Yields of fission products produced by thermal-neutron fission ofCm245

Abstract

Absolute yields have been determined for 105 gamma rays emitted in the decay of 95 fission products representing 54 mass chains created during thermal-neutron fission of $^{245}\mathrm{Cm}$. These results include 17 mass chains for which no prior yield data exist. Using a Ge(Li) detector, spectra were obtained of gamma rays between 30 sec and 0.3 yr after very short irradiations of thermal neutrons on a 1 \ensuremath{\mu}g sample of $^{245}\mathrm{Cm}$. On the basis of measured gamma-ray yields and known nuclear data, total chain mass yields and relative uncertainties were obtained for 51 masses between 84 and 156. The absolute overall normalization uncertainty is 8%. The measured $A$-chain cumulative yields make up 81% of the total light mass ($A\ensuremath{\le}121$) yield and 92% of the total heavy mass yield. The results are compared with fission-product yields previously measured with generally good agreement. The mass-yield data have been compared with those for thermal-neutron fission of $^{239}\mathrm{Pu}$ and for $^{252}\mathrm{Cf}(\mathrm{s}.\mathrm{f}.)$; the influences of the closed shells $Z=50$, $N=82$ are not as marked as for thermal-neutron fission of $^{239}\mathrm{Pu}$ but much more apparent than for $^{252}\mathrm{Cf}(\mathrm{s}.\mathrm{f}.)$. Information on the charge distribution along several isobaric mass chains was obtained by determining fractional yields for 12 fission products. The charge distribution width parameter, based upon data for the heavy masses, $A=128 \mathrm{to} 140$, is independent of mass to within the uncertainties of the measurements. Gamma-ray assignments were made for decay of short-lived fission products for which absolute gamma-ray transition probabilities are either not known or in doubt. Absolute gamma-ray transition probabilities were determined as (51 \ifmmode\pm\else\textpm\fi{} 8)% for the 374-keV gamma ray from decay of $^{110}\mathrm{Rh}$, (35 \ifmmode\pm\else\textpm\fi{} 7)% for the 1096-keV gamma ray from decay of $^{133}\mathrm{Sb}$, and (21.2 \ifmmode\pm\else\textpm\fi{} 1.2)% for the 255-keV gamma ray from decay of $^{142}\mathrm{Ba}$.