Cottrell−Stokes Law for Ni3Ge Intermetallic Single Crystals with the [ 2 ¯ $$ \overline{2} $$ 3 4] Compression Axis

Russian Physics Journal - In an experiment on the temperature variation during plastic deformation of Ni3Ge alloy single crystals with the [ $$ \overline{2} $$ 3 4] orientation of the deformation...     

Novel features of the fragment mass variance in fission of hot nuclei

On the basis of data obtained by the incomplete fusion reactions ⁷Li(43A MeV)+²³²Th and ¹⁴N(34A MeV)+¹⁹⁷Au, the energy dependence of the variance (σ _M ² ) of the fragment mass in fission of highly heated nuclei has been investigated for total excitation energies E _tot ^* ranging from 50 up to 350 MeV. The dependence σ _M ² E _tot ^* shows some unexpected features when E _tot ^* exceeds a value of about 70 MeV. After this value, the steady increase of σ _M ² expected from its temperature dependence changes to some kind of plateau between 100 and 200 MeV. Further on, at E _tot ^* in excess of about 250 MeV, the variance is found to increase again sharply. In order to analyze this behavior quantitatively, a dynamical stochastic model has been developed. The model employs the one-body dissipation mechanism and describes the decay of highly excited and rotating nuclei by fission and light-particle evaporation. It satisfactorily explains the measured prior-to-scission neutron multiplicities and the experimental mass variances up to E _tot ^* ?250 MeV, but the stochastic treatment does not reveal any increase in σ _M ² at higher excitation energies in contradiction with the data.     

Multidimensional dynamical-statistical model for describing the fission of excited nuclei

A multidimensional stochastic model for describing the decay of excited nuclei is presented. The model takes into account the dynamics of thermal fluctuations of collective variables, the dissipation of the kinetic energy of collective motion, and the emission of light particles from excited nuclei. The potential energy of a deformed nucleus is calculated within the liquid-drop model with a sharp surface and within the finiterange-interaction model. The friction parameters are calculated on the basis of the one-body-dissipation model. The inertia parameters are found in the Werner-Wheeler approximation. The drift components of forces are determined in terms of the entropy of an excited nucleus. The latter in turn is computed within the Fermi gas approximation with allowance for the deformation dependence of the density-level parameter. The fission probability, the mean multiplicity of neutrons emitted prior to scission (prescission neutrons), and the variances of the mass distributions of fission fragments at the most probable kinetic-energy value are calculated on the basis of the model developed here and are compared with experimental data. The dependences of these quantities on the model parameters are considered in detail.     

The creep behavior of single-crystalline Ni<Subscript>3</Subscript>Ge alloys

The creep of single-crystalline Ni₃Ge alloys subjected to compression along the strain axis [001] has been investigated. The resulting creep curves have revealed low and high secondary-creep rates. Inverse hightemperature creep behavior has been observed.