Asymmetry in nuclear fission

Abstract

The deformation energies for fissioning nuclei in the actinide region are calculated using the Strutinsky shell-correction method. Instability of the second barriers against an asymmetric shape degree of freedom is found in agreement with Mb[ier "rod Nilsson. The inclusion of these asymmetric deformations improves the agreement between calculated and experimental barrier heights. The asymmetries found have the correct magnitude in order to explain the experimental mass ratios of the fission fragments.

Four Channels in the Fission of 252Cf

“…Their shapes were parametrized in cylindrical coordinates (r, z) as [7] r2 = (/h ~ z2) («o + a \( z -zn)/rcn…”

“…That the vicinity o f the second saddle should be con sidered as the birth-place o f mass asymmetry, was shown long ago [23,7]. Pashkevich predicted two channels for lead [24].…”

Role of transitional levels inNp237(γ,f): Perspectives for studying highly deformed systems

“…3 we show our calculated static fission barriers as functions of ε and α 4 , and with three different formulations for the macroscopic part [22][23][24]. As shown, the deformation coordinates are insensitive to the adopted macroscopic model, which only changes the relative height of the saddle points.…”

“…It is important to remark that the general behavior of the barrier heights obtained by the BARRIER code is similar to those obtained when using the LDM parameterization proposed in Refs. [22,24]. Before commenting on our results, we would like to add a few more arguments on the barrier heights and transition levels issues.…”

“…(i) In the first place, there are several works presenting calculations of fission barrier heights, using semimicroscopic models based on the Strutinsky [26][27][28] and Hartree-Fock [29,30] methods. However, absolute values for barrier heights from these theoretical approaches, are systematically lower than those obtained from the fitting of cross sections by means of statistical model calculations [11][12][13][14][15][16]23,24]. (ii) In the second place, and considering that the uncertainties associated with our measurements [15] are modest, we note that small differences between the selected barrier heights entering our model calculations could eventually destroy the agreement between level groups (and level voids) and the corresponding structures in the measured cross sections.…”