Isomere Wirkungsquerschnittsverhältnisse beim thermischen Neutroneneinfang im Bereich der 2p _1/2 und 1g _9/2 Schalenmodellzustände

Abstract

Thermal capture cross sections and isomeric cross section ratios in thermal neutron capture were determined for even-even nuclei in the region of the 2p _1/2-1g _9/2 neutron shell. Capture cross sections for formation of Zn 69^m, Zn 71^m, Zn 71, Ge 71, Ge 75^m, Ge 77^m, Se 77^m, Se 79^m, Se 83^m, Se 83, Sr 85^m and Sr 87^m were measured by the activation method. From these data and additional measurements of cross section ratios the isomeric ratios for thermal capture in Zn 68, Zn 70, Ge 70, Ge 74, Ge 76, Se 76, Se 78, Se 80, Se 82 and Sr 84 were determined. In addition epithermal capture isomer ratios were determined for Zn 68, Ge 74, Ge 76, Se 80 and Sr 84. The isomer ratios are compared with calculations based on the statistical model ofHuizenga andVandenbosch. With the exception of Se 80 the measured ratios can be explained theoretically with reasonable values of the spin-cutoff-factorσ and gamma-ray multiplicityN, however there seems to be unexplained difference in eitherσ orN between the two groups of nuclei leading to either 1/2–7/2 or 1/2–9/2 isomers.