China
Africa
Explore chapters and articles related to this topic
N
Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[atomic, nuclear] Metallic element discovered in 1940. The first isotope was produced in the University of California, Berkeley by Edwin Mattison McMillian (1907–1991) and Philip Hauge Abelson (1913–2004) by bombarding uranium with slow moving neutrons, creating neptunium-239, with a half-life of approximately 2.3–2.4 days, decays to plutonium-239 by beta decay. The most stable configuration is neptunium-237, discovered in 1942 by A. C. Wahl and Glenn T. Seaborg, has a half-life of 2,144,000 years, decays into protactinium-233 through alpha decay and is a by-product of the production of plutonium (94244Pu).
Japanese evaluated nuclear data library version 5: JENDL-5
Published in Journal of Nuclear Science and Technology, 2023
Osamu Iwamoto, Nobuyuki Iwamoto, Satoshi Kunieda, Futoshi Minato, Shinsuke Nakayama, Yutaka Abe, Kohsuke Tsubakihara, Shin Okumura, Chikako Ishizuka, Tadashi Yoshida, Satoshi Chiba, Naohiko Otuka, Jean-Christophe Sublet, Hiroki Iwamoto, Kazuyoshi Yamamoto, Yasunobu Nagaya, Kenichi Tada, Chikara Konno, Norihiro Matsuda, Kenji Yokoyama, Hiroshi Taninaka, Akito Oizumi, Masahiro Fukushima, Shoichiro Okita, Go Chiba, Satoshi Sato, Masayuki Ohta, Saerom Kwon
Neptunium-237 is one of the important minor actinides for the design of the nuclear fuel cycle. The improvement of the accuracy of capture cross section, which is larger than the fission cross section below 400 keV, has been requested for reactor design of an accelerator-driven system [77]. The resonance parameters up to 109.1 eV were taken from the data1 of Rovira et al. [78], in which the capture measurements were made by the NaI detector of ANNRI and the parameters were extracted by REFIT [79,80]. The parameters above 109.1 eV were the same as those of JENDL-4.0. The thermal capture cross section obtained by Rovira et al. was 177.6 (38) b, which is consistent with that of JENDL-4.0 (178.1 b). The recent activation measurements favor a smaller cross section by 2%, which was taken into account for JENDL-5 (173.9(92) b) by the parameter modifications of negative resonances. The capture cross sections between 500 eV and 230 keV were revised, based on the data measured at ANNRI and integral benchmark tests.
Measurements of thermal-neutron capture cross-section and resonance integral of neptunium-237
Published in Journal of Nuclear Science and Technology, 2019
Shoji Nakamura, Fumito Kitatani, Atsushi Kimura, Akihiro Uehara, Toshiyuki Fujii
The thermal-neutron capture cross-section σ0 and resonance integral I0 were derived by analysis based on Westcott’s convention with the obtained reaction rates and information on the neutron flux components. The results of σ0, s0, I0ʹ, and I0 obtained by the three irradiation sets are summarized in Table 8 together with the weighted averages. Firstly, the thermal-neutron capture cross-section σ0 and the parameter s0 were derived for three irradiation sets only with the statistical error, and then weighted averages were obtained both for the σ0 and s0. The variations in values due to irradiations were estimated to be ±3 barn for the σ0 and ±0.3 for the s0, respectively. Next, for the results of the weighted averages of the σ0and s0, the systematic errors and the error of the variation due to measurement were taken into consideration. Finally, I0ʹ and I0 were derived from Equations (3) and (9) using the σ0 and s0 in consideration of systematic errors as described above. In the present work, the thermal-neutron capture cross-section σ0 was obtained as 186.9 ± 6.2 barn. The present results for the thermal-neutron capture cross-section σ0 and the resonance integral I0 are summarized in Table 9 together with the past reported values and evaluations. The evaluation value based on reported experimental data is 178.1 barn in JENDL-4.0 [16], and the present result is found to be about 5% larger than that. That is, 237Np tends to absorb thermal-neutrons by about 5% from the evaluated data. Neptunium-237, which has along half-life of 2.14 × 106 years [1], is transmuted to 238Np through the neutron capture reaction. Since 238Np decays in only 2.117 days [1], it is expected to artificially accelerate the decay of long lived 237Np nuclide.