Measurement of the double-differential cross section for electronic emission accompanying the interaction of fission fragments with nitrogen and carbon dioxide molecules

Conclusions Experimental data on the double-differential (with respect to angle of emergence and energy of the electrons) cross section for electron emission from nitrogen and carbon dioxide molecules bombarded with fission fragments were obtained under conditions of low data acquisition rate and high background level due to accompanying particles. Russian Science Center of the Russian Federation — A. I. Leipunskii Physics and Power Engineering Institute. Translated from Atomnaya énergiya, Vol. 82, No. 5, pp. 365–369, May, 1997.     

Vaporization of metals by fission fragments

The number of atoms evaporating from the surface of a metal when it emits fission fragments or alpha particles was measured for U²³³ and Pu²³⁹. This quantity depends considerably on the presence of an oxide layer on the surface of the metal and for U²³³-emitting fission fragments changes from 24 to 1200 atoms for a change from an oxidized to a cleaned surface. For Pu²³⁹ with a cleaned surface the value is 3500 atoms per fragment. For alpha particles leaving Pu²³⁹ the value is 0.02. Approximate computations indicate that the number of atoms in the zone heated by the passing of the fragment to a temperature insuring evaporation of the metal is for uranium 5,6 × 10⁶. The kinetic energy which the fragment imparts to the atoms of the lattice, apparently exceeds the value accepted in the literature at the present time.     

Determination of the ionization and charge-transfer cross sections in interactions of fission fragments with helium and argon atoms

Conclusions Experimental data on the differential cross section of electron emission from helium and argon atoms with respect to the electron energy during bombardment by fission fragments were obtained under conditions of low data acquisition rate and high background level due to concomitant particles. The results were compared with a theoretical calculation of the ionization and charge-transfer cross sections of helium and argon atoms by the method of classical trajectories in the collision studied and attest to a good agreement between experiment and the proposed theoretical model. This work was supported by the Russian Foundation for Fundamental Research under projection No. 96-02-17443a. Joint Institute of Nuclear and Thermal Power Production, V. A. Rykov, Main Science Center of the Russian Federation — A. I. Leipunskii Physics and Power Engineering Institute. Translated from Atomnaya énergiya, Vol. 84, No. 1, pp. 29–34, January, 1998.     

Absolute measurements of U and Pu fission cross-sections with photoneutron sources

the fission cross-sections of ²³⁵U and ²³⁹Pu for Na---Be, La---Be, Na---D and Ga---D photoneutrons have been measured absolutely. The neutron source strength was measured using a manganese bath to compare the photoneutron yield from the sources with the standard source NBS-II. Fission counts were accumulated with the source positioned symmetrically between two identical fission foils in an experiment package suspended in a low-albedo laboratory. Fission fragments passing through limited solid angle apertures were recorded on polyester track-etch films. The masses of the foil deposits were determined by microbalance weighings and confirmed by thermal neutron fission and alpha counting. After making a correction for the calculated energy distribution of the source neutrons, values of 1.471 ± 0.029, 1.274 ± 0.026, 1.162 ± 0.025 and 1.195 ± 0.026 barns were obtained for the ²³⁵U fission cross-section at the source median energies of 140, 265, 770 and 964 keV, respectively. Corresponding values of 1.469 ± 0.045, 1.515 ± 0.038, 1.670 ± 0.039 and 1.643 ± 0.038 barns were determined for ²³⁹Pu.     

Microstructure damage of titanium films by irradiation with fission fragments

Radiation damage caused by fission fragments to metal surfaces is an important research topic. Thin titanium foils were irradiated with a continuous wave beam of 132 MeV ¹³²Xe⁺²⁹ at the current intensity of 2 pnA. Pre- and post-irradiated surface topologies were investigated using atomic force microscopy and the observed defects were quantified by root mean square roughness, depth profile of the disordered zones, size and areal density of the voids, and discussed as a function of the applied fluencies (1-9) × 10¹³ Xe/cm². The first ellipsoidal dislocation loops appeared at the fluence of 3.0 × 10¹³ Xe/cm² with the areal density of 1.56 × 10⁶/cm² that increased to 2.0 × 10⁷ cm⁻² when the dose rose to 9.0 × 10¹³ Xe/cm². At this point also the first dislocation lines with the density of 1.3 × 10⁷ cm⁻² were seen. Our results suggest that the fission fragments might maximize large voids and dislocations and increase the degradation in depth resolution.     

Statistical theory for the ancle distribution of fission fragments

The angle distribution for fission fragments is considered at high excitation levels; in this case the angular momentum is distributed over a large number of nucleons and statistical theory can be applied to the nucleus. The distribution of states of the transition nucleus over values of the quantity K. the projection of the moment of the compound nucleus along the fission axis, is computed. The most probable state is found to be that with K = 0, which, in the case of neutron-induced fission leads to the appearance of maxima in the fragment angle distribution at 0 ° and 180 °. The results are compared with experiment; the moment of inertia of the transition nucleus with respect to the symmetry axis is determined (fission direction). The fragment angle distribution for fission induced by charged particles and -rays is also analyzed.