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

Abstract

Background: Measurements of $\beta$ decay provide important nuclear structure information that can be used to probe isospin asymmetries and inform nuclear astrophysics studies. Purpose: To measure the $\beta$-delayed $\gamma$ 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 $\beta$-delayed $\gamma$-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 $\beta$-delayed $\gamma$-rays were determined. A total of six new $\beta$-decay branches and 15 new $\gamma$-ray lines have been observed for the first time in ${}^{26}$P $\beta$-decay. A complete $\beta$-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 $\beta$-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 ($\delta =51(10)\%$) may be evidence for a proton halo in ${}^{26}$P.

arXiv comment15 pages, 10 figures, 7 tables

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• Doppler Broadening in ${}^{20}$Mg($\beta p\gamma$)${}^{19}$Ne Decay
• The Gamow-state description of the decay energy spectrum of neutron-unbound ${}^{25}$O
• Spectroscopy and lifetime measurements near the proton drip line: ${}^{26,27,28}$P
• ${}^{25}$Si ${\beta }^{+}$-decay spectroscopy
• Neutrino Spectra from Nuclear Weak Interactions in $sd$-Shell Nuclei Under Astrophysical Conditions
• Confirmation of the isomeric state in 26P
• The 2025 Evaluation of Experimental Thermonuclear Reaction Rates (ETR25)
• Shell model study of isobaric analog states for $T_z=\pm 2$ nuclei using isospin non-conserving interactions