Paper detail

Beta-delayed gamma decay of 26P: Possible evidence of a proton halo

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 $^{26}$P and compare the results with previous experimental results and shell-model calculations. Method: A $^{26}$P 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 $^{26}$P $β$-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 $^{26}$P $β$-decay. A complete $β$-decay scheme was built for the allowed transitions to bound excited states of $^{26}$Si. $ft$ values and Gamow-Teller strengths were also determined for these transitions and compared with shell model calculations and the mirror $β$-decay of $^{26}$Na, 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 $^{26}$P.