Reaction mechanism in odd-even staggering of reaction cross sections

Abstract

It was recently suggested that the odd-even staggering of reaction cross sections is an evidence of the pairing anti-halo effect on projectile radii. We define the dimensionless staggering parameters, Γ rds and ΓR, for projectile radii and reaction cross sections, respectively, and analyze the relation between Γ rds and ΓR for the scattering of 14,15,16 C from a 12 C target at 83 MeV/A by taking account of projectile-breakup and nuclearmedium effects newly with the microscopic version of the continuum discretized coupled-channels method. The value of ΓR is deviated from that of Γ rds by the projectile-breakup effect, the nuclear-medium effect and an effect due to the fact that the scattering are not the black-sphere scattering (BSS) exactly. The projectile-breakup and nuclear medium effects are nearly canceled for ΓR. The remaining non-BSS effect becomes small as an incident energy decreases, indicating that nucleus-nucleus scattering at lower incident energies are a good probe of evaluating Γ rds from measured reaction cross sections.PACS numbers: 24.10. Eq, 25.60.Gc, 25.60.Bx Introduction. Interaction cross section σ I and reaction cross section σ R are an important tool of determining radii of unstable nuclei. Actually, the halo structure as an exotic property was reported for unstable nuclei like 11 Li through analyses of measured σ I [1, 2]. Very recently, σ I was measured for Ne isotopes [3] and it is suggested by the analyses [4,5] that 31 Ne is a halo nucleus with large deformation.The difference between σ I and σ R is considered to be small for scattering of unstable nuclei at intermediate energies [6]. The reaction cross section is nearly proportional to a raidus of projectile; for example, see Ref.[6] for detailed analyses. Meanwhile, it is well known that pairing correlations are important particularly in even-N nuclei. The correlations become essential in weakly bound nuclei, since they are not bound without the correlations. Effects of the correlations on nuclear radii of unstable nuclei were investigated by the Hartree-Fock Bogoliubov (HFB) method [7]. In the meanfield picture, the correlations make the quasi-particle energy larger and hence reduce the root-mean-square radius of the HFB density. Obviously, this effect is conspicuous for unstable nuclei with the separation energy smaller than the gap energy. Thus, the pairing correlation suppresses the growth of halo structure for even-even unstable nuclei. This is now called the pairing anti-halo effect.The pairing anti-halo effect is an interesting phenomenon, but any clear evidence is not shown for the effect yet. Very recently, however, Hagino and Sagawa suggested that observed odd-even staggerings of σ R are possible evidence of the effect [8][9][10]. They introduced the staggering parameter [10]

Microscopic calculations based on chiral two- and three-nucleon forces for proton- andHe4-nucleus scattering

“…The DF-FDA model includes projectile-excitation effects approximately. The model based on the Melbourne g matrix well reproduces measured σ R for 12,14−16 C [29,30] and Ne and Mg isotopes [21,31]. As an important result, the microscopic analyses conclude that 31 Ne and 37 Mg are deformed halo nuclei.…”

New concept for the pairing anti-halo effect as a localized wave packet of quasiparticles

“…[14][15][16], we have argued that the odd-even staggerings observed in reaction cross sections [17,18] can be interpreted in terms of the pairing anti-halo effect (see also Refs. [19,20]). …”

Study Of Halo Nature Via Reaction And Neutron Removal Cross Sections

“…The detail of the calculation is shown in Refs. [21,22]. In the present analysis, we discuss which is better configuration.…”