Determination of the probabilities of spontaneous fission in U233, U235, and Am243

The periods of spontaneous fission were determined for urnaium and americium by means of fission-fragment detectors in the form of glass plates; these were: (1.2±0.3)·10¹⁷ years for U²³³, (3.5±0.9)·10¹⁷ years for U²³⁵, (3.3±0.3)·10¹³ years for Am²⁴³. An attempt was made to systematize experimental data on the spontaneous-fission periods of odd-even and even-odd nuclei.Translated from Atomnaya Énergiya, Vol. 20, No. 4, pp. 315–317, April, 1966.     

Fission Product Yields of U, U, U and Pu in Fields of Thermal Neutrons, Fission Neutrons and 14.7-MeV Neutrons

The yields of more than fifteen fission products have been carefully measured using radiochemical techniques, for ²³⁵U(n,f), ²³⁹Pu(n,f) in a thermal spectrum, for ²³³U(n,f), ²³⁵U(n,f), and ²³⁹Pu(n,f) reactions in a fission neutron spectrum, and for ²³³U(n,f), ²³⁵U(n,f), ²³⁸U(n,f), and ²³⁹Pu(n,f) for 14.7 MeV monoenergetic neutrons. Irradiations were performed at the EL3 reactor, at the Caliban and Prospero critical assemblies, and at the Lancelot electrostatic accelerator in CEA-Valduc. Fissions were counted in thin deposits using fission ionization chambers. The number of fission products of each species were measured by gamma spectrometry of co-located thick deposits.     

Theoretical cross sections of Bi,Th, U and U on deuteron-induced reactions

There are many application fields for fast neutrons. The main application fields of the fast neutrons are accelerator-driven sub-critical systems (ADS) and fusion–fission (hybrid) reactor systems for fission energy production. Thorium (Th) and uranium (U) are nuclear fuels in fusion–fission (hybrid) reactor systems and bismuth (Bi) is also the target nucleus in the ADS reactor systems. In this study, neutron production cross sections produced by (d, xn) reactions for spallation targets such as ²⁰⁹Bi, ²³²Th, ²³⁵U and ²³⁸U have been investigated. New evaluated hybrid model and geometry dependent hybrid model have been used to calculate the pre-equilibrium neutron production cross sections. For the reaction equilibrium component, Weisskopf–Ewing model calculations have been preferred. The obtained results have been discussed and compared with the available experimental data and found in agreement with each other.     

A measurement of the U233, U235, Pu239 total cross sections. As well as the fission cross section of U235 for resonance neutrons

The measurement of the interaction cross sections between resonance neutrons and fissionable isotopes are of definite importance both for reactor calculations and for the construction of various nuclear models. In this work we present the results of measurements of the U²³³, U²³⁵, and Pu²³⁹ total cross sections, as well as the fission cross section of U²³⁵. The measurements were performed on a mechanical neutron spectrometer (neutron chopper) with a resolution of 0.1–0.2 sec/m in the neutron energy region from 3–5 to about 500 ev. The resonance parameters are calculated to energies of about 30–50 ev, for which the levels may still be considered resolved. For these resonances the neutron widths g_n are determined; the total widths are determined for sufficiently excited levels when the uncertainty in this determination is no greater than about 50%. For U²³⁵ resonance in the energy region from 2.5 to 20 ev, in addition to the above parameters, the ratio of the fission width _f to the total width is found.     

Excitation functions of the individual levels of the nuclei U235, U233, and Pu239, including competition between inelastic neutron scattering and fission of the nuclei

N. Bohr's statistical theory [1, 2] has been used to calculate the excitation functions for inelastic scattering of neutrons at the individual levels of the target nuclei U²³⁸, U²³³, and Pu²³⁹ including competition between inelastic scattering and fission. The fission width was found from N. Bohr and Wheller's formula [3] including the penetrability of the fission barrier as given by Hill and Wheller [4]. The fission thresholds and the number of transition states at the saddle point were taken both from the experimental data of [5], and the theoretical data of [6].In conclusion the authors express their gratitude to L. N. Usachev, V. S. Stavinskii, and N. S. Rabotnov for their valuable comments and discussions as well as to L. S. Anufrienko for doing the calculational work.     

Measurement of the delayed-neutron yields in the fission of233U,236U,237Np,240Pu,and241Pu by neutrons from the spectrum of a fast reactor

Translated from Atomnaya Énergiya, Vol. 66, No. 2, pp. 100–103, February, 1989.     

Uncertainty Analyses in the Resolved Resonance Region of 235U, 238U,and 239Pu with the Reich-Moore R-Matrix Theory for JENDL-3.2

A simple method to estimate covariances for resolved resonance parameters was developed. Although a large number of resolved resonances are observed for major actinides, uncertainties in averaged cross sections are more important than those in resonance parameters in reactor calculations. The method developed here derives a covariance matrix for the resolved resonance parameters which gives an appropriate uncertainty of the averaged cross sections. The method was adopted to evaluate the covariance data for ²³⁵U, ²³⁸U, and ²³⁹Pu resonance parameters in JENDL-3.2, with the Reich-Moore R-matrix formula.