Mass distribution in thermal-neutron-induced fission of long-lived 236Np

Reactor Neutron Fission Characteristics of the Long-Lived Isomer of Neptunium 236

“…Since the R value may be considered to be a "shape factor" relative to 235 U, values between masses 100 and 130 (for which R > 1) imply that "valley" yields for 236 Np are larger than those for 235 U. Although we were unable to observe fission products in this low-yield region, the conclusion confirms the result observed directly by Gindler et al [2], All of the fission yield data for 235 U thermal fission listed in col. 6 were taken from the evaluation of Rider [5]. Together with the observed R values, we then used Eqn.…”

“…Table 3 summarizes the results, together with the average number of neutrons emitted from the compound nucleus, 237 Np. Although our results for the average masses of the light and the heavy peaks agree well with the work of Gindler et al [2], our value for the neutrons emitted per fission was such a small difference between two fairly large numbers that our resultant precision for that quantity was very poor.…”

“…It appears, however, that the maximum yields of the heavy peak are larger than those of the light peak. Although Gindler et al [2] reached the same conclusion, theirs was based upon a very high yield at mass 134 and a rather "normal" one at mass 135. Unfortunately, although both 134 Te and 134 I could be detected in our gamma spectra, we were unable to extract useful data from either, and so were unable to confirm their result.…”

“…The thermal fission cross section of long-lived 236 Np has long been known to be several kilobarns [1], Recently, Gindler et al [2], reported a distribution of product yields from thermal-neutron induced fission obtained from beta-and gamma-ray counting of samples chemically separated from a neptunium source containing 20 percent 236 Np. We reported results of a similar irradiation [3] but our measurements were made quite differently.…”

“…All are expressed as percent fission yields. For comparison, we have listed in col. 9 the values found by Gindler et al [2], Columns 10 -12 list the data pertinent to the absolute atom method for determination of the 236 Np fission yields. Column 11 lists the fission-product atoms in the sample while col. 12 gives the abundance relative to the number of atoms of "Mo.…”