1. Thermal annealing effect on fission fragment track recording
properties of polycarbonate
Rakesh Kumar1,* S. K. Arya1, B. K. Nayak2, and R.K.Jain1
1Dept. of Applied Sciences, ABES Institute of Technology, Campus -2 , NH-24, Vijay Nagar ,Ghaziabad (U.P.)
2Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai , India *
Polycarbonate Track Detector is a commonly used Solid State Nuclear Track Detector (SSNTD) to identify the fission fragment. The present paper deals with the study of thermal annealing and the mass distribution of 252Cf fission fragments using unannealed and annealed Makrofol-N detectors. In addition a novel method is introduced for identifying the light and heavy fission fragment groups [1]. 
Experimental Details
Makrofol-N detectors, 200μm thick, were purchased from Bayer Co., Germany. Three sets of detectors were prepared for this experiment, and each was exposed to a deposited source of 252Cf that had an alpha activity of μCi. A thin aluminium sheet, 1mm in thickness, was used as a collimator to minimize the area of source to Makrofol-N distance five hundred holes, 0.4 mm in diameter spaced 0.3 mm apart were drilled in the aluminium plate. The collimator was put on the 252Cf source with a thin space. Irradiation was done in the air maintaining 2 mm space between source and aluminium sheet using 2π geometry for 10 minutes. These detectors were annealed in a temperature controlled oven for 30 minutes at different annealed temperatures (100,150,200oC) After irradiation and annealing or vice versa, the detectors were chemically etched in a 6.25N NaOH solution at 60oC in a microprocessor controlled oven with a maximum uncertainty of ±1oC. The etched pit diameters were used to measure the mass of the particles [2-4]
Results and Discussion
Track diameters were measured to estimate the atomic mass ratio of the fission fragments emitted from a 252Cf source using unannealed and thermally annealed Makrofol-N. For unannealed detector irradiated to a 252Cf source, the diameter of the tracks along the minor axis were measured keeping 3hrs of etching time at 60oC. Fig.1 shows the photomicrograph of fission fragments in unannealed Makrofol-N detector. 
Fig.1 Photomicrograph of fission fragment in Makrofol-N
In Fig. 2, a plot of the number of track counts versus track diameters shows that the fission fragments are clustered into a “heavy group” indicating a clear peak, while the other “light group” is not clear.
Fig. 2 Diameter of distribution of tracks along the minor axis for the fission fragment from 252Cf using unannealed Makrofol-N.
In case of pre annealing irradiation the fission fragments recorded also exhibit a mass distribution with a clear peak of heavy group, while the other light group is contributing significantly as shown in Fig.3, at different annealing temperatures.
Fig.3 Diameter of distribution of tracks along the minor axis for the fission fragment from 252Cf using preannealed Makrofol-N
At an annealing temperature of 100oC, heavy mass group peak remains same as in case of unannealed, while at the higher annealing temperatures i.e and 200oC, peaks shift
towards larger diameters. In all cases of post. annealing irradiation the plot of the number of track counts shows two clear peaks. The light group of fission fragments is observed clearly as shown in fig.4. It should be noted that in case of post annealing two peaks attributed due to the modification of the registrations properties of heavy ions in a polycarbonate track detectors induced by thermal annealing[1].
Fig.4 Diameter of distribution of tracks along the minor axis for the fission fragment from 252Cf using postannealed Makrofol-N
Conclusions
It has been summarized that nuclear fission is normally asymmetric either spontaneous or neutron induced fission. In case of spontaneous fission from 252Cf, two peaks with average mass number of 108 and 143 appear as discussed in our earlier work [2] and gives a ratio of 1.32±0.01 as discussed in a book of Knoll [5]
References
[1] A. F. SAAD, N.A. HAMED, Y. K. ABDALLA, Turk. J. Phys., 37, 356,
(2013).
[2] R. K. Jain, P. Uniyal, Ashok Kumar and B. K. Nayak, ISST J. App.
Phys. 4, 19, (2013). [3] D. Paul, S. Subrata, G. Debasis and R. C. Sastri, Radiat. Meas., 30,
127, (1999). [4] D. Paul, S. Subrata, G. Debasis and R. C. Sastri, Radiat. Meas., 29,
133, (1998). [5} G. F. Knoll, Radiation detection and Measurment, John Wiley & Sons,
New York , (1989).
Introduction
75-years of Nuclear Fission: Present status and Future Perspectives, May 08-10, 2014,
Bhabha Atomic Research Centre, Mumbai , India