246–248Cm Neutron fission cross sections and resonance integrals

Abstract

The fission cross sections of [246][247][248] Cm nuclei for neutron energies 0.1 eV-20 keV have been measured using an SVZ-100 lead moderation time neutron spectrometer at the Institute of Nuclear Research of the Russian Academy of Sciences. The fission resonance integrals have been calculated. The results are compared with the existing data and recommended evaluations.The measurement of the neutron-fission cross sections of Np, Am, and Cm is a priority problem which is important for transmutation of wastes and for the development of models of transitional states in the theory of fission of heavy nuclei.In the present work, the fission cross sections of 246-248 Cm for neutron energies <20 keV were measured at the Institute of Nuclear Research of the Russian Academy of Sciences (IYaI RAN) as part of the program of study of the fission of transuranium nuclei using an SVZ-100 lead moderation time neutron spectrometer [1][2][3][4][5]. Even though their resolution is low such spectrometers are used successfully to measure the cross section of nuclides which are difficult or impossible to study by other methods [6].Experimental and Recommended Data. The fission cross sections of curium isotopes, especially even-even nuclei, in the resonance neutron energy range are poorly studied nuclear constants. The main information has been obtained in two works. In the first one an experiment was performed on neutrons from an underground nuclear explosion Physics 8 (USA) by the time-of-flight method at energies above 10 eV [7]. 246 Cm targets with mass m = 16.3 μg and content of the main isotope 94.7%, 247 Cm (m = 26.9 μg, 20.9%), and 248 Cm (m = 67.6 μg, 89.3%) were used in the studies. The lowest error in the data taking account normalization was 8-11% and on average was worse than 20%.In a second work, also performed in the USA, an RINS moderation time spectrometer was used [8,9]. Its neutron energy range was 0.1 eV-80 keV. Here 246 Cm (m = 17 μg, 96.87%), 247 Cm (m = 10.6 μg, 29.8%), and 248 Cm (m = 31.2 μg, 96.89%) targets were used. The error in the data taking account of the normalization for energy above 3 eV reached 7-11%. At low energy, the error was 30-50%. Data for the strongly fissile odd isotope 247 Cm were obtained in the energy range 20 meV < E < 9.8 keV at the LANSCE meson factor in Los Alamos (USA) [10]. The target was the same as the one used in [9]. The measurement error taking account of normalization was no better than 10%.Data at energies above 20 keV were obtained in [11] (All-Russia Research Institute of Experimental Physics, VNIIEF, in Sarov) using the underground nuclear explosion method. The error in the data below 100 keV is 17-30%.

Parameters of s-resonances in 246–248Cm fission cross sections

“…Assume that the first three moments of the random quantity ξ, which is related with the other random quantities x, y, and z by the relation ξ = ϕ x,y,z , have been measured and their a priori distribution known, where t 0 is the average value, and s i is the variance. Figure 1 shows the fission cross section 〈σ√ ⎯E〉 measured with an SVZ-100 spectrometer in the neutron energy range 0.2eV < E < 400 eV [4]. The expressions for the a posteriori distributions of other random quantities (y, z) have a similar form.…”

Development of an Evaluated Nuclear Database for Modern Technologies

“…For this reason, in the energy range from thermal to 20 keV the fission cross section of the isotopes 241,242m,243 Am and 243-248 Cm was measured with a spectrometer according to the retardation time of neutrons in lead (jointly with the Institute of Nuclear Research of the Russian Academy of Sciences). The new results showed that the existing evaluations must be re-examined [6].…”

243Am neutron fission cross section and resonance parameters

“…The results were compared with existing data and recommended evaluations.Subbarrier fission cross section of 243 Am in the resonance neutron energy range and the properties of the resonances have not been studied sufficiently to construct reliable data libraries which are necessary to study the transmutation of wastes and to improve models of transitional states in the theory of fission of heavy nuclei.The present work was performed as part of research on the fission of transuranium nuclei using the SVZ-100 lead moderation time neutron spectrometer at the Institute for Nuclear Research of the Russian Academy of Sciences (IYaI RAN) [1][2][3][4][5]. The resonance fission integrals and the area and fission width of the resolved resonances were calculated.…”

“…The present work was performed as part of research on the fission of transuranium nuclei using the SVZ-100 lead moderation time neutron spectrometer at the Institute for Nuclear Research of the Russian Academy of Sciences (IYaI RAN) [1][2][3][4][5]. Even though their resolution is low, such spectrometers are successfully used to measure nuclide cross sections which are difficult or impossible to study by other methods [6,7].…”