Half-lives andP n values of delayed-neutron precursors in the mass chains 85?87, 92, 135, 136 and 145

Abstract

Further results are presented on half-lives and neutron emission probabilities (P,) of short-lived delayed-neutron precursors in the mass chains 85-87, 92, 135, 136 and 145 obtained with the recoil focussing parabola-type mass separator for unslowed fission products LOHENGRIN installed at the Grenoble high-flux reactor. A new P,-value of (44_14)% is given for the (0.73 +0.06)s 87As; the P,-values of seven precursor nuclides have been redetermined: (1.9 • s 85As with (22_+8) %, 0.9 s 86As with (10.5 _+2.2)%, (0.35 _+0.04)s 92Br with (21 _+8)%, (1.6 _+0.15)s ~35Sb with (14-t-1)%, (0.9• 136Sb with (19___9)%, (17.5_+0.2)s 136Te with (2.0_+1.0)% and 0.6s 145Cs with (12.5 _+3.0)%. The results are compared with the existing data, and the neutron emission probabilities are discussed within a simple semi-empirical picture.

Delayed neutron emission probabilities of gallium, bromine, rubidium, indium, antimony, iodine, and cesium precursors

“…Our value 17.5+2.0 % for 13SSb is in fair agreement with the value of Rudolph et al [28] (see Table 5). The value obtained by Crancon et al [29] is significantly lower, For this precursor the uncertainty in average neutron energy is of importance and accounts for the main part of the total uncertainty of our value,…”

Beta-delayed-neutron studies of $^{135,136}$Sb and $^{140}$I performed with trapped ions

“…5. In the direct measurements, P n was determined either from the fission yield and neutrons-per-fission of the isotope [43][44][45][46][47][48], or by counting β particles and neutrons separately [49][50][51][52][53], usually with plastic scintillators and neutron detectors (e.g., BF 3 tubes, 3 He tubes), respectively. For each isotope, there is roughly a factor of two spread among the P n results, despite the fact that in many cases, the quoted uncertainties are significantly smaller than these differences.…”