Physical Origin of the Transition from Symmetric to Asymmetric Fission Fragment Charge Distribution

Abstract

Using the improved scission-point model, the isotopic trends of the charge distribution of fission fragments are studied in induced fission of even-even Th isotopes at low-and high-excitation energies.

Deformation parameter changes in fission mass yields within the systematic statistical scission-point model

“…The transition of mass yields from symmetric (asymmetric) to asymmetric (symmetric) occurs by increasing the mass number of thorium (fermium) isotopes. Although the statistical scission point model can predict transition from asymmetric to symmetric fission for heavy actinides [9], the calculated results are not accurate compared with experimental data. This problem is found where the calculated results were refined, as far as they smeared each calculated yield by the Gaussian with the width 1.5 amu to obtain a smoother curve.…”

“…With this model, Wilkins was able to explain the transitions between symmetric to asymmetric fission modes. These models have been developed in many branches, such as the Gaussian model [3][4][5] and the modified scission point models [7][8][9][10][11][12]. Recently, the time-dependent model has been significantly developed by Randrup [14][15][16] and some researchers [17][18][19][20][21] to evaluate the mass yields of pre-actinides and actinides.…”

Deformation Parameters and Collective Temperature Changes in Photofission Mass Yields of Actinides Within the Systematic Statistical Scission Point Model

“…The most widely used theoretical model to study mass yields is the statistical model which was founded by Fong and Wilkins [1,2]. This model has been developed in many branches, such as the Gaussian model [3,4] and modified scission point models [6][7][8][9][10][11][12][13]. The time-dependent model has been significantly developed by Randrup [14][15][16] and others [17][18][19][20][21][22] to predict the shape of mass yields (symmetric or asymmetric modes).…”

“…Although the statistical model can predict transitions between symmetric and asymmetric modes in the region of heavy actinides, the calculated results are inaccurate compared to the experimental data. This problem is found where the calculated results were smeared (refined) by the Gaussian model with the width 1.5 amu to obtain a smoother curve [8].…”

“…On the other hand, some researchers [6][7][8][9] added some terms to neutron kinetic energy or gamma endpoint energy, E (as the initial excitation energy), to obtain the excitation energy of the fissioning nucleus, E*, for example, Pasca [7,9] added the Q-factor and the difference between the potential energy of the fissioning nucleus and the potential energy of one of the fragments at the scission point to the initial excitation energy to obtain excitation energy (i.e., E* Q+E+U cn −U i ). Some others [10,11] took available energy as the difference between the potential energy of the fissioning system at the scission point and the energy of the excited compound nucleus, which is the sum of Q-factor and initial excitation energy (E* Q+E).…”