No abstract

Fast neutron induced fission / Highly pure 238 U / Fission yield / Track etch-cum gamma spectrometric technique SummaryThe absolute yields of 45 fission products in 39 mass chains were determined in the fast neutron induced fission of 99.9997 atom % pure 238 U employing the fission track etch-cum gamma spectrometric technique developed in our laboratory. The neutron spectrum in the irradiation position of the light water-moderated, highly enriched uranium-fuelled swimming pool reactor APSARA was measured and delineated in the thermal to 10 MeV region using threshold activation detectors. The total number of fissions were measured by registering the fission tracks on small strips of lexan or mica solid state track detectors immersed in a dilute solution of the target of known concentration. The low-yield symmetric fission products, e.g. Ag, Cd and Sb, as well as some of the asymmetric fission products, e. g. Br and rare earths, were analysed gamma spectrometrically after separating them by using a few steps of radiochemical separations to ensure gross decontamination from high-yield fission products. The high yield asymmetric products were analysed by direct gamma spectrometry. Comparison of the measured yield values with the ENDF/B-VI and UKFY2 compilations shows a general agreement for most fission products except for those in the mass region 133-139. A possible explanation for the observed higher yields and the fine structure effect is given on the basis of the shell closure proximity and odd-even effects. An average neutron number of 3.01 ± 0.27 was estimated for this fissioning system and the yield ratio of "Mo to " 7 Cd was found to be 167. We believe this represents the first experimental fission yield data on the fast neutron fission of "PURE" 238 U.

No abstract

No abstract

No abstract