β-delayed γ decay of 26P: Possible evidence of a proton halo

Abstract

Background: Measurements of β decay provide important nuclear structure information that can be used to probe isospin asymmetries and inform nuclear astrophysics studies. Purpose: To measure the β-delayed γ decay of 26P and compare the results with previous experimental results and shell-model calculations. Method: A 26P fast beam produced using nuclear fragmentation was implanted into a planar germanium detector. Its β-delayed γ-ray emission was measured with an array of 16 high-purity germanium detectors. Positrons emitted in the decay were detected in coincidence to reduce the background. Results: The absolute intensities of 26Pβ-delayed γ rays were determined. A total of six new β-decay branches and 15 new γ-ray lines have been observed for the first time in 26Pβ decay. A complete β-decay scheme was built for the allowed transitions to bound excited states of 26Si. ft values and Gamow-Teller strengths were also determined for these transitions and compared with shell-model calculations and the mirror β decay of 26Na, revealing significant mirror asymmetries. Conclusions: A very good agreement with theoretical predictions based on the USDB shell model is observed. The significant mirror asymmetry observed for the transition to the first excited state (δ=51(10)%) may be evidence for a proton halo in 26P.