Observation of Doppler broadening in ${\hat{I}}^2$-delayed proton-${\hat{I}}^3$ decay

Abstract

Background: The Doppler broadening of ${\hat{I}}^3$-ray peaks due to nuclear recoil from ${\hat{I}}^2$-delayed nucleon emission can be used to measure the energies of the nucleons. This method has never been tested using ${\hat{I}}^2$-delayed proton emission or applied to a recoil heavier than $A=10$. Purpose: To test and apply this Doppler broadening method using ${\hat{I}}^3$-ray peaks from the ${}^{26}$P(${\hat{I}}^{2}p{\hat{I}}^3$)${}^{25}$Al decay sequence. Methods: A fast beam of ${}^{26}$P was implanted into a planar Ge detector, which was used as a ${}^{26}$P ${\hat{I}}^2$-decay trigger. The SeGA array of high-purity Ge detectors was used to detect ${\hat{I}}^3$ rays from the ${}^{26}$P(${\hat{I}}^{2}p{\hat{I}}^3$)${}^{25}$Al decay sequence. Results: Radiative Doppler broadening in ${\hat{I}}^2$-delayed proton-${\hat{I}}^3$ decay was observed for the first time. The Doppler broadening analysis method was verified using the 1613 keV ${\hat{I}}^3$-ray line for which the proton energies were previously known. The 1776 keV ${\hat{I}}^3$ ray de-exciting the 2720 keV ${}^{25}$Al level was observed in ${}^{26}$P(${\hat{I}}^{2}p{\hat{I}}^3$)${}^{25}$Al decay for the first time and used to determine that the center-of-mass energy of the proton emission feeding the 2720-keV level is 5.1 $\pm$ 1.0 (stat.) $\pm$ 0.6 (syst.) MeV, corresponding to a ${}^{26}$Si excitation energy of 13.3 $\pm$ 1.0 (stat.) $\pm$ 0.6 (syst.) MeV for the proton-emitting level. Conclusions: The Doppler broadening method has been demonstrated to provide practical measurements of the energies for ${\hat{I}}^2$-delayed nucleon emissions populating excited states of nuclear recoils at least as heavy as $A=25$.