Abstract
The independent isomeric yield ratio of 148 Pr in thermal neutron induced fission of 235 U has been determined experimentally. The fission product 148 Pr isomers, extracted directly by on-line mass separation technique, have high-spin (J=4) to low-spin (J=1) isomer ratio of 0.14±0.04 using growth and decay analysis. Statistical model calculation of isomeric yeild ratio using constant initial r.m.s. angular momentum J rms can not reproduce either present results or other recent measurements of isomer ratios. The J rms derived from isomer ratio data in all thermal fissioning systems indicate a wide spread ranging from 2 h{combining short stroke overlay} to 13 h{combining short stroke overlay}. No clear correlation between J rms and isomeric spins or number of neutrons of isomers is found, thus, more model refinements and experimental works should be done in order to evaluate independent isomeric yields correctly. © 1984 Springer-Verlag.