s a tot h e r t em p er a tu r es m a y u su a lly b e r e se r ved for op e r a t ion s wh e r e t h ey n eedt a k e u p on ly sm a ll am ou n t s o f h e a t .

Ad sor p t ion a n d Ad sor p t ion Tech n iq u esBy fa r t h e m a jor it y of sep a r a t ion s of r a r e ga se s t o b e fou n d in t h e lit e r a -

t u r e h a ve emp loyed a d sor p t ion t e ch n iqu e s. Of th e la r ge n umbe r of a d sor b en tm a t e r ia ls a va ila b le , a ct iva t ed ch a r coa l h a s m ost oft en been u sed beca u se ith a s t h e la r ge st su r fa ce a r ea (la r gest a d sor p t ive ca p a cit y) p e r u n it m a ss a n dbeca u se t h e r a r e ga ses a d sor b on ch a r coa l t o w id e ly d iffe r in g ext en t s.

F or a given a d sor b a t e ga s a n d a d sor b en t m a t e r ia l t h e am ou n t a d sor b edp er u n it m a ss of a d sor b en t , ca lled v a n d u su a lly exp r essed a s cc STP(St a n da r d Temp er a tu r e a n d P r e ss u r e , i . e . , OC a n d 76o mm Hg) of ga s p erg r am a d sor b en t , is a fu n ct ion of t em p er a t u r e of t h e a d ~or b en t a n d p a r t ia lp r es su r e of t h e ga s ove r t h e a d sor b en t . Th r ee fu n ct ion a l r e la t ion sh ip s am on gt h e se va r ia b les a r e of in t e r es t : 1 ) Isot h e rm s sh ow in g t h e d ep en d en ce of von P a t con s t a n t t em p er a tu r e ; 2) Isos t e r e s r e la t in g P a n d T a t con s t a n t v ;a n d 3 ) Isoba r s r e la t in g v a n d T a t con s t a n t P . Ln exp er im en t a l s t u d ies ofa d sor p t ion t h e iso t h er m s a r e m ost u su a lly d e t e rm in ed a t a se r ies of t em p e r a -t u r e s . F r om t h e se d a t a t h e oth e r r e la t ion sh ip s m a y be ob t a in ed if d e sir ed .Th e Cla u s iu s -Cla p eyr on equ a t ion a lso r e la t e s h e a t s of a d sor p t ion a n d th e p r es -su r e ch a n ge w it h t em p er a t u r e (sh a p e of t h e isos t e r e ).

A n um ber of equ a t ion s h a ve b een u sed t o exp r e ss a d sor p t ion isot h e rm s ,m ost of wh ich a r e em p ir ica l in n a t u r e . La n gmu ir fir st d e r ived t h e h yp er bo lic

26isot h e rm for m on ola yer a d sor p t ion fr om th eor e t ica l con sid er a t ion s .Br u n a u e r , Emmet t , a n d Te lle r 27 la t e r d e r ived eq u a t ion s for m u lt ila yer a d -so r p t ion wh ich r ed u ce t o La n gmu ir Is equ a t ion in th e ca se of a m on ola yer . Th eh fie r bolic isot h e rm may b e w r it t en v = vsbP /(1 t bP ) , P = vfi(vs v) , orP /v = l/bv s + P /vs , w h er e v~ is t h e cc STP of a d sor b a t e r equ ir ed t ofor m a mon ola ye r p er gr am of a d sor b en t , a n d b is a con st a n t d ep en d en t ont em pe r a t u r e a n d th e n a t u r e of t h e a d sor b a t e a n d a d sor b en t . Th e la s t form isp a r t i c u l a r l yP /v ver su s

u sefu l for t h e ext en s ion of d a t a b y in t e r p ola t ion s in ce t h e p lot ofP is lin ea r . At low p r essu r e s , or p er h a p s m or e d efin it ive ly low

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v , it i s fou n d t h a t a d sor p t ion ob eys Hen r yfs law (v = kP ), a n d in t e r p ola t ion .ona lin ea r p lot of P ver su s v is p oss ib le . I t w ill b e n ot ed th a t for P mu ch lesst h a n l/b , o r v m u ch less t h a n v~ , t h e h yp er bolic isot h e rm r ed u ces to Hen r yr slaw w it h k eq u a l t o bv F r eu n d lich a p a r a bo lic equ a t ion (sem i-em p ir ica l insn a t u r e ) is o ft en u sefu l for lin e a r in t e r p ola t ion on a log -log p lot in ca ses wh er e

1/nit is ob eyed : v = KP . P e t e r s a n d We il 28 s tu d ied t h e a d sor p t ion of a r gon ,k r ytp on a n d xen on on ch a r coa l a n d ca lcu la t ed t h e con st a n t s in t h e F r eu n d lichequ a t ion fr om t h e ir d a t a a t seve r a l t em p er a t u r es . Th ese a r e g iven in Ta b le2 for h a n d y r e fe r en ce . Ad sor p t ion d a t a for a n umbe r of ga se s on ch a r coa l a r et a bu la t ed in Ch a p t e r 8 of Du shm an . 23 Th e a d sor p t ion p r oce ss r e le a se s h ea ta n d a s exp ect ed fr om LeCh a t e lie r IS p r in cip le a d sor p t ion d ecr ea se s w it h in -cr e a s in g t em p er a t u r e , o t h e r fa ct or s r em a in in g con st a n t . Ad~or p t ion in cr ea s -e s w ith in cr ea sin g p r essu r e . Ad sor p t ion of d iffe r en t ga se s t en d s to in cr e a sew ith d ecr ea s in g vo la t ili t y (ext en t of a d sor p t ion t en d s t o in cr e a se in t h e sam eor d er a s t h e bo ilin g p oin t s of t h e ga se s ).

Ta b le 2. Ad sor p t ion con st a n t s for a r gon , k r yp ton1/na n d xen on : v = KP

T C K 1/n

Argon -80 0.500 0.950-18 0.0764 1.0

0 0.0581 1.0Kryp ton -80 , 2.927 0.711

-18 0.497 0.8850 0.340

Xenon1,0

-80 15.99 0.574-18 2.4580

0.6921.583 0.77

Th eor e t ica l t r ea tm en t s d iscu ss a d sor p t ion in t e r m s of: 1) form a t ion ofa m on ola ye r of a d sor b a t e on t h e su r fa ce , 2) for m a t ion of m u lt i la yer s on p la n esu r fa ces , a n d 3) ca p illa r y con d en sa t ion in sm a ll p or es . Ad sor p t ion of a ga sis con s id er ed th e r esu lt of va n d er Wa a ls for ces of t h e sam e t yp e in vo lved init s con d en sa tion . Th e m agn it u d e of t h e in t e r a c t ion s r esu lt in g in a d sor p t ion isin d ica t ed by t h e fa ct t h a t h e a t s of a d sor p t ion a r e gen er a lly comp a r a b le t o t h eh ea t o f con d en sa t ion for a g iven ga s , Exp er im en t a l isot h e rm s m ay con for move r w id e r a n ges t o t h eor e t ica lly d er ived equ a t ion s (a s t h e h yp e r bo lic iso-t h e rm ) for Eu it a b le va lu e s of t h e con s t a n t s in t h e equ a t ion . How ever , va lu e sof t h e con st a n t s t h u s ob t a in ed a r e oft e n n ot e a s i ly r e la t ed t o th e p h ys ica lm od e ls u sed in th e d er iva t ion s . F or d iscu ss ion of a d sor p t ion in gen er a l a n da k ey t o t h e lit e r a t u r e on t h e su b ject t h e r ea d e r is r e fe r r ed t o Ch a p t e r s 7 a n d8 in Du shm an 23 29or t o S. Br u n a u s ls book on p h ysica l a d sor p t ion .

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Som e comm en t s on t h e n a t u r e of a c t iva t ed ch a r coa lTh e s e a r e m os t ly fr om two r ecen t r eview a r t ic le s. 30,31

m a y be w or t h w h ile .Th e r e a r e n t im er -

ou s m a t e r ia ls fr om wh ich a c t iva t ed ch a r coa l m a y be p r ep a r ed a n d m an y m et h -32od s of p rep ar at ion , F or examp le , on e m igh t s t a r t w it h cocon u t sh e lls a n d

h ea t in t h e a b sen ce of a ir t o r em ove t h e gr e a t e r p a r t o f t h e e lem en t s ot h e rt h a n ca r b on a s vola t i le m a t e r ia ls . Th e r e su lt in g m a t e r ia l i s t h en a c t iva t edw it h s t e am a t 7OO-1OOOC. Th e la r ge sp ec ific su r fa ce a r e a of ch a r coa l (oft h e or d e r of 1000 sq u a r e m et e r s p e r g r am ) is d u e t o i t s h igh p or os it y, a sop p osed t o t h e n on p or ou s a b sor b en t s su ch a e lam p b la ck w h ose la r ge sp ec ificsu r fa ce a r ea is t h e r e su lt of ex t r em ely sm a ll p a r t ic le s ize . Th u s t h e su r fa cep e r gr am of lam p b la ck is a m a r k ed fu n ct ion of t h e a ve r a ge p a r t icle s ize ,w h e r e a s t h e sp e cific su r fa ce of a ct iva t ed ch a r coa l is a lm os t in d ep en d en t o fp a r t ic le s ize . F u r t h e r m or e , m os t o f t h e su r fa ce a r e a in ch a r coa l a p p a r en t lyr e s id e s in p or e s w it h d iam e t e r s comp a r a b le t o mole cu la r d im en s ion s . I tfollow s th a t on e m igh t exp ect p r in cip a lly m on ola ye r a d sor p t ion on ch a r coa l.Th u s a d sor p t ion on ch a r coa l m igh t b e exp ec t ed t o ob ey t h e h yp er bo lic iso -t h e r m , a n d d oes so ove r w id e r a n ge s . Th e p ot en t ia l p or e s t r u c t u r e of a ch a r -coa l i s d ep en d en t on bo t h th e st a r t in g m a t e r ia l a n d t h e con d it ion s of p yr olys is .Ch a r coa ls fr om h a r dwood s , n u t sh e lls a n d cer t a in gr a d e s of coa l gen e r a llyg ive t h e h igh es t p or os it y. Th e m a t e r ia l a ft e r p yr olys is (t h ou gh p or ou s ) s t i llh a s low a d sor p t ive ca p a cit y a n d t h e p r oce ss of a c t iva t ion con s is t s e ssen t ia llyof b u r n in g ou t m or e m a t e r ia l in or d e r t o e i t h e r op en n ew p or e s or t o en la r geex is t in g p or e s t o d iam e t e r s w h ich w ill a ccomm od a t e a d sor b a t e m ole cu le s(p er h a p s b ot h p r oce sses occu r ). .St eam is w id e ly u sed for a c t iva t ion a s th er ea c t ion is en d ot h e r m ic , a n d b e t t e r t em p e r a t u r e con t r ol i s p oss ib le . On e ex-p ec t s t h en t h a t t h e p r op er t ie s of t h e m a t e r ia l h e r e ce ives in t h e la bor a t o r yd ep en d n ot on ly on m a t e r ia ls u eed in p r ep a r a t ion bu t a lso ve r y m a r k ed ly ont h e h is t o r y of it s p yr o lys is a n d a c t iva t ion . E xce ss ive a c t iva t ion ca n in fa ctr em ove mor e su r fa ce a r ea t h a n it c r e a t es , t h e a d sor p t ive ca p a c it y go in gt h r ou gh a m a fim um a s jh e a ct iva t ion p r oce ed s. Sin ce t h e d is t r ib u t ion of p or e sa s t o s ize in clu d e s m a n y w it h d iam et e r s comp a r a b le t o m olecu la r d im en s ion s ,a Bim olecu la r s ie ve !! e ffec t m a y be exp ect ed t o som e ex t en t . Th u s som e p or e sw ill a ccomm od a t e a g iven mole cu le b u t a r e t oo sm a ll for a s ligh t ly la r ge rm olecu le . Du r in g a c t iva t ion t h e a d sor p t ive ca p a cit y for va r iou s sp e c ie s m a yt h e r e for e n ot b e in cr e a s in g in th e s am e r a t io. Ch a r coa l h a s in t h e p a st b e enr e fe r r ed t o a s a n a llot r op e of ca r bon , bu t e lem en t a l a n a lyse s in d ica t e a t omp e r cen t s o f ca r b on a lw a ys le ss t h h 100% a n d eom e t im e s a s low a s 757.. Th eo t h e r e lem en t e p r e sen t a r e p r in cip a lly h yd r ogen a n d oxygen , b u t a p p r e cia b leam ou n t s of n it r ogen , su lfu r , ch lor in e , a n d in or ga n ic a sh m a y a lso b e p r ee en t .I t a p p ea r s lik e ly th a t t h e su r fa ces on w h ich a d sor p t ion occu r s a r e n ot ca r bonsu r fa ce e bu t h yd r oca r bon e u r fa ce e m od ifie d b y th e p r esen ce of oxygen a n d

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t r a ces of o th e r e lem en t s. Th is im p lies t h a t a ll a d sor p t ion s i t es a r e ve r y lik ely n ot id en tica l.

Act iva t ed ch a r coa l is t h u s a c la ss of su b s t a n ces w h ose ch em ica l a n dp h ys ica l p r op er t ie s m a y va r y w it h in r a t h er w id e lim it s . Le t UH h a s t en to a ddth a t t h is d oe s n o t r ea lly im p a ir it s u se fu ln e ss a s a n a d sor b en t . Th e a d sor p-t ive p r op er t ie s of ch a r coa ls in sep a r a t ion sys t em s a r e u su a lly n ot so cr it ica lt h a t even va r ia t ion s lik e fa ct or s of two or m or e w ill r esu lt in loss of sep a r a -t ion , t h ou gh su ch va r ia t ion s ce r t a in ly a ffect t h e p r Qced u r e in d e t a il, Th ein t en t is t o p oin t ou t t h a t t h e exp er im en t e r sh ou ld n ot b e su r p r ised if t h e a d -sor p t ive p r op e r t ie s of h is ch a r coa l d iffe r fr om t h ose h e se e s qu ot ed in t h el i t e r a t u r e . In on e st u d y of t h e a d sor p t ion of xen on on seven ch a r coa ls a t r oomtem p er a t u r e , t h e am ou n t p e r g r am of ch a r coa l a d sor b ed a t a given p r essu r eva r ie d a s m u ch a s a fa ct or of five . 33 Th ese ch a r coa ls w e r e of cou r se ch osenon t h e ba ,s is of d iffe r en ce s in m a t e r ia ls a n d p r ep a r a t ion s exp ect ed t o p r od u cea r a n ge of a d sor p t ion ch a r a c t e r ist ic s . Ln or d er t h a t e a r ly exp e r ien ce m ay beu sed t o p r ed ict w it h fa ir a ccu r a cy t h e cou r se of sep a r a t ion s in sys t em s bu ilta t la t e r d a t es , it is p r oba b ly w ise to or igin a lly p u r ch a se a qu a n t it y of ch a r -coa l su fficien t for m a n y yea r s n eed s .

Be for e u se a n d be tween su cce ssive u se s it is n e ce ssa r y t o ou t ga s ch a r -coa l, b ot h t o p r even t con t am in a t ion of sam p les w it h sm a ll am ou n t s of r e sid u a lga se s fr om p r e t iou s r u n s a n d t o r em ove a d sor b ed m a t e r ia ls (su ch a s wa t e r )w h ose a ccumu la t ion m a y a d ve r se ly a ffe ct t h e a d sor p t ive p r op er t ie s of t h echa r co a l . Th is p r oce ss sh ou ld n ot b e so ext r em e a s t o ch a n ge t h e m a t e r ia lt h rou gh fu rt h er a c t iva t ion . A r ou t in e w h ich h a s p r oved sa t isfa ct or y is ou t -ga ss in g in va cu o a t 350-400C. At Law r en ce Ra d ia t ion La bor a t or y t h e ou t -

-4ga ss in g is r ou t in e ly con t in u ed u n t il t h e p r essu r e is 10 mm Hg or le ss a sju d ged by a th e rm ocou p le va cu um ga u ge in t h e va cu um sys t em man ifold .

On e m ay op e r a t e in va r iou s w a ys t o a ch ieve sep a r a t ion s of ga se s t h r ou ghd iffe r en ces in t h e a d sor p t ion on ch a r coa l (or a n y o th e r a d sor b en t ). I t m a yp r ove u sefu l t o p oin t ou t t h a t su ch sep a r a t ion s a r e b a s ica lly sim ila r t o sep -a r a t ion s of sp e cies in solu t ion u s in g ion exch a n ge r e s in s , Th e m an y r a d io -ch em is t s wh o a r e fam ilia r w it h sep a r a t ion s u s in g su ch r e s in s w ill n ot e c losea n a log ies even in t h e va r iou s t ech n iq u es u sed .

Sep a r a t ion p r oced u r es m u s t b e d e s ign ed w it h k in e t ic con s id e r a t ion s in m in d -- a d sor p t ion fr om a s t r e am of ga s is n ot a n in s t a n t a n eou s p r ocess . I tw a s st a t ed ea r lie r t h a t t h e a d sor p t ive ca p a c it y of ch a r coa ls d oe s n ot d ep en don pa r t ic le s ize , bu t it is e xp ec t ed t h a t r a t es of a d sor p t ion w ill b e so d ep en d -e n t . A r ed u ct ion in th e a ve r a ge p a r t icle d iam e t e r in c r ea se s t h e ext e r io rsu r fa ce (p er gr am a d sor b en t ), p r esen t ed t o t h e ga s p h a se a n d sh or t en s p a t h st h r ou gh cr a ck s a n d p or es a lon g w h ich a d sor b a t e m olecu le s m u st d iffu se inor d e r t o r e a ch a d sor p t ion c it es in t h e p a r t ic le in t e r ior . Ap p r oa ch t o equ i -

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lib r ium con d it ion s sh ou ld t h u s im p r ove w it h sm a lle r p a r t icle s ize a n d in -c r ea sed con t a ct t im e w it h t h e a d sor b en t (d e cr e a sed flow r a t e ), A comp r om iseis n e ce ss a r y a s t oo sm a ll p a r t ic le s ize w ill r e su lt in h igh r e s is t a n ce t o ga sflow , In flow sys t em s low t em p er a t u r e a d sor b en t b ed s m a y n ot b e m a in t a in edin t h er m a l equ ilib r iu m w it h t h e r e fr ige r a n t if t h e ga s en t e r s t h e b ed a t e le -va t ed t em p e r a t u r e or if t h e r a t e of h ea t r e le a se fr om t h e a d sor p t ion p r oce ssesoccu r r in g is h i,gh . F low r a t es a n d con d it ion s a ffe ct in g t h e r a t e of h e a t t r a n s -fe r a r e t h u s im p or t a n t in t h is r e sp ec t . Alt h ou gh it i s ce r t a in ly of gr e a t in t e r -e s t a n d lon g-r a n ge u se fu ln ess t o u n d e r s t a n d in d e t a il t h e k in e t ics of t h e sep r ocesse s , t h e m or e p r a c t ica l a n d fa s t e r a p p r oa ch t o d e s ign is em p ir ica l.De s ign fa ct o r s a r e ch osen to im p r ove t h e k in e t ics in sofa r a s p oss ib le a n d t h eexp er im en t is t r ie d . Lf t h e exp er im en t su cceed s , fa ct o r s a ffec t in g k in e t icsa r e u su a lly n ot va r ied t o d e t e r m in e t h e ext r em e con d it ion s u n d er wh ich th ep r oced u re is sa t is fa ct o r y. Th u s in p la ces su ch a s t h e De t a iled P r oced u r e sw h e r e flow r a t e s a n d ch a r coa l p a r t icle s ize s m a y be qu ot ed it sh ou ld b e u n d er -s t ood th a t t h e se a r e su fficien t for t h e sep a r a t ion , bu t m a y or m a y n ot b en ece ssa r y sh ou ld o t h er con s id e r a t ion s m a k e ch a n ge s d es ir a b le .

Mos t r a r e ga s sep a r a t ion s w ill comm en ce w it h t ot a l a d sor p t ion of a llt h e ga se s of in t e r es t in a n a d sor b en t t r a p . k t h is m a n n er on e m a y m in im izep r ob lem s a r is in g fr om n on -u n i for m in t r od u c t ion of sam p le , t em p e r a t u r ev a r i a t i o n s , a n d a d sor p t ion k in e t ics b y u s in g low er t em p e r a t u r e s a n d m or ea d sor b en t t h a n sh ou ld r ea lly b e n ece ssa r y. By t r ea t in g a ll a d sor p t ion s t ep sin t h is m a n n e r on e t en d s to r ed u ce 10S se s , s in ce in su b sequ en t d ea or p t ions t ep s s low p r oce sses m a y a ffec t t h e h is t or y of t h e sep a r a t ion in d e t a il b u tw ill n o t r esu lt in a ct u a l loss of sam p le .

In t h e ir e a r ly w or k on r a r e ga se s , P e t e r s a n d Weil 28 sh ow ed t h a t a r gon ,k r yp t on a n d xen on cou ld b e sep a r a t ed by t ot a l a d sor p t ion followed b y fr a ct ion a lr e sor p t ion in va cu um fr om a ct iva t ed ch a r coa l. Th ey a d sor b ed t h e m ix t u r eon ch a r coa l a t - 1 90 C (r ou gh ly 10CC STP of e a ch ga s w a s u sed on 38 gr am sof ch a r coa l) a n d t h en r a ised t h e t r a p t o a su it a b le t em p e r a t u r e a n d d esor b edt h e ga s e s u s in g a m er cu r y d i ffu s ion p ump ba ck ed b y a Toep leT p~p t o t r a n s -fe r t h em t o a ga s bu r e t fo r m ea su r em en t . Temp er a t u r es a t wh ich ea ch ga sm ay be d e sor b ed I Ip u r e !i of t h e o t h e r s a r e som ewh a t a comp r om ise be tw eensp eed a n d sep a r a t ion fa ct or -- r em ova l o f a r gon a t -93 c , k r yp ton a t -800ca n d xen on a t O C wou ld b e t yp ica l. F r om kn ow led ge of t h e iso t h e r m s , am om t sof a d sor b en t a n d of e a ch a d sor b a t e in it ia lly , a n d t h e vo lum e w it h w h ich t h ea d sor b en t b ed is equ ilib r a t e d be for e e a ch lift of t h e Toep le r p ump on e cou ldca lcu la t e in a s t r a igh t fo r w a r d bu t la b or iou s fa sh ion t h e comp os it ion of t h ega s in t h e a d sor b ed a n d ga seou s p h a se s a ft e r e a ch s t r ok e , a ssu m in g u n ifo r md is t r ib u t ion of t h e ga s e s on t h e a d sor b en t . E ven cu r sor y exam in a t ion of t h e

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iso t h er m s su gges t s t h a t wh ile sep a r a t ion s p er for m ed in t h is m a n n e r m a y p r o-du ce ga se s w h ich a r e a r ou n d 99% pu r e , sep a r a t ion fa c tor s of a bou t 100 a r et h e lim it ob t a in a b le a n d wou ld n ot b e sa t is fa c to r y in m ost r a d io ch em is t r y.It m igh t b e n ot ed t h a t Glu eck a u f 34 a n a lyzed m a t h em a t ica lly t h e op er a t ion ofa sys t em in wh ich r a r e ga se s a r e su cce ssive ly a d eor b ed a n d d esor b ed on aser ies of ch a r coa l t r a p s a n d u sed su ch a sys t em for sep a r a t in g h e lium a n dn eon a s t h e fin a l s t ep in t h e d e t e r m in a t ion of t h e ir a bu n d a n ce in a ir . A s im i-la r sys t em w a s la t e r u sed

35for t h e Hep a r a t ion of a r gon , k r yp ton a n d xen on

in a n exp er im en t t o d e t e r m in e th e r e la t ive yie ld s of k r yp t on a n d xen on isot op esfr om u r a n ium fiss ion b y vo lum e m ea su r em en t s on t h e sep a r a t ed ga se s a n dla t e r m a ss sp e ct r ogr a p h ic a n a lys is . In t h ese p r oced u r e s a se r ie s of m a n yt r a p s w a a r equ ir ed .

A sid e ligh t in t h e wor k of P e t e r s a n d Weil 28 .1s w or t h m en t ion in g t op oin t ou t a m a t t e r of sa fe t y. Th ey p er for m ed a n exp er im en t in wh ich it w a s

22 2sh ow n t h a t Rn a d sor b ed qu a n t it a t ive ly fr om liqu id a ir on t ~ s ilica ge l. Ast h ey p oin t ou t , s ilica ge l w a s u sed beca u se of t h e exp los ive p ot en t ia li t ie s o fch a r coa l a n d liqu id oxygen . Beca u se of t h is h a za r d it seem s a d visa b le t o u seliqu id n it r ogen , r a t h e r t h a n liqu id a ir or oxygen , t o r e fr ige r a t e ch a r coa lt r a p s a s a sa fegu a r d in ca se of b r ea k a ge , a n d t o op er a t e a t r e du ced p r e ssu r ew h en in t r od u cin g a ir t o a ch a r coa l t r a p cooled in liq u id n it r ogen t o a vo id con -d en sa t ion of liq u id a ir in t h e t r a p it se lf.

Th e t ech n iqu e s of P e t e r s a n d We il a n d of Glu ecka u f m en t ion ed a b oveh a ve t od a y b een r ep la ced by wh a t m a y be gen er a lly t e r m ed ch r om a togr a p h ict e ch n iqu e s. Th e se u su a lly in volve a d sor p t ion of a sam p le on on e en d of a na d sor b en t colum n , a n d su b sequ en t p a ssa ge of som e e lu en t ga s t h r ou gh th ecolum n to a ch ieve sep a r a t ion . In fa c t , Glu eck a u f21 in h is la t e r d e t e rm in a t ionof t h e Kr a n d Xe con t en t s of t h e a tm osp h e r e sep a r a t ed t h e r a r e ga se s by e lu -t ion fr om a ch a r coa l colum n r a th er t h a n by t h e m et h od u sed in t h e He a n d Ned e t e r m in a t ion a lr e a d y m en t ion ed . Keu lem a n s r ecen t b ook

36w ill se r ve a s

a n in t r od u ct ion t o t h e su b jec t of ga s ch r om a t ogr a p h y a n d a s a n u p -t o-d a t esou r ce of li t e r a t u r e r e fe r en ce s. On ly a few r em a r k s w ill b e m ad e h er e a n dsom e jou r n a l r e fe r en ce s cit ed . Ch r om a t ogr a p h ic sep a r a t ion s in volve a s t a :t ion a r y bed of liq u id or solid a d sor b en t t h r ou gh wh ich a s t r eam of liqu id orga s m oves . R a r e ga s sep a r a t ion s on ch a r coa l in volve a s t r e am of ga s m ovin gt h r ou gh a p acked colum n of solid a n d t h u s w ou ld be cla ss ified a s ga s -solidch roma tog r aphy . Met h od s of op er a t in g ch r om a t ogr a p h ic colum n s w ill gen e r -a lly fa ll in t o on e of t h r ee ca t egor ies : 1 ) E lu t ion d eve lopm en t in wh ich asam p le of t h e ga se s t o b e sep a r a t ed is a d sor b ed a t on e en d of t h e colum n a n da flow of sligh t ly a d sor b ed ca r r ie r ga s (e lu en t ) se t u p t h r ou gh t h e colum n .2) F r on t a l a n a lysis in wh ich a s t r eam of ga s con t a in in g t h e sam p le m ixt u r e

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is con t in u ou sly p a ssed t h r ou gh t h e colum n . 3) Disp la cem en t d eve lopm en t inw h ich t h e sam p le m ixt u r e is a d sor bed a t on e en d of t h e colu m n a n d a con t in -u ou s flow in it ia t ed of ga e m or e st r on gly a d sor b ed t h a n a n y of t h e ga ee s in t h esam p le . E lu t ion d eve lopm en t r e su lt s in t h e even t u a l em er ge n ce fr om th ecolum n of b a n d s or lp ea k si of t h e sam p le com p on en t s (d i lu t ed of cou r se w it he lu en t ) in t h e or d e r of t h e ir in cr ea s in g a d sor p t ion . If t h e com p on en t s d iffe re n ou gh in t h e ir a d sor p t ion it i s p oss ib le u n d e r p r op e r con d it ion s t o ob t a inea ch com p on en t in p u r e for m a s a p ea k sep a r a t ed b y p u r e e lu en t fr om a d ja -cen t p ea k s. I f t h e s t r e am of ga s con s is t s of a n u n a d eor b ed ca r r ie r ga s ina d d it ion t o t h e m ixt u r e of sam p le ga se s , fr on t a l a n a ly s is r e su lt s fir s t in t h eem e r gen ce of p u r e ca r r ie r a n d t h en of t h e le a s t a d sor b ed sam p le com pon en t ,d ilu t ed w it h ca r r ie r . Even t u a lly t h e com pon en t w h ich i s n ext t o t h e le a s t a d -sor b ed a lso b r e a k s t h r ou gh , a n d so on u n t i l t h e colu m n is comp le t e ly sa t u r a t -ed w it h a ll com p on en t s a n d t h e in flu en t a n d efflu en t ga Be s h a ve t h e sam e com -p osi t ion . On ly a sam p le of t h e le a s t a d sor b ed com p on en t m a y b e ob t a in edp u r e of o t h e r sam p le comp on en t s . In d isp la cem en t d eve lopm en t , b a n d s oft h e com p on en t s sep a r a t ed b y zon es con t a in in g a m ixt u r e of t h e sp ecie s ina d ja cen t b a n d s em er ge in or d e r of in c r ea s in g a d sor p t ion . E ven t u a lly t h e p u r ed isp la ce r em er ge s . P a r t ia l r e cove r y of fa ir ly p u r e comp on en t s is p oss ib le .

Th eor e t ica l p r ed ic t ion s a s t o t h e d e t a i ls of ch r om a t ogr a p h ic sep a r a t ion sva r y a s t h e a d sor p t ion iso t h e r m is lin ea r or n on lin ea r , a n d t h e p r oce s s I lid ea lll(t h e r m odyn am ica lly r eve r s ib le ) or In on -id ea lll. Lin ea r -id ea l a n d n on lin ea r

37id ea l ch r om a t ogr a p h y w e r e t r e a t ed b y Wilson 38a n d b y d e Va u lt . L i ne a rn on -id ea l ch r om a t ogr a p h y h a s b e en t r e a t ed b y a n um be r of in ve st iga t or fl , 39-46a n d n on lin ea r n on -id ea l ch r om a t ogr a p h y b y Klin k en b e r g a n d Sjen it ze r , 47 ~ve r y la r ge a m ou n t s of ga s a r e in volved , a d sor p t ion iso t h e r m s w ill u su a lly b en o n l i n e a r . Ga s -so lid ch r om a t ogr a p h y i s a lso lik e ly t o b e n on -id ea l a s t h ea t t a inm en t of eq u ilib r iu m b e tw ee n t h e p h a se s oft en ca n n ot b e con sid e r ed in -s t a n t a n eou s , am on g ot h e r t h in gs . Th u s t h e r a d ioch em ist m a y w e ll b e con -ce r n ed in h is sep a r a t ion s w it h t h e n on lin ea r n on -id ea l ca se , t h e le a s t a cce s-s ib le t o a ccu r a t e t h eor e t ica l t r e a tm en t . Th e t h eor y of t h e s im p le s t c a se oflin ea r -id ea l ch r om a t ogr a p h y for a s in gle a d sor b a t e p r ovid e s u se fu l q u a lit a t ivein s igh t in t o t h e p r oce s se s occu r r in g , h ow eve r . K eu l emans 36 t r e a t s t h is ca seon p a ge 112 e t se q . of h is b ook . A b r ie f a ccou n t of t h e r ea son in g w -ill b egive n h er e.

Con sid e r a n a d sor b en t u n ifor m ly p a ck ed in t o a cylin d r ica l colu m n ofcon s t a n t d iam e t e r a n d a t con m t a n t t em p e r a t u r e t h r ou gh ou t . I f a n a d s or ba t eis p r e sen t in som e sm a ll cylin d r ica l e lem en t of t h e colu m n t a k en in c r os s -~ec t ion , it w ill d is t r ib u t e i t s e lf so t h a t a fr a c t ion o of t h e t ot a l is in t h e ga sp h a se a n d a fr a c t ion ( 1 -~) on t h e a d sor b en t , As a fr a c t ion o of t h e a d sor b a t e

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i s in t h e ga s p h a se , a given a d sor b a t e m ole cu le r e s id e s in a n d t h u s m ove sw it h t h e ga s p h a se o of t h e t im e on t h e a ve r a ge , It t h en follow s th a t t h e r a t eof m ovem en t of a d sor b a t e t h r ou gh t h e e lem en t is ju s t o t im e s t h e lin e a r flowr a t e F of e lu en t ga s . Assum in g t h e p er fect ga s la w s , on e m ay ca lcu la t e ~a n d F , Le t u s ca ll Ge t h e vo lu m e a va ila b le t o t h e m ovin g ga s a n d Ae t h ew e igh t of a d sor b en t in t h e e lem en t e . P a ie t h e p a r t ia l p r e s su r e of a d eor b a t ea n d v t h e am ou n t a d sor b ed in cc STP p e r gr am of a d sor b en t . Th e fa ct or forcon ve r t in g ga e vo lu m es in cc-mm of Hg a t colum n t em p e r a tu r e t o s t a n d a r dcon d it ion s m a y b e ca lled C = 273K/(T. K X 76o mm Hg). Th e fr a c t ion ofa d sor b a t e in t h e ga s p h a se w ill t h en b e o = C P a Ge /(GP a Ge + vAe) = (1 +vAe /CP a Ge)-l . As t h e co lum n is u n ifo rm ly p a ck ed t h e r a t io of Ae/Ge w ill b et h e sam e in a n y e lem en t o f co lum n volum e a n d eq u a l t o t h e r a t io of t ot a l w e igh tA of a d sor b en t t o t ot a l void sp a ce G in t h e colum n , F u r t h er m or e , V/Pa .k w ill b e con s t a n t fo r a ll v if t h e isot h er m is lin ea r , in w h ich ca se k may,b e r e fe r r ed t o a s t h e Hen r yle law con s t a n t . In t h ie ca se , ~ . (1 + kA/CG) -1a n d is t h e s am e a t con s t a n t t em p er a t u r e eve r yw h e r e in t h e co lum n r ega r d leseof a dsor ba t e con cen tr at ion . Th e lin ea r flow r a t e of e lu en t w ill b e F =q L/C GP tot , w h er e q is t h e ga s flow in cc STP p er m in u t e , L is t h e colum nle ng t h in ce nt im et er s, G is t h e cc of t ot a l colu m n void sp a ce , P tot is t ot a lga s p r e ssu r e in mm Hg, a n d C is t h e con s t a n t d e fin ed a b ove . Th e r a t e ofm ovem en t of a d sor b a t e is t h en OF . ( 1 + kA/C G)- 1 (q L/C G P t ot ) = q L /P t ot(C G -1-U). In m os t in st a n ces 0> 1, so th a t t h is exp r e s -s ion sim p lifie s t o OF = q L /kA P tot . In e it h e r ca se t h e r a t e of a d sor b a t em ovem en t is con st a n t eve r yw h e r e a lon g th e co lum n r ega r d le ss of t h e con cen -t r at ion of a dsor ba te . I t follow s t h a t t h e r a t e of m ovem en t of a ll p o in t s in ab a n d is t h e sam e , a n d t h e ba n d sh a p e d oe s n ot ch a n ge d u r in g i t s t r a ve l a lon gt he colu mn .

In id e a l ch r om a t ogr a p h y, fr on t a l a n a lys is r e su lt s in t h e gr a d u a l ext en -s ion of a b a n d of a d sor b a t e a t con s&n t con cen t r a t ion d own t h e co lum n , a s s um -in g con st a n t colu m n t em p e r a t u r e a n d con s t a n t p a r t ia l p r e ssu r e of a d sor b a t ein t h e ga s en t e r in g t h e colu m n . By eq u a t in g to t a l a d s or b a t e in t r od u ced t o t b ecolum n t o t h e am ou n t p r e sen t in t h e ga s p h a se p lu s a d sor b en t p h a se in a b a n dof len gt h fa on t h e co lum n , on e a r r ive s a t la = (q L/P t o~(CG + vA/P a )-l t ,w h e r e t i s t ot a l t im e of flow in m in u t e s , In t h e ca se of a lin e a r iso t h e r mt h is i s ju st la = OF t , a s on e in t u it ive ly exp ec t s . Even if t h e isot h er m isn o n l i n e a r , (v /P a ) is con e t a n t eve r yw h e r e in t h e ba n d , for P a con s t a n t . Th isfor m u la is t h u s a u se fu l a p p r ox im a t ion in t h is ca se if P is k n own a n d con -as t a n t in t h e ga s en t e r in g t h e colum n , a n d t h e isot h er m is k n own a t co lum nt emp e r a t u r e . All t h e a b ove d iscu ss ion is s t r ic t ly for a s in gle a d sor b a t e , a sa pp re cia ble con cen tr a t ion sof t h e fir st .

of a se con d a d sor b a t e m a y a ffe ct t h e a d sor p t ion .

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In m a n y exp er im en t s , t h e sam p le in t r od u ct ion isn e r cor r e sp on d in g t o fr on t a l a n a lys is , w i t h su b sequ en tp on en t s by e lu t ion d eve lopm en t . De@i Led P r oced u r e 1

a ccom p lish ed in a m a n -sep a r a t ion of t h e com -(see la st ch a p t e r ) in

wh ich a ir con t a in in g Kr a n d Xe is a dm it t ed to a ch a r coa l colum n over a lon gp er iod is a n examp le . Aft e r t h e a dm iss ion of t h e sam p le is comp le t e , t h e Kra n d Xe a r e sep a r a t ed a n d r ecover ed b y e lu t ion in t o a su it a b le . r ecep t a c le w it hh e lium a t su i t a b le colum n t em p er a t u r es . In su ch ca se s a m in im a l r eq u ir em en tfor sa t is fa ct o r y op er a t ion is t h a t t h e len gt h of t h e b a n d of lea s t a d sor b ed su b -s t a n ce be le ss a t t h e en d of sam p le in t r od u ct ion t h a n t h e co lum n len gt h .. T h u sin P r oced u r e 1, t h e fin a l le n gt h of t h e ba n d of k r yp t on mu st b e le ss t h a n t h eco lu mn len gt h . In t h e su b sequ en t sep a r a t ion b y e lu t ion t h e r a t es of m ovem en tfor two a d sor b a t es a r e OIF a n d 02F , so t h a t t im e s of em e r gen ce ca n b eca lcu la t ed . F or sep a r a t ion t o be a ch ieved t h e r e a r of t h e fir st b a n d mu stover t a k e t h e fr on t o f t h e se con d b a n d , Th u s w h e r e T is t h e t im e for em e r -gen ce of t h e r ea r of t h e fir s t b a n d , T OIF = T 02F + 12 = L, w h er e fz is t h eb a n d w id t h of t h e m or e h igh ly a d sor b ed compon en t . Th u s L = 12k 2~kZ k l)i s t h e m in im um column len gt h in wh ich sep a r a t ion of tw o compon en t s m a y bea ch ieved , in t h e lin e a r -id e a l ca se .

If, a s i s u su a lly t h e ca se w it h ch a r coa l, t h e isot h er m is h yp er bo lic ,t h en v/P =b (vs v).a Th u s , a s v in cr e a se s t owa r d vs (t h a t is , t h e fr a ct ionof t h e su r fa ce cover ed w it h a d sor b a t e b e com es a p p r ec ia b le 25), v/P a d ecr ea s -e s . I t w ill b e se en t h a t o t h u s in cr e a se~ a s v in cr e a se s , a n d t h e m or e con -cen t r a t ed r eg ion s in a ba n d move fa st e r . Assum in g id ea l con d it ion s t h e r e -su it i s a n em er gen t b a n d w it h a ve r y sh a r p fr on t a n d a lon g t a il. In a p r a c-t ica l sen se , if on e h a s u sed a va lu e of k ob t a in ed fr om t h e lin e a r low p r essu r er eg ion of t h e isot h er m t o es t im a t e t h e em er gen ce t im e , t h e p ea k fr on t w illem e r ge e a r lie r t h a n ca lcu la t e d . In t h e la t t e r p or t ion s of t h e p ea k t a il w h er econ cen t r a t ion s lie in t h e lin e a r r eg ion of t h e iso t h er m , r a t e of m ovem en t w illa pp r oxim at e t h at ca lcu la t ed .

Dep a r t u r es fr om id ea lit y 1! su ch a s t h ose d u e t o a p p r ec ia b le r a t es oflon git u d in a l d iffu s ion in t h e ga s or n on -in s t a n t a n eou s m a s s t r a n s fe r b e tw eenp h a ses r e su lt in b r oa d en in g of b a n d s d u r in g t h e ir t r a ve l, u su a lly in a n ea r lysymm et r ica l fa sh ion . Su p e r p os it ion of t h e se effec t s ca n g ive u sefu l q u a lit a -t ive p ic t u r es of t h e ba n d s a n d t h e ir m ot ion in t h e va r iou s ca ses . Th u s n on -lin ea r , n on -id e a l con d it ion s le a d t o a symme t r ic b a n d s em e r gin g ea r lie r t h a nu n d e r lin e a r -id e a l con d it ion s . As t o p ea k sh a p e , on e m igh t exp ect t h e em e r -gen ce fir s t of a r eg ion in w h ich a d sor b a t e con cen t r a t ion in cr ea se s s low ly ,t h en a e t eep m a in p ea k fr on t , a le ss s t e ep m a in p ea k b a ck , a n d fin a lly a lon gt a il in wh ich a d sor b a t e con cen t r a t ion s low ly a p p r oa ch e s ze r o.

Th e r e a r e tw o gen e r a l a p p r oa ch es t o m or e r igor ou s t h eor e t ica l t r ea t -m en t of ch rom at ogr ap hy .

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Th e Ip la t e t h eor y t r ea t s t h e colu m n a s a se r ie s of ju xt a p osed equ iv -a len t t h eor e t ica l p la t e st i in e a ch of w h ich a sep a r a t ion fa c t or b e tw een twosp ec ie s cor r e sp on d in g t o t h e r a t io of t h e i r d is t r ib u t ion coe ffic ie n t s is a ch ieved .Th e d is t r ib u t ion coeffic ie n t is a r a t io of con cen t r a t ion s in t h e tw o p h a se s fora su bs t an ce .

Th e r a t e t h eor y t a k e s in t o a ccou n t t h e p h ys ica l p r oces ses su ch a scon vect ion a n d d iffu s ion , a n d se t s u p p a r t ia l d iffe r en t ia l e q u a t ion s to d e sa r ib et h em . Th e solu t ion of t h e se eq u a t ion s (in t h e a d s or b a t e con cen t r a t ion s a n dt h e ir d e r iva t ive s , w it h t im e a n d a x ia l d is t a n ce a lon g t h e colu m n a s in d ep en d en tva r ia b le s ) i s t h en es sa yed .

Bot h a p p r oa ch e s in vo lve va r iou s sim p lify in g a s s u mp t ion s, Th e jou r n a lr e fe r en ce s t o t h eor y g iven ea r lie r in clu d e a ccou n t s o f bot h t r e a tm en t s. I t

48m igh t b e sp ec ifica lly n ot ed th a t on e a r t ic le by Glu eck a u f d ea ls w i t h t h eeffe ct s o f h e a t in g on m ovem en t a n d sh a p e s of p ea k s w h en t h e a d sor b a t e is a

85h igh ly r a d ioa ct ive ga s su ch a s Kr . P e a k s a r e sh a r p en ed a n d sep a r a t ion simp roved . On e m igh t sa y qu a lit a t ive ly t h a t a s t h e la t t e r p or t ion s of t h e ba n dm ove t h r ou gh r egion s w a rm ed by p a ssa ge of t h e a c t ive ga s , o is la r ge r t h e r e .Th e t a il w ou ld t h u s t en d t o m ove fa st e r a n d ca t ch u p w it h t h e m a in p ea k .In t h e even t t h a t t h e r a d ioch em ist h a s n e ed t o u se ch a r coa l a ft e r exp osu r e t oh igh r ad ia t ion fie ld s , i t . m igh t b e n o t ed t h a t t h e a d sor p t ion of k r yp t on a n dxen on on ch a r coa l w a s fou n d to b e u n a ffec t ed by p r ev iou s ir r a d ia t ion w it h 1-Mev e le ct r on s (d oses u p to 1350 w a t t -h r p e r gr am ). 49

Th e r a t e t h eor y p r ed ict s t h e n a t u r e of t h e d ep en d en ce of co lum n e ffi-c ie n cy (i . e . , t h e fh e igh t of a n eq u iva len t t h eor e t ica l, p la t e li ) on va r iou s fa c-t or s su ch a s e lu en t flow r a t e , a d sor b en t p a r t ic le s ize , COIUmn in le t a n d ou t le tp r e ssu r e , n a t u r e of t h e e lu en t ga s , e t c . Alt h ou gh t h e d eve lopm en t of t h et h eor y b ecom es m a t h em a t ica lly fa ir ly comp lica t ed , a p p lica t ion of t h e r e su lt st o p r a c t ice is o ft en r e la t ive ly s im p le . Th e r a d ioch em is t w h o p la n s t o m a k em u ch u se of ga s ch r om a t ogr a p h y w ill ce r t a in ly fin d s t u d y of t h e t h eor y in t e r -e s t in g a nd p rofit ab le .

Howeve r , on e a ct u a lly n e ed s ,on ly a b a r e a cq u a in t a n ce w it h t h e t h eor y t obu ild a sys t em t o sep a r a t e r a r e ga se s . Th e follow in g p a r a gr a p h s a r e w r it t enfo r t h e r a d ioch em is t w h o m eet s a p r ob lem in vo lv in g r a r e ga s sep a r a t ion s , a n dw h o w ish e s t o so lve it w it h a m in im um exp en d it u r e of t im e a n d effor t . F ort h is p u r p ose t h e equ a t ion s g iven ea r lie r for t h e lin e a r -id e a l ca se m a y p r oveusefu l . Th e a ssum p t ion of lin e a r -id e a l con d it ion s is of cou r se a cor m id e r a b led ep a r t u r e fr om r ea li t y in m os t ca se s , a n d t h e t r e a tm en t r e cor d ed ea r lie r i sove r ly sim p lified in som e r esp ec t s even for t h ese con d it ion s . Un le ss on ea c t u a lly d e t e r m in e s t h e a d sor p t ive p r op e r t ie s of h is ch a r coa l, h e m u st a lsok eep in m in d th a t t h ese m ay va r y by fa ct o r s o f two or m or e fr om qu ot ed va lu e s

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in t h e lit e r at u re . Th e a u t h or is in fa ct u n aw a r e of a d sor p t ion d a t a in t h e lit -e r a t u r e for Kr a n d Xe a t t em p er a t u r es le e s t h a n -80C. Isot h e r m s a t low ert em p er a t u r es (su ch a s - 1 95C) mu st t h u s b e es t im a t ed b y r a t h e r d u b iou s ex-t r a po l a t i o n s .

Th e d is t r ib u t ion of r a r e ga se s w ill gen e r a lly b e h ea v ily in fa vor of t h ea d sor b en t p h a se in sep a r a t ion sys t em s so th a t r a t e of b a n d movem en t m a y b ew r it t e n OF . q L@~t . Not a ll of t h e se q u a n t i t ie s m a y b e va r ied a t w ill w it h -ou t im pa i r in g colu mn efficien cy . Th u s t h eor y p r ed ic t s a n op t im um va lu e fort h e lin e a r flow r a t e of ga s t h r ou gh t h e co lum n , Lin e a r flow r a t e s of t h e or d e rof 10 cm /sec m igh t b e con sid e r ed t yp ica l, t h ou gh t h is p a r am e t e r i s n o t p a r -t i t u la r ly c r it ica l a n d m a y be va r ie d b y fa c t or s of tw o or t h r ee w i th ou t se r iou seffec t . Co lum n e ffic ie n cy d r op s le s s r a p id ly n ea r t h e op t im um va lu e w it hin cr e a sed lin e a r flow t h a n w i t h d ecr ea sed lin e a r flow . E ffic ien cy is a lsoim p a i r ed a t ve r y la r ge colum n d iam et e r s . Co lu m n d iam et e r s a r e gen e r a llya r ou n d 1 cm or le ss , Aga in , e ffic ien cy is n ot a r a p id ly va r yin g fu n c t ion ofd i ame t e r , a n d colum n s of seve r a l cen t im et e r s d iam e t e r h a ve b een su cce s s -fu lly u sed (e . g . ,, De t a ile d P r oced u r e 1, g iven in la s t ch a p t e r ). A* t h e bu lkd en s i t y of ch a r coa l gen er a lly lie s in t h e r a n ge O, 5 q O, 2 gm /cm 3, it fo llo wst h a t ext r em e va lu e s of L/A, colum n len g t h p e r gr am of ch a r coa l, fou n d inva r iou s sa t is fa ct or y co lu m n s w ill d iffe r b y on ly a b ou t a fa c t or of 10. Ina d d it ion , L/A is n o t con ven ien t ly va r ie d on ce on e h a s con s t r u ct ed h is sys t em .Colum n s a r e m os t o ft en op e r a t ed w it h a n in le t p r e ssu r e of e lu en t su ffic ien t lya b ove a tm osp h e r ic p r e ssu r e t o su s t a in t h e d e s ir ed flow , a n d w it h a tm osp h e r icp r e ssu r e a t t h e ou t le t . Th u s ~t is n e a r ly a lw a ys close t o 760 mm Hg. On ew ish e s t h e lin e a r flow r a t e of e lu en t t o b e a s n ea r ly con s t a n t a s p oss ib lea lon g t h e len gt h of t h e colum n , a n d it i s t h u s d e si r a b le t h a t t h e r a t io of in le tt o ou t le t p r e ssu r e b e a s n ea r u n it y a s p oss ib le . As a cer t a in d iffe r en ceb e t w een in le t ou t ou t le t p r e ssu r e is r equ ir ed t o m a in t a in t h e d e s ir ed flow ina g iven co lum n , r ou gh ly sp ea k in g, it fo llow s th a t h igh e r op er a t in g p r e ssu r e sa r e p r e fe r a b le in t h is r esp e c t . Ba n d ve loc it ie s for a g iven a d sor b a t e a r em os t con ven ien t ly va r ie d ove r w id e r a n ge s b y a d ju s t in g t h e colum n t em p e r -a t u r e , i . e . , b y ch a n g in g t h e r ~t io v /P a = k wh ich in th e ca se of a lin ea riso t h e r m is a con s t a n t . Ad sor p t ion gen e r a lly in c r e a se e r a p id ly w i t h d ecr e a s -in g t em p er a t u r e , a n d b a n d ve loci t ie s w ill oft e n va r y seve r a l or d e r s o fm a gn it u d e ove r a cce ss ib le t em p er a t u r e r a n ges . Th u s for Kr a t 1 mm Hgp a r t ia l p r e ssu r e over ch a r coa l, t h e va lu e s of v in cc STP p er gr am a r ea bou t O. 1 a t 25C, 3 a t -80C a n d 100 ( a r ou gh gu e ss ) a t -195C . Th u s fora t yp ica l ch r om a t ogr a p h ic co lum n on e m a y gen er a lly fin d som e t em p e r a t u r ea t w h ich t h e b a n d ve loc it y of a n a d sor b a t e of in t e r e s t i s su ch a s t o g ive asu i t a b le r e t en t ion t im e .

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In a d d it ion to a d ju st in g ba n d ve locit y, on e m a y a d ju s t colum n len gt h t oa ch ieve in it ia l sam p le r e t en t ion . In c r ea ses in colum n len gt h w ill u su a llyim p r ove ,9ep a r a t ion e of seve r a l compon en t s a lso , s in ce r e t en t ion t im es a r ep r op or t ion a l t o L, t h e colum n len gt h , wh ile b a n d b r oa d en in g in cr e a se s

1/2r ou gh ly a s L .A few examp le s of p r ior ca lcu la t ion s wh ich on e m igh t p er form in es -

t im a t in g t h e p er form a n ce of a p r op osed ch r or n a t ogr a p h ic colum n a r e givenbe low . I f &e ca lcu la t ion s in d ica t e t h a t t h e p r op osed op er a t ion is u n sa t is fa c -t or y or bor d e r lin e , t h en va r iou s colum n p a r am et e r s a n d /or op e r a t in g con -d it ion s m a y be a d ju st ed in t h e in d ica t ed d ir ec t ion s b efor e con s t r u ct ion of t h esyst em . If t h e op er a t ion a p p ea r s t o b e sa t is fa ct or y w it h a su it a b le m a r gin ofsa fe t y , p a r t icu la r ly a s r ega r d s in it ia l r e t en t ion of sam p le . in a b a n d of w id thsm a ll w it h r esp ect t o co lum n len gt h , t h e sys t em m igh t b e t r ied a s p r op osed .In t h e la t t e r ca e e , fu r t h e r ch a n ges wh ich m a y p r ove n ece ssa r y ca n p r oba b lybe m ad e on t h e ba s is of a ve r y few t r ia l r u n s .

Th e len gt h of a n a d sor b a t e b a n d w a s g iven ea r lie r a s la = (q L t /P t ot )(C G + vA/P a )- 1, a n d for t h e u su a l ca se w h er e G G


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t h a t Xe t ill b e in it ia lly r e t a in ed in a ba n d n a r r ower t h a n th e ba n d of Kr .Beyon d t h is, n o st a t em en t a s t o th e a ct u a l d isp os it ion of Kr a n d Xe on t h ecolum n w ill b e a t t em p t ed . Th e va lu es of v be in g d iscu ssed h er e a r e comp a r -a b le t o vS, t h e cc STP r equ ir ed t o for m a mon ola yer , wh ich is of t h e or d er of100 cc STP p er gr am of ch a r coa l. Th e p or t ion s of t h e isot h e rm s in vo lved a r eu n k n own , bu t d efin it e ly n on lin ea r . A mor e se r iou s comp lica t ion is t h e fa ctt h a t a t t h e se con cen t r a t ion s on t h e a d sor b en t t h e a d sor p t ion of ea ch r a r e ga sw ill ce r t a in ly b e a ffect ed by t h e p r esen ce of t h e oth e r , a n d by t h e a d sor p t ionon t h e colum n of la r ge qu a n t it ie s of a ir .

Ha v in g r e t a in ed t h e Kr a n d Xe in su it ~b ly sm a ll p or t ion s of t h e colum n ,t h e ir sep a r a t ion b y e lu t ion deve lopm en t m a y be a t t em p ted . As t h e a d sor p t ive -t ie s , a n d t h u s t h e ba n d ve loci t ie s, d iffe r by a bou t a n or d e r of m a gn it u d e u n d erm os t con d it ion s , su ffic ien t sep a r a t ion s a r e ea s ily ob t a in ed , even a llow in g forb a n d Wilin g. How ever , b e ca u se of t h is t a ilin g th e p u r it y of t h e Kr w ithr esp ect t o Xe m a y b e exp ect ed t o be be t t e r in gen er a l t h a n t h e pu r it y of t h eXe w it h r e sp ec t t o Kr . Th e pu r it y of bot h fr a c t ion s w ill u su a lly b e su ffic ien tfor m os t p u r p ose s. Alt h ou gh th e equ a t ion g iven ea r lie r for m in im um columnlen gth to a ch ieve sep a r a t ion , L = 12 k 2/(k 2 k ~) w h er e 2 r e fe r s t o t h em or e a n d 1!111 t o th e less a d sor b ed compon en t , m a y b e u sefu l in o th

the radio chemistry of rare gases.us aec

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