Binary decay of light nuclear systems

Abstract

A review of the characteristic features found in fully energy-damped, binarydecay yields from light heavy-ion reactions with 20 ≤ A target + A projectile ≤ 80 is presented. The different aspects of these yields that have been used to support models of compound-nucleus (CN) fission and deep-inelastic dinucleus orbiting are highlighted. Cross section calculations based on the statistical phase space at different stages of the reaction are presented and compared to the experimental results. Although the statistical models are found to reproduce most of the observed experimental behaviors, an additional reaction component corresponding to a heavy-ion resonance or orbiting mechanism is also evident in certain systems. The system dependence of this second component is discussed. The extent to which the binary yields in very light systems (A CN ≤ 32) can be viewed as resulting from a fusion-fission mechanism is explored. A number of unresolved questions, such as whether the different observed behaviors reflect characteristically different reaction times, are discussed. I. INTRODUCTIONAs the interaction energy for a heavy-ion reaction increases above the Coulomb barrier, the reaction grazing angle moves to more forward angles so that, by a value of about 20% above the barrier, very small quasielastic and single-nucleon transfer reaction yields are expected at larger scattering angles. Instead, the incident flux that might be expected to scatter to larger angles, corresponding to smaller impact parameters, is trapped by the formation of a compound nucleus. For lighter systems, this compound system subsequently decays by light particle and γ-ray emission, with a very small heavy-fragment (A > 4) emission component. The experimental observation of significant large-angle, elastic-scattering cross sections at energies well above the Coulomb barrier has therefore been viewed with Calculation of fission cross sections in the statistical models is based on the Hauser-Feshbach formalism. For a compound nucleus of spin J that is populated with a partial fusion cross section of σ J , the partial fission cross section is given in terms of the ratio of the fission decay width Γ f is J to the total decay width for this spin Γ tot J , with

Emission of intermediate mass fragments from hot116Ba* formed in low-energy58Ni +58Ni reaction

“…However, the 12 C decay is still striking since it is the best α-nucleus decay even now, particularly at lower energies (inspite of the lower preformation factor P 0 at these energies). At higher energies, the lighter α-like fragment 8 Be competes with it, though we know that 8 Be is unbound in the ground state. Note that the charge number Z changes with T for some fragments (here for the mass 17 fragment) and hence at higher T's the measurements of charge distributions become equally important [1,16].…”

Cluster formations in deformed states forSi28andS32Ichikawa1, Kanada-En’yo2, Möller3 2011Phys. Rev. C299730View full textAdd to dashboardCite

“…In this approach the clusters are joined by a neck region with a lower single-particle density. For lighter mass systems, such treatments are essential for a unified description of the whole process, because the scission point shape closely resembles that of the saddle point, as has been well established in fusionfission processes below the Businaro-Gallone point [18]. We calculate and analyze total-energy surfaces which are the sums of a potential-energy surface and a rotational-energy contribution, which both are functions of five shape-degrees of freedom.…”

Binary reaction decays fromMg24+C12

“…In the MWCs, the in-plane and out-of-plane scattering angles and , respectively, are derived from the position (x and y) measurements. As already shown in previous studies [40,41], the in-plane angular correlations of two fragments need coincidence measurements for binary fission yields to be measured adequately. Unfortunately, the MWC of BRS telescope 2 could not provide us with a well-functioning y-position signal (i.e., 2 ), which is essential information for checking kinematical conditions of the out-of-plane correlations of ternary fission fragments.…”

“…HD bands in the 36 Ar nucleus and its related ternary clusterizations are theoretically predicted [31]. With the exception of the cluster decay of 60 Zn [32,33] and 56 Ni [34][35][36] recently studied using charged particle spectroscopy, no evidence for ternary breakup has yet been reported [13,[37][38][39][40][41] in light nuclei; the particle decay of 36 Ar SD bands (and other highly excited bands) is still unexplored. The main binary reaction channels of the 24 Mg + 12 C reaction, for which both quasimolecular structures [4,42,43] and orbiting phenomena [44] have been observed, is investigated in this work by using charged-particle-γ -ray coincidence techniques.…”