A detailed $\ensuremath{\beta}$-decay spectroscopic study of $^{22}\mathrm{Al}$ was performed at the Radioactive Ion Beam Line in Lanzhou. With the $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$-particle coincidence measurement by a high-resolution DSSD particle detection array and a high efficiency $\ensuremath{\gamma}$-ray detection array, total eight excited states in $^{22}\mathrm{Mg}$ fed by Gamow-Teller transitions was newly identified. The one-proton, two-proton, and $\ensuremath{\alpha}$ decays of the IAS at 14046(5) keV in $^{22}\mathrm{Mg}$, which were partly observed in different experiments before, were identified simultaneously in the present work, providing accurate spectroscopic information about its decay. A more complete $\ensuremath{\beta}$-decay scheme of $^{22}\mathrm{Al}$ was constructed and compared to the shell-model calculations with the USD-type Hamiltonians, USDC and USDB.
Context. Accurate 42 Ti( p , γ ) 43 V reaction rates are crucial for understanding the nucleosynthesis path of the rapid capture process ( rp process) that occurs in X-ray bursts. Aims. We aim to improve the thermonuclear rates of 42 Ti( p , γ ) 43 V based on more complete resonance information and a more accurate direct component, together with the recently released nuclear masses data. We also explore the impact of the newly obtained rates on the rp process. Methods. We reevaluated the reaction rate of 42 Ti( p , γ ) 43 V by the sum of the isolated resonance contribution instead of the Hauser-Feshbach statistical model. We used a Monte Carlo method to derive the associated uncertainties of new rates. The nucleosynthesis simulations were performed via the NuGrid post-processing code ppn. Results. The new rates differ from previous estimations due to the use of a series of updated resonance parameters and a direct S factor. Compared with the previous results from the Hauser-Feshbach statistical model, which assumes compound nucleus 43 V with a sufficiently high-level density in the energy region of astrophysical interest, large differences exist over the entire temperature region of rp -process interest, up to two orders of magnitude. We consistently calculated the photodisintegration rate using our new nuclear masses via the detailed balance principle, and found the discrepancies among the different reverse rates are much larger than those for the forward rate, up to ten orders of magnitude at the temperature of 10 8 K. Using a trajectory with a peak temperature of 1.95×10 9 K, we performed the rp -process nucleosynthesis simulations to investigate the impact of the new rates. Our calculations show that the adoption of the new forward and reverse rates result in abundance variations for Sc and Ca of 128% and 49%, respectively, compared to the variations for the statistical model rates. On the other hand, the overall abundance pattern is not significantly affected. The results of using new rates also confirm that the rp -process path does not bypass the isotope 43 V. Conclusions. Our study found that the Hauser-Feshbach statistical model is inappropriate to the reaction rate evaluation for 42 Ti( p , γ ) 43 V. The adoption of the new rates confirms that the reaction path of 42 Ti( p , γ ) 43 V( p , γ ) 44 Cr( β + ) 44 V is a key branch of the rp process in X-ray bursts.
Three three-quasiparticle isomers, one at an excitation energy of 2.3 MeV with ${T}_{1/2}=0.48(4)\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$, and two shorter-lived with unknown half-lives at slightly lower energies have been identified in $^{129}\mathrm{Nd}$ using the MARA $+$ JUROGAM 3 setup and the recoil tagging technique. All three isomers present decay patterns characteristic of high-$K$ isomers. The known 6.7 s $\ensuremath{\beta}$-decaying isomer previously assigned to the $5/{2}^{+}$ level is now assigned to the new $7/{2}^{\ensuremath{-}}$ ground state. A new low-spin $5/{2}^{+}$ isomeric state with a half-life of a few tens of nanoseconds has been identified, while a previously known 2.6 s $\ensuremath{\beta}$-decay activity was assigned to the band head of the $\ensuremath{\nu}1/{2}^{+}[411]$ band. The transitions depopulating the high-$K$ isomers to low-lying states also establish the relative energies of three low-lying one-quasiparticle bands, leading to a new spin-parity assignment of $7/{2}^{\ensuremath{-}}$ to the ground state of $^{129}\mathrm{Nd}$. The partial half-lives of the depopulating transitions suggest spin-parities $21/{2}^{+}, 19/{2}^{+}$, and $17/{2}^{+}$ for the three high-$K$ isomers. The properties of the band built on the $21/{2}^{+}$ isomeric state suggest a one neutron-two proton configuration. Based on the results of extensive calculations with different models, we also assign one neutron--two proton configurations to the $19/{2}^{+}$ and $17/{2}^{+}$ isomeric states. The assigned configurations of the $17/{2}^{+}$ and $21/{2}^{+}$ isomeric states involve the $\ensuremath{\pi}9/{2}^{+}[404]$ orbital, which is identified in three-quasiparticle bands of proton-rich $A\ensuremath{\approx}130$ nuclei.
β decay of proton-rich nuclei plays an important role in exploring isospin mixing. The β decay of ^{26}P at the proton drip line is studied using double-sided silicon strip detectors operating in conjunction with high-purity germanium detectors. The T=2 isobaric analog state (IAS) at 13 055 keV and two new high-lying states at 13 380 and 11 912 keV in ^{26}Si are unambiguously identified through β-delayed two-proton emission (β2p). Angular correlations of two protons emitted from ^{26}Si excited states populated by ^{26}P β decay are measured, which suggests that the two protons are emitted mainly sequentially. We report the first observation of a strongly isospin-mixed doublet that deexcites mainly via two-proton decay. The isospin mixing matrix element between the ^{26}Si IAS and the nearby 13 380-keV state is determined to be 130(21) keV, and this result represents the strongest mixing, highest excitation energy, and largest level spacing of a doublet ever observed in β-decay experiments.
Abstract Accurate nuclear reaction rates for 26 P( p , γ ) 27 S are pivotal for a comprehensive understanding of the rp -process nucleosynthesis path in the region of proton-rich sulfur and phosphorus isotopes. However, large uncertainties still exist in the current rate of 26 P( p , γ ) 27 S because of the lack of nuclear mass and energy level structure information for 27 S. We reevaluate this reaction rate using the experimentally constrained 27 S mass, together with the shell model predicted level structure. It is found that the 26 P( p , γ ) 27 S reaction rate is dominated by a direct capture reaction mechanism despite the presence of three resonances at E = 1.104, 1.597, and 1.777 MeV above the proton threshold in 27 S. The new rate is overall smaller than the other previous rates from the Hauser–Feshbach statistical model by at least 1 order of magnitude in the temperature range of X-ray burst interest. In addition, we consistently update the photodisintegration rate using the new 27 S mass. The influence of new rates of forward and reverse reaction in the abundances of isotopes produced in the rp -process is explored by postprocessing nucleosynthesis calculations. The final abundance ratio of 27 S/ 26 P obtained using the new rates is only 10% of that from the old rate. The abundance flow calculations show that the reaction path 26 P( p , γ ) 27 S( β + , ν ) 27 P is not as important as previously thought for producing 27 P. The adoption of the new reaction rates for 26 P( p , γ ) 27 S only reduces the final production of aluminum by 7.1% and has no discernible impact on the yield of other elements.
Using a novel method of isochronous mass spectrometry, the masses of $^{62}\mathrm{Ge}$, $^{64}\mathrm{As}$, $^{66}\mathrm{Se}$, and $^{70}\mathrm{Kr}$ are measured for the first time, and the masses of $^{58}\mathrm{Zn}$, $^{61}\mathrm{Ga}$, $^{63}\mathrm{Ge}$, $^{65}\mathrm{As}$, $^{67}\mathrm{Se}$, $^{71}\mathrm{Kr}$, and $^{75}\mathrm{Sr}$ are redetermined with improved accuracy. The new masses allow us to derive residual proton-neutron interactions ($\ensuremath{\delta}{V}_{pn}$) in the $N=Z$ nuclei, which are found to decrease (increase) with increasing mass $A$ for even-even (odd-odd) nuclei beyond $Z=28$. This bifurcation of $\ensuremath{\delta}{V}_{pn}$ cannot be reproduced by the available mass models, nor is it consistent with expectations of a pseudo-SU(4) symmetry restoration in the $fp$ shell. We performed ab initio calculations with a chiral three-nucleon force (3NF) included, which indicate the enhancement of the $T=1$ $pn$ pairing over the $T=0$ $pn$ pairing in this mass region, leading to the opposite evolving trends of $\ensuremath{\delta}{V}_{pn}$ in even-even and odd-odd nuclei.
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