Characteristics of mass and nuclear charge distributions of229th(nth, f). implications for fission dynamics

Abstract

The mass and nuclear charge distributions of fission fragments from 2Z9Th(nth,f) have been measured at several kinetic energies with the mass spectrometer Lohengrin (ILLGrenoble). The average proton e-o effect, which reaches 41%, induces large oscillations in the parameters of the isotopic charge distribution. A comparison of the data from different fissile nuclei shows the importance of the last stage of the process for intrinsic excitations.

Influence of asymmetry and fissility on even-odd effect in fission-fragment yields

“…Precise information has been obtained for the light part of the asymmetric fission-fragment distribution [1,[9][10][11][16][17][18][19][20][21]. They coincide with a heavy charge distribution centred on a constant value Z = 54, independently of the fissioning nucleus, as was already reported in [22].…”

“…The large amplitude of this staggering, which may reach 40% in the case of thorium [1], has always been fascinating to nuclear physicists. The observation of odd-Z fragments from an even-Z fissioning nucleus testifies the re-organisation of the intrinsic structure of the fissioning nucleus on its path towards scission.…”

“…A simple method to quantify the pairing effect in the fragment production is to define the global even-odd staggering δ as the average difference between even-and odd-Z yields over the full available distribution [1]. In the measurement of fragment yields of fissile actinides, it has been observed that the global even-odd staggering decreases with the fissility of the fissioning system [4].…”

“…f [1] and therefore, the evolution of the even-odd staggering with the fissioning nucleus is usually investigated as a function of the Coulomb parameter [5,6]. The evolution of the global even-odd staggering is displayed in Fig.…”

“…The local even-odd staggering δ(Z) is a measure of the deviation of the element distribution from a smooth behaviour, and is usually studied following the prescription of Tracy et al [8]. For different fissioning systems [1,[9][10][11], the even-odd staggering has been shown to be larger for large asymmetry. This experimental observation, reproduced in Fig.…”