Studies on Trace Element Analysis of Uranium Using Soild State

Nuclear Track Detection Technique

DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS

FDR THE AWARD OF THE DEGREE OF

MASTER OF PHILOSOPHY FN

PHYSICS

BY

AMEER AZAM

Under the Supervision of

Dr. Rajendra Prasad

ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA)

1988

DS1197

h C K M 0 W L 3 D G E H E N T G

I am hlgi i ly indeb ted to my s u p e r v i s o r Dr . Raj endra Prasad ,

Reader, Ai 'plied Phys ics Department/ Z.ii . Co l l ege of Engg. Si

Technology v;ho guided me a t every s t a g e of my r e s e a r c h culminat inc

i n the p rc i sen ta t ion of t h i s d i s s e r t a t i o n . I wish to thank

Prof . R.K. Tyagi, Chainnan, AJ 'p l ied Phys i c s Department and

P ro f . l-i. Sbc.fi, Cnaiinuin, Phys ic s Department, A.M.U. for p rov id inc

t h e l a b o r a t o r y and S'-jminar f a c i l i t i e s .

I am ( j ra te fu l to Dr. D . 3 . S r i v a s t a v a who i n t r o d u c e d me

t h e t echn i ^ue o i Uolid s t - i t o t l a c l e a r Track D e t e c t i o n and gave

many useful sm. .- oi> Lions . I am al^o thankful to D r . L . Chand

who helpi:-!.! ino in l o a i n i n o tht^ J o l i d S t a t e Nuclear Track D e t e c t i o n

Techni^jUe. rtuinKs . i i r ,il;-o Liu>i to i^.iss V. liansal t o r g iv ing me

some s u g g e s t i o n s .

In t h e end i i n . i n c i a l suppor t r e c e i v e d from t h e Department

Sc ience jind Technology i s t h a n k f u l l y acknowledged.

i^-^^^

(AMEER AZAM)

P R E F A C E

This dissertation is aeing submitted in partial

fulfilment of the degree of Master of Philosophy (M.Phii) in

Physics, which is an essential pre-Ph.D. requirement in the

Aligarh Muslim University, Aligarh.

This dissertation has been divided into three chapters.

Chapter I contains brief description of the occurrence

and uses of Uranium. This chapter also contains the mechanism

of nuclear fission and the process of detection of fission

fragments using plastic track detectors. Tovjaxds the end of

the chapter a specific mention of the aims ana results of present

investigations has been made.

Chapter II contains brief description of historical

cevelopment of the Solid State Nuclear Track Detection Technique

The track formation mechanism and track development process

have also been explained in this chapter. Methods of track

visualization and evaluation and threshold characteristics of

the SSNTDs axe also mentioned.

Chapter III is the original contribution of the author.

Chapter III describes the application of Melinex-0

plastic track detector for the measurements of uranium content

in Soil and plant samples collected from various places of

Utter Pradesh, The chapter contains all experimental details

result and discussion on the determination of Uranium

content in various soil and plant samples. Finally

the dissertation ends with a list of references of the

v/ork consulted by the author in the preparation of this

dissertation.

^ o N T j E j i s a

Page No,

CHAPTfiR 0MB

1.1 I n t r o d u c t i o n • . • • • 1

1.2 N u c l e a r F i s s i o n • • • • • 4

1.3 Mechanism o f N u c l e a r F i s s i o n • • , . . 7

1.4 Spon taneous F i s s i o n and l i q u i d

Drop Model 7

1.5 Defor tna t lon of t h e L i q u i d Drop , i . , , , 11

1.6 D e t e c t i o n of F i s s i o n F r a g m e n t s U s i n g P l a s t i c T rack D e t e c t o r s • . . . . , 18

1.7 The P r e s e n t I n v e s t i g a t i o n s 21

CHAPTER T/VQ

2 . 1 I n t r o d u c t i o n 22

2 .2 P r i n c i p l e of D e t e c t i o n 23

2 . 3 H i s t o r i c a l Background 2 5

«i.4 Treek F o r m a t i o n Mechanism , . . , . . 27

2 . 5 Methods of T r f c k R e v e l a t i o n and v i s u a l i z a t i o n 3O

2 .6 Methods of T r a c k E v a l u a t i o n 39

2 . 7 T h r e s h o l d C h Q r > x : t e r i s t i c s of SSNTDs and P l a c e of P l a s t i c Among These D e t e c t o r s 40

GHAPPER THREE

3 . 1 I n t r o d u c t i o n 44

3 .2 E x p e r i m e n t a l D e t a i l s 47

3 . 3 R e s u l t s and D i s c u s s i o n s 52

REFERENCES 56

CHAPTER ~ I 1

1 . 1 INTRODUCTION s

Uranium I s a h e a v i e s t n a t t o r a l l y occx i r r ing t r a c e

e l e m e n t . I t h a s w i d e s p r e a d o c c u r r e n c e and i s found i n

minu te q u a n t i t i e s i n d l l r o c k s , sand and s o i l . Al though

r e g a r d e d a s a r a r e e l e m e n t i t h a s a c o n s i d e r a b l e h i g h e r

c o n c e n t r a t i o n i n t h e e a r t h ' s c r u s t t h a n o t h e r t o x i c e l e m e n t s

such a s SD, Cd, Bi and Hg and t h e p r e c i o u s m e t a l s . I t i s

n o t u n i f o r m l y d i s t r i b u t e d and o c c u r s m a i n l y i n a d i s p e r s e d

s t a t e . U 7SCF:AR r e p o r t s 1966;, 197 2 ^ ' ^ i n d i c a t e t h e t y p i c a l

c o n t e n t of u ran ium i n t h e a c c e s s i b l e l i t h o s p h e r e a b o u t

2 . 8 ppm bu t t h e c o n t e n t v a r i e s w i d e l y i n d i f f e r e n t t y p e of

r o c K s , Some a p p r o x i m a t e a b u n d a n c e s a r e shown i n t h e f o l l o -3

wing t a b l e .

U P^^S ppm of

Mafic i g n e o u s r o c k s - o a s a l t C , g a b b r o s

I n t e r m e d i a t e i g n e o u s r o c k s - d i o r i t e s

A::id i g n e o u s r o c k » - g r a n o d i o r i t e s

- g r a n i t e s

S e c i m e n t s - n o r m a l s h a l e s

- l i m e s t o n e s

- b l a c k s h a l e s

1

2

2 .6

4 .7

4

2

8

330

660

860

1600

13oO

660

2600

There h a s been found a l a r g e v a r i a t i o n (250-500)ppm

i n t h e c o n c e n t r a t i o n of u ran ium w i t h i n each t y p e of r o c k s .

In the economically viable uranium ores the conosntratlon

var ies from 1000"fe3000 ppm while in few of the pitchblende 4

samples 72% of U-Og has been found in lenses or veins ,

l^e concentration in phosphate rcrcks can be as high as 0,12

mg/g • Sea water uranium concentration has been found to

vary from 0.000 3 to 0.00 3 mg/1 ' . All of these sources

come in contact with water and thus t ransfer ce r ta in con­

centrat ion of uranium.

Uranium has also been found in phosphate deposits

and can come from t a i l i n g s and phosphate deposits as well o

as runoff from phosphate f e r t i l i z e r , The average f e r t i l i z e r uranium concentration i s about loO /ig/g. Phosphate mineral

5 from Florida indicate uranium concentrat ions 4,5-83,4 pCi/g ,

After processing uranium follows the phosphoric acid whereas

radium found in phosphate deposit follows the by-product

gypsum and i s thus separated. In ammoniated phosphate and

t r i p l e superpnosphate the uranium contents have been estimated

to be 25.3 and 26 pCl/g respec t ive ly . The use of phosphate

f e r t i l i z e r may lead to increase the uranium concentration in

r i v e r s and thereby in the so i l in i t s neighbourhood and in

the p lan t s grown there . More than 99% of the uranium t r ans ­

ported by runoff from land to fresh water systems remains

with suspended p a r t i c u l a t e s on the sediments. Only a small o

amount of uranium remains in true solution in fresh water .

3

Uranium may be found in valence s t a t e s +2, +3,

+4, +5 or +6, the most comroon being the hexavalent and

t e t r ava len t s t a t e s , AP almost a l l the tetravalent compounds

are p r a c t i c a l l y Insoluble, the hfexavalent state i s important

one in water. Natural uranium has 99.2756 ^ , 0-7256 ^ TT 234 and 0.00 6% U and 1 ^g of uranium has an a c t i v i t y of

2+ 0.67 pCi, The uranium i s found as uranyl ionCUO* Jin nature

9 and a l l the natura l compounds of uranium contain oxygen .

The main use of uranium i s in the form of fuel in

nuclear power reac to rs and in nuclear weapons. I t a lso

finds uses in in te rna l guidance devices, gyrocompasses, as

a counterweight for mi^ile r e -en t ry vehicles and as A-ray

t a r g e t s , Urcinium compounds are also used in photographic

toners , coloured glasses^ceramic glasses , t i l e s and as

c a t a ly s t .

Hydrolysis competes with organic and inorganic

complexation dnd control the environmental behaviour of

uranium. At pH6 and iaelow uranium forms very stable coro-

plexes with oxygen r ich organic cornpoxinds in the form of

humic and fulvic acids in the na tura l environment. This

in te rac t ion involves peats , coals , asphal t s , as well as

inorganic i n t e r ac t ions with s" a les , phosphorites, and g

carbonates , When put into solution uranium forms the 2+ uranyl ion (UO' ) and this ion forms soluble salts with

4

10 a l l common anions except phosphate , Uranium can a l s o be

in t roduced i n t o the water supply by human a c t i v i t y in tne

mining and m i l l i n g of uranium o r e , Ihe uranium concen t ra -

t i o n s of water may be i n f e r r e d from nearby ground and

surface s o i l .

1.2 NUCLE>iR FISSION :

11 12 Nuclear f i s s i o n ' was d iscovered in 1939 as a

p r o c e s s in which a uranium nuc leus a f t e r cap ture of

neu t rons s p l i t s up i n t o two p a r t s which a re c o n s i d e r a b l y

d i f f e r e n t from the t a r g e t nuc l eus . Although n u c l e a r

f i s s i o n has been produced from the bombardment of heavy

n u c l i d e s by neu t rons , p ro tons , deu t rons , a lpha p a r t i c l e s

and even e l ec t rons4nd gamma r a y s , nuc l ea r f i s s i o n of

p r a c t i c a l importance i s the neutron induced f i s s i o n of

uranium and plutonlura. A number of rev iews of v a r i o u s

13-21 a s p e c t s of f i s s i o n have been puo l i shed by many workers

The only n a t u r a l l y occuring n u c l e i t h a t can be f i s s i o n e d

with thermal neu t rons i s U v>*iich c o n s i t u t e s 0*11% of

n a t u r a l l y occur ing uranium, Vlhen a nuc leus of high atomic

number undergoes f i s s i o n , f i s s i o n fragments having two

dlmost equal p a r t s a re produced. The f i s s i o n fragments

con ta in too many neu t rons for them to be s t a b l e , Ihey can

approach s t a b i l i t y e i t h e r by e j e c t i n g one o r more neu t rons

or by the the emiss ion of b e t a - p a r t i c l e s ob ta ined from

the convers ion of neut ron i n t o p ro ton .

5

Fission in to more than two intermediate mass frag­

ments i s extremely r a r e . The f iss ion fragments can be

anyone of the nuclides in centre t h i r d of the Periodic

Table. The f ission yield curvl^fcr ^ ^ U by thermal

neutrons has been shown in Figure 1,1, From the f iss ioning

of uranium ^itoyether about 300 s table and radioact ive

nucl ides have been found. About 180 dif ferent beta-emiters

have been iden t i f i ed among the products r e su l t ing from

uranium f iss ioning. As can be seen from the figure the

maximum yield occurs for mass numbers near 9 5 and 140.

The energy released for f iss ion of uranium has been

estimated to be around 200 MeV. About 17o MeV of t h i s energy

i s provided as the k inet ic energy of the f ission fragments.

Except for a very small fraction a l l f iss ion neutrons are

emmitted v i r t u a l l y instantaneously and are ca l led prompt

neutrons. According to the compound nucleus p ic tu re , these

are the neutrons which are boiled offftbm the highly exci ted

compound nucleus. In case of u 0.64% delayed neutrons are

emitted having a time lag of several seconds to more than

a minute af te r the f i ss ion. They a r i s e out of the rad io­

active decay of a f ission fragment. The energy d i s t r ibu t ion

cons is t s of two d i s t i n c t groups having mean energies about

70 and loO MeV. Later s tudies based on the measurement of

ionizat ion v e l o c i t i e s of the f iss ion fragments indicate tha t

6

10

0 I

0 01

oooi

rt) I I I 1 I 1 I I I I 1 I

90 IK) 130 150 170 Moss

Figure 1,1

the K.5. of t-hese fragments is 167 Mev for ^^ fission

produced by slow neutrons. The two groups of energies have

maximum of about 6d and 9y Me».

1.3 MECHANISM OF IJUCLS.^ FISSION t

The mechanism of nuclear iission has been explained

23 by means of liquid drop model of the nucleus. It is

capable of explaining some of its chief features and gives

fair agreement with many experimental results.

According to this model the nucleus in equilibrium corresponding to its most stable configui

assumes a spherical shape/ . As long as the nucleus

is not disturbed, it remains in this state and shape under

the joint action of the

1) Cohesive shiort range nuclear forces acting throughout

its volume and along its surface.

2) The C-iloumb force of repulsion between the protons

present in the nucleus. This force tries to disrupt

the nucleus.

1 . 4 S P O N T A N S O U S F I S S I O N AtJD LIQUID EROP MODEL :

Spontaneous f iss ion can be predicted by emperical

nuclear mass equation. Assuming tne symmetric f iss ion as

a special case, the energy released, E^, upon f iss ioning

in to two equal par t s -

8

= 2 (B.B)^2 - (B.E.)^

Considering Vfelxsaker's semi-emperlcal mass

formula

E^ = ( - 3.42 A /- + 0.22 Z^/A^/^) MeV.

From t h i s equation i t i s c lear t ha t sp l i t t ing of

the nucleus a f fec t s coulomb energy and surface energy in

such a way tha t the change in one tends to cancel the

change in the other p a r t i a l l y . This i s expected as the

separation betv^en the proton groups increases by the

division of the nucleus. Therefore reduces t he i r coulomb

po ten t i a l energy. On the other hand the t o t a l nuclear

surface i s increased re su l t ing in the increase of surface

energy. Thus for spontaneous f i ss ion.

^ f > 0

or [- 3.42 A^/^ + 0 . 2 2 Z^A^/^J^O

or ~ r - > 15

Therefore the nuclear fission should be energetically

possible for nuclei with AN. 85. However the slow neutron

fission does not take place even in many of the heavy

nuclei. This discrepancy was explained by Bohr and wheeler

9

considering the conlomb potential barrier of the two frag-

iTients dt the instant of separation. Hie coulomb potential

carrier prevents the immediate splitting of these two. The

barrier height corresponding to the coulomb potential

between the two symmetric fragments v^en they are just in

contact with each otner is given Dy

^b

/Z, 2 2

47r£, 2R

1 Z2 e2

^/^Co 8 \ ^ t^''''

o 0.15 - ^ j - MeV

Thus the condition of Stability becomes

\ - \ ' ^ 0

or ~ <C 49

It is concluded that nuclei for v^ich the condition

of stabili ty is not fulfilled can not exist as the smallest

disturbance would be sufficient to trigger the disCruption

of the nucleus.

Figure 1.2 shows the relationship between E and

E, and their general behaviour as a function of A. Ihe

10

,

200

? 150 5

J 100

50

E

1 ' I

1 ^iy\

1 1

^J^E^

\ 1

1

/ -

1 50 100 150 200

Mass number

250 300

Figure 1,2

11

graph shows that for A = 250 E, becomes equal to B_, so

t h a t one does not expect nuclei \)ith A>250 to be found

in nature .

1.5 DSFORMATION OF THE LIQUID CROP j

If the force is applied to the drop of the liquid,

so that it is set into oscillations, the system passes

through the series of stages some of vhich are shown in

Figure 1,3.

The drop is elongated into an elipsold (B), If not

enough energy is available to overcome the siirface tension^

the drop will return to its original shape, but if the

deforming force is sufficiently large, the liquid acquire

a shape similar to the dumb-bell (C), Once this stage is

reached, it can not return to its Spherical shape but will

split into two droplets. These will be somevhat deformed (D)

but finally will become spherical (E),

Oho situation in nuclear fission is believed to be

analogous to the liquid drop. A compound nucleus is formed

by the absorption of a neutron by the target nucleus. Its

excitation energy is equal to the binding energy of the

neutron and the kinetic energy, if any, the neutron may

have had before capture. Ihe introduction of excitation

energy into nuclear system disrupts the equilibrium of the

nucleus. Once the incoming neutrons sufficiently distort

12

A B C D l .iquiil-droi) IIHMIC! of fission

Figure 1.3

• CRITICAL ENERGY

DiSIf lNCE: i iETWEEN FRAGMENTS

Fiyure 1,4

13 the Spherical shape of the nucleus, the equilibrium t h a t

exis ted in the undisturbed nucleus i s i r revocably destroyed.

If the energy i s insuf f ic ien t to cause deformation beyond (B)

the in t - ranuclear forces wil l compel the nucleus to i t s

o r ig ina l Spherical form and the exci ted compound nucleus

wil l get r i d of i t s excess energy by the ejcpulsion of a

p a r t i c l e . But once tlie c r i t i c a l point of d i s to r t ion i s

reached, the t o t a l energy of the nucleus wil l continue to

decrease v/ith increai^inc deformation and wil l f i na l l y lead to an i r r e v e r s i o i e oroaK up of the nuclear drop. The mutual po ten t ia l onertj/ oi the rwo symetrical f iss ion fragments

against the distance betv.eon them i s shown in Figure 1.4,

At E t'..'o f ission fragments are far apart so tha t the

po ten t i a l ener^iy is zero. As the fragments come close

together, there i s an increase in the po ten t ia l energy due

to coulor.'h force of repulsion between the fragments, Vhen

the fragments are roughly in contact, a t the point C, the

nuclear forces b' come dominant and the po ten t i a l energy

s t a r t decreasing.

Tho |,ot^t)Llal curve has a maximum value a t C, Tl:!e hump

rcprcs-^nts the ba r r i e r against spontaneous s p l i t t i n g , Ihe

po ten t i a l energy ba r r i e r as seen from the inside of the

nucleus i s oiven by E. - S^ vA ere E, denotes the height of • ' o f D

coulomb barrier and S is the deformation energy available

for fission. The presence of this barrier explains why

fission does not take place Spontaneously in all cases

14 where E,->0. An addi t ional amount of energy B « E. - B-.,

the ac t ivat ion energy i s required by the nuclear system to

allow the f iss ion to take place.

The f i r s t t h e o r i t i c a l treatment of the f i ss ion process

was given toy Bohr and wheeler in 19 39 and they made deta i led

ca lcu la t ions about the behaviour of a nuclear drop under

deformation. For small ax i a l l y syBainetric d i s t o r t i ons the

radius can oe written as

R (er) = R Q L^ "*• 2 ^^°^ ^ 1

where ©"is the angle of the radius vector, cCn is a parameter

describing quadrupole distortion and R is the radius of the

undistorted sphere. For spheroidal distortions additional

terms starting with <^APA ^^^ required. However for small

spheroidal distortions o is considerably less than (A~2*

The surface and coulomb energies for small distortions are

given by (Bhor t« Wieelar 19 39).

% = E° ( 1 - - I - ^ ^ •

where E and E^ are the surface and coulomb energies of

undistor ted spheres. For the charged l iqu id drop to be

stable against small d i s to r t i ons the decrease In coulomb

energy AE = - -r— oC E° must be smaller than the

15

increase in surface energy A B = » ^^ B^, The drop

becomes unstable when | E I -^ E = 1 or \^en

I C • ' S

E° /2E° = 1 . E° / 2 E° i s known as the f i s s i l i t y

parameter x.

For X - 1 the drop will be stable against small

d i s to r t i ons . For x^ 1 there wil l be no potential barrier

to i nh ib i t spontaneous division of the drop. Star the

ideali/ied spherical nucleus we have

v^ere 2 i s the number of protons, Ihe surface energy

where Jlis the surface tension. Green (19 54) performed the

analys is of these equations expressed in terms of mass

number A and nuclear charge Z oy f i t t i n g experimental

masses with the semi-empirical masses and obtained

E° = 0.710 3 Z^ / A /-

and E° = 17,80 A^^^

2 Subst i tut ing those values one gets x = 2 /SO. 13 A.

2 Some typ ica l values of Z / A and x are 35.56 and 0.71

16

for - U and 38.11 and 0.76 for ^^^C{ and are well below

the limiting value of 45, This indicates that all naturally

occuring nuclides are stable with respect to small defor-

mation. For deformations that exceeds the critical limit,

the nucleus breaks apart. The critical energy required to

cause such a break up (activation energy E ) calculated on a

tne b a s i s of Bohr - '.iSieeler theory i s given oy the expre ­

s s i o n . E = S, - E-a b f

2 = A^/^ X 0.89 (1-0.0 22 — • )

If E is less than the excitation energy S provi­

ded by the absorption of a thermal neatron by a particular

nucleus, the fission can be produced in this nucleus by

thermal neutrons. The excitation energy, contributed to the

resultant compound nucleus by the capture of a neutron is

equal to the binding energy of the neutron in the compound

nucleus,

E = B (A + 1, 2) - B (A, Z)

and can be c a l c u l a t e d from the semi-emperical mass formula.

The Taole 1,1 shows the v a l u e s of E and E^ for some n u c l e i , e a

17

YAF3LB 1. 1

Compound E (MeV) B (MaV) E^ - B

(MaV)

^^S 6.6 4.6 2.0

2^^U 6 .6 5 . 5 1.1

^^^U 5.9 6 . 5 - 0 . 6

^^•^Th 5.1 6 .S - 1 . 4

^^^Np 5.0 4 . 2 0 . 8

^ ^ P u 6 .4 4.0 2 . 4

18

238

It is clear that in the case of U a critical deforma­

tion energy of 6,5 MeV is necessary for fission but it

acquires only 5.9 MeV by absorbing a neutron of zero

kinetic energy. Thus no fission is possible in ^

with thermal neutrons, vghereas the thermal neutrons can

23 5 produce fission in U as the excitation energy provided

by the thermal neutrons is greater than the activation

238 energy. However fast fission i s possible vdth U. The

238 experimental threshold energy for fast fission of U is 1.1 MeV as compared to th' predicted value of 0.6 MeV.

The liquid drop model has been applied success­

fully to explain some of the main feat\ires of nuclear

fission. I t fails to explain the observed non-symmetry

of the masses of the fission fragments as syrrenetrlc

fission should be most favoured division according to

t h i s t h e o r y .

1.6 DETSCTIQN 0 [•' FISSION FRAGMENTS USING PLASTIC

TRACK ©BTSCTOiiS:

Nowadays a large number of plastic track detectors

are available which can be used as a charged particle

detector. The Commonly used plastics are Cellulose Nitrate,

Cellulose Acetate, Polycarbonates, Polyethylene terephthalates

e t c . In the follovjing table 1,2 are l i s t e d some well known

p l a s t i c detectors used to record the t racks of charged

p a r t i c l e s . Column 2 gives t h e i r chemical composition. They

have been l i s t e d in order of t h e i r increasing sens t iv i ty .

The l a s t column ind ica tes the smallest ionizing ion being

detected by them.

I t can be observed that Cellulose Ni t ra te and

CR_39 p l a s t i c s can even record the lowest ionizing ion

(proton) vrfiereas polycarbonates can not record proton.

The polycarbonates such as Lexan, Makrofol etc , do not

produce etchable t racks of protons but they are sens i t ive

to low energy c?(,-particles and a l l other heavy ions* The

polyethylene te rephthala te p l a s t i c l ike Melinex, Cronar

and Mylar e t c . a r e not able to record the t racks of

p/C-particles and protons but they do record the t racks

of heavier iono>^B. Therefore, the sui table p l a s t i c

det(^ctors con \y^. used for the detection of f iss ion frag­

ments in the presence of l i gh t charged p a r t i c l e s l ike

e^-par t ic les , protons e t c . \'^.ich they can not record. For

the detection of f ission fragmenijLexan and Makrofol

p l a s t i c de tec tors have been very extensively used. Melinex-0

p l a s t i c has been r a r e ly used as a f iss ion product detector 24

although i t appears to be be t t e r than Lexan and Makrofol

TADLB 1^2

20

Name of p l a s t i c d e t e c t o r

Chemica l c o m p o s i t i o n

Least i o n i z i n g i on d e t e c t e d

CH, Polyethylene

Polyvinylchloride(PVC)

Polyimide

P o l y e t h y l e n e t e r e p l i t h a l a t e Cj. H. 0

(Cronar^ Nfellnex, Mylar)

CH3CI + CjHjCl

S i "4 °4 "2

Polyoxymethy lene

(Cfelrin)

CH^O

F i s s i o n F ragmen t s

42 MeV ^^S

36 I^V ^^0

28 MBV 1 4 N

28 hfeV ^ ^

B i s p h e n o l A _ p o l y c a r b o n a t e ^1 g^i 4* -1

(Lexan, Makrofo l , Kimfol ,

Merlon)

0 . 3 MeV *He

C e l l u l o s e t r i a c e t a t e

( C e l l i t _ T , T r i a t o l - T ,

KG dace 1 TA-401

u n p l a s t i c i z e d )

S"4°2 3 I^V ^He

C e l l u l o s e a c e t a t e

B u t y r a t e

C e l l u l o s e N i t r a t e

( D a i c e l l , Nixon-Baldwin)

S2"l8°7

^ 6 " 8 ° 9 ^ 2

3 MeV 'He

0 . 5 5 MeV - H

P o l y t e c h GR-.39 S 2 " l 8 S 1 MeV proton

21

p l a s t i c a s i t does not r e co rd the t r a c k s of charged

p a r t i c l e s having low i o n i z i n g power. Also the backi-

ground e t ch p i t s developed due t o i t i ^ r f e c t i o n S a r e much

l e s s and e a s i l y i d e n t i f i a b l e than those in the oase of

Lexan and jMakrofol e t c . . Therefore^ we have used Melinex-O

p l a s t i c d e t e c t o r to r ecord the t r a c k s of f i s s i o n p roduc t s

produced by (n, f) r e a c t i o n used for the determination of

uraniMTO con ten t in s o i l and p l a n t samples,

1.7 THE PRBS' IJT INVESTIGATIONS:

The aim of the p r e s e n t i n v e s t i g a t i o n s was t o

measure the uranium con ten t c?f s o i l and p l a n t samples

c o l l e c t e d from d i f f e r e n t p l a c e s of U t t a r Pradesh us ing

SSNTD Technique. The a p p r o p r i a t e e t c h i n g cond i t ion for

Melinex-0 was used a s 6N, NaOH a t 60 C for 90 minutes .

In our s t u d i e s on uranium con ten t measurement in

s o i l and p l a n t samples, we have found t h a t the U-content

v a r i e s very vddely from p lace t o p l a c e . Wie v a l u e s of

U-content v a r i e s from 0.0 23 ppm t o 0 .43 ppm in s o i l

samples and from 0.026 ppm t o C.'206 ppm in p l a n t

samples.

CHAPTER - II 22

2.1 INTRODUCTION :

Unique information can be ext rac ted from the per­

manent ' track* l e f t in the s t ruc tures of certain minerals

and mater ia ls by the passage of high-energy, sub-atomic

p a r t i c l e s . Materials in which nuclear t racks have been

observed are:

Glass Materials : Volcanic g la s s (obsidian), t e k t l t e s ,

soda lime g lass , phosphate g lass ,

meteori tes (glass and ol ivine) e t c ,

ii^^atite, epidote, quartz, micas,

sphene, zircon e t c .

Cellulose n i t r a t e (LR - 115, Dalcel

e tc^ , ce l lu lose accetate , polycarbonates

(Lexan, Makrofol), polyethylene t e r e -

pthala te (Cronar, Melinex), CR-39 e t c .

These mater ia ls , vh^jn used to detect the charged p a r t i c l e s ,

are known as Soli a State Nuclear Track Etetectors (SSNTDs)

and the technique of detecting charged p a r t i c l e s by these

mater ia ls i s known as Solid State Nuclear Track Detection

(S»]TD) Technique, The so-cal led SSNTDs were f i r s t i n t r o ­

duced as an important tool for appl ica t ions in Nuclear

Minerals

Organic Polymers

23

Science and Geophysics in the e a r l y n in t een s i x t e e s by 25

F l e i s c h e r e t a l .

2.2 PRINCIPLE OF D5T5CTI0N :

All charged p a r t i c l e s cause narrow t r a i l s of r a d i a ­

t i o n damage in the m a t e r i a l s v^en they p a s s through them.

As a r e s u l t of e x c i t a t i o n and i o n i z a t i o n m a t e r i a l damage

t a k e s p lace along t h e i r t r a j e c t o r y . The damaged reg ion of

the s o l i d has d i f f e r e n t chemical and p h y s i c a l p r o p e r t i e s

than the bulk m a t e r i a l and i s c a l l e d ' l a t e n t t r a c k ' which

i s in the form of a c y l i n d e r o f ^ 5 0 - l o O A° r a d i u s . This

l a t e n t t r a c k i s i n v i s i b l e under o p t i c a l microscope. However^

the l a t e n t t r a c k can be seen d i r e c t l y a s d i f f r a c t i o n c o n t r a s t

images us ing t r ansmiss ion e l e c t r o n microscopy (TEM), If,

however, one p l a c e s the o rgan ic p l a s t i c m a t e r i a l in a

chemical e t ch ing s o l u t i o n ( e , g , 6N, NaOH) the volume around

the l a t e n t t r ^ c k vdU be a t t a c k e d p r e f e r e n t i a l l y .

The t r a i l of the nuc lea r p a r t i c l e becomes v i s i b l e under an

o p t i c a l microscope as a c y l i n d r i c a l cone-shaped ho le of

^—1-30 pm leng th , i f we cons ide r <7(.-particles or f i s s i o n

fragments.

Nowadays Sol id S t a t e Nulcear Track Etetectors (SSNTDs)

a re p r e f e r r ed over o t h e r p r e v a l e n t nuc l ea r d e t e c t o r s ^s they

24

have in themselves the proper t ies of track recording detec­

to r s l ike the cloud chambers, nuclear emulsions e tc , together

with th' ' compactness and single p a r t i c l e counting a b i l i t y

of semiconductor detectors without requir ing any special

dark room processing or cos t ly e lectronic equipments,

Da^ to t he i r many useful feature^^ these detectors have been

used extensively for the l a s t two decades in almost a l l

branches of nuclear science and technology, radiation dosi-

metry, health physics and geo-sciences , SSNTDs have wide

appl icat ions in the study of low cross-section nuclear

reac t ions , nuclear f ission reac t ions , identif ication of

cosmic-ray p a r t i c l e s of solar a r i galactic origin, neutron

flux riioasurements, study of rad ia t ion history of meteorites

and lunar samples, age determination of geological and

archaeolo; ical samples, microdistr ibut ion s tudies and

microanalysis of some elements l ike U, Th, I^i, Li, B, Be

e t c , neutron and charged p a r t i c l e radiography, radon and

thoron dosinr^try and th^ i r study for predict ion of earth

quakes, study of spreadin'-, of sea-beds, as micropore f i l t e r s

for f i l t e r a t i o n of cancer blood c e l l s ^ virus and bac te r ia

in beer industry, for measuring f l igh t a l t i t ude of birds ajnci

for heavy ion l i thography e t c . In fact these detectors

have been found to have po ten t ia l appl ica t ions in almost

every branch of Science and Technology. In addition to the

25

0 ft

book written by Fleischer e t a l . having exce l len t

t r e a t i s e on t h i s subject and elaborate l i s t of l a t e s t

references covering a l l top ics many review a r t i c l e s have «

a p p e a r e d on s p e c i a l r e f i n e m e n t s o f t h e SSNTD t e c h n i q u e s 25-37 and i t s a p p l i c a t i o n s

2 .3 HISTORICAI., BACKGROUND :

The N u c l e a r T rack E te tec t ion Techn ique (SSNTD) began

i n t h e l a t e n i n t e e n - f i f t i e s wi th two n e a r l y s i m u l t a n e o u s

b u t a p p a r e n t l y i n d e p e n d e n t works by members o f t h e same

e s t a b l i s h m e n t , t h e Atomic Energy E s t a b l i s h m e n t a t H a r w e l l ,

38

Eng land . In t h e f i r s t of t h e s e ifoung , i n v e s t i g a t i n g t h e

c o l o r a t i o n indi.iced In KCl by f i s s i o n f r a g m e n t s showed t h a t

f i s s i o n f r a g m e n t s i n L i F l e f t i n d i v i d u a l t r a i l s o f damage

v/hich c o u l d be e t c h e d by a s u i t a b l e r e a g e n t t o r e v e a l

i n d i v i d u a l e t c h - n i t s . Each p i t c o r r e s p o n d s t o t h e p a s s a g e 39 of a s i n g l e f i s s i o n f r a g m e n t . E.C.H. S i l k and R. S, Ba rnes

t i i r e c t l y obt ;erved a f l a k e of mica bombarded wi th f i s s i o n

f r a g m e n t s by e l e c t r o n microscopy.* The r e s u l t i n g ( u n - e t c h e d )

t r a c k s , a n n e a l e d o u t and d i s a p p e a r e d d u r i n g p r o l o n g e d

o b s e r v a t i o n u n d e r t h e e l e c t r o n beam.

26

In 1961, P.O. Price and R.M. Vfalker of the General

E lec tr i c Company Research and Development Centre, a t

Schncctady (Hew York), apparently ignorant of the Young's

o b s e r v a t i o n s , followed up th^ l i lk-Barnes work by r e d i s ­

covering the chemical e t c h i n g of f i s s i o n tracks and showed

t h a t the e tched t r a c k s in mica l e f t permanent features

v/hich may be s t ud i ed a t l e i s u r e . In 1963, R, L, Fle ischer

jo ined th-^ ter^m of Price and Walker. Afterwards for

several yea r s , almost a l l the work in t h i s f i e l d was

c a r r i e d cvit by these i n v e s t i g a t o r s . During t h i s time

t hey not only developed and put the technique on firm

footir.g but a l s ; aop l i ed i t very s u c c e s s f u l l y to Neutron

dosiroetry, Fissi ' jn s t u d i e s , Biology, Cosmology, Geophysics,

•Archaeology e t c . F i n a l l y they showed that f o s s i l tracks

could be induced in many m a t e r i a l s other than mica. In

f ac t they showed t h a t almost any i n s u l a t o r could be used

40-43 ao a ch:iryed p a r t i c l e t r a c k d e t e c t o r .

Today GS 'TDs are being used in more than f i f t y

l a b o r a t o r i e s of the v;orld i n c l u d i n g Australia, Austria,

Bangladesh, B raz i l , China, Czechoslovakia, England, France,

Hungary, I nd i a , I r a q , I r a n , I t a l y , Japan, Mexico, Pakistan,

Spain, Sweden, the U.S.A., the U. S. S.R., Vfest Germany and

Yugoslavia. C.'--/. Np.eeer (USA), D. Lai ( India) , E. V. Benton

27

(trSA)-, G.A. Wagner (W. Germany), G. Sotnogj|l (Hungary),

H.A, Khan ( P a k i s t a n ) , H. S, Virk ( I n d i a ) , L. Tommasino

( I t a l y ) , M. Monnin (France) , R, %)hor (w. Germany),

R.H. Iye r ( I n d i a ) , V,p. Pe re lyga in (US^) and W, Bnge

(W, Germany) are some of tue S c i e n t i s t s who have made

some impor tan t c o n t r i b u t i o n s t o t h i s new f i e l d .

2.4 TR^K FORMATICK MECHANISM :

Charged p a r t i c l e t r a c k s in s o l i d s a re narrow

( < 50A^ r a d i u s ) , s t a b l e , chemica l ly r e a c t i v e c e n t r e s of

s t r a i n t h a t are composed most ly of d i sp laced atomic

r a t h e r than e l e c t r o n i c de fec t s . On the b a s i s of

exper imenta l t e s t s conducted (a) on the measuremeitit of

e f f e c t s of e l e c t r o n i r r a d i a t i o n on chemical d i s s o l u t i o n

r a t e s of s o l i d s and (b) on the measurement of the r a d i a l

d i s t r i b u t i o n of e t c h a b l e damage in s o l i d s . I t h a s )Deen

concluded t h a t two sepa ra te mecJianisms of trac)c formation

e x i s t . One for the i no rgan i c s o l i d s and g l a s s and the

o the r for tho oruanic s o l i d s or polymers ( p l a s t i c s ) ,

(A) For Inorgan ic Sol ids : VJien a heavy charged p a r t i c l e

pa s se s through a s o l i d i t e x c i t e s a s well a s ionizes^ the

atoms of s o l i d in i t s p a t h . In the case of i n o r g a n i c s o l i d s

28

the primary damage tha t r e s u l t s from the excitation and

ionizat ion caused by the incident heavy ion i s believed to

be roainly responsible for the development of an etchable 4

t rack i . e . for the higher chemical e tchabi l i ty of the

damaged t r a i l s . There are strong evidences t ha t the

secondary e f fec t s of del ta rays are uniJfiportant for the 44 45

case of inorganic so l ids ' . Infact , in the inorganic

solicSs the las t ing the raa l ly etchable damage cons i s t s of

atomic disorder and vacancies. Fig. 2.1 shows the formation of t racks in the

inorganic so l ids according to the Ion-Explosion spike 46 model of Fleischer e t a l , . The incoming heavy ion f i r s t

knocks out e lec t rons (black c i rc les ) 4* om the atoms in

i t s path (open c i r c l e s ) thus creat ing an unstable array

of adjacent +ve ions. The charge centres or +ve ions, so

produced, may produce secondary e lec t rons or de l ta - rays

from tVie atoms of the solid v^ich may further produce

exc i ta t ion and ionizat ion i f they carry enough energy,The

del ta rays deposit energies around the t r a j ec to ry of the

incident p a r t i c l e , Then the +ve ions repel and force one

another away from tiieir normal s i t e s in to the i n t e r s t i t i a l

pos i t ions in the c rys t a l l a t t i c e , thus creat ing vacant

29

iJlgure 2.1

30

lattice sites due to their coulomb repulsive forces.

Thereafter the elastic relaxation reduces the intense

local stresses by spreading the strain more widely. The

damage produced by atomic collosions consist of displaced

atoms and resultant vacancies ani can be etdied pre­

ferentially with respect to the host.

(B) For Organic Polymers or Plasticsx In the case of

organic polymers or plastics the belief is that both the

primary and secondary ionization and excitation play roles

in the production of etchable tracks. In plastics, the

long chain molecules that makeup the material are broken

by the energetic charged particles. Ftee radicals and

excited molecular states are produced which increase in

the chemical reactivity at the broken ends, making the

track areas more susceptible to etching (Pig 2,2). In the

case of plastics the contribution of delta-rays in

depositing the energy sideways of the trajectory of the

48 49 incident ion is most important ' ,

2.5 METHODS OF TRACK REVELATION AND VISUALIZATION*

Many methods have so far been used for the revela­

t ion and visual izat ion of charged p a r t i c l e t racks in

31

Figure 2.2

32

dielectric solids. They are as follows:

(i) Direct observation of latent tracks In thin crys-

tallins solids using Scanning Electron Microscope

(11) Selective chemical etching for all types of SSNTD

41 40 42 viz plastics ^ glasses and minerals and their subsequent observation using optical microscope.

(iii) Track decoration in minerals and their observations

with optical microscope using violet or near ultra-

52 5T violet light^^' - .

(iv) Track revela t ion in photochromic mater ials with the 54 help of colour centre ,

(v) Detecting the presence of l a t en t damage t rack in 55 c rys ta l s using X-rays ,

(vi) Grafting and dyeing of t racks in some selected p l a s t i c s 56-58 and the i r observation using opt ica l microscope .

(vii) Electro Chemical Etching (ECE) technique^^~ ^.

All the above mentioned methods except the se lec t ive

chemical etching have some drawbacks and l imi ta t ion asso­

c ia ted with them. Although electrochemical etdhing (ECE)

enlarges the t racks to very large s izes , i t s appl icat ion i s

33

l imited to , some p l a s t i c s only and for specif ic type

of t r a c k s , I t also requi res high frequency and high voltage

c i r c u i t elements. The se lect ive chemical etcSiing of t racks

revela t ion and t h e i r v i sua l iza t ion using opt ica l microscope

i s the simplest and convenient technique. I t has been most

extensively used in the case of a l l types of SSNTDs

(p l a s t i c s , glasses and minerals) from the very inception

of t he i r discovery.

In the case of se lec t ive chemical etching the d i ­

e l e c t r i c sol id containing charged p a r t i c l e damage t r a i l s

i s immersed in su i table etching solution ( S ^ Table 2,1)

maintained at a fixed temperature. Inside the solut ion,

the bulk material of solid dissolves in general a t a

constant r a t e , V known as bulk or general etch r a t e vhile

the material along damaged region dissolves at a mudi

fas ter ra te V^ cal led the t rack etch r a t e , here assumed

to be constant at every point on the trajectory of the

p a r t i c l e . Since v^ i s greater than V , after soroetiiije the

p re fe ren t i a l chemical a t tack enlarges the damaged region

in the form of a conical e t c h - p i t . When the size of the

e t ch -p i t becomes comparable to the wavelength of v i s i b l e

l i gh t , i t s t a r t s scat t3r ing the l i g h t and can be seen by

op t ica l microscope a t magnifications of 100 x or more.

TABLE 2 . 1

E t c h i n g c o n d i t i o n s for Some D s t e c t o r i

34

S,No, Name o f t h e D e t e c t o r E t c h i n g Condi t ion

1.

2.

3 .

4 .

5.

6.

7 .

8 .

9 .

Soda Lime G l a s s

V i t r e o u s U u a r t z G l a s s

Muscov i t e Mica

Makrofo l -E

Makrofol-N

Lexan

M e l i n e x - 0

CR - 39

Ho s t a p h an

489i HF, 22°C

43% HF, 22®C

48% HF, 22°C

6N, NaOH, 50+1°^

6N, NaOH, 50t l °C

6N, NaOH, 50+1 °C

6N, NaOH, SOtl^C

6N, NaOH, 10±l^C

33% 6N, NaOH +

33% H^O + 33% CH^OH,

40+l°C.

35

Figure 2,3 shows the <3evelopment of charged p a r t i c l e

t rack by chemical etching process in an i so t rop ic sol id

( l ike g lass or p las t i c ) assuming tha t the p re fe ren t i a l

t rack etching s t a r t s j u s t from the surface of the detector

i t s e l f . Since V > V , an etched p i t i s formed. The etched

t rack remains conical t i l l tho time v^en the etchant

reaches the end of tlie par t ic le ' s t r a j ec to ry (Fig. 2,3c)

After tha t the p re fe ren t i a l etching along the t r a j ec to ry

stops and the material etches out a t the same general bulk

r a t e V_ a l l along the surface of the t rack hollow ,

Tho wall of the t rack remains conical

but the end of the t rack becomes spherical (Fig 2,3d) . C o

This i s ca l led the t r ans i t i on phase

Prolonged etching will lead to a posi t ion v*iere the

conical walls of the track-hollow wil l also vanish, and

the en t i r e etched hollow wil l become spherical (Fig 2 ,3e) ,

This i s known as ' spher ica l phase*.

The shape and size of the t racks depend upon the

type of the p a r t i c l e as well as on the c h a r a c t e r i s t i c s of

the detector and etchants , These a l so vary with angle of

entrance. The' t rack saci-ion of normally entering p a r t i c l e

i s in general c i r cu la r and tha t of obliquely enter ing

pa r t i c l e i s e l l i p t i c a l . Grazing t racks show conical

36

Unetched defector S u r f j c f

, P»rf ,c(e '» t r a j t c t o r y

fa)

Etch ing Solt .on

(b)

(Conrcal phase)

]

(e)

(d) ( • )

Figure 2 . 3

37 projections for short etching times (Fig 3^,4),

The geometry of etched tracks for the isotropic as

well as anisotropic so l ids haVe been' studied in great

detai l s by Henke and Bentom. # Soroogyi and flzalay , All

and Durrani , and Somagyi , The expressions for the

diameter of the track d, c r i t i ca l angle ^ , and etching

eff ic iency ^^2^ in 2 rT -geometry are:

= 2 V^. t / VT - Vg ( i )

V + V

L = ^ and

^T

V

( i i )

7 ] . ^ = 1 - _ !G_ ( i i i ) ^T

V„ T Obviously, the greater the value of -Tf , the

smaller will t>? the c r i t i c a l angle ^^ and the greater

will be the etching eff ic iency 7l2jr for trac^ etching

in 2tf -geometry.

38 itrt

» o

o M

v?x

N s / ' > '

-{"-'/ • i -; ,> ' V / ' «-

< A . L ' '

X ' - <

< "*! V

H M

rn

)(

m »o « ' 3 7 IAJ

"» , -a. 'u.

I C

r i-K -< i4>

^ .^ -»

» , n c/>

-» o •»•©

O 3

a o # - f» m o n or * >—

c u •• C - .

O Q. » *

3 O

T

1

I > ' * ^ \

• * !

39

2 . 6 METHODS OF TR.^^K BVALUATION :

G e n e r a l l y e t c h e d t r a c k s a r e o b s e r v e d u s i n g an

o p t i c a l b i n o c u l a r r e s e a r c h m i c r o s c o p e a t m a g n i f i c a t i o n

of 100 X t o 1500 X, In some c a s e s t o t a l number o f t r a c k s

and i n some o t h e r s t r a c k c f e n s i t y _ ^ ( t r a c k s / c m ) i s

r e q u i r e d . For f i n d i n g t r a c k d e n s i t y t r a c k s a r e c o u n t e d i n

a b o u t 50 t o 100 f i e l d s and a v e r a g e i s d e t e r m i n e d . A s q u a r e

g r a t i c u l e i n t h e f i e l d of v iew i s c a l i b r a t e d for . i t s a r e a

by u s i n g a s t a g e m i c r o m e t e r g l a s s s l i d e .

The t r a c k l e n g t h and d i a m e t e r o f t r a c k s c o n t a i n

i n f o r m a t i o n a b o u t t h e p a r i c l e ' s c h a r g e - ~ 2, mass M

7 3 - 7 5 and e n e r g y 2 . The measurement o f d i a m e t e r t h d l e n g t h

i s done by u s i n g a F i l l e r t y p e e y e - p i e c e m i c r o m e t e r .

E n t r a n c e a n g l e o f t h e p a r t i c l e t r a c k can be measured by

u s i n g '^ - a x i s mot ion sc rew o f t h e microscope . 2he v i s u a l

c o u n t i n g u s i n g o p t i c a l m ic roscope I s v e r y t ime 'consuming

and t i r i n g , e s p e c i a l l y i n t h e c a s e of l a r g e number o f 4

t r a c k s ;?- l o . For a v o i d i n g such p r o b l e m s many more methods

have been d e v e l o p e d fo r t r a c k r e v e - l a t i o n b u t t h e s e have

s t i l l n o t found g r e a t p o p u l a r i t y among t r a c k o l o g i s t s

b e c a u s e of t h e i r i n h e r e n t p r o b l e m s . V a r i o u s me thods o f

t r a c k e v a l u a t i o n s a r e :

40

( i ) Scanning E l e c t r o n Microscope and R e p l i c a t i n g

T e c h n i q u e ,

( i i ) T rack c o u n t i n g by R e f l e c t a n c e and T r a n s m i t t a n c e

Measurements .

( i i i ) Coun t ing wi th u n a i d e d Eye Uging P r o j e c t i o n

iMicroscope o r S l i d e P r o j e c t o r .

( i v ) Automat ic Scanning us ing E l e c t r o n i c C i r c u i t o r

Image Ana lys ing Dev ices wi th O p t i c a l M i c r o s c o p e s .

(v) Automat ic Scanning u s i n g Jumping ^ a r k T e c h n i q u e .

( v i ) L o c a t i n g c h a r g e d p a r t i c l e t r a c k s by Naked Eye .

( v i i ) T rack c o u n t i n g by C o n d u c t i v i t y ^ a s u r e m e n t s

th rough E tched T r a c k s .

2 .7 THRESHOLD CHARACTERISTICS OF SSNTDs AND PL/CE

OF PL-AJTICS AMOUG TH33E DETECTORS:

Sxpor inK-n ta l ly i t h a s been found t h a t t h e SSNTDs

a r e t h r e s h o l d type of p a s s i v e d e t e c t o r s , ^ e r e l a t i v e

s e n s i t i v i t y of t h e SSNTDs i s unote rs tood i n t e r m s of c r i t i c a l

16 v a l u e of pr irr .ary i o n i z a t i o n ( J ) c r l t • ^ c r i t i c a l v a l u e

dE 77

of r e s t r i c t e d e n e r g y l o s s r a t e CRSL)^,J.J^^ o r (;jir")v/<.wCvif •

P r a c t i c a l l y for e v e r y SSNTD t h e r e e x i s t s a c r i t i c a l v a l u e

o f m a t e r i a l damage o n l y above which t h e t r a c k s become

41

etchabla, ,^J)crlt ^^ ^^'^^W^ Wfcrit ^QP^o»en*» *hi» c r i t i c a l

damage. If a par t ic le produces an excitation and ionization

in a SSNTD to such an ext»nt that result ing damage i s above

the ('J)crit °^ ^^^^cr i t ^°^ ^^^^ material, i t s tracks can

be preferential ly etched and observed with the help of a

microscope. If the damage produced by any par t ic le i s less

than ( J )c r i t ' ^^^^ par t icular pa r t i c l e ' s trade can not be

etched in that 3SNTD. These threshold or c r i t i c a l values

are shown by horizontal l ines in Fig, 2,5.PleJL8cher et al

obtained these lings by experimentally detecting the

registration and non-registration of tracks of accelerated

heavy ions. The open c i rc les represent non-registration,

while the f i l led circles represent 100% regis t ra t ion.

I t is evident from this -figure that plast ic track

detectors are most sensit ive as the threshold represented by

c r i t i c a l value of primary ionization («I)cj.it ^° lower for

p las t ics (f'ig 2.5), Among the plast ics themselves, the

Oaicell CN is more sensit ive than Nixon-Baldwin, Malinex-0

i s the leas t sensitive p las t ic as i t has th« highest value

of c r i t i c a l primary ionization (J)cx:it* *^i''*«*-0 can not

record the tracks of protons ojf o'-particle and i s e n a b l e

of racording the tracks of ions heavier than oxygen and fission

fragmaits, The Lexan polycarbonate p las t ic records tracks

12

5 10 20 • T

ENERGY / NUCLEON (MeV)

50 100 200 300 • i(fO 1000 20QQ

|iiTlQ»iJUC_¥iliLRA!.4_:

0.4 0.5 0.6 VELOCITY, /^-v/e

Figure 2 , 5

13

of f i s s i o n fragments and low energy a lpha p a r t i c l e s

(belovv'^0.5 5eV> v?hile i t does not record the tracks of

p r o t o n s . S imi l a r l y the g l a s s e s a re more s e n s i t i v e than

mica and m e t e o r i t i c mine ra l s . Muscovite mica and g l a s s do

not r ecord the t r a c k s of l i g h t e r charged p a r t i c l e s v i z

alpha p a r t i c l e s and p ro tons viiereas they record the tracks

of f i s s i o n fragments and o t h e r ions h e a v i e r than oxygen.

S i m i l a r l y the mica r eco rds the Ne ions of energy upto 20 2 feV while the g l a s s r eco rds Ne heavy ions of energy

upto 20 NteV.

CFU39 p l a s t i c t r a c k d e t e c t o r s have been found to

be the most s e n s i t i v e t r a c k d e t e c t o r known so far . This

p l a s t i c i s made by the po lymer iza t ion of a l iqu id monomer

of a l l y l d ig iyco l carbonate and I s ab le to record even the 78

t r a c k s of 1 MeV pro tons

CHAPTER . Ill 44

3.1 INTRODUCTION;

Uranium is a normal constituent of organism and its

-4 -9 concentration in organism varies between 10 % and 10 % by

79 80 weight »^^, it plays an important role in various cosmo-

chronological, nucleo-synthesis events, , toxicity and environ­

mental pollution hazard. Its toxicity to plant is moderate

but it can result in variation of colour in flowers, presence

of abnormal fruits, increase in chromosomes of nucleus sti-

81 mulation . Plant ash normally contains 0.2 to 1.0 ppm

uranium. The uranium content of plants grown in ore however,

may range from 1 to 100 ppm, Iberefore, the high content of

uranium in plant sample may be an indication of mineralized

ground.

I t has been e s t a b l i s h e d t h a t some p l a n t s p e c i e s

absorb much more uranium than o t h e r s . The underground r o o t 82

vege t ab l e s are high mineral absorber and can absorb the

high degree of uranium from s o i l and v ien consumed by human

be ings can pose a h e a l t h hazard . I t has a l so been

observed t h a t p l a n t s t h a t r e a d i l y absorb large amount of

sodium, sulphur, selenium and calcium bu t small amount of

potass ium wi l l a l s o absorb xxranium r e a d i l y . Due to t h i s .

Coni fe rs and d e s e r t shrubs of the ro se family can be used

45

t s indicator plants in sanpling programs in uranium d i s t r i c t s .

238 The radioactivity from U ser ies i s transferred to

plants and water from s o i l . When radio-isotopes are inside

the body, they cause greater health hazard because the

internal t i ssues are irradiated continuoixsly t i l l the isotope

loses i t s radioactivity by natural decay or e l se eliminated

in the feces and urine. The tetravalent form of natural

uranium being unstable i s oxidised to the more toxic hexa.

valent form. The hexavalent form then combines with active

s i t e s (phosphate gro\:{j) on the surface of c e l l s blocking 83 normal metabolic processes for c e l l ' s survival .

Several methods such as Mass spectrometry. Activa­

tion analysis, X-rayfluorescence, Delayed neutron coun­

ting^ Radiometric titethod. Alternating current polazo-

graphy e tc . are available for the determination of trace

quantities of uranium. Sol id State Nuclear Track d«tectors

provide cheap, rapid and ef fect ive technl(|a« #or trace

element analysis . The technique having n««(ted s ens i t i v i ty

and potwitial capability of mlcroroa^plng ev«i at sub ppb

levels of f issionable impurities with (n , f ) , (n, a) md (p,o:)

reactions e tc . i s the so-ca l led Solid State Nuclear Track Detec­

tion (SSNTD) Technique. I t has beoai widely used In diverse f ie lds

l ike anthropology, archaeology, biology, medical scitnces and

46

technology \ Many workers have u t i l i s ed th is techni-^

que for tha detenidnation of uranium in water, milk powders,

semiconductors, c i ga r e t t e s tobacco, human blood, plants,

so i l s , Portland cement, detergents and soaps, coal, flyash

and s tee l e t c . In the present case th i s technique has been

exploited for the t race determination of so i l and plant

samples col lected from various places of Uttar Pradesh,

The external detector method was used in our cftse, I h i s

method consis ts of placing a sample whose uranium concent­

ration i s to be measured in intimate contact with a uranium

poor t rack detector . A standard glass sample of known

uranium concentration i s also included and the entire

assembly i s i r r ad i a t ed with thermal neutrons in a reactor. 235

Tlie thermal neutrons cause f iss ion in U and f iss ion fracjm-^nts produce / a t e n t damage in the p las t ic detectors

232

which are in close contact with the samples. Th if present

in the sample contributes very little to the total damage

from the (n,f) reaction due to its very low fission cross-

section i.e. 40 micro barn as compar^gd to 580 barn for 235

U. Following irradiation, the detectors are etched in a

proper etching so,lution and scanned under an optical micro­

scope. The uranium concentration C of unknown samples can

be calculated by compring the measured track densities directly

47

with those of standard materials, simultaneously irradia-

8 16 ted ' using the relation

A -^ s

'•"^ere y ^ r e f e r s t o t r a c k d e n s i t i e s and s u b s c r i p t

s and X r e f e r t o t h e s t a n d a r d and the unknown, r e s p e c t i v e l y

3 . 2 I XP' RIKSNT.AL DGT.^^LS :

The s o i l and p l a n t s amples were c o l l e c t e d from the

p l a c e s of Agra, J a w a l a p u r (Har idv /a r ) , Nadrai ( S t a h ) ,

R i s h i k e s h , S a h a s t r a d h a r a , Dehra Ran s i t u a t e d i n the s t a t e of

U t t a r P r a d e s h . Washed p o l y t h e n e b a g s were used for c o l l e c t i n g

s a m p l e s . In Agra ©oi l samples were taken from the bank o f

t h 3 R i v e r Yamuna, K a t o l a and Company Garden, P l a n t samples

were a l s o c o l l e c t e d from t h e company Garden, Agra,

5 o i l samples were t a k e n from t h e bank of the Ganges cana l

and some d i s t a n t p l a c e s In Jawalcour (Haridwar). Samples were

a l s o c o l l e c t e d from d i f f e r e n t depths a t Jawalapur t o s tudy

t h e v a r i a t i o n of U - c o n t e n t wi th d e p t h . In the same way

Samples were chosen from t h e bank of t h e River Kal i and,

T a t a r p u r colony^ some' d i s t a n c e away from t h e bank. The s o i l

Samples were chosen from t h e bank and some d i s t a n c e p l a c e s

,/^ 400. Nc. Y ,

is

to study the possible contr ibution of water in r a i s ing the

U-contant of the so i l of the r i ve r bank as i t might t ranspor t

uranium from some d i s t an t source.

Soil samples were grinded properly and sieved through

a 100 mesh sieve. Plant samples were f i r s t dried in an

oven a t 160 G for 24 hours. These plant samples were fused

in a contamination free s i l i c a crucible in a furnace a t

700^C for 2 hours. After grinding the plant Rskes. properly,

•ikese w® - sieved through IQQ mesh sieve (1.5 x 10 cm

ape r tu re ) . A homogeneous mixture of accurately weighed

sample powder and methyl ce l lu lose in the r a t i o l i 2 by

weight was press-^d in to a f l a t p e l l e t of about 1,3 Cm dia­

meter by the ha^'^-p^^sssing p e l l e t making machine, spec ia l ly

d'^sgined for t h i s purpose. The p e l l e t making machine i s shown

in Fig.3.land cons i s t s of the following p a r t s .

Part A- M.S. p la te of size 1.25" x 5" x lO" having four holes ,

of size 3/8'* for f i t t i n g the machine on table and

having two side holes of the same size to support

the p i l l a r s G St F,

Part B - M. S. adjustable guide of size I"x4"xl0" to support

the p i l l a r s having two side holes of size 3/8" to

adjust the same upward & downward.

9i-'f Si

Hri5"K'S'kio')

0 7'J'W- -r\07S"i

PKLLBI MAKING MACH(N£

St

50

Par t C - M.S. guide of s ize 1. 25''x4"xlO" f ixed with p i l l a r s

by H. S. n u t s of heavy duty.

P a r t D _ M. 3. handle of s i ze 0 .73" ^ x 16" to rotate the

p a r t K upward or downward.

P a r t S _ C . I . tush to support p a r t H,

Pa r t F & G - M. S. |> i ] l a r s of s i ze 1" (j> x 15" having upper

p a r t 0 . 7 5 " x 1.25" duly threaded to f i x i t with

p a r t C with n u t s and lower part of s i z e 0 ,75"xl ,25"

to f i x them in the b a s e .

Pa r t H _ High carbon s t e e l screw of s i ze 1" 0 x 10,5" having

upper p a r t of 2" ^ having hole of s i z e 0,7 5" 6 x

1,5" for hand le .

Pa r t J - M.S. d i sc of 1.5" (j> x 0 , 7 5 " as per drawing.

Par t )< - 3p<?cial K s t e e l punch having upper part of

0 .5" (f) X 1.5" and lower part of 13 rron ^ x 3" duly

hardened, tempered and gr inded surface.

P a r t L _ Special K s t e e l die of 1.5" f x 3.75" duly hardened,

tempered and gr inded s u r f a c e .

Pa r t M - Special K s t e e l base of 2" f x 0.7 5" lower part and

13 mm ^ X 0.75" upper part duly hardened, tempered

and gr inded su r f ace .

51

Each p e l l e t was sandwi-ched between two already

washed in double d i s t i l l e d water Meline:&-0 detector pieces

of the same s ize . Several such 'sandwi-ched p e l l e t s along

with a standard glass with known U-content >«ere packed in

an aluminium capsule and sealed t i g h t l y to make the

intimate contact . This assembly was i r r ad i a t ed with thermal

netitrons in the core of APSARA reactor for one hours a t a 12 2

place where the nominal neutron flux was 2 x 10 n/cm /See (10 to 15% fast neutrons) .

After i r r ad i a t i on detector pieces were taken out and

washed. These washed pieces were etched in 6N, NaOH a t 6o°C

for 90 min as i t i s the optimum etching condition for

Melinex-0 p l a s t i c de tec tors . The etched detector pieces were

a i r dried and scanned under binocular research microscope

at a magnification of 430 X, The t rack dens i t i es were deter­

mined by counting the fission t racks in the e n t i r e area of

the detector . Trncko were counted on both the pieces of the

detector and mean was taken to determine the t rack densi ty .

The square marked on the g r a t i cu l e in the eye piece represen--4 2

ting one field had a calibrated area of 1.69 x 10 cm . The

standard glass detector was etched in 48% HF at 23°C for

5 sec and track density was calculated.

52

3.3 RESULTS AIN D DISCUSSION;

Uranium c o n t e n t o f unknown samples was d e t e r m i n e d

u s i n g t h e r e l a t i o n (3 .1 )»The Ul-conten t of s o i l s amples and

p l a n t samples a r e summarised i n T a b l e 3 . 1 and Tab le 3 .2

r e s p e c t i v e l y .

I t i s obse rved^rom Tab le 3 . 1 t h a t U - c o n t e n t of

s o i l samples v a r i e s from 0 . 0 2 3 t o 0 .430 ppm. I t i s a l s o

e v i d e n t t h a t t h e U - c o n t e n t of t h e s o i l samples c o l l e c t e d

from t h e bank h a s h i g h e r v a l u e t h a n t h a t of t h e s o i l

3ampl'-»s c o l l e c t o d from some d i s t a n t p l a c e s . The h i g h e r

v a l u e of u ran ium i n t h e s o i l a c r o s s t h e bank of t h e r i v e r s

may i n d i c a t e t h e c o n t r i b u t j ^n of w a t e r i n r a i s i n g t h e

u ran ium c o n t e n t t h r o u g h r u n o f f p h o s p h a t e f e r t i l i z e r s and

some o t h e r s o u r c e s . Among t h e r i v e r bank s o i l s a m p l e s , t h e

s o i l sample c o l l e c t e d from t h e Yamuna r i v e r bank h a s t h e

h i g h e s t Value of u ran ium c o n t e n t (0 .430 ppm). T h i s sample

was t aken fro"i a p l a c e b e h i n d t h e Ta j Mahal. P r e v i o u s l y

waste p r o d u c t s were dumped i n t h e r i v e r b e f o r e t h i s p l a c e ,

v/hich migh t be t h e p o s s i b l e c a u s e of t h i s h i g h e r v a l u e .

The u ran ium c o n t e n t of s o i l s amp le s c o l l e c t e d from t h e

p l a c e 15 mete r away from t h e c a n a l bank and from d i f f e r e n t

d e p t h s v;ere found t o d e c r e a s e wi th i n c r e a s e i n d e p t h . Across

t h e bank s o i l i s d e p o s i t e d by w a t e r l a y e r a f t e r l a y e r , I he

TABLE g-i

Uranium Content of Soi l Samples

53

S.No. Location Total No, of U-content in ppm tracks

4.

5.

6.

7 .

8.

9 .

10.

1 1 .

Bank of Ganges Canal, Jawalapur (Haridwar)

A p lace about 15 meter away from the Ganges cana l bank and

(a) 6" deep from the upper surface

(b) 12" deep from the upper surface

(c) 18" deep from the upper surface

A f i e l d about 4 Khi away from the canal bank, Jawalapur,

Yamuna River Bank Agra

Matola, Agra

Company Garden, Agra

Kali River bank Nadrai (Btah)

Tatarpur Colony about 300 meter away from the Kali River bank

Sahas t radhara (Dshra EVin)

Local Bus s t a n d . D ^ r a Dun

Bus Stand, Rishikesh

1537 0.2331.00 54

1300

850

611

937

2786

151

1620

1044

508

1489

1208

1500

O.a02i.OO5O

0. 132 Qt, 004

0.093±.003 5

0.143t .0042

0. 430±.0073

0 .023t .00 l7

0. 2471.0056

0 . l 6 1 t . 0 0 4 5

0.077+.0031

0.23 2+^0053

0,2631.0048

0.2301^0054

54

OS U1 U) to

^1 Oi 3

o cu •1

s-3

>

0 X

JO

& h*

g" s-

1 O

0) 3

o 0) •1

» 3

3 (D CO 3

> O iQ O

3 1 0> 3

O (U H

^ 3

M 3 M M-

^ ^1

o

J Qi 3

O (U 1-1

» 3

o H

• 0 0) 3

s? 3*

01

3

P ^ 0)

^ t M

c n

o c

cu

o o

o

cn

3

n

w O

• o to OH

o o )-» CD

3 W

H-iQ O H-

0)

3 a a •I

O O

0)

3 0) a 3 H- (0

3

1 ^ o o p. O

f ir o> 3 f t Qi

<Q "O C (fl 0> H-i_». Cu 01 H-

< c 0) 3

>Q ^3 C CO 0) H-

«_.. a 01 H-< c 0> 3

CA

.? CO 0

Ti 3*

^ ff

(A

o •o 3-S ^

1 0) O V 3"

*< ??

1 W 0 tJ 3-

^ /?

i? CO o

^ < sr

1 s ^ s; 1?

H-» - J tn

ON ON t-»

-0 •J -J

o 00 -^

»-» en >t^

10 00 (O

u> vO l-»

o w

o o

CD

O o u>

o

o o m

- J

o o :5

o to

o o

o

to

(0

o

o (0

O 3

OH •1 O O O

•o o

O »

O

a* ?r as (0 O

o ft

•1 (U 3 H-

3

3 ?f 3 (+ O M>

•O M

s > fO

55

lower value of the uranium content indicates the higher

age of the so i l and the higher value indicates the lower

age of the so i l of tha t pa r t i cu l a r place.

I t i s c lear from Table 3,2 tha t the uranium

content of plant leaves samples var ies from 0.0 26 to

0.206 ppm and tha t var ia t ion takes place from plant to

plant and place to p lace . This i s due to the fact that

the uranium content might be d i f ferent in so i l and water

where the p lan t s were grown.

The uranium content of so i l and p lant samples

reported by u.s ^.re d i f ferent from those reported by til 91

Goswani e t a l . and Virk e t a l . This disagreement i s due

CO the fact that the p lan t s samples chosen by Goswani e t a l .

and Virk e t a l . v;ere of different v a r i e t i e s from those

invest igated by us and the soi l belongs to d i f ferent regions

of the country.

56 R E F B R B N C S S

1 . UNSCEAR

2 . UNSCSAR

IAEA

4 , Hardy, C . J .

: Report of Uni ted Nations S c i e n t i f i c -

Committee on t h e Effec ts of Atomic

Radia t ion , Uni ted Nat ions ,

New York, (1966) .

: " I o n i z i n g Rad ia t i on : Levels and

Ef fec t s " , Vol I , Report of t h e

United Nat ions S c i e n t i f i c

Committee on t h e Ef fec t s of Atomic

Radiat ion, Uni ted Nat ions ,

New York, (1972) .

: " s i g n i f i c a n c e of Mineralogy in t h e

Development of Flowsheets fo r

f ' rocessing Uranium Ores", Technical

Report S e r i e s No. 196, I n t e r n a t i o n a l

Atomic Energy Agency, Vienna, (1980)

: "The Chemistry of Uranium Milling",

Rad. Chlm. Acta, 25 (1978) 121-134.

226, 5 . Roess le r , C.E. , : "Uranium and Radium " * ' i n F lor ida

smith Z.A., bolch, w.F. Phosphate M a t e r i a l s " , Heal th Phy.

and Pr ince R.J . 37 (1979) 269-2 77 .

6 , Turkian K.K. and

Chan, L.H.

"The Marine Geochemistry of Uranium

I so topes , " Th and ^^^Pa, from

Activation Analysis", ins Geochemistry

57

J and Cosmochemistry (Edltad by

A.O. Brunfe l t an<3 E. Ste lnnes) ,

UNIVERSITETSPOR-LAGET, Oslo-Berger-

Tromso (1971).

7 . Rd»na E., G^iipatrick: •njranium Dsterminat ion in Sea Water",

L.O. and Je f f rey , Trans, Am. Geophys. U. 37 (19 56),

L.M. 697-701.

8. Spalding R. F. and : '•Uranium in Runoff from the Gulf of

Sacke t t W.M. Mexico D i s t r i b u t i o n Province Momalous

Conc' n t r a t i o n s " . Science 17 5 (1972)

629-631.

9. Kat^, J . J . and : "The Chemistry of Uranium, the Element

Rabinowitch E, I t s Binary and Rela ted Compounds (New

Yor.<: Ebver) (19 51),

10. Longane, J. J . , : "Analyt ica l Chemistry of Selected

M e t a l l i c Elemeftts (New York*

Reinhold) (1966).

11. Turner L. A. t Rev. >tod. Phys . , 12 (1940), 1,

12. Glass tone S., : "Sourcebook on Atomic Energy", D, van

Nostrand Co., I n c . , Chapters XIII and

XIV. (19 50) .

13. Halpern I . : Ann. Rev. Nuc. S c l . , 9 , (1959), 245.

58

14, Hui^enga J . R. and

Vandenbosch R.

15. V*ieelar J . A.

16. Hui?ienga J . R.

17. Wile ts L.

18. Fraser J . S. and

Milton J .C. D.

19. Gindler J . E. and

Hui,6enga J . R.

20. Fong P.

20. Bohr N, and Wheeler J .A ,

: In "Nuclear Reac t ions" , (Edi ted

by P.M. Endt and P. B. Smith),

Chapter I I , North-Holland P u b l . ,

Ansterdam (1962),

I In "Pas t Neutron P h y s i c s " (Edited

by J . B. Marion and J . L, Ibwle r ) .

Wiley ( I n t e r s c i e n c e ) , New York

(1963).

J In "Nuclear S t ruc tu re and

Elec t romagnet ic I n t e r a c t i o n s "

(Edi ted by N. Mac Donald), Plenum,

New York (19 65) .

: "Theories of Nuclear F i s s i o n " .

Oxford Univ. P r e s s (Clarendon),

London and New York (1964).

: Ann. Rev. Nuc. Sc i . 16 (1966), 379.

: In "Nuclear Ghemistry" (Edi ted by

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