Observation of a Strongly Isospin-Mixed Doublet in Si26 via β-Delayed Two-Proton Decay of P26

Abstract

<p>β decay of proton-rich nuclei plays an important role in exploring isospin mixing. The β decay of 26P at the proton drip line is studied using double-sided silicon strip detectors operating in conjunction with high-purity germanium detectors. The T=2 isobaric analog state (IAS) at 13 055 keV and two new high-lying states at 13 380 and 11 912 keV in 26Si are unambiguously identified through β-delayed two-proton emission (β2p). Angular correlations of two protons emitted from 26Si excited states populated by 26P β decay are measured, which suggests that the two protons are emitted mainly sequentially. We report the first observation of a strongly isospin-mixed doublet that deexcites mainly via two-proton decay. The isospin mixing matrix element between the 26Si IAS and the nearby 13 380-keV state is determined to be 130(21) keV, and this result represents the strongest mixing, highest excitation energy, and largest level spacing of a doublet ever observed in β-decay experiments.<br></p>