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Bennett, M. B.

Publications and source records attributed to Bennett, M. B..

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Doppler broadening in Mg 20 ( β p γ ) Ne 19 decay

The $^{15}$$\textbf{O}$$\Big({α,γ}\Big)$$^{19}$$\textbf{Ne}$ bottleneck reaction in Type I x-ray bursts is the most important thermonuclear reaction rate to constrain experimentally, to improve the accuracy of burst light-curve simulations. A proposed technique to determine the thermonuclear rate of this reaction employs the $^{20}$$\textbf{Mg}$$\Big({βpα}\Big)$$^{15}$$\textbf{O}$ decay sequence. The key $^{15}$$\textbf{O}$$\Big({α,γ}\Big)$$^{19}$$\textbf{Ne}$ resonance at an excitation of 4.03 MeV is now known to be fed in $^{20}$$\textbf{Mg}$$\Big({βpγ}\Big)$$^{19}$$\textbf{Ne}$ however, the energies of the protons feeding the 4.03 MeV state are unknown. Knowledge of the proton energies will facilitate future $^{20}$$\textbf{Mg}$$\Big({βpα}\Big)$$^{15}$$\textbf{O}$ measurements. To determine the energy of the proton transition feeding the 4.03 MeV state in $^{19}$$\textbf{Ne}$. A fast beam of $^{20}$$\textbf{Mg}$ was implanted into a plastic scintillator, which was used to detect $β$ particles. 16 high purity germanium detectors were used to detect $γ$ rays emitted following $βp$ decay. A Monte Carlo method was used to simulate the Doppler broadening of $^{19}$$\textbf{Ne}γ$-ray lines and compare to the experimental data. The center of mass energy between the proton and $^{19}$$\textbf{Ne}$, feeding the 4.03 MeV state, is measured to be $1.21^{+0.25}_{-0.22}$ $\textbf{MeV}$, corresponding to a $^{20}$$\textbf{Na}$ excitation energy of $7.44^{+0.25}_{-0.22}$$\textbf{MeV}$. Absolute feeding intensities and $γ$-decay branching ratios of $^{19}$$\textbf{Ne}$ states were determined including the 1615 keV state, which has not been observed before in this decay. A new $γ$ decay branch from the 1536 keV state in $^{19}$$\textbf{Ne}$ to the ground state is reported. The lifetime of the 1507 keV state in $^{19}$$\textbf{Ne}$ is measured to be $4.3^{+1.3}_{-1.1}$ ps resolving discrepancies in the literature. Conflicting $^{20}$$\textbf{Mg}$$\Big({βp}\Big)$ decay schemes in published literature are clarified.The utility of this Doppler broadening technique to provide information on $β$-delayed nucleon emission and excited-state lifetimes has been further demonstrated. In particular, knowledge of the proton energies feeding the 4.03 MeV $^{19}$$\textbf{Ne}$ state in $^{20}$$\textbf{Mg}$ $β$ decay will facilitate future measurements of the $α$-particle branching ratio.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Toward complete spectroscopy using β decay: The example of Cl 32 ( β γ ) S 32

$^{32}\textbf{Cl}$ is a neutron-deficient isotope with a $β$-decay half-life of 298 ms and a spin and parity of $J^π=1^+$. Previous measurements of $^{32}\textbf{Cl}$ $β$-delayed $γ$ rays have yielded a $β$-decay scheme with twelve $β$-decay transitions, contributing to studies of nuclear structure and fundamental symmetries. Those experiments have been limited to the observation of $^{32}\textbf{S}$ states with $J^π = 0^+,1^+, 2^+$. Our goal is to search for new $β$-delayed $γ$ rays and $β$-decay transitions of $^{32}\textbf{Cl}$ to $^{32}\textbf{S}$. A measurement of $^{32}\textbf{Cl}$ $β$-delayed $γ$ decay has been performed using the Clovershare array of high-purity germanium detectors at the National Superconducting Cyclotron Laboratory. By acquiring the highest-statistics $^{32}\textbf{Cl}$ $β$-delayed $γ$-ray spectrum to date and exploiting a new sensitivity to $γ-γ$ coincidences, this experiment has enabled the observation of nine previously unobserved $β$-delayed $γ$-ray transitions, leading to the inference of five $β$-decay transitions never before observed in $^{32}\textbf{Cl}$ $β$-delayed $γ$ decay. The set of observed states includes negative-parity states for the first time. By combining the new information with data from previous work, the lifetimes and partial widths of the 8861- and 9650-keV states of $^{32}\textbf{S}$ have been determined. In addition, the $^{31}\textbf{P}$($p,α$)$^{28}\textbf{Si}$ resonance strength of the 9650-keV state has been limited to $ωγ<9.8$ meV, which is an improvement over direct measurements. An enhanced decay scheme has been constructed. Most of the excited bound $^{32}\textbf{S}$ states that would correspond to allowed and first-forbidden $β$-decay transitions have been observed, demonstrating the potential of $β$-decay experiments to approach complete spectroscopy measurements at the next generation of radioactive beam facilities. The observed positive-parity levels are well matched by $sd$ shell-model calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Detailed study of the decay Cl 31 ( β γ ) S 31

Background: 31 Cl is a neutron-deficient isotope with a half-life of T 1/2 = 190 (1) ms. The nuclear structure of its daughter, 31 S, is important for the determination of the thermonuclear 30 P(p,γ) 31 S reaction rate, which affects the final isotopic abundances of the ejecta from classical oxygen-neon novae. Purpose: Here, we aim to determine the β feedings, γ-decay branchings, and excitation energies of states populated in 31 S and create a comprehensive decay scheme for comparison with predictions based on the shell model. Methods: Using a 31 Cl rare istope beam implanted into a plastic scintillator and an array of high-purity Ge detectors, γ rays from the 31 Cl(βγ) 31 S decay sequence were measured. Shell-model calculations using the USDB and the recently-developed USDE interactions were performed for comparison. Results: A 31 Cl β-decay scheme was constructed from the experimental data and compared to the USDB and USDE shell-model calculations based on the β feeding and γ-decay branches of each observed state. 33 new γ-ray transitions and ten new β decay branches were observed. The β feeding and γ-decay branches of each observed state were compared to those from the USDB and USDE shell-model calculations. For every allowed transition predicted by the USD calculations up to an excitation energy of 6.4 MeV in 31 S, an analogous transition was found in the experimental data, enabling a one-to-one comparison with the shell model. Using these identifications, spin and parity arguments were made for observed states. Conclusions: The new 31 Cl γ-decay scheme presented in this work is the most complete and precise one for this nucleus constructed to date, incorporating statistics over an order of magnitude higher than previous work on 31 Cl β-delayed γ decay. Of particular interest is the discovery of a 6390-keV state that mixes with the isobaric analog state and affects the 30 P(p,γ) 31 S reaction rate. Other states observed in the decay are not expected to strongly affect the 30 P(p,γ) 31 S reaction rate, but the comprehensive comparison to the shell model helps to clarify spin and parity assignments of resonances that might affect the rate.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗