J

Indian Journal or Pure & Applied Physic� Vol. :19. March 2()() I. pp. 117-122

Inner@remsstrahlung accompanying p- decay in 147�1 S LJKeshava*�Gopala;' &.!JVenkataramaiah**

'�artment or Radiation Physics. Kidwai Memorial Institute of Oncology. Hosur Road. Bangalore 560 02:) ';'Dcparlment of SllIdies in Physics. Manasagangothri. Uni . ity or Mysorc. Mysorc 570 ()(l(,

k' a. Shimoga District. Karnatak

I I X INDIAN J PURE & APPL PHYS, VOL 39, MARCH 2()() I

R CA80.'i:\ photo-mu l t i pi ier tube, pre-amp l i fier, ampl ifier and EG & G ORTEC Model 7 1 50 Mul t i channd A n a l y ser. The acti v i ty a t the t i me of conducti ng the ex peri ment was 27.'i48 B q . The spectrometer was ca l i hrated Ll s i n g the known monoenerget ic gamma sources. The source to detector d i stance was 1 ..'i8 cm and it was posit ioned in the center of the detector. The spectrometer cal i brati on was 1 .26 ke V per channe l . First 26 channels were b l ocked by the l ower d i scri mi nator sett i n g to e l i m inate i nstru ment noise pu l ses. The source and I he detector system i n c l u d i ng the photo-mu l t i p l ier tuhe and pre-amp l i fier assembly was sh ie lded by kacl hous ing which had :2 mm a l u m i n i u m l i n i n g on I h e i n ner surfac e . The lead housi ng hel ps i n red uc ing the background counts and the a l u m i n i u m l i n i ng he l ps i n prevent i n g e lectron transport ( i n the case of a �. emitter) to the lead housi n g (which may res u l t in the production of u n wanted external Bremsstra h l u n g and lead K-x ray s ) . The source t h ickness was sma l l enough so that the selfabsorption and producl ion of EB are neglected : Tile source was houseci i n a perspex c y l i ndrica l box which pro v i ded a m i n i mu m th ickness of 0 .8 cm of pl' rspc x for , llle nuati n!:' I h e sou rce r3 part ic les . A s per' pe x i ., , I l o w Z maLeri , t I ( mean Z "" 6.5) t h e EB prodl lc t ion in that a l so i s neg lected . H owever, the c orrect ion due to the absorpt ion of IB in the B sl opper mater ia l as we l l as the a l u m i n i u m cover ing of the Nal detector i s i n corporated i n the cal cu l at i on of I he geometric effic iency. Ten samples count i ng of .'iO hr each and s i m i l a r s i ze background count ing were performed .

The stat i st ica l strength of the data is determi ned hv the sta t i sl ica l s i �n ificance of the d ifference h�tween the mean sO�l rce p l u s backgroun d (X) and t he mean background ( /3 ) cou nts . Noting that the nuc lear cou n t i ng fo l l ows Poisson d i stri but ion which approaches Norma l or Gauss ian d i str ibution when the number or measurements are l arge, the d i stri but ion of sample means too fo l l ow the normal d i slri but ion and so a l so the d i str ibut ion of tbe d ifference between any two sample means . In any �i ven channel both source plus background and IXlck !!1"Oll ll d counls are considered as the samples of " pr�) lt l a t i on I 'm the pu rpose of conducting thc slat i s t ic� t I test . The standard error 0 for :the d i sl r i bu l ion of t he d i fference between any two sample llle�I I lS i:; gi ven h y :

Denot i n g the d i fference X-B a s lib. t h e n I hc stat i st ic t = lil)0 determines the confidence l evd of li lh which can be read from the Standard Nbrm,t i Curve Area Tab les (Armitage and Berry ' l ) for which mean = 0, standard dev iat i on = I and I is the absc i ssae exten d i ng from -00 ( i nfi n i t y ) to +00 . p i \; the rati o of the area u nder the Standard Norma l Curve l y i n g between any gi ven value o f I and 1 = 00 to the area u nder the Standard N ormal C ur ve l y i n g between f = 0 a n d f = 00 . The p value correspo n d i n g t o I = lil'/0 determi nes t h e req u i red confidence leve l .

( i ) i f lih :::: 3cr, then i t can be considered a � t rut' IH i ntens i ty at a confidence leve l of (U ,:�: or Ie�� ( I ' ::; .00:\) . The data can be cons idered 10 he exce l len t : ( i i ) if 20 ::; lih < 30, then the confidence leve l o f fH i n tens i ty l ies between .'i % and ( U % ((l.( )m < p ::; 0.05 ) . The data can be considered to be good ; ( i i i ) i f 1 0 ::; lih < 20, then the confidence l eve l or II3 i ntens i ty l ies between 32 % & .'i ryo (0 .0) < p ::; (U2 ) . T h e d ata c a n b e considered to b e fai r. ( i v) i r lib < 10, , then at a confidence level of more t han :\2 % ( p > 0·.32) , the data is considered to be stat i st ica l l y poor and the n u l l hypothe:; i :; may he accepled ( i .e .. I ht'. d ifference between X and n i ., c() l l s i dc rl:d i n s ign ificant and both X and n a re trea ted a� �ampl l'. mean s comin g from the same popu la t ioll of coun l � .

I f i t i s dec ided t o termi nale I he cial ; t a t , I l lY desired confidence leve l (for examp l e 32 ('In or ) 'Ir or 0 . :\ %) which may correspond to some c h a n n e l n umber say N, T h e cou nts i n t h e N+ I th c h a n n e l c ; tn be treated essent ia l l y as background o n l y . This magn i tllde of counts may be subtracted fro l11 a l l channe l s . Th is i s s i m i l ar t o correct i n g pos i t i ve z.ero error i n any measur ing i n stru ment . Th is proced l l l"t: may a l so be termed as base l i ne s h ifl ( I3 LS )

The d ata obtai ned from 1 17Pm was exce l lent l i p 1 0 1 80 keY and good u p t o the end poi nt e nert-' y . S izab l e counts were present a t t h e e n d poi nr energy and beyond . Even though. efforts are made to mai ntain the stab i l i ty of the i n stru me n t . hec ml st' nf the l ong hours of count i ng and a l so the background counts and source counts bei n g recorded at d i fferen t t i me!i; the fact that the i n herent f1uctu�lt ions ex i �t i n both, make the d i fference counts lib e i t her pns i t i VL' or negat i ve towards the end point energy where l I i l counts are expected . Th i s fact a l so .i us t i fies the I3 LS descri bed above for pos i t i ve d i fferences .

KESHA V A et al. : B REMSSTRAHLUNG IN �-DECA Y I 1 9

In our present experiment, the data terminated at di fferent levels of confidence (0.1 % and 5 %) was processed with and without BLS. The unfolding of the m intensities from the raw data was carried out adopting the step hy step procedure of Liden and Starfelt l �, details of which can be found elsewhere (Basavaraju et ai. I '; and Babu et ai. I f' ) . After initial background subtraction and pile-up correction, the intensity spectrum is corrected for the finite energy resolution of the NaI(TI ) detector. The resolution function is taken as Gaussian. Next, the correction due to the compton electron distribution is made. Further the data i s subjected to iodine K X-ray escape correction and the geometric detection efficiency of the detector-source spatial configuration including the attenuation of photons by the aluminium covering of the detector and the �. absorber (if used, as in the case of �. emitters). Finally the spectrum being corrected for the photo peak efficiency of the detector.

However, it is necessary to mention, the distortion caused by the detector resolution correction. The IB spectral data undergoing this correction tend to show false higher intensities in a few channels at the beginning and in a few channels towards the encl . Due to the absence of counts on one side, the convolution procedure adds counts to the above said channels and hence the corrected data show false higher intensities. Except for this, most of the spectrum is well

1 :20 INDJ A N .T PURE & APPL PHYS, VOL 39, M ARCH 20(H

. - Bac k g ro u n d .- . S o u rce count� I��:\

W , OOO r " .... ,

\ \ C ::J I \ \

\ \ '-

\ '-. ' . . "

. - . " . . 1 ,000 � . . -:I=-----'------.l--_� __ _L __ __L __ _.J.. __ _.l o 20 40 60 ..�I----__ � ____ -L _____ �_ j

U1

4 1 0 . -

' c 3 �, 1 0 -.�

o 1 0

1 0 o

80 1 00 1 20 1 40 1 60 1 80 200 220 Ph oto n En ergy (I

KESHAYA et al. : BREMSSTRAHLUNG IN �-DECA Y 1 2 1

... . - .

����--�-- - - - - - 0 . ' .. . . :'.' . : : ;, .. . . . • ,, '.

' ." E,.

o

C • .. ;, E

Fig . 3 - Compari son of experi mental resul t with theoret ical spectrum . A : Lewis and Ford (first f orhidden w i th e x aci Fermi fu nction replac i n g i ls approxi mat ion) ; B: Ford and M arti n (with exact Fermi fu nction ) : C : Experi mental I I I spectrum us i n g raw data a l a confidence level o f :s; 0.3 % with base l i ne sh ift ( normal ized to L F a t 1 1 0 keY) ; U : Experi mental IB spectrum using raw data u p to end point energy w it hout base l i ne s h i ft ; E : Experi mental IB spectrul l l usi ng data as i n D with base l i ne sh ift: F: E xperi mental IB spectrum from publ ished l i terature rBabu cl (fl . , Pll I's /?IT r. :\2 ( l lJR5 ) 1 0 1 0 1

:S( U% with I3LS . Fig . � shows the IB intensities obtained by different statistical considerations. Theoretical distributions based on LF and FM theories are also shown. For the purpose of direct comparison with the past experimental results. one such result from Babu el al. 1O is also shown. The IB intensities calculated by terminating the raw data at the end point energy position: ( i) without BLS, (ii) with BLS, both deviate from the theories, The shape of intensity curve whose calculation is based on terminating the clata at ( ) . � % confidence level and with BLS, very c lose l y follows LF distribution ( up 1 0 ahout 1 70 keY ) , barring the distortion produced hy the resolution correction at the low energy end. Thi s curve is normalized at the middle of the energy range to the LF spectrulll ( i .e . at 1 1 0 keY) . Beyond 1 7 ( ) keY , the statistical insufficiency of the data makes it difficult to arrive at any conclusion. In this study, the authors intended to study the shape of the m spectrum only rather than the absolute intensities. It may be concluded that most of the discrepancies found in the experimental study of IE intensities can he attributeci to counting statistics. Our conclusion is

based on the study of six other isotopes which ga ve meaningful results without unrealistic high intensi ties near the end point energies hy the l ise or counts with good statistical strength and base l i nl' shifting.

Acknowledgement

Thanks are due to Prof L Paramesh and Prof M S Madhava, of the Department of Studies in Physics, Manasagangothri, M ysore 570 O()6, f0r laboratory facilities and Kidwai M emorial Institute of Oncology, Bangalore 560 029. for computer fac i lities.

References

Knipp J K & Uh lenhcck G E. Pln's;'·lI . .'\ ( I ' ) ' ! I ) 'I � 'i . 2 B loch F. PhI'S Nt'I'. 50 ( 1 1):1(,) 2 7 � .

:I Lewis R R & Ford G W. PhI'S N" I ' . 1 07 ( 1 '):; 7 ) 7 .�! l . 4 Ford G W & Marl i n C F. Nllel Pin's A . 1 .'\4 ( 1 0(,1) 457. 5 Wang C S Chang & Fal ko!'!' D L. Ph l'.I' NI' I ' . 7(, ( I 'WJ) :16:;. 6 Boehm F & Wu C S. I'hl'.I' Nl'I'. 1):1 ( 1 054) 5 1 X. 7 Langewin Jol iol H. C r AUIlI Sci. 24 1 ( 1 1)55 ) 1 2X(,. X Starfe l t N & Ceclurl u nd .1 . 1>11." .1' Nt'I'. l OS ( I 'J.� 7 ) 24 I .

1 :22 I NDIAN .T PURE & APPL PHYS. VOL 39. M ARCH 2()( ) I

(i S i n�h 13 & AI-Dargazc l l y . PhI's Nl'v C. 3 ( 1 97 1 ) 3M. I ( ) I:Ld111 B R S . Basavaraju A . Venkalaramaiah P. Gopala K &

S,m jccvaiah H . PhI's NI' I ' C. 32 ( 1 9X5) 1 0 1 0.

I I l)r,l�ad Bahll R. Narasi lllhaillurthy V A & Narasi lllhal1lu rthy K . .I IJ/I '·.1 1\ : Mal" Nwl allt/ Cm . 7 ( 1 974) 2295 .

I ::' Kcsh;lva S L. Vcnkalaral 1 la iah P. Gopala K & Gopinalh D V. Illt/iall .I 1'1/ 1'.1 A. 7 1 . 1 I ()(n ) 4X I .

I ; Arill i lagl� P & Berry C. SUll i.l'liea/ 11I1'111Ot/S ill. //I I't/ica I

resl'arch. Thi rd cd. B lackwe l l Scicn l i ri l' PlI h l i c'< l l i o I IS . ( 1 994). 4 1 - 1 46.

14 Liden K & Starkl t N. A rk FI',I. 7 ( 1 9):'\ ) 427. 1 5 l3asflvnraju A. Venkataramniah P. Gopal" K & S;m jecv" iah

H . .1 Ph I's C. 1 0 ( 1 9X4) 5 6 3 . 1 6 Bahu B R S . Venkntaralll;l i"h P. Gopala K 8:. S; l IljCl' v < l i ; i l l

H . . 1 Phys C. I I ( 1 98 5 ) 1 2 1 3 . 1 7 Huhbe l l J H . Nail [J Sills NSIWS NIIS-2() ( I l)(,li ) .