A Comparison of Triton and Alpha Emission Characteristics in Ternary Fission

Abstract

In the first part of this paper, the fundamental and applied interest of ternary particle emission is briefly outlined. The main emission characteristics of ternary a's and tritons (angular and energy distributions, yields) are compared and discussed. Special attention is given to observed differences between tritons and a's, such as the strong difference in yield, the (apparent?) difference in energy distribution and the fluctuations of the t/a ratio. In a second part we report on recent progress in our systematic study of the tritonand a-emission characteristics in spontaneous and thermal neutron induced fission. In the third part of the talk, a detailed discussion and interpretation of the observed phenomena is given. Concerning ternary a-emission, we highlight the strong influence on the ternary a-emission probability of both the fission modes followed by the fissioning nucleus and the a-cluster preformation probability. Concerning triton emission, we establish a new correlation between the triton emission probability (t/B) extrapolated to zero excitation energy with the average number of prompt neutrons (< v >) emitted by the same compound nucleus at zero excitation energy. This correlation allows to treat simultaneously all ternary fission data coming from spontaneous as well as thermal neutron induced fission. Lastly, we discuss the impact of the fissioning nucleus excitation energy on the ternary emission probability: the different behaviour of tritons and a's suggests a possible difference in their emission mechanism.

Local and global even-odd effects in prompt emission in fission

“…The same periodicity was seen in experimental data of charge polarization Z(A) and the root-mean-square rms(A) of the isobaric charge distribution p(Z,A), well described by the Zp model of Wahl [11][12][13], in the asymmetric fission region [6]. Gönnenwein has made a connection between the oscillations of Z(A) and rms(A) with a period A ≈ 5 and the presence of even-odd effects in charge yield Y(Z) [6].…”

“…The main features of the global Z even-odd effect in prompt emission [1][2][3] are similar with those in fission fragment charge yields Y(Z) [6][7][8][9]:…”

“…Gönnenwein has made a connection between the oscillations of Z(A) and rms(A) with a period A ≈ 5 and the presence of even-odd effects in charge yield Y(Z) [6].…”

“…We have studied even-Z nuclei fissioning spontaneously or induced by thermal neutrons, like 233,235 U(n,f), 234 U(n,f), 239 Pu(n th ,f), 236,238,240,242,244 Pu(SF), 252 Cf(SF), because the extensive studies (e.g., [6][7][8][9]) regarding the Z even-odd effect in fragment distributions showed that the effect is most pronounced for this type of nuclei.…”

Tritium production from ternary fission

“…Since the average prompt neutron multiplicity ν p is a measure of the deformation energy, a correlation between t/B values and ν p values is expected. In particular, it has been shown already [6] that the spontaneous fission data follow the simple relation:…”