The lattice thermal conductivity for bulk β-Ga2O3 is computed from the phonon Boltzmann transport equation using first-principles methods to obtain scattering rates. Force constants for both the second and third order potential interactions are computed with a real-space finite-displacement approach. Phonon band structures as well as anharmonic properties are then computed and used to calculate the bulk thermal conductivity tensor κ, for temperatures ranging from 25 K to 1050 K. The calculated conductivity tensor components and analytic fits to their temperature dependences are elaborated. We compare our results with available data and show good agreement with experimentally observed values. Decomposing κ into mode contributions reveals that optical phonon modes contribute significantly to the overall thermal conductivity, as much as 44% at 300 K in the [010] direction, which differs from previous interpretations of experimentally observed thermal conductivity tensor anisotropy.

Classical novae are expected to contribute to the 1809-keV Galactic γ-ray emission by producing its precursor 26Al, but the yield depends on the thermonuclear rate of the unmeasured 25Al(p,γ)26Si reaction. Using the β decay of 26P to populate the key J(π)=3(+) resonance in this reaction, we report the first evidence for the observation of its exit channel via a 1741.6±0.6(stat)±0.3(syst)  keV primary γ ray, where the uncertainties are statistical and systematic, respectively. By combining the measured γ-ray energy and intensity with other experimental data on 26Si, we find the center-of-mass energy and strength of the resonance to be E(r)=414.9±0.6(stat)±0.3(syst)±0.6(lit.)  keV and ωγ=23±6(stat)(-10)(+11)(lit.)  meV, respectively, where the last uncertainties are from adopted literature data. We use hydrodynamic nova simulations to model 26Al production showing that these measurements effectively eliminate the dominant experimental nuclear-physics uncertainty and we estimate that novae may contribute up to 30% of the Galactic 26Al.

Background: Measurements of β decay provide important nuclear structure information that can be used to probe isospin asymmetries and inform nuclear astrophysics studies.Purpose: To measure the β-delayed γ 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 β-delayed γ-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 β-delayed γ-rays were determined. A total of six new β-decay branches and 15 new γ-ray lines have been observed for the first time in 26 P β-decay. A complete β-decay scheme was built for the allowed transitions to bound excited states of 26 Si. f t values and Gamow-Teller strengths were also determined for these transitions and compared with shell model calculations and the mirror β-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 (δ = 51(10)%) may be evidence for a proton halo in 26 P.

Background: The Doppler broadening of γ-ray peaks due to nuclear recoil from β-delayed nucleon emission can be used to measure the energies of the nucleons. This method has never been tested using β-delayed proton emission or applied to a recoil heavier than A = 10. Purpose: To test and apply this Doppler broadening method using γ-ray peaks from the 26 P(βpγ) 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 β-decay trigger. The SeGA array of high-purity Ge detectors was used to detect γ rays from the 26 P(βpγ) 25 Al decay sequence. Results: Radiative Doppler broadening in β-delayed proton-γ decay was observed for the first time. The Doppler broadening analysis method was verified using the 1613 keV γ-ray line for which the proton energies were previously known. The 1776 keV γ ray de-exciting the 2720 keV 25 Al level was observed in 26 P(βpγ) 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 ± 1.0 (stat.) ± 0.6 (syst.) MeV, corresponding to a 26 Si excitation energy of 13.3 ± 1.0 (stat.) ± 0.7 (syst.) MeV for the proton-emitting level. Conclusions: The Doppler broadening method has been demonstrated to provide practical measurements of the energies for β-delayed nucleon emissions populating excited states of nuclear recoils at least as heavy as A = 25.