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Register a new userThe beta-gamma decay of 21Na
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A new and independent determination of the Gamow-Teller branching ratio in the beta-decay of 21Na is reported. The value obtained of 5.13 +- 0.43 % is in agreement with the currently adopted value and the most recent measurement. In contrast to previous experiments, the present method was based on the counting of the parent 21Na ions and the resulting 351 keV gamma-rays without coincident beta-particle detection.
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We have measured the beta-decay branching ratio for the transition from 21Na to the first excited state of 21Ne. A recently published test of the standard model, which was based on a measurement of the beta-nu correlation in the decay of 21Na, depended on this branching ratio. However, until now only relatively imprecise (and, in some cases, contradictory) values existed for it. Our new result, 4.74(4)%, reduces but does not remove the reported discrepancy with the standard model.
Remarkable results have been published recently on the $beta$ decay of $^{56}$Zn. In particular, the rare and exotic $beta$-delayed $gamma$-proton emission has been detected for the first time in the $fp$ shell. Here we focus the discussion on this exotic decay mode and on the observed competition between $beta$-delayed protons and $beta$-delayed $gamma$ rays from the Isobaric Analogue State.
Background: The Doppler broadening of $gamma$-ray peaks due to nuclear recoil from $beta$-delayed nucleon emission can be used to measure the energies of the nucleons. This method has never been tested using $beta$-delayed proton emission or applied to a recoil heavier than $A=10$. Purpose: To test and apply this Doppler broadening method using $gamma$-ray peaks from the $^{26}$P($beta pgamma$)$^{25}$Al decay sequence. Methods: A fast beam of $^{26}$P was implanted into a planar Ge detector, which was used as a $^{26}$P $beta$-decay trigger. The SeGA array of high-purity Ge detectors was used to detect $gamma$ rays from the $^{26}$P($beta pgamma$)$^{25}$Al decay sequence. Results: Radiative Doppler broadening in $beta$-delayed proton-$gamma$ decay was observed for the first time. The Doppler broadening analysis method was verified using the 1613 keV $gamma$-ray line for which the proton energies were previously known. The 1776 keV $gamma$ ray de-exciting the 2720 keV $^{25}$Al level was observed in $^{26}$P($beta pgamma$)$^{25}$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 $beta$-delayed nucleon emissions populating excited states of nuclear recoils at least as heavy as $A=25$.
In an experiment performed at the LISE3 facility of GANIL, we studied the decay of 22Al produced by the fragmentation of a 36Ar primary beam. A beta-decay half-life of 91.1 +- 0.5 ms was measured. The beta-delayed one- and two-proton emission as well as beta-alpha and beta-delayed gamma decays were measured and allowed us to establish a partial decay scheme for this nucleus. New levels were determined in the daughter nucleus 22Mg. The comparison with model calculations strongly favours a spin-parity of 4+ for the ground state of 22Al.
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.
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