Isomeric yield ratio of fission product148Pr in235U(n th,f)

Abstract

The independent isomeric yield ratio of 148Pr in thermal neutron induced fission of 2asU has been determined experimentally. The fission product 14~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~ms can not reproduce either present results or other recent measurements of isomer ratios. The Jrms derived from isomer ratio data in all thermal fissioning systems indicate a wide spread ranging from 2h to 13h. No clear correlation between Jrm~ 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.

Isomeric yield ratios of fission products in the system of 24 MeV proton-induced fission of238U

“…Figure 2a shows the obtained isomeric yield ratios plotted against the fragment mass number. And the published results in the thermal neutron induced fission of 233U [16,17,[55][56][57][58][59], 235U [15][16][17][58][59][60][61][62][63] and 239pu [16,17,57,59] are summarized in Fig. 2b.…”

“…The angular momentum of fission products is considered to be determined by the following factors; the excitation energy and the spin of fissioning nucleus [14], the mass splitting [8], the charge distribution [ 11,15], the fragment kinetic energy [ 12], the atomic and neutron numbers or their closed shell effect [16,17], the internal excitation (or deformation) energy of fragments [12,13,18,19], and so on. Until now, it has been understood that the isomeric yield ratio is related to the angular momentum of primary fragment.…”

“…Thus the isomeric yield ratio have been used to investigate collective rotational degrees at scission configuration [ 14,19,20]. However, the study of the isomeric yield ratio has been restricted for only several nuclides, because most of these measurements were performed by applying radiochemical separation [16][17][18][19][20][21][22][23] or by use of an ordinary isotope separator [ 15,24]. As these methods usually take a long separation time, it is difficult to measure the many fission products having a short half life.…”

Beta-decay of148,150,152Pr into levels of148,150,152Nd

“…In all measurements with sources from the a35U(n~,, f) reaction, including the present ones, the intensities for the 451 and 615 keV v-rays are about 5% and 4%, but 20% and 2%, respectively, in sources from the i48Nd(n, p)-reaction. This has led [5][6][7] to the postulation of a 2.02-min high-spin isomer (I~=4-) of 148pr. This isomer is not populated in the ft--decay of 148Ce and its direct production in the 235U(nth , f)-reaction is small, with an isomeric yield ratio of 0.14 [6].…”

“…This has led [5][6][7] to the postulation of a 2.02-min high-spin isomer (I~=4-) of 148pr. This isomer is not populated in the ft--decay of 148Ce and its direct production in the 235U(nth , f)-reaction is small, with an isomeric yield ratio of 0.14 [6]. We estimated from these data that this isomer contributed less than 1% to the 14Spr activity in our measurements.…”