Emission Probabilities of Gamma Rays from the Decay of 233Pa and 238Np, and the Thermal Neutron Capture Cross Section of 237Np

Abstract

In order to determine the thermal neutron capture cross section of 237 Np, the relevant emission probabilities of the 312-keV -ray from the decay of 233 Pa and the 984-keV -ray from the decay of 238 Np are deduced from the ratio of the emission rate to the activity. The emission rate and activity are measured with a Ge detector and a Si detector, respectively. The measured emission probability for 312-keV -ray is 41:6AE0:9% and that for 984-keV -ray is 25:2AE0:5%. The emission probabilities are used to correct the thermal neutron capture cross section of 237 Np reported previously, and gives 168AE6 b. The neutron capture cross section is also determined as 169AE6 b by -ray spectroscopic method. The measured emission probabilities and capture cross section are compared with others from references. By averaging these values deduced by different methods, the value of 169AE4 b is recommended as the thermal neutron capture cross section of 237 Np for 2,200 m/s neutrons.

Neutron capture cross section measurements on 237Np with a 4π Ge spectrometer

“…To obtain absolute value of the present capture cross section, the previous experimental and evaluated data were referred. The data by Weston and Todd [1], Kobayashi et al [2], Harada et al [4], the evaluated data of JENDL-3.3 [11], and the recommended value by Mughabghab [12] are 180 ± 6, 158 ± 3, 169 ± 4, 161.73 and 175.9 ± 2.5, respectively, which are within about 10% variation. By referring these values, the present data were normalized to the reference value of 179 b at 0.025 eV.…”

“…237 Np is one of the most important nuclei in the minor actinides. In the past, several groups have measured the neutron capture cross section of 237 Np in the thermal neutron and resonance energy range [1][2][3][4].…”

“…The previous measurements were performed by the neutron time-of-flight (TOF) method using an electron Linac in the resonance region [1][2][3][4] as a pulsed neutron source and used C 6 F 6 , C 6 D 6 or BGO detectors. To reduce the high background caused by γ-rays of the radioactive sample, the pulse-height bias corresponding to 0.5 ∼ 1.0 MeV was used and it was necessary to insert rather thick lead shieldsbetween the sample and detectors or to arrange coincidences between the detectors in order to obtain a good signal-to-noise ratio.…”

Precise Measurements of Neutron Capture Cross Sections for LLFPs and MAs

“…The results for LLFPs are listed in Table 5.1, and for MAs [24][25][26][27][28][29][30][31] in Table 5.2, together with previously reported data. Here, the symbols σ eff , σ 0 , and I 0 denote the effective cross section, the thermal neutron capture cross section, and the resonance integral, respectively; σ 0 is the cross section at the neutron energy of 25.3 meV.…”

Accuracy Improvement of Neutron Nuclear Data on Minor Actinides

“…However, accurate γ ray emmision probability is necessary to be precisely determined. In this project, the relevant γ ray emmision probabilities for MA samples are measuerd using a combination of α-ray and γ-ray spectroscopic methods [12]. 237 Np and 241, 243 Am standard solutions were supplied by Japan Radioisotope Association to prepare samples.…”