Asymmetry parameter of Mg-23 beta decay

Abstract

The asymmetry parameter (A) of the Mg-23 beta decay was measured using RIPS (RIKEN (Institute of Physical and Chemical Research) Projectile Fragment Separator). The beta decay asymmetry AP (P: polarization) was measured by means of asymmetric beta-ray emission for both ground state transition and the decay branch to the first excited state. The beta-ray asymmetries were obtained from beta-ray singles and the beta-gamma coincidence with several different conditions. Correcting the beta-gamma angular correlation, beta-ray scattering effect, and gamma-ray background, the ratio A(sub ex)/A(sub 0) was obtained to be 0.990 +/- 0.012. Since the transition to the excited state is pure Gamow-Teller, A(sub ex) is precisely predicted to be -3/5. Thus the preliminary result for the asymmetry parameter A(sub 0) was obtained to be -0.606 +/- 0.007.

Mg-23のβ崩壊の非対称性パラメータAを、理化学研究所のRIPS(RIKEN(理化学研究所) Projectile Fragment Separator)を用いて測定した。基底状態遷移と第一励起状態への崩壊分岐の両方における非対称性β線放出を用いて、β崩壊非対称性パラメータ(AP、Pは偏極を示す)を測定した。異なる条件における、β線単独測定とβ線とγ線の同時測定から、β線非対称性を得た。β線とγ線の角度相関、β線散乱効果、γ線バックグラウンドを補正することにより、A(sub ex)/A(sub 0)=0.990±0.012を求めた。励起状態への遷移は、純粋なガモフ-テラー型遷移であるため、A(sub ex)は、正確に-3/5であると考えられる。このため、非対称性パラメータは、A(sub 0)=-0.606±0.007であることが推定できる。