The 63Ga(p, gamma)64Ge and 64Ge(p, gamma)65As thermonuclear reactions connect the ZnGa and GeAs cycles by diverting the flow of the rapid proton-capture process from 63Ga to 65As. Changes in these two reaction rates regulate the ZnGa and GeAs cycles and may affect the modeled properties matching with the observed counterparts of a type I X-ray burster. We implement the latest 63Ga(p, gamma)64Ge and 64Ge(p, gamma)65As reaction rates to the state-of-the-art self-consistent one-dimensional multizone thermohydrodynamic code Kepler to study the influence of these new reaction rates on the models of the GS 1826-24 clocked burster and SAX J1808.4-3658 photospheric radius expansion burster. Both new reaction rates obtained by Lu et al. are determined from complementing the experimental input with the nuclear spectroscopic information deduced from the full pf-shell space configuration interaction shell model calculations. By constraining the models on reproducing the observed burst peak, light-curve profile, fluence, and recurrence time, we find that the impact of the newly measured proton thresholds and respective proton-capture reactions on the burst light-curve profile of the GS 1826-24 clocked burster is, in fact, not as significant as claimed by Zhou et al. With or without the inclusion of the newly determined reaction rate of the highly influential 22Mg(alpha, p)25Al reaction, the impact of the new 63Ga(p, gamma)64Ge and 64Ge(p, gamma)65As reaction rates on SAX J1808.4-3658 photospheric radius expansion bursts is evident. Our finding indicates that the models reproducing the 2002 October epoch of the SAX J1808.4-3658 photospheric radius expansion burster are more sensitive to the uncertainties of thermonuclear reaction rates.

Using the relativistic Hartree–Bogoliubov approach with separable pairing force coupled with the latest point-coupling and meson-exchange covariant density functionals, i.e., PC-L3R, PC-X, DD-MEX, and DD-PCX, we systematically explore the ground-state properties of all isotopic chains from oxygen (Z=8) to darmstadtium (Z=110). These properties consist of the binding energies (Eb), one- and two-neutron separation energies (Sn and S2n), root-mean-square radii of matter (Rm), of neutron (Rn), of proton (Rp) and of charge (Rc) distributions, Fermi surfaces (λ), ground-state spins (J) and parities (π). We then use these calculated properties to predict the edges of nuclear landscape and bound nuclei for the isotopic chains of Z = 8–110. The number of bound nuclei predicted by PC-L3R, PC-X, DD-MEX, and DD-PCX, are 9004, 9162, 7112, and 6799, respectively. These latest covariant density functionals produce a set of rather similar proton drip lines due to the strong repulsive Coulomb force shifting up the single-proton energy of the proton-rich nuclei. PC-L3R and PC-X estimate more extended borders of the neutron-rich region compared with the neutron drip lines estimated by DD-MEX, and DD-PCX. Meanwhile, the root-mean-square deviations of one- (two-) neutron separation energies yielded from PC-L3R, PCX, DD-MEX, and DD-PCX are 0.962 (1.300) MeV, 0.920 (1.483) MeV, 1.010 (1.544) MeV, and 0.993 (1.753) MeV, respectively. The deviations of theoretical Sn, S2n, and charge radii from the available experimental ones increase at the regions further away from the proton magic numbers, indicating the important role of deformation in these regions. The root-mean-square deviations of charge radius distributions of comparing the available experimental values with the theoretical counterparts resulted from PC-L3R, PC-X, DD-MEX, and DD-PCX are 0.035 fm, 0.037 fm, 0.034 fm, and 0.035 fm, respectively. We compute and present the root-mean-square radii of neutron distributions for all isotopes of 8≤Z≤110 with respect to the empirical Rn. Basically, the systematic trends of the theoretical root-mean-square radii of neutron distributions generated from PC-L3R and PC-X closely follow the empirical Rn, except for the region of extreme neutron-rich nuclei, whereas DD-PCX produces a trend lower than the empirical Rn at the N<150 region. We notice pronounced differences between the empirical and theoretical Rn at nuclei near the neutron drip line of the Mg, Ca, and Kr isotopic chains, suggesting the possible existence of the halo or giant halo phenomena.

We compute the 63Ga(p, gamma ) 64Ge and 64Ge(p, gamma ) 65As thermonuclear reaction rates using the latest experimental input supplemented with theoretical nuclear spectroscopic information. The experimental input consists of the latest proton thresholds of 64Ge and 65As and the nuclear spectroscopic information of 65As, whereas the theoretical nuclear spectroscopic information for 64Ge and 65As are deduced from the full pf-shell space configuration-interaction shell-model calculations with the GXPF1A Hamiltonian. Both thermonuclear reaction rates are determined with known uncertainties at the energies that correspond to the Gamow windows of the temperature regime relevant to type I x-ray bursts, covering the typical temperature range of the thermonuclear runaway of the GS 1826-24 periodic bursts and SAX J1808.4-3658 photospheric radius expansion bursts.

We propose a newly optimized nonlinear point-coupling parameterized interaction, PC-L3R, for the relativistic Hartree-Bogoliubov framework with a further optimized separable pairing force by fitting to observables, i.e., the binding energies of 91 spherical nuclei, charge radii of 63 nuclei, and 12 sets of mean pairing gaps consisting of 54 nuclei in total. The separable pairing force strengths of proton and neutron are optimized together with the point-coupling constants, and are justified in satisfactory reproducing the empirical pairing gaps. The comparison of experimental binding energies compiled in AME2020 for 91 nuclei with the ones generated from the present and other commonly used point-coupling interactions indicates that the implementation of PC-L3R in relativistic Hartree-Bogoliubov yields the lowest root-mean-square deviation. The charge radii satisfactory agree with experiment. Meanwhile, PC-L3R is capable of estimating the saturation properties of the symmetric nuclear matter and of appropriately predicting the isospin and mass dependence of binding energy. The experimental odd-even staggering of single nucleon separation energies is well reproduced. The comparison of the estimated binding energies for 7,373 nuclei based on the PC-L3R and other point-coupling interactions is also presented.

We reassess the 65 As(p, γ ) 66 Se reaction rates based on a set of proton thresholds of 66 Se, S p ( 66 Se), estimated from the experimental mirror nuclear masses, theoretical mirror displacement energies, and full p f -model space shell-model calculation. The self-consistent relativistic Hartree–Bogoliubov theory is employed to obtain the mirror displacement energies with much reduced uncertainty, and thus reducing the proton-threshold uncertainty up to 161 keV compared to the AME2020 evaluation. Using the simulation instantiated by the one-dimensional multi-zone hydrodynamic code, K epler , which closely reproduces the observed GS 1826−24 clocked bursts, the present forward and reverse 65 As(p, γ ) 66 Se reaction rates based on a selected S p ( 66 Se) = 2.469 ± 0.054 MeV, and the latest 22 Mg( α ,p) 25 Al, 56 Ni(p, γ ) 57 Cu, 57 Cu(p, γ ) 58 Zn, 55 Ni(p, γ ) 56 Cu, and 64 Ge(p, γ ) 65 As reaction rates, we find that though the GeAs cycles are weakly established in the rapid-proton capture process path, the 65 As(p, γ ) 66 Se reaction still strongly characterizes the burst tail end due to the two-proton sequential capture on 64 Ge, not found by the Cyburt et al. sensitivity study. The 65 As(p, γ ) 66 Se reaction influences the abundances of nuclei A = 64, 68, 72, 76, and 80 up to a factor of 1.4. The new S p ( 66 Se) and the inclusion of the updated 22 Mg( α ,p) 25 Al reaction rate increases the production of 12 C up to a factor of 4.5, which is not observable and could be the main fuel for a superburst. The enhancement of the 12 C mass fraction alleviates the discrepancy in explaining the origin of the superburst. The waiting point status of and two-proton sequential capture on 64 Ge, the weak-cycle feature of GeAs at a region heavier than 64 Ge, and the impact of other possible S p ( 66 Se) are also discussed.

In Type-I X-ray bursts (XRBs), the rapid-proton capture (rp-) process passes through the NiCu and ZnGa cycles before reaching the region above Ge and Se isotopes that hydrogen burning actively powers the XRBs. The sensitivity study performed by Cyburt et al. [1] shows that the 57Cu(p,γ)58Zn reaction in the NiCu cycles is the fifth most important rp-reaction influencing the burst light curves. Langer et al. [2] precisely measured some low-lying energy levels of 58Zn to deduce the 57Cu(p,γ)58Zn reaction rate. Nevertheless, the order of the 1+1 and 2+3 resonance states that dominate at 0:2 ≲ T(GK) ≲ 0:8 is not confirmed. The 1+2 resonance state, which dominates at the XRB sensitive temperature regime 0:8 ≲ T(GK) ≲ 2 was not detected. Using isobaric-multipletmass equation (IMME), we estimate the order of the 1+1 and 2+3 resonance states and estimate the lower limit of the 1+2 resonance energy. We then determine the 57Cu(p,γ)58Zn reaction rate using the full pf -model space shell model calculations. The new rate is up to a factor of four lower than the Forstner et al. [3] rate recommended by JINA REACLIBv2.2. Using the present 57Cu(p,γ)58Zn, the latest 56Ni(p,γ)57Cu and 55Ni(p,γ)56Cu reaction rates, and 1D implicit hydrodynamic Kepler code, we model the thermonuclear XRBs of the clocked burster GS 1826–24. We find that the new rates regulate the reaction flow in the NiCu cycles and strongly influence the burst-ash composition. The 59Cu(p,γ)56Ni and 59Cu(p,α)60Zn reactions suppress the influence of the 57Cu(p,γ)58Zn reaction. They strongly diminish the impact of the nuclear reaction flow that bypasses the 56Ni waiting point induced by the 55Ni(p,γ)56Cu reaction on burst light curve.

During the X-ray bursts of GS 1826−24, a “clocked burster”, the nuclear reaction flow that surges through the rapid-proton capture process path has to pass through the NiCu cycles before reaching the ZnGa cycles that moderate further hydrogen burning in the region above the germanium and selenium isotopes. The 57 Cu(p, γ ) 58 Zn reaction that occurs in the NiCu cycles plays an important role in influencing the burst light curves found by Cyburt et al. We deduce the 57 Cu(p, γ ) 58 Zn reaction rate based on the experimentally determined important nuclear structure information, isobaric-multiplet-mass equation, and large-scale shell-model calculations. Based on the isobaric-multiplet-mass equation, we propose a possible order of 1 1 + - and 2 3 + -dominant resonance states and constrain the resonance energy of the 1 2 + state. The latter reduces the contribution of the 1 2 + -dominant resonance state. The new reaction rate is up to a factor of 4 lower than the Forstner et al. rate recommended by JINA REACLIB v2.2 at the temperature regime sensitive to clocked bursts of GS 1826−24. Using the simulation from the one-dimensional implicit hydrodynamic code K epler to model the thermonuclear X-ray bursts of the GS 1826−24 clocked burster, we find that the new 57 Cu(p, γ ) 58 Zn reaction rate, coupled with the latest 56 Ni(p, γ ) 57 Cu and 55 Ni(p, γ ) 56 Cu reaction rates, redistributes the reaction flow in the NiCu cycles and strongly influences the burst ash composition, whereas the 59 Cu(p, α ) 56 Ni and 59 Cu(p, γ ) 60 Zn reactions suppress the influence of the 57 Cu(p, γ ) 58 Zn reaction and diminish the impact of nuclear reaction flow that bypasses the important 56 Ni waiting point induced by the 55 Ni(p, γ ) 56 Cu reaction on the burst light curve.

We deduce $^{65}$As(p,$\gamma$)$^{66}$Se reaction rates based on a set of proton thresholds of $^{66}$Se, $S_\mathrm{p}$($^{66}$Se), estimated from the experimental mirror nuclear masses, theoretical mirror displacement energies, and full $pf$-model space shell-model calculation. The self-consistent relativistic Hartree-Bogoliubov theory is employed to obtain the mirror displacement energies with much reduced uncertainty, and thus reducing the proton-threshold uncertainty up to 161 keV compared to the AME2020 evaluation. The influence of this set of $S_\mathrm{p}$($^{66}$Se) on the $^{65}$As(p,$\gamma$)$^{66}$Se forward and reverse reaction rates is presented. Using the one-dimensional multi-zone implicit hydrodynamic code, KEPLER, that closely reproduces the observed GS 1826$-$24 clocked bursts, the present $^{65}$As(p,$\gamma$)$^{66}$Se forward and reverse reaction rates based on a selected $S_\mathrm{p}$($^{66}$Se) = 2.469$\pm$0.054 MeV, and the latest $^{22}$Mg($\alpha$,p)$^{25}$Al, $^{56}$Ni(p,$\gamma$)$^{57}$Cu(p,$\gamma$)$^{58}$Zn, $^{55}$Ni(p,$\gamma$)$^{56}$Cu, and $^{64}$Ge(p,$\gamma$)$^{65}$As reaction rates, we find that though the GeAs cycles is weakly established in the rapid-proton capture process path during the clocked X-ray bursts of GS 1826$-$24 burster, the $^{65}$As(p,$\gamma$)$^{66}$Se reaction still strongly characterizes the burst tail end due to the two-proton sequential capture on $^{64}$Ge, not found by Cyburt et al. (2016) sensitivity study. The $^{65}$As(p,$\gamma$)$^{66}$Se reaction influences the abundances of nuclei $A$ = 64, 68, 72, 76, and 80 up to a factor of 1.4. The inclusion of the updated $^{22}$Mg($\alpha$,p)$^{25}$Al reaction rate influences the production of $^{12}$C up to a factor of 4.5 that could be the main fuel for Type-I X-ray superburst. The status of $^{64}$Ge waiting point and the influence of other $^{66}$Se are also discussed.