Fission cross-section measurement for the 238U(n,f)89Rb reaction induced by D-T neutrons

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Abstract

The fission reactions of 238U induced by D-T neutrons were investigated by neutron activation technique and low-background HPGe-γ spectrometer. The half-life was used to identify the possible daughter nuclide. The fission cross-sections of 238U(n,f)89Rb reaction induced at the neutron energy around 14 MeV, i.e., 14.1 ± 0.3, 14.5 ± 0.3 and 14.7 ± 0.3 MeV, were measured precisely. The neutron flux was monitored by accompanying α-particle of the T(d,n)4He reaction and the neutron energies were determined by the cross-section ratio of 90Zr(n,2n)89Zr to 93Nb(n,2n)92mNb reaction. The fission cross-sections of the 238U(n,f)89Rb reaction are 33.2 ± 2.1 mb, 32.2 ± 2.0 mb, and 32.6 ± 2.1 mb, corresponding to the above neutron energy points.

Introduction

Neutron-induced reactions play an essential role in nucleosynthesis, advanced nuclear reactor design, and stockpile stewardship. Neutron-induced reaction cross-sections data are crucial, not only for fundamental research on nuclear science [1], [2], but also for practical applications in nuclear technology [3], [4], [5]. Thus, it is necessary to measure the precise cross-section values and update database constantly.

238U constitutes more than 90% of nuclear fuel in power reactors [6], [7], [8] with a relative abundance of 99.27%. Deuterium-tritium fusion reaction produces 14 MeV neutrons, which are 2–5 orders of magnitude lower in flux than a 1 MW TRIGA reactor [9], [10]. Accurate knowledge of neutron induced reaction cross-sections around 14 MeV plays a key role in nuclear engineering designs and safe operation of various reactors. It is important to study the fission cross-sections of 238U and 232Th induced by neutrons besides the (n,γ) and (n,xn) reactions.

Many research groups have studied on the cumulative fission yields and description of the fission fragment mass distribution for the 238U(n,f) and 232Th(n,f) reactions by using time-of-flight [11], [12] and off-line γ-ray spectrometric [13], [14] techniques. Our group has performed a series of measurements [15], [16], [17], [18], [19], [20], [21], [22], [23] on the fission data for 232Th induced by D-T and D-D neutrons. In this work, we focus on the measurement of fission cross-sections of 238U induced by D-T neutron. The half-life of fission product was used to identify the possible radionuclide. Pure/background-less activation targets, monoenergetic neutron beams with high flux, and high-resolution low-background γ-ray spectroscopy helped minimize the uncertainties of the measurements.

Section snippets

Experimental details

The irradiation experiment was performed at the K-400 Intense Neutron Generator at the Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics. Neutrons around 14 MeV were produced from T(d,n)4He reaction, and the details of neutron generator were described in our previous articles [15], [16], [17], [18], [19], [20], [21], [22], [23]. The neutron was monitored by accompanying α-particles to make a correction caused by the flux fluctuation in the neutron activation

Fission cross-section estimation

The fission cross-section (σx) can be deduced as the following with the developed NAA formula [26]:σx=[εIγηKSMD]mλAFCx[εIγηKSMD]x[λAFC]m·σm,where, the subscripts m and x represent the terms associated with the monitor (m) and measured (x) reaction, respectively. σm is the cross-section of the monitor reaction. ε is the detection efficiency. Iγ is the gamma intensity. η is the isotopic abundance of target nuclide. M is the mass of sample. A is the atomic weight. C is the measured gamma count of

Results

Using the time schedule from Fig. 1, a series of gamma spectra were obtained. As shown in Fig. 2, (a) is a full gamma ray spectrum obtained from the UO2(NO3)2 sample, which was irradiated at the neutron energy of 14.1 MeV; (b) is the partial spectrum of the full gamma spectrum with the interested gamma ray of 89Rb. The half-life helped to determine the gamma spectrum with a certain time schedule of cooling and measuring. Identification of the daughter nuclide in the gamma spectrum was based on

Summary

The fission reactions of 238U induced by D-T neutrons were investigated. The half-life was used to identify the possible fission product. The cumulative fission cross-sections of 238U(n,f)89Rb reaction channel were estimated by the selected characteristic γ-peaks (1031.92 keV and 1248.14 keV) with a simple averaged value, i.e., 33.2 ± 2.1, 32.2 ± 2.0, and 32.6 ± 2.1 mb, related to En = 14.1 ± 0.3, 14.5 ± 0.3, and14.7 ± 0.3 MeV, respectively. The cross-sections of 238U(n,f)89Kr fission channel

CRediT authorship contribution statement

Qiang Wang: Writing - original draft, Writing - review & editing, Methodology. Yafei Han: Investigation, Validation, Methodology. Luocheng Yang: Validation, Data curation. Lixin Qin: Formal analysis, Investigation. Changlin Lan: Funding acquisition. Kaihong Fang: Conceptualization, Project administration, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the Fundamental Research Funds for the Central Universities of China (No. lzujbky-2019-53), and the Lanzhou Talent Innovation and Entrepreneurship Project (2019-1-51), and the National Natural Science Foundation of China (No. 11975113).

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