Extraction of Weak Transition Strengths via the (He3,t) Reaction at 420 MeV

Abstract

Differential cross sections for transitions of known weak strength were measured with the (3He, t) reaction at 420 MeV on targets of 12C, 13C, 18O, 26Mg, 58Ni, 60Ni, 90Zr, 118Sn, 120Sn, and 208Pb. Using these data, it is shown that the proportionalities between strengths and cross sections for this probe follow simple trends as a function of mass number. These trends can be used to confidently determine Gamow-Teller strength distributions in nuclei for which the proportionality cannot be calibrated via beta-decay strengths. Although theoretical calculations in the distorted-wave Born approximation overestimate the data, they allow one to understand the main experimental features and to predict deviations from the simple trends observed in some of the transitions.

High-resolution study of theBe9(He3,Scholl1, Fujita2, Adachi3 et al. 2011Phys. Rev. CSelf Cite492220View full textAdd to dashboardCite

“…The reason is thought to be that the contribution of the tensor-τ part of the effective projectile-target interaction can be large in these cases [14][15][16]41]. Since the systematic study of Zegers et al [16] excludes these effects, the agreement of the GT unit cross-section derived from the empirical formula [Eq. (5)] and the experimental GT unit cross-section indicates that we do not suffer much from this effect.…”

“…We can thus rely on the proportionality and the deduced GT unit cross-section as a calibration standard. It should however be noted that the trendline for the unit crosssection in [16] was only determined down to A=12 and that we use an extrapolation to a lower mass number. This can be a further source of uncertainty.…”

“…As a result of these investigations, the empirical formulaê σ F = 72 · A −1.06 mb/sr (4) σ GT = 109 · A −0.65 mb/sr (5) have been shown to be a good approximation of the massnumber dependence of the unit cross-sections. The observed data points have a maximal deviation from the systematics of 5% forσ GT and 15% forσ F [16]. The cross-section at linear momentum transfer q=0 and the (experimental) cross-section at zero degree scattering angle are related via kinematic and distortion factors [3].…”

“…(2) has been previously examined by comparing the GT transition strengths derived in the ( 3 He,t) measurements with those from mirror β decays for a number of cases in which multiple pairs of analogous GT transitions could be compared, and a good agreement has been found in most cases [11][12][13][14][15]. The absolute values of the Fermi and Gamow-Teller unit cross-sections for the ( 3 He,t) reaction at 140 MeV/nucleon were studied across a wide range of nuclear masses [16]. As a result of these investigations, the empirical formulaê σ F = 72 · A −1.06 mb/sr (4) σ GT = 109 · A −0.65 mb/sr (5) have been shown to be a good approximation of the massnumber dependence of the unit cross-sections.…”

Effects of Three-Nucleon Forces and Two-Body Currents on Gamow-Teller Strengths

“…Here g A is the axial-vector coupling, σ denotes the spin, and τ ± changes the isospin. GamowTeller strength functions [14,15] are of particular interest also because of their astrophysical relevance [16]. Chargeexchange measurements on 90 Zr and other medium mass nuclei have suggested that the total strength for β decay is quenched by a factor of q 2 ≈ 0.88 − 0.92 [17][18][19][20] when compared to the Ikeda sum rule [21].…”