Effect of Increasing Excitation Energy on Nuclear Charge Distribution in Fission
Abstract
The independent fractional chain yields of Y^{90}, Nb^{96}, and La^{140} have been measured from fission of Th^{232} with alpha particles. The excitation energy was varied from about 20 to 40 MeV. Yields are also calculated for Cs^{136} from data previously published. In addition, the independent fractional chain yields of Y^{92}, Nb^{96}, and La^{140} were measured from fission of U^{235} with 14.9MeV neutrons. From these data, smoothly varying plots of independent yield versus excitation energy were constructed for Y^{90}, Nb^{96}, Cs^{136}, and La^{140}. The data from 14.9MeV neutron fission of U^{235} are in good agreement with those from alphaparticle fission of Th^{232} at the same excitation energy. It is shown that, within the limits of certain assumptions regarding the charge dispersion curves, the shift in Z_{p} (the most probable charge for a given mass number) with increasing excitation energy varies among the nuclides studied. In particular, it appears that dZ_{p}dE may be significantly greater for heavy fragments than for light fragments. The data for Y^{90}, Nb^{96}, and La^{140} are consistent with linear plots of Z_{p} versus E^{*}, except that the value for Nb^{96} for thermalneutron fission of U^{235} is off the curve by 0.1 charge unit. The value of dZ_{p}dE for Cs^{136} decreases with energy in this energy range, possibly because of shell effects at low excitation energies.
 Publication:

Physical Review
 Pub Date:
 September 1965
 DOI:
 10.1103/PhysRev.139.B1505
 Bibcode:
 1965PhRv..139.1505N