We have evaluated the electron capture rates on ${}^{20}\mathrm{Ne}$, ${}^{20}\mathrm{F}$, ${}^{24}\mathrm{Mg}$, and ${}^{24}\mathrm{Na}$ and the $\beta$ decay rates for ${}^{20}\mathrm{F}$ and ${}^{24}\mathrm{Na}$ at temperature and density conditions relevant for the late-evolution stages of stars with $M=8M_{\odot }$–12$M_{\odot }$. The rates are based on recent experimental data and large-scale shell-model calculations. We show that the electron capture rates on ${}^{20}\mathrm{Ne}$ and ${}^{24}\mathrm{Mg}$ and the ${}^{20}\mathrm{F}$ and ${}^{24}\mathrm{Na}$ $\beta$-decay rates are based on data in this astrophysical range, except for the capture rate on ${}^{20}\mathrm{Ne}$, which we predict to have a dominating contribution from the second-forbidden transition between the ${}^{20}\mathrm{Ne}$ and ${}^{20}\mathrm{F}$ ground states in the density range ${log}_{10}\rho Y_e\left(\mathrm{g}{\mathrm{cm}}^{-3}\right)=9.3$–9.6. The dominance of a few individual transitions allows us to present the various rates by analytical expressions at the relevant astrophysical conditions. We also derive the screening corrections to the rates.

The question of isospin-symmetry breaking in nuclei of the $sd$ shell is addressed. We propose a new global parametrization of the isospin-nonconserving shell-model Hamiltonian which accurately describes experimentally known isobaric mass splittings. The isospin-symmetry violating part of the Hamiltonian consists of the Coulomb interaction and effective charge-dependent forces of nuclear origin. Particular attention has been paid to the effect of the short-range correlations. The behavior of $b$ and $c$ coefficients of the isobaric-mass-multiplet equation (IMME) is explored in detail. In particular, a high-precision numerical description of the staggering effect is proposed and contribution of the charge-dependent forces to the nuclear pairing is discussed. The Hamiltonian is applied to the study of the IMME beyond a quadratic form in the $A=32$ quintet, as well as to calculation of nuclear structure corrections to superallowed $0^{+}\to 0^{+}$ Fermi $\beta$ decay and to amplitudes of Fermi transitions to nonanalog states in $sd$-shell nuclei.

We report the first (in)elastic scattering measurement of ${}^{25}\mathrm{Al}+p$ with the capability to select and measure in a broad energy range the proton resonances in ${}^{26}\mathrm{Si}$ contributing to the ${}^{22}\mathrm{Mg}(\alpha ,p)$ reaction at type I x-ray burst energies. We measured spin-parities of four resonances above the $\alpha$ threshold of ${}^{26}\mathrm{Si}$ that are found to strongly impact the ${}^{22}\mathrm{Mg}(\alpha ,p)$ rate. The new rate advances a state-of-the-art model to remarkably reproduce light curves of the GS $1826–24$ clocked burster with mean deviation $<9\%$ and permits us to discover a strong correlation between the He abundance in the accreting envelope of the photospheric radius expansion burster and the dominance of ${}^{22}\mathrm{Mg}(\alpha ,p)$ branch.

The extent of nucleosynthesis in models of type I X-ray bursts (XRBs) and the associated impact on the energy released in these explosive events are sensitive to nuclear masses and reaction rates around the ⁶⁴Ge waiting point. Using the well known mass of ⁶⁴Ge, the recently measured ⁶⁵As mass, and large-scale shell model calculations, we have determined new thermonuclear rates of the ⁶⁴Ge(p,γ)⁶⁵As and ⁶⁵As(p,γ)⁶⁶Se reactions with reliable uncertainties. The new reaction rates differ significantly from previously published rates. Using the new data, we analyze the impact of the new rates and the remaining nuclear physics uncertainties on the ⁶⁴Ge waiting point in a number of representative one-zone XRB models. We find that in contrast to previous work, when all relevant uncertainties are considered, a strong ⁶⁴Ge rp-process waiting point cannot be ruled out. The nuclear physics uncertainties strongly affect XRB model predictions of the synthesis of ⁶⁴Zn, the synthesis of nuclei beyond A = 64, the energy generation, and the burst light curve. We also identify key nuclear uncertainties that need to be addressed to determine the role of the ⁶⁴Ge waiting point in XRBs. These include the remaining uncertainty in the ⁶⁵As mass, the uncertainty of the ⁶⁶Se mass, and the remaining uncertainty in the ⁶⁵As(p,γ)⁶⁶Se reaction rate, which mainly originates from uncertain resonance energies.

High-precision mass measurements of exotic ^{95-97}Ag isotopes close to the N=Z line have been conducted with the JYFLTRAP double Penning trap mass spectrometer, with the silver ions produced using the recently commissioned inductively heated hot cavity catcher laser ion source at the Ion Guide Isotope Separator On-Line facility. The atomic mass of ^{95}Ag was directly determined for the first time. In addition, the atomic masses of β-decaying 2^{+} and 8^{+} states in ^{96}Ag have been identified and measured for the first time, and the precision of the ^{97}Ag mass has been improved. The newly measured masses, with a precision of ≈1 keV/c^{2}, have been used to investigate the N=50 neutron shell closure, confirming it to be robust. Empirical shell-gap and pairing energies determined with the new ground-state mass data are compared with the state-of-the-art ab initio calculations with various chiral effective field theory Hamiltonians. The precise determination of the excitation energy of the ^{96m}Ag isomer in particular serves as a benchmark for ab initio predictions of nuclear properties beyond the ground state, specifically for odd-odd nuclei situated in proximity to the proton dripline below ^{100}Sn. In addition, density functional theory calculations and configuration-interaction shell-model calculations are compared with the experimental results. All theoretical approaches face challenges to reproduce the trend of nuclear ground-state properties in the silver isotopic chain across the N=50 neutron shell and toward the proton dripline.