Thermal neutron capture cross sections of the palladium isotopes

Abstract

Abstract.We have measured precise thermal neutron capture γ-ray cross sections σ γ for all stable Palladium isotopes with the guided thermal neutron beam from the Budapest Reactor. The data were compared with other data from the literature and have been evaluated into the Evaluated Gamma-ray Activation File (EGAF) [1]. Total radiative neutron capture cross-sections σ 0 can be deduced from the sum of transition cross sections feeding the ground state of each isotope if the decay scheme is complete. The Palladium isotope decay schemes are incomplete, although transitions deexciting low-lying levels are known for each isotope. We have performed Monte Carlo simulations of the Palladium thermal neutron capture de-excitation schemes using the computer code DICEBOX [2]. This program generates a level scheme where levels below a critical energy E crit are taken from experiment, and those above E crit are calculated by a random discretization of an a priori known level density formula ρ(E, J π ). Level de-excitation branching intensities are taken from experiment for levels below E crit and the capture state, or calculated for levels above E crit assuming an a priori photon strength function and applying allowed selection rules and a Porter-Thomas distribution of widths. The calculated feeding to levels below E crit can then be normalized to the measured cross section deexciting those levels to determine the total radiative neutron cross-section σ 0 . In this paper we have measured σ 0 [ 102 Pd(n,γ)]=0.9±0. We have also determined from our statistical calculations that the neutron capture state in 107 Pd is best described as 2 + (60%)+3 + (40%). Agreement with literature values was excellent in most cases. We found significant discrepancies between our results for 102 Pd and 110 Pd and earlier values that could be resolved by re-evaluation of the earlier results.

Measurement of theMo97(n,γ)reaction with the DANCEγcalorimeter array

“…This expectation is consistent with the observation that differences of experimental MSC spectra from different resonances seem to be very similar to fluctuations among them predicted by simulations using the statistical model. This is also in accord with conclusions made from analysis of TSC [6] and MSC spectra [7] in 96 Mo and indicates that the statistical model can be used for the description of γ decay following radiative neutron capture in even-even nuclei in this mass region.…”

“…Analysis in Refs. [6,7] also indicated that the maximum allowed PSFs enhancement is given by a weak resonance postulated near E γ = 1 MeV that reproduces the Oslo experimental data and gives as small as possible PSFs at very low E γ .…”

“…There exist theoretical explanations of a low-E γ enhancement utilizing both E1 [3] and M 1 [4,5] transitions. However, this enhancement is not supported by the data from two different 95 Mo(n,γ) experiments: (i) measure-ment of the two-step γ cascades (TSCs) following the capture of thermal neutrons using a HPGe detector coincidence setup [6], and (ii) measurement of spectra of the multi-step γ cascades (MSCs) following neutron capture at isolated resonances using the highly segmented BaF 2 Detector for Advanced Neutron Capture Experiments (DANCE) at Los Alamos [7].…”

“…Later, analysis of data from radiative neutron capture on 95 Mo [6,7] clearly showed that the soft pole dependence is unrealistic for a description of PSFs at very low E γ . Analysis in Refs.…”

“…Analysis of TSC spectra following thermal neutron capture [6] and of MSC spectra following resonance neutron capture [7] demonstrated that the γ decay of 96 Mo can be well described using the model combination given by…”