Background: Positron decays of proton-rich nuclides exhibit large $Q$ values, producing complex cascades which frequently involve various radiations, including protons and $\gamma$ rays. Often, only one of the two is measured in a single experiment, limiting the accuracy and completeness of the decay scheme. An example is ${}^{31}\mathrm{Cl}$, for which protons and $\gamma$ rays have been measured separately in detail but never with substantial sensitivity to proton-$\gamma$ coincidences.

Purpose: Provide detailed measurements of ${}^{31}\mathrm{Cl} \beta$-delayed proton decay including $\beta \text{−}p\text{−}\gamma$ sequences, extract spectroscopic information on ${}^{31}\mathrm{S}$ excited states as well as their ${\beta }^{+}$ feedings, and compare to shell-model calculations.

Methods: A fast fragmented beam of ${}^{31}\mathrm{Cl}$ provided by the National Superconducting Cyclotron Laboratory was deposited in the Gaseous Detector with Germanium Tagging (GADGET) system. GADGET's gas-filled Proton Detector was used to detect $\beta$-delayed protons, and the Segmented Germanium Array was used to detect $\beta$-delayed $\gamma$ rays.

Results: As many as 20 previously unobserved $\beta$-delayed proton transitions have been discovered in the present data, most of which populate excited states of ${}^{30}\mathrm{P}$. The first detailed ${}^{31}\mathrm{Cl}$($\beta p\gamma ){}^{30}\mathrm{P}$ decay scheme is presented, including updated $\beta$-delayed proton-decay energies and intensities, as well as several new ${}^{31}\mathrm{S}$ levels. Improved agreement is found with theoretical calculations of the Gamow-Teller strengths $B\left(\text{GT}\right)$ for ${}^{31}\mathrm{S}$ excitation energies $7.5<E_x<9.5$ MeV.

Conclusions: The present work demonstrates that the ability to detect $\beta$-delayed protons and $\gamma$ rays in coincidence is essential to construct accurate positron decay schemes for comparison to theoretical nuclear structure calculations. In some respects, this phenomenon for $\beta$-delayed protons resembles the pandemonium effect originally introduced for $\beta$-delayed $\gamma$ rays.

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• Beta decay
• Energy levels
• Nuclear spin & parity
• Nuclear structure & decays
• Proton emission
• Rare & new isotopes
• 20 ≤ A ≤ 38
• Monte Carlo methods
• Nuclear data analysis & compilation
• Radiation detectors
• Radioactive beams
• Shell model