Jointly published by Elsevier Sdence S. A., Lausanne and Akad~miai Kiad6, Budapest

J.Radioanal.Nucl.Chem.,Letters 201 (6) 481-493 (1995)

C H A R A C T E R I Z A T I O N OF TWO I R R A D I A T I O N P O S I T I O N S FOR F I S S I O N T R A C K D A T I N G AT THE L E N A T R I G A M A R K II R E A C T O R

G. B i g a z z i ,

Istituto

J.C.

H a d l e r Neto*, P. Iunes*, M. O d d o n e * * *

S. M e l o n i * * ,

CNR di G e o c r o n o l o g i a e G e o c h i m i c a Pisa, I t a l y

. *Instituto

de F i s i c a

"Gleb W a t a g h i n " , SP, Brazil

Isotopica,

UNICAMP,

Campinas,

* * C e n t r o C N R per la R a d i o c h i m i c a e l ' A n a l i s i per A t t i v a z i o n e , D i p a r t m e n t o di C h i m i c a G e n e r a l e , U n i v e r s i t l di Pavia, Pavia, Italy * * * D i p a r t i m e n t o di C h i m i c a G e n e r a l e , U n i v e r s i t ~ di Pavia, Pavia, Italy

Received Accepted

8 September 22 S e p t e m b e r

1995 1995

In the p r e s e n t p a p e r the use of two n a t u r a l u r a n i u m d o s i m e t e r s is described. D a t a are c o m p a r e d w i t h f l u e n c e v a l u e s o b t a i n e d by u s i n g N I S T glass s t a n d a r d s and t h e tradit i o n a l a c t i v a t i o n of m e t a l foils. F i n a l l y an e x a m p l e is r e p o r t e d for a p p l i c a t i o n of n e u t r o n d o s i m e t r y to the dating of the Fish C a n y o n Tuff age standard.

INTRODUCTION Fission butions

track d a t i n g

disciplines, ogy.

However,

requires

(FTM)

to the a d v a n c e m e n t

such as geology, the r e l e a s e

a careful

in d i f f e r e n t

geochemistry

and a r c h a e o l -

of h i g h l y r e l i a b l e

evaluation

0236-5731/95/US $ 9.50 Copyright 9 1995 Akadgmiai Kiad6, Budapest All rights reserved

has b r o u g h t g r e a t c o n t r i -

of k n o w l e d g e

481

age d a t a

of the m e t h o d o l o g i c a l

ap-

BIGAZZI el al.: FISSION TRACK DATING

proach

and a c r i t i c a l

r e v i e w of p o s s i b l e

sources

of er-

rors. In any c a s e the use of FTM i n v o l v e s a nuclear occur.

reactor

so t h a t the

In an ideal e x p e r i m e n t a l

s h o u l d be v e r y w e l l

thermalized

s h o u l d be n e g l i g i b l e ence s h o u l d propagated tions

(n,f)

(or w e l l

be p r e c i s e l y

set-up, and

The n e u t r o n

These

are n o t u s u a l l y m e t and t h e r e f o r e

tion b e c o m e s

a relevant

flux

gradients flu-

as its u n c e r t a i n t y

up to the e r r o r in age.

in

on 235U m a y

the n e u t r o n

spatial

known).

known

an i r r a d i a t i o n

reaction

ideal

condi-

neutron

s o u r c e of s y s t e m a t i c

is

irradia-

errors

in

FTM. Interlaboratory fluences

comparisons

are g i v e n w i t h

t u a t i o n of age v a l u e s larger than expected

have

shown that,

satisfactory

around

precision,

the m e a n

by s t a t i s t i c s .

are

which

fluence

determination.

In o r d e r worthwhile the used

(n,f)

could cause

Probably

systematic

nuclear

for dating,

and for w h i c h

tity can be d e t e r m i n e d related

to n e u t r o n

pointed

out that, w h e n

independently

can o c c u r d u r i n g n e u t r o n in n e u t r o n

energy

and burn-up,

the n u m b e r

of c a d m i u m

Therefore,

same as

uranium

quan-

a u t h o r s I-3 and a s p e c i m e n

any a n o m a l y

that

such as v a r i a t i o n

ratio,

the e x p r e s s i o n

for the n a t u r a l

to be dated.

on

c h a n g i n g of fuel g e o m e t r y

of f i s s i o n e v e n t s

the same both specimen

irradiation,

spectrum,

variation

e f f e c t on both.

together,

it seems

of any p a r a m e t e r

Several

such d o s i m e t e r s

to be d a t e d are i r r a d i a t e d

in

operate

just the

the n a t u r a l

irradiation.

dosim-

differencies

dosimetries which

r e a c t i o n on 235U,

fluc-

an e x p l a n a -

neutron

to cut down the e r r o r i n c i d e n c e , to use n e u t r o n

the

significantly

tion m a y be f o u n d in the use of d i f f e r e n t etries,

although

per u r a n i u m uranium

Of c o u r s e 482

have the

same

that d e s c r i b e s target

atom is

dosimeters

the o c c u r r e n c e

and the

of the

BIGAZZI et al.: FISSION TRACK DATING

same n a t u r a l samples

isotopic

is a s s u m e d

Neutron propriate

ratio

and,

dosimeters if other

between

if necessary,

using

natural

fissionable

for instance,

produce

fission

events

specimen.

be i g n o r e d

if i r r a d i a t i o n s

thermalized

neutron

In the p r e s e n t dosimeters values

traditional ample

dosimetry

are not apsuch as

non-negligible This

amounts

interference

are c a r r i e d

paper

of

may

out in h i g h l y

the use of two natural Data

by u s i n g N I S T

activation

is r e p o r t e d

uranium

fluxes.

is described.

obtained

verified.

impurities,

thorium

in the

235U and 238U in both

are c o m p a r e d w i t h glass

of m e t a l

standards

foils.

of a p p l i c a t i o n

to the d a t i n g

uranium fluence

and the

Finally

of n e u t r o n

an ex-

fiuence

of the Fish C a n y o n

Tuff

age

standard.

EXPERIMENTAL Neutron

dosimeters

Different ate n e u t r o n I - Gold

neutron fluences

fluence

glasses

sheets

induced

sandwiched are those

for S c i e n c e

glasses

where

by c o u n t i n g

on the g l a s s

by NIST

and T e c h n o l o g y ,

to evalu-

irradiated.

the

irradiated

483

Standard

facilities

Insti-

Standard Two g l a s s e s

at the N I S T

flux and t h e r m a l i z a t i o n

Flux monitoring

or on a

(National

USA).

Neutron

fission

surface

in a 6 sheet kit.

in two i r r a d i a t i o n

acterized.

to be n e u t r o n

to it 4. The m o s t u s e d

are a v a i l a b l e

neutron

been u s e d

loaded w i t h uranium.

released

had been p r e v i o u s l y reactor

foils

can be d e t e r m i n e d

density

detector

tute

glass

have

for FTM.

and c o b a l t m e t a l

2 - Artificial

track

dosimeters

nuclear

(RT3 and RT4), are w e l l

was p e r f o r m e d

char-

by m e a s u r i n g

BIGAZZI et al.: FISSION TRACK DATING

the i n d u c e d son w i t h ating

fission

the N I S T

uranium

Experiments

tored

number 140Ce

starting

(stable),

Parent

whose

with

times

end of i r r a d i a t i o n produced

during

irradiation during

Yagoda's

lodium

selected

surface. used

10 -2 ~m.

In the case

short

amounts

thin

stage

attached

on a a low

a thin

film to the

A second

heat-

to get a

to the m u s c o v i t e thin

films

from 3.0 x 10 -4 to 3.7 x atoms

by n u c l e a r

film is c l o s e l y 484

nitrate,

adhering

of the u r a n i u m

of u r a n i u m

surface was evaluated

a m i c a with

to

a col-

spread

is then r e q u i r e d

ranged

parent

of longer

of uranyl

is obtained.

film

at the

according

and p a r l o d i u m

sheet

to as-

140Xe

and parlodium,

a drying

for

(and of 140La)

and c a r e f u l l y

After

and

into a c c o u n t 7.

prepared

of m u s c o v i t e ,

The n u m b e r

thin u r a n i u m

k n o w n 5-6.

140Ba

from the

of 140Ba

alcohol,

The t h i c k n e s s

in this w o r k

at m a s s

is w e l l

I%, that

be taken

(I h at 400 ~

trioxide

chain

140Ba have v e r y

only

film,

nitrate

support muscovite

at

they can be i g n o r e d

should

are m i x e d

content.

stage

yield

less than

thin

surface

o f dry u r a n y l

uranium

before

the d e c a y

in ethyl

form,

uranium

fission

p r o c e d u r e 8. E q u a l

dissolved

fission

irradiation.

times

uranium

emission

140Xe and e n d i n g w i t h

derives

irradiation

4 - Natural

to the

and

is moni-

up to 10 h it is p o s s i b l e

an e r r o r

closely

from R e a c t o r

on 235U

140Ba y - r a y

and t h e r e f o r e

irradiation

detector

obtained

reaction

with

radionuclides

half-lives

sume,

the

or by evalu-

12.7 mm in d i a m e t e r

(n,f)

140Ba b e l o n g s

140,

glasses,

by c o m p a r i -

the glass.

disk,

(USA),

The

by m e a s u r i n g

537 keV.

with

metal

Inc.

0.18 mm thick.

either

in a m u s c o v i t e

and i r r a d i a t e d

3 - Natural

density

irradiated

the FT d e n s i t y

packed

ing

track

on the

film

e m u l s i o n s 9. The

packed

to a n o t h e r

mus-

BIGAZZI et al.: FISSION TRACK DATING

covite

sheet and both

radiation.

are s u b m i t t e d

The d e n s i t y

the m u s c o v i t e

of i n d u c e d

detector,

e n c y is known,

allows

once

to n e u t r o n

fission

tracks

its c o l l e c t i o n

fluence

iron

effici-

e v a l u a t i o n I0-11

Irradiations Neutron MARK

irradiations were

II r e s e a r c h r e a c t o r

while

the r e a c t o r was

power.

cadmium

by d i f f e r e n t

at 250 kW s t e a d y

state

facilities were

selected,

nominal

neutron

thermal

char-

flux and

ratio:

I - Rotatory s

out at the T R I G A

of the U n i v e r s i t y of Pavia,

operated

Two i r r a d i a t i o n

acterized

carried

--I

specimen

, Cd r a t i o

2 - Thermalizing 2.5x108

rack

(thermal

6.5 for gold and column

48 for cobalt);

(outer end,

n cm -2 s -I , Cd r a t i o

Ixi012 n cm -2

flux

thermal

flux

92 for gold and 752

for

cobalt). Radioactivity measurement Induced etry,

r a d i o a c t i v i t y was m e a s u r e d

u s i n g a 30 cm 3 Ge(Li)

detector

puter assisted multichannel located

counting

The d e t e c t o r was

(10 cm thick),

and c o p p e r

152Eu

lined w i t h

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

e f f i c i e n c y was e x p e r i m e n t a l l y

a standard

spectrom-

c o u p l e d t 0 a com-

analyzer.

inside a lead s h i e l d

0.5 cm of c a d m i u m

by y-ray

source h a v i n g

measured,

the s a m e

geometry

The using as neu-

tron monitors. Fission

track d e n s i t y m e a s u r e m e n t s

Fission by s t a n d a r d 15 m i n

track d e n s i t y m e a s u r e m e n t s optical methodS

at 40 ~

after

The o p t i c a l

were

etching

efficiency

carried

for f i s s i o n

fragment track counting

in u r a n i u m

sidered unity

to l i t e r a t U r e v a l u e s 10-11

according

485

out

in 40% HF for

thin films was

con-

BIGAZZI el al.: FISSION TRACK DATING

RESULTS

AND D I S C U S S I O N

Neutron

fluences

in the r o t a t o r y

in the t h e r m a l i z i n g of the U n i v e r s i t y 2. I n d i v i d u a l deviation Table

derived

over

10800

s). For

different

neutron

reproducibility power data,

and u r a n i u m for the

for 100

1800 and 3600 monitors

was

especially disks,

obtained

in the

neutron

times

useful

dosim-

(60 to for d a t i n g of

repeated

the

flux.

to v e r i f y

and the s t a b i l i t y The p r e c i s i o n

increases s runs

with

of re-

irradiation

it is u s u a l l y

of

foils

time,

below

is shown by fluences

and

3%. An

obtained

s irradiations.

different

occurrence

of n e u s

distances

experimental

Cd ratios,

gold

47.9• data

foils

equatorial

was o b s e r v e d

at

plane,

beyond

the

spatial

gradients,

if any,

g o l d and cobalt

activation

foils

also in c a d m i u m

evaluate

Reported

gradi-

negligible.

instances

irradiated

so that

spatial

activation

from the r e a c t o r

errors,

considered

In m a n y

flux

by i r r a d i a t i n g

up to 10 cm. No flux v a r i a t i o n

and

standard

in the case of a c t i v a t i o n

poor precision

ents was v e r i f i e d

were

the

I and

s, the i r r a d i a t i o n

Of the p r o c e d u r e

and n e u t r o n

The actual

were

times

II r e a c t o r

statistics.

range of i r r a d i a t i o n

1800 and 3600

unexpected

with

fluences

some i r r a d i a t i o n

namely

ported

counting

and

in T a b l e s

rack by using d i f f e r e n t

a wide

purposes,

reactor

from

together

the n e u t r o n

specimen

eters

are r e p o r t e d

are given only

rack

of the T R I G A M a r k

of Pavia

data

I shows

rotatory

column

specimen

which were

capsules found

in order

to

to be 6.46•

for

for cobalt. indicate

are shown by the n e u t r o n

that no m e a n i n g f u l fluences

obtained

differences

by d i f f e r e n t

i

monitors.

Activation

nuclear

sion m a y be c o n s i d e r e d

reactions

equivalent 486

and i n d u c e d

for n e u t r o n

fis-

monitor-

BIGAZZI et al.: FISSION TRACK DATING

TABLE

I

Neutron fluences in t h e r o t a r y s p e c i m e n r a c k of t h e T R I G A M A R K II r e s e a r c h r e a c t o r of t h e U n i v e r s i t y of P a v i a , as o b t a i n e d using different neutron monitors Irradiation time, s

Neutron monitor

Fluence, n am -2 x 1015

Au Co Ba

(6.6 • 0.3)xi0 -2 (6.2 -+ 0.2)xi0 -2 (6.1 -+ 0.5)xi0 -2

60 (I run)

Average 100

(2 runs)

Co Au(1) Au(2) Au(3) Ba(1 ) Ba(2)

0.I0 0.I0 0.11 0.11 0.I0 0.II Average

600

(I run)

Am Ba NIST 962a - cO NIST 962a - Cu NIST 962a - Au Thin film Average

1800

(5 runs)

Co(I ) Co(2) Co(3) Au(1) Au(2) Au (3) Au(4) Au(5) Au(6) I~

(6.3 +- 0 . 3 ) x 1 0 - 2 -+ 0.06 +- 0.02 -+ 0.02 -+ 0.03 + 0.08 -+ 0.05

0.105 + 0.005 0.60 0.60 0.53 0.53 0.58 0.54

+ 0.03 -+ 0.03 + 0.03 -+ 0.02 -+ 0.02 -+ 0.02

0.56 + 0.02 1.81 _+ 0.02 I .77 _+ 0.07 2.05 _+ 0.09 1 . 8 1 _+ 0.02 1.81 1.81 1.81 1.98 1.79 1.81

-+ -+ + ,+ ,+ ,+ 1 . 8 -+

(1 )

Ba(2) Ba(3)

0.01 0.02 0.02 0.05 0.05 0.02 0.2

2.0 -+ 0.I Average

487

1.8

+- 0.1

BIGAZZI et al.: FISSION TRACK DATING

Table

I - continued

Irradiation time, s 3600 (8 runs)

Neutron monitor Co (I) co (2) Co (3) Co (4) Co (5) Co(6) co(7) co(8) Co (9) Au(1) Au(2) Au(3) Au(4) Au(5) Au(6) Au(7) Au(8) Au(9) Au (I0) Au(11) Au(12) Au (13) Au(14) Ba(1) Ba(2) Ba(3) Ba(4) Ba(5) Ba (6) Ba(7) ~ S T 962a - C o NIST 962a - C u NIST 962a - A u NIST 963a - C o NIST 963a - C u NIST 963a - A u Average

488

Fluence, n cm -2 x I 0 3.61 3.64 3.64 3.65 4.0 4.0 4.0 3.6 3.9 3.62 3.60 3.68 3.57 3.61 3.61 3.80 3.62 3.63 3.97 3.79 3.92 3.71 3.99 3.61 3.62 3.63 3.63 4.0 4.0 4.0 3.0 3.0 3.22 3.1 2.91 3.20

• 0.03 • 0.07 t 0.06 -+ 0.09 • 0.1 -4 0.1 -4- 0.1 • 0.1 -+ 0.1 • 0.02 • 0.01 • 0.05 • 0.04 • 0.05 • 0.05 • 0.05 • 0.05 • 0.07 + 0.04 • 0.07 • 0.03 • 0.07 • 0.09 • 0.03 • 0.04 • 0.04 • 0.04 • 0.2 -%+ 0.2 • 0.2 -+ 0.2 • 0.1 • 0.09 • 0.2 • 0.07 • 0.08

3.7 -+ 0.2

15

BIGAZZI el al.: FISSION TRACK DATING

Table

I - continued

Irradiation time, s

Neutron monitor

3660 (I run)

Fluence, n cm -2 x 1015

Au Ba NIST 962a - Cu

3.7 -+ 0.3 3.7 -+ 0.3 2.90 _+ 0.08

Average 4800 (I run)

3.7

4.8 4.4 4.1 4.5

Au NIST 963a - Co NIST 963a - Cu NIST 963a - Au Average

4.5 -+ 0.3

co(I) co (2)

7200

(1 run)

7.2-+0.1 7.4-+0.3 7.7-+0.2 7.9-+0.2 7.2-+0.5 6.7-+0.2 7.4-+0.2

Au(1) Au(2) NIST 963a - Co NIST 963a - C u NIST 963a - Au Average 10800 (I run)

-+ 0.2 -+ 0.3 -+ 0.2 -+ 0.2

7.4 -+ 0.4

Co(I) Co(2) Au(1) Au(2) Au(3)

10.9 10.8 "11.2 10.2 11 .I Average

+ 0.2 +- 0.2 -+ 0.4 + 0.3 -+ 0.2

10.8 -+ 0.4

Co, Au = activation foils; Ba = 140Ba activity from uranium disk; Thin film = thin uranium film on muscov i t e s u p p o r t ; N I S T 9 6 2 a , 9 6 3 a (Co, Cu, Au) = g l a s s with different calibrations carried out at NIST.

ing.

Therefore

radiation tion

time

never

may

be

and

963a

an

average

may

exceeds

observed glasses

be

evaluated,

5.5%.

for and

neutron

However,

fluences thin

whose

for

each

standard

a systematic

obtained

uranium 489

fluence

using

films:

deviatrend

NIST

their

ir-

962a

values

BIGAZZI et al.: FISSION T R A C K DATING

TABLE

2

Neutron fluences in t h e t h e r m a l i z i n g c o l u m n of the T R I G A M A R K II r e s e a r c h reactor of t h e U n i v e r s i t y of P a v i a , as obt~:~ined u s i n g d i f f e r e n t neutron monitors Irradiation time, s 1020 (I run)

Neutron monitor

Fluence, n cm -2 x 1015

Au Ba

(2.50 • 0.05)xi0 -4 (2.50 + 0.05)xi0 -4 2.50xi 0 -4

Average 1800 (I run)

-~ Ba

(7.04 • 0.05)xi0 -4 (7.79 • 0.05)xi0 -4 Average

36640

nu Ba NIST 961 - Cu NIST 961 - Au Thin film Average

39600 (I run)

187 • o.4)xlOJ (8.8 (8.2 (9.1 (9.4

• 0.4)xI0_~ -+ 0.4)xI0_~ • 0.5)xI0_~ + 0.4)xi0-

(8.8 • 0.4)xi0 -3 (9.1 -+ 0.3)xi0 -3 (8.22 • 0.03)xi0 -3 (9.3 • 0.3)xi0 -3

Co Au Ba Average

257940

(7.4 _+ 0.5)xi04

Co Au Ba NIST 962a - Co NIST 962a - Cu NIST 962a - Au Average

(8.9 + 0.3)xi0 -3

(64 • 0.31xI0(6.5 (6.3 (6.3 (5.9 (6.4

• • • f •

0.3)xI0_~ 0.3)xi0 2 0.3)xi0- 9 0.2)xI0-~ 0.3)xi0--

(6.3 +- 0.3)xi0 -2

Co, A u = a c t i v a t i o n f o i l s ; Ba = 1 4 0 B a a c t i v i t y from uranium disk; Thin film = thin uranium film on muscovite support; N I S T 961, 9 6 2 a (Co, CU, Au) = g l a s s with different calibrations carried o u t at N I S T .

490

BIGAZZI et al.: FISSION TRACK DATING

are always

lower. At the moment,

no explanation may be

advanced. Table

2 shows the neutron

thermalizing

fluences

column by using different

eters over a wide range of irradiation this case precision

dosim-

times.

for gold and 752•

for this irradiation

tained by activation

facility

reactions errors.

for cobalt.

and induced

fission agree

occur,

In the 1800 s run the fluence m o n i t o r e d

a lower fluence,

in the 39600

Agreement

is also very good with

uranium

film).

an overall

by

and thin

than the Cu calibration.

time may be evaluated, below 7%. A l t h o u g h

characterized

ization,

no differences

whose

for each

standard

devia-

in this irradiation

among the different

the time required

long and makes

fluence

by a better neutron

dated a neutron dose useful is very

(NIST glasses

average neutron

sitions,

are shown,

fluences obtained

In the former the NIST Au and Co calibra-

tions provide better results

tion remains

Yet gold foil activa-

s run.

track density measurement

irradiation

by 140Ba

compared to cobalt and

fission

Therefore,

some discrepancies

is higher with respect to the one

by gold foil activation.

tion yields 140Ba,

However

ratios

the fluences ob-

experimental

activity m e a s u r e m e n t

(greater

column a n d

within

obtained

Also in

below 5%. Cadmium

also in the thermalizing

found to be 92.3• Also

neutron

and for long irradiations

s) it is normally

have been m e a s u r e d

in the

increases w i t h induced radioactiv-

ity or track density than 36000

obtained

po-

flux thermaldosimeters

to give the samples to be for FT dating

this f a c i l i t y

(1015 n cm -2)

impractical

for

dating purposes. Fluence

data obtained

in the thermalizing

in the rotary

specimen

rack and

column of the TRIGA Mark II reactor

491

BIGAZZI et al.: FISSION TRACK DATING

of the U n i v e r s i t y stability power

of Pavia,

and r e p r o d u c i b i l i t y

conditions,

criticality

parameters

reactivity)

and n a t u r a l (burn-up,

must

fact if i r r a d i a t i o n are c o r r e l a t e d

of r e a c t o r

even if i r r a d i a t i o n s

o v e r a long time p e r i o d

excess

are i n d i c a t i v e

to a v e r a g e

out

of r e a c t o r

rods p o s i t i o n ,

As a m a t t e r

irradiation

fluences,

state

are c a r r i e d

control

for both

steady

variation

be c o n s i d e r e d .

times

of a great

highly

of

positions

significant

linear

c o r r e l a t i o n s are o b t a i n e d : y = 1.00 x 1012 X 13 1.5 x 10 and r = 0.9993 for the r o t a r y s p e c i m e n rack

and y = 2.4 x 108 X thermalizing In o r d e r

- 1.3 x 1011

to e m p h a s i z e

Fish Canyon Tuff

the u s e f u l n e s s

age

by USGS

Apatfte radiated the T R I G A

Canyon

apatite

operating

by the

9 6 3 a glass.

from the tuff,

in the r o t a r y

reactor while

The

fission

were

specimen

at 250 kW.

simultaneous

and N I S T

Survey),

M a 12

separated

for two h o u r s

Fish

is an i n t e r n a t i o n a l

(United S t a t e s G e o l o g i c a l

crystals,

Tuff

rock,

age is 2 7 . 8 •

d o s e was m o n i t o r e d the N I S T

the d a t i n g of

(USA) w a s c a r r i e d out by FTM.

a crystal-rich

reference

of an a c c u r a t e

for age d e t e r m i n a t i o n ,

C a n y o n Tuff, standard

for the

column.

neutron dosimetry

whose

and r = 0.9998

ir-

rack of Neutron

irradiation

track d e n s i t y

963a w a s m e a s u r e d

of

in F i s h by opti-

cal m e t h o d . The d e r i v e d agreement with

age is 2 7 . 9 • the r e f e r e n c e

that the n e u t r o n to yield, accurate

which age.

dose m o n i t o r i n g

u n d e r the d e s c r i b e d and r e l i a b l e

This

results

confirm

step used

is a d e q u a t e

experimental

conditions,

age d e t e r m i n a t i o n .

492

is in v e r y g o o d

BIGAZZI e! al.: FISSION TRACK DATING

REFERENCES I. J.C. Hadler, C.M.G. Lattes, A. Marques, M.D.D. Marques, D.A.B. Serra, G. Bigazzi, Nucl. T r a c k s Radiat. Meas. 5 (1981) 45. 2. J.C. Hadler, M e d i d a da c o s t a n t e de d i s i n t e g r a c a o por fissao espotanea, Ph.D. Thesis, U n i v e r s i d a d e E s t a t u a l de Campinas, C a m p i n a s SP (Brazil) (1982). 3. P.F. Green, A.J. 9 (1984) 231. 4. R.L. Fleischer, Eng., 22 (1965)

Hurford,

Nucl.

P.B. Price, 153.

R.M.

Tracks

Radiat.

Walker,

Nucl.

Meas.,

Sci.

5. D.M. Gillian, R.G. Helmer, R.C. G r e e n w o o d , J.W. Rogers, R.R. Heinrich, R.J. Popek, L.S. Kellog, E.R. Lippocoot, G.E. Hansen, W.H. Zimmer, Proc. 2nd ASTME u r a t o m Symp. R e a c t o r Dosim., Palo Alto, CA, R e p o r t N U R E G / G P - 0 0 0 4 , vol. 3 (1977) 1289. 6. S.A. Chitambar, Acta, 42 (1987)

H.C. 169.

Jain,

V. Ramaniah,

7. F.E. Senftle, T.A. Farley, L.R. Cosmochim. Acta, 6 (1954) 197. 8. H. Yagoda, Emulsions,

Stieff,

Radioactive Measurements Wiley, New York, 1949.

9. G. Bigazzi, J.C. Hadler, P.J. S.R. Paulo, G. Poupeau, Nucl. 17 (1990) 217.

Nucl.

Tracks

Radiat.

Geochim.

with N u c l e a r

Iunes, M. Oddone, Tracks Radiat. Meas.,

10. J.H. Roberts, F.H. Ruddy, R. Gold, Radiat. Meas., 8 (1984) 365. 11. T. Wall,

Radiochim.

Nucl.

Meas.,

12

Tracks,

(1986)

12. C.W. Naeser, R.A. Zimmermann, G.T. Cebula, Tracks Radiat. Meas., 5 (1981) 65.

493

887.

Nucl.