Gamow-Teller unit cross sections for (t,He3) and (

Abstract

The proportionality between differential cross sections at vanishing linear momentum transfer and Gamow-Teller transition strength, expressed in terms of the unit cross section (σGT ) was studied as a function of target mass number for (t, 3 He) and ( 3 He,t) reactions at 115 AMeV and 140 AMeV, respectively. Existing ( 3 He,t) and (t, 3 He) data on targets with mass number 12 ≤ A ≤ 120 were complemented with new and reevaluated (t, 3 He) data on proton, deuteron, 6 Li and 12 C targets. It was found that in spite of the small difference in beam energies between the two probes, the unit cross sections have a nearly identical and simple dependence on target mass number A, for A ≥ 12: σGT = 109/A 0.65 . The factorization of the unit cross sections in terms of a kinematical factor, a distortion factor and the strength of the effective spin-isospin transfer nucleus-nucleus interaction was investigated. Simple phenomenological functions depending on mass number A were extracted for the latter two. By comparison with plane and distorted-wave Born approximation calculations, it was found that the use of a short-range approximation for knock-on exchange contributions to the transition amplitude results in overestimated cross sections for reactions involving the composite ( 3 He,t) and (t, 3 He) probes.

Gamow-Teller transition strengths fromFe56extracted from theFe56(t,Scott1, Shimbara2, Austin3 et al. 2014Phys. Rev. CSelf Cite110110View full textAdd to dashboardCite

“…Figure 2 shows an example for the MDA for the peak at 1.17 MeV, which is predominantly associated with L = 0 but has a significant L = 2 component, as can be expected for a 0 + → 1 + transition (see, e.g., Ref. [37]). No statistically significant dipole ( L = 1) contribution was observed for this particular fit, and the systematic uncertainties were small.…”

“…As inputs to the calculation, one-body transition densities (OBTDs) associated with different angularmomentum transfers were obtained in the normal-modes formalism using the code NORMOD [45]. Following previous analyses [37], single-particle binding energies for 56 Fe and 56 Mn, obtained from NUSHELLX@MSU [46] using the SK20 interaction [47], were used in the calculation of radial wave functions in a Woods-Saxon potential. For the t and 3 He particles, radial densities obtained from variational Monte Carlo calculations [48] were used and all protons and neutrons were assumed to be in the 1s 1/2 orbit.…”

“…Cross sections were determined relative to those of the 12 C(t, 3 He) 12 B(1 + ,g.s.) reaction for which accurate absolute cross sections were measured previously [37]. For that purpose, data were taken on the same 10 mg/cm 2 CH 2 foil used for measuring the absolute 12 C(t, 3 He) 12 B(1 + ,g.s.)…”

“…Since Q g.s. = 3.677 MeV, the extracted differential cross sections were extrapolated to Q = 0 on the basis of the DWBA calculations using the relation [37] dσ d…”

“…(2) as a smooth function of Q, the ratio was generated for 100 reaction Q values in the excitation energy range of interest. The unit cross sectionσ GT was calculated by using the empirical mass-dependent relationship [37,38] σ GT = 109 A −0.65 (mb/sr). [26], which had an excitation-energy resolution of 1.3 MeV (where the strength was extracted in 1-MeV-wide bins).…”