{"title":"239Pu(n, F) 和 235U(n, F) 裂变中子谱图的各向异性","authors":"V. M. Maslov","doi":"10.1134/S1547477123060262","DOIUrl":null,"url":null,"abstract":"<p>Angular anisotropy of secondary neutrons is evidenced in neutron emission spectra (NES) and prompt fission neutron spectra (PFNS). In case of NES that is due to angular dependence of elastic scattering, direct excitations of discrete collective levels and pre-equilibrium/direct emission of (<i>n</i>, <i>nX</i>)<sup>1</sup> neutrons, while in case of PFNS it is because of these neutrons are evidenced in exclusive pre-fission neutrons in (<i>n</i>, <i>xnf</i>)<sup>1</sup>. In <sup>239</sup>Pu(<i>n, xnf</i>)<sup>1,...<i>x</i></sup> and <sup>235</sup>U(<i>n</i>, <i>xnf</i>)<sup>1,...<i>x</i></sup> PFNS demonstrate different responses to forward and backward (<i>n, xnf</i>)<sup>1</sup> neutrons emission with respect to the incident neutron momentum. Average energy of (<i>n</i>, <i>nf</i>)<sup>1</sup> neutrons depends on the emission angle θ, i.e., fission cross section, prompt neutron number and total kinetic energy depend on θ as well. Exclusive neutron spectra (<i>n, xnf</i>)<sup>1,...<i>x</i></sup> at θ ~ 90° are consistent with <sup>235</sup>U(<i>n</i>, <i>F</i>)(<sup>235</sup>U(<i>n</i>, <i>xn</i>)) and <sup>239</sup>Pu(<i>n</i>, <i>F</i>)(<sup>239</sup>Pu(<i>n, xn</i>)) reaction cross sections within <i>E</i><sub><i>n</i></sub> ~ 0.01–20 MeV energy range. Exclusive neutron spectra of (<i>n</i>, <i>xnf</i>)<sup>1,..<i>x</i></sup>, (<i>n</i>, <i>n</i>γ) and (<i>n</i>, <i>xn</i>)<sup>1,<i>...x</i></sup> are calculated within Hauser–Feshbach formalism alongside with (<i>n</i>, <i>F</i>) and (<i>n</i>, <i>хn</i>) reaction cross sections, angular dependence of first neutron (<i>n</i>, <i>nX</i>)<sup>1</sup> emission <span>\\(\\omega (\\theta )\\)</span> being included. Approximation obtained for <span>\\(\\omega (\\theta )\\)</span> fits the measured NES at 14 MeV. The correlation of angular dependence of (<i>n</i>, <i>xnf</i>)<sup>1</sup> neutron emission with emissive fission (<i>n</i>, <i>xnf</i>) contribution to the observed fission cross section and angular anisotropy of NES. The ratios of mean PFNS energies <span>\\(\\left\\langle E \\right\\rangle \\)</span> for forward and backward emission of <sup>235</sup>U(<i>n</i>, <i>xnf</i>) and <sup>239</sup>Pu(<i>n</i>, <i>xnf</i>) pre-fission neutrons are consistent with measured data.</p>","PeriodicalId":730,"journal":{"name":"Physics of Particles and Nuclei Letters","volume":null,"pages":null},"PeriodicalIF":0.4000,"publicationDate":"2023-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Anisotropy of Prompt Fission Neutron Spectra of 239Pu(n, F) and 235U(n, F)\",\"authors\":\"V. M. Maslov\",\"doi\":\"10.1134/S1547477123060262\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>Angular anisotropy of secondary neutrons is evidenced in neutron emission spectra (NES) and prompt fission neutron spectra (PFNS). In case of NES that is due to angular dependence of elastic scattering, direct excitations of discrete collective levels and pre-equilibrium/direct emission of (<i>n</i>, <i>nX</i>)<sup>1</sup> neutrons, while in case of PFNS it is because of these neutrons are evidenced in exclusive pre-fission neutrons in (<i>n</i>, <i>xnf</i>)<sup>1</sup>. In <sup>239</sup>Pu(<i>n, xnf</i>)<sup>1,...<i>x</i></sup> and <sup>235</sup>U(<i>n</i>, <i>xnf</i>)<sup>1,...<i>x</i></sup> PFNS demonstrate different responses to forward and backward (<i>n, xnf</i>)<sup>1</sup> neutrons emission with respect to the incident neutron momentum. Average energy of (<i>n</i>, <i>nf</i>)<sup>1</sup> neutrons depends on the emission angle θ, i.e., fission cross section, prompt neutron number and total kinetic energy depend on θ as well. Exclusive neutron spectra (<i>n, xnf</i>)<sup>1,...<i>x</i></sup> at θ ~ 90° are consistent with <sup>235</sup>U(<i>n</i>, <i>F</i>)(<sup>235</sup>U(<i>n</i>, <i>xn</i>)) and <sup>239</sup>Pu(<i>n</i>, <i>F</i>)(<sup>239</sup>Pu(<i>n, xn</i>)) reaction cross sections within <i>E</i><sub><i>n</i></sub> ~ 0.01–20 MeV energy range. Exclusive neutron spectra of (<i>n</i>, <i>xnf</i>)<sup>1,..<i>x</i></sup>, (<i>n</i>, <i>n</i>γ) and (<i>n</i>, <i>xn</i>)<sup>1,<i>...x</i></sup> are calculated within Hauser–Feshbach formalism alongside with (<i>n</i>, <i>F</i>) and (<i>n</i>, <i>хn</i>) reaction cross sections, angular dependence of first neutron (<i>n</i>, <i>nX</i>)<sup>1</sup> emission <span>\\\\(\\\\omega (\\\\theta )\\\\)</span> being included. Approximation obtained for <span>\\\\(\\\\omega (\\\\theta )\\\\)</span> fits the measured NES at 14 MeV. The correlation of angular dependence of (<i>n</i>, <i>xnf</i>)<sup>1</sup> neutron emission with emissive fission (<i>n</i>, <i>xnf</i>) contribution to the observed fission cross section and angular anisotropy of NES. The ratios of mean PFNS energies <span>\\\\(\\\\left\\\\langle E \\\\right\\\\rangle \\\\)</span> for forward and backward emission of <sup>235</sup>U(<i>n</i>, <i>xnf</i>) and <sup>239</sup>Pu(<i>n</i>, <i>xnf</i>) pre-fission neutrons are consistent with measured data.</p>\",\"PeriodicalId\":730,\"journal\":{\"name\":\"Physics of Particles and Nuclei Letters\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":0.4000,\"publicationDate\":\"2023-12-04\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Physics of Particles and Nuclei Letters\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://link.springer.com/article/10.1134/S1547477123060262\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q4\",\"JCRName\":\"PHYSICS, PARTICLES & FIELDS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Physics of Particles and Nuclei Letters","FirstCategoryId":"1085","ListUrlMain":"https://link.springer.com/article/10.1134/S1547477123060262","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"PHYSICS, PARTICLES & FIELDS","Score":null,"Total":0}
Anisotropy of Prompt Fission Neutron Spectra of 239Pu(n, F) and 235U(n, F)
Angular anisotropy of secondary neutrons is evidenced in neutron emission spectra (NES) and prompt fission neutron spectra (PFNS). In case of NES that is due to angular dependence of elastic scattering, direct excitations of discrete collective levels and pre-equilibrium/direct emission of (n, nX)1 neutrons, while in case of PFNS it is because of these neutrons are evidenced in exclusive pre-fission neutrons in (n, xnf)1. In 239Pu(n, xnf)1,...x and 235U(n, xnf)1,...x PFNS demonstrate different responses to forward and backward (n, xnf)1 neutrons emission with respect to the incident neutron momentum. Average energy of (n, nf)1 neutrons depends on the emission angle θ, i.e., fission cross section, prompt neutron number and total kinetic energy depend on θ as well. Exclusive neutron spectra (n, xnf)1,...x at θ ~ 90° are consistent with 235U(n, F)(235U(n, xn)) and 239Pu(n, F)(239Pu(n, xn)) reaction cross sections within En ~ 0.01–20 MeV energy range. Exclusive neutron spectra of (n, xnf)1,..x, (n, nγ) and (n, xn)1,...x are calculated within Hauser–Feshbach formalism alongside with (n, F) and (n, хn) reaction cross sections, angular dependence of first neutron (n, nX)1 emission \(\omega (\theta )\) being included. Approximation obtained for \(\omega (\theta )\) fits the measured NES at 14 MeV. The correlation of angular dependence of (n, xnf)1 neutron emission with emissive fission (n, xnf) contribution to the observed fission cross section and angular anisotropy of NES. The ratios of mean PFNS energies \(\left\langle E \right\rangle \) for forward and backward emission of 235U(n, xnf) and 239Pu(n, xnf) pre-fission neutrons are consistent with measured data.
期刊介绍:
The journal Physics of Particles and Nuclei Letters, brief name Particles and Nuclei Letters, publishes the articles with results of the original theoretical, experimental, scientific-technical, methodological and applied research. Subject matter of articles covers: theoretical physics, elementary particle physics, relativistic nuclear physics, nuclear physics and related problems in other branches of physics, neutron physics, condensed matter physics, physics and engineering at low temperatures, physics and engineering of accelerators, physical experimental instruments and methods, physical computation experiments, applied research in these branches of physics and radiology, ecology and nuclear medicine.