Influence of secondary decay on odd-even staggering of fragment cross sections

Abstract

Odd-Even Staggering (OES) appears in many areas of nuclear physics, and is generally associated with the pairing term in the nuclear binding energy. To explore this effect, we use the Improved Statistical Multifragmentation Model to populate an ensemble of hot primary fragments, which are then de-excited using the Weisskopf-Ewing statistical emission formalism. The yields are then compared to experimental data. Our results show that, before secondary decay, OES appears only in the yields of even mass fragments and not in the yields of odd mass fragments. De-excitation of the hot fragments must be taken into account to describe the data, suggesting that the OES in fragment yields is a useful criterion for validating or adjusting theoretical de-excitation models.

Influence of the density of states on the odd-even staggering in the charge distribution of the emitted fragments in nuclear heavy-ion collisions

“…1, odd-even effects in the primary distribution quickly disappear as the excitation energy increases, being barely noticeable at E * /A ≈ 2.5 MeV. On the other hand, these effects are significantly enhanced in the final yields, as already suggested in former studies [18,19,21]. They also tend to be smoothed out as Z increases, in agreement with the findings of Ref.…”

“…The primary and final yields are respectively displayed at the top and bottom panels. In both cases, odd-even staggering is clearly seen in the charge distribution which, in the framework of the model, can be explained only by the presence of the pairing term in the fragments' binding energy [21], as is explicitly written in Eqs. (2) and (4).…”

“…Analyses based on the fragmentation of the quasi-projectile have been made at relativistic energies [18] as well as at much lower bombarding energies [21]. In both cases, clear odd-even effects have been observed in the fragment size distribution.…”

“…Odd-even effects on the fragment charge distributions produced in different reactions have been recently reported in the literature [18][19][20][21][22]. Analyses based on the fragmentation of the quasi-projectile have been made at relativistic energies [18] as well as at much lower bombarding energies [21].…”

“…In Ref. [21], it is demonstrated that the deexcitation of the primary hot fragments plays a very important role. Indeed, it was found that the adopted deexcitation process leads to the appearance of staggering effects in charge correlations of fragments with odd neutron excess, not observed in the primary fragments.…”