Observed mass distribution of spontaneous ®ssionfragments from samples of limeÐan SSNTD study

Debasish Paula, 1, J.C. Majumdarb, Debasis Ghosec, R.C. Sastria,*aDepartment of Physics, Jadavpur University, Calcutta, 700 032, IndiabDepartment of Chemistry, Gurucharan College, Silchar, Assam, India

cVariable Energy Cyclotron Centre, 1/AF Bidhannagar, Calcutta, 700 064, India

Received 18 November 1998; accepted 7 April 1999

Abstract

SSNTD is one of the most commonly used detectors in the studies involving nuclear phenomena. The ease ofregistration of the presence of alpha particles and ®ssion fragments has made it particularly suitable in studies wherestable long exposures are needed to extract reliable information. Studies on the presence of alpha emitting nuclides

in the environment assume importance since they are found to be carcinogenic. Lime samples from Silchar in Assamof Eastern India have shown the presence of spontaneous ®ssion fragments besides alphas. In the present study welook at the ratio of the average mass distribution of these ®ssion fragments, that gives us an indication of thepresence of the traces of transuranic elements. # 1999 Elsevier Science Ltd. All rights reserved.

1. Introduction

Exposure to radiations, particularly to the alphas, is

found to cause serious damage to biological tissues.

Incidentally, we have come across medical reports

from the Silchar Medical College (Bhattacharjee, 1996)

indicating a preponderance of cancer in Barak Valley

in Assam, Eastern India. A large population in this

area consume lime along with betel leaves and a large

quantity of the same lime is also used in white washing

houses and in ®lter beds for water treatment. Earlier,

presence of the traces of uranium in the samples of

lime from the local market of Gauhati, Assam was

reported (Choudhury and Goswami, 1986). So, we

wanted to look again at these samples of lime when we

found them fogging the normal photographic ®lms

covered in black paper. A test with an end windowG.M. counter and aluminium absorbers con®rmed thatthese samples exhibit beta and gamma activity. Thus,

we felt encouraged to investigate the presence of alphasand surprisingly found ®ssion fragments along with thealphas. Since alphas are well known carcinogens, we

may reasonably infer that sources giving out ®ssionfragments besides alphas could also cause cancer.

2. Experimental

Five di�erent samples of lime collected from the

local market at Silchar were powdered and labelled. Aplastic cup of about 7 cm height and 5.5 cm diameterwas ®lled with lime powder to a height of 6 cm. This

was covered with a plastic lid, and at the centre of itsinner portion a CR-39 (standard grade) detector of20 � 10 mm size obtained from Page Mouldings

(Pershore) Ltd, England, was pasted. This arrangementwas kept undisturbed in a desiccator for 45 days. The

Radiation Measurements 30 (1999) 699±701

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1 On study leave from Bangladesh Atomic Energy

Commission.

* Corresponding author.

exposed CR-39 detectors were etched following the

method of Pandey et al. (1993) for sequential etching

in 6 N NaOH solution at 708C in a constant tempera-

ture bath. Scanning successively at the end of 60 min

and 90 min etching times under an optical microscope

with 400� magni®cation revealed tracks of only one

type in size, comparable to ®ssion fragments as seen

earlier under similar conditions for 252Cf (Paul et al.,

1998a). Further, etching for another 2 h has brought

out tracks of two distinct sizes corresponding to alphas

and ®ssion fragments (Bhanu and Iyer, 1986).

However, all the CR-39 detectors exposed to lime

samples were ®nally etched for 6 h to ensure better

and well distinguishable track diameters.

Measurements of the track diameters for ®ssion frag-

ments along the minor and major axes were done

under an optical microscope with 675� magni®cation.

3. Results and discussion

A plot of frequency of occurrence of track diametershas given, in all cases, a distribution indicating that ®s-sion fragments cluster into two groups as is evident

from the typical histogram plot shown in Fig. 1 for thedata taken along the minor axis. This distributionappears to be asymmetric and indicates that ®ssion

fragments are clustered into a light group and a heavygroup (Knoll, 1989). Further, we can see from Table 1that the ratio of the diameters at peak positions, corre-

sponding to average mass distribution of the clusters,for the samples studied varied from 1.1920.03 to1.3620.04 for the measurement along the minor axisand the corresponding values along the major axis var-

ied between 1.1720.03 to 1.3520.03. These ratios arecomparable to those for 252Cf as seen from the litera-ture (Knoll, 1989). It is true that in this case it is di�-

cult to specify the nature of the radionuclide simply bylooking at the distribution of average mass ratios ofthe ®ssion fragments. However, when we look at this

data along with the corresponding values of the alphato spontaneous ®ssion fragment ratios in the ranges of1.7420.06 to 8.4020.31 (Paul et al., 1998b, commu-

nicated) we may infer that these ®ssion fragments orig-inate from nuclides of transuranic elements that havehalf lives for emission of alphas and spontaneous ®s-sion not too far from each other.

It is a well established fact that alphas are highlycarcinogenic and their presence in the environmentcould be one of the contributory factors for the inci-

dence of cancer (Martell, 1982). Presumably, ®ssionfragments jointly with alphas are responsible for caus-ing cancer. A more detailed study of the natural en-

vironmental radiation should help in understandingbetter the contribution of these ®ssion fragments ina�ecting genetic or other disorders besides cancer, inhumans.

Acknowledgements

One of the authors, Debasish Paul, is grateful toIndian Council for Cultural Relations (ICCR) andJawaharlal Nehru Memorial Fund for ®nancial sup-

port.

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Fig. 1. A histogram plot of the number of tracks versus track

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Table 1

Ratio of track diameters at the peak positions of two clusters

of the spontaneous ®ssion fragments

Sample No. Ratio of the minor axes Ratio of the major axes

1 1.2020.03 1.1720.03

2 1.3620.04 1.3520.03

3 1.3520.04 1.2820.03

4 1.1920.03 1.2820.03

5 1.2820.03 1.2120.03

D. Paul et al. / Radiation Measurements 30 (1999) 699±701700

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