In a recent study, Perez Velasquez, Caballero, and Kelkar report a dramatically enhanced α decay rate of the nucleus 212 Po at high temperatures which reaches almost five orders of magnitude at a temperature of 2 Giga-Kelvin. Contrary to that finding, only a moderate enhancement by a factor of three is found in the present comment which is based on a careful study of the properties of excited states in 212 Po.

The yrast band in the heavy N = Z nucleus ^88 Ru is studied in the framework of the α -cluster model in combination with double-folding potentials. It is found that the excitation energies of the yrast band in ^88 Ru can be nicely described within the α -cluster approach using a smooth and mildly L -dependent adjustment of the potential strength. This result is similar to well-established α -cluster states in nuclei with a (magic core ⊗ α ) structure. Contrary, the yrast bands in neighboring N Z nuclei deviate from such a typical α -cluster behavior. Finally, the α -cluster model predicts reduced transition strengths of about 10 Weisskopf units for intraband transitions between low-lying states in the yrast band of ^88 Ru.

Annual modulation of $\gamma$ rays from ($\alpha$, $\gamma$) reactions in the Soudan Underground Lab has been observed using a 12-liter scintillation detector. This significant annual modulation, measured over 4 years, can mimic the signature for dark matter and can also generate potential background events for neutrinoless double-$\beta$ decay experiments. The measured annual modulation of the event rate from ($\alpha$, $\gamma$) reactions is strongly correlated with the time-varying radon concentration observed independently in the Lab. The $\alpha$ flux from radon decay is simulated starting from the measured radon concentration, and the $\gamma$-ray flux is determined using the convolution of the $\alpha$ flux and the cross sections for ($\alpha$, $\gamma$) reactions. The calculated $\gamma$-ray flux is sufficient to generate the measured event rate that exhibits an annual modulation.

Cross-sections for [Formula: see text]Ca + [Formula: see text] at low energies have been calculated from two different models and three different [Formula: see text]-nucleus potentials. The first model determines the cross-sections from the barrier transmission in a real nuclear potential. Second, cross-sections are derived within the optical model (OM) using a complex nuclear potential. The excitation functions from barrier transmission are smooth, whereas the excitation functions from the OM show a significant sensitivity to the chosen imaginary potential. Cross-sections far below the Coulomb barrier are lower from barrier transmission than from the OM. This difference is explained by additional absorption in the tail of the imaginary part of the potential in the OM. At higher energies, the calculations from the two models and all [Formula: see text]-nucleus potentials converge. Finally, in contradiction to another recent study where a double-folding potential failed in a WKB calculation, the applicability of double-folding potentials for [Formula: see text]Ca + [Formula: see text] at low energies is clearly confirmed in the present analysis for the simple barrier transmission model and for the full OM calculation.

The cross section of the ^9Be(n,γ)^10Be reaction was calculated in the direct capture model. All parameters of the calculations were adjusted to properties of the ^9Be + n system at thermal energies. The calculated cross section at thermonuclear energies shows the expected 1/v behavior of s-wave capture at low energies, but increases towards higher energies as typical p-wave capture. Excellent agreement between new experimental data in the astrophysically relevant energy region and the present calculation is found.

The cross section of the Be-9(n, gamma)Be-10 reaction was calculated in the direct capture model. All parameters of the calculations were adjusted to properties of the Be-9 + n system at thermal energies. The calculated cross section at thermonuclear energies shows the expected 1/v behavior of s-wave capture at low energies, but increases towards higher energies as typical p-wave capture. Excellent agreement between new experimental data in the astrophysically relevant energy region and the present calculation is found.

As suggested in a Comment by Peters [Phys. Rev. C 96, 029801 (2017)2469-998510.1103/PhysRevC.96.029801], a correction is applied to the C13(α,n)O16 data of Harissopulos et al. [Phys. Rev. C 72, 062801(R) (2005)PRVCAN0556-281310.1103/PhysRevC.72.062801]. The correction refers to the energy-dependent efficiency of the neutron detector and appears only above the (α,n1) threshold of the C13(α,n)O16 reaction at about Eα≈5 MeV. The corrected data are lower than the original data by almost a factor of 2. The correction method is verified using recent neutron spectroscopy data and data from the reverse O16(n,α)C13 reaction.

In a recent review it was shown that the cross sections of α-induced reactions in the A ≈ 20 − 50 mass range follow a general and smooth trend in most cases. For comparison of cross sections of different targets at various energies the method of reduced cross sections σ red and reduced energies E red was used. Four outliers were identified: 36Ar and 40Ar with unusal small cross sections and 23Na and 33S with unusual huge cross sections. New data for 23Na were presented at this NPA-7 conference; contrary to the previous data, these new data fit into the general systematics. In addition, a relation between the most effective energy E 0 for astrophysical reaction rates (the so-called Gamow window) and the reduced energy E red is presented.

In a recent review it was shown that the cross sections of alpha-induced reactions in the A approximate to 20 - 50 mass range follow a general and smooth trend in most cases. For comparison of cross sections of different targets at various energies the method of reduced cross sections sigma(red) and reduced energies E-red was used. Four outliers were identified: Ar-36 and Ar-40 with unusal small cross sections and Na-23 and S-33 with unusual huge cross sections. New data for Na-23 were presented at this NPA-7 conference; contrary to the previous data, these new data fit into the general systematics. In addition, a relation between the most effective energy E-0 for astrophysical reaction rates (the so-called Gamow window) and the reduced energy E-red is presented.

\( \alpha\)-cluster states in 46Cr and 54Cr are investigated in the double-folding model. This study complements a recent similar work by Souza and Miyake, Eur. Phys. J. A 53, 146 (2017), which was based on a specially shaped potential. Excitation energies, reduced widths, intercluster separations, and intra-band transition strengths are calculated and compared to experimental values for the ground state bands in 46Cr and 54Cr . The \( \alpha\)-cluster potential is also applied to elastic scattering at low and intermediate energies. Here, as a byproduct, a larger radial extent of the neutron density in 50Ti is found.

alpha-decay properties of the yet unknown nucleus (296)118 are predicted using the systematic behavior of parameters of alpha-nucleus double-folding potentials. The results are Q(alpha) = 11.655 +/- 0.095 MeV and T-1/2 = 0.825 ms with an uncertainty of about a factor of 4.

$\\ensuremath{\\alpha}\\text{\\ensuremath{-}}\\mathrm{decay}$ properties of the yet unknown nucleus $^{296}118$ are predicted using the systematic behavior of parameters of $\\ensuremath{\\alpha}$-nucleus double-folding potentials. The results are ${Q}_{\\ensuremath{\\alpha}}=11.655\\ifmmode\\pm\\else\\textpm\\fi{}0.095\\phantom{\\rule{4pt}{0ex}}\\mathrm{MeV}$ and ${T}_{1/2}=0.825\\phantom{\\rule{4pt}{0ex}}\\mathrm{ms}$ with an uncertainty of about a factor of 4.

alpha-cluster states in Cr-46 and Cr-54 are investigated in the double-folding model. This study complements a recent similar work by Souza and Miyake, Eur. Phys. J. A 53, 146 (2017), which was based on a specially shaped potential. Excitation energies, reduced widths, intercluster separations, and intra-band transition strengths are calculated and compared to experimental values for the ground state bands in Cr-46 and Cr-54. The a-cluster potential is also applied to elastic scattering at low and intermediate energies. Here, as a byproduct, a larger radial extent of the neutron density in Ti-50 is found.

Background: Because of its half-life of about 35 million years, Nb-92 is considered as a chronometer for nucleosynthesis events prior to the birth of our sun. The abundance of Nb-92 in the early solar system can be derived frommeteoritic data. It has to be compared to theoretical estimates for the production of Nb-92 to determine the time between the last nucleosynthesis event before the formation of the early solar system.Purpose: The influence of a low-lying short-lived isomer on the nucleosynthesis of Nb-92 is analyzed. The thermal coupling between the ground state and the isomer via so-called intermediate states affects the production and survival of Nb-92.Method: The properties of the lowest intermediate state in Nb-92 are known from experiment. From the lifetime of the intermediate state and from its decay branchings, the transition rate from the ground state to the isomer and the effective half-life of Nb-92 are calculated as functions of the temperature.Results: The coupling between the ground state and the isomer is strong. This leads to thermalization of ground state and isomer in the nucleosynthesis of Nb-92 in any explosive production scenario and almost 100% survival of Nb-92 in its ground state. However, the strong coupling leads to a temperature-dependent effective half-life of Nb-92 which makes the Nb-92 survival very sensitive to temperatures as low as about 8 keV, thus turning Nb-92 at least partly into a thermometer.Conclusions: The low-lying isomer in Nb-92 does not affect the production of Nb-92 in explosive scenarios. In retrospect this validates all previous studies where the isomer was not taken into account. However, the dramatic reduction of the effective half-life at temperatures below 10 keV may affect the survival of Nb-92 after its synthesis in supernovae, which are the most likely astrophysical sites for the nucleosynthesis of Nb-92.

Background: The astrophysical r-process occurs in an explosive astrophysical event under extremely neutron-rich conditions, leading to (n,gamma)-(gamma,n) equilibrium along isotopic chains which peaks around neutron separation energies of a few MeV. Nuclei with larger Z are usually produced by beta(-) decay, but under certain conditions also alpha-induced reactions may become relevant for the production of nuclei with Z + 2.Purpose: The uncertainties of the reaction rates of these alpha-induced reactions are discussed within the statistical model. As an example, alpha-induced (alpha, n) and (alpha, xn) reaction cross sections for the neutron-rich Se-86 nucleus are studied in detail.Method: In a first step, the relevance of (alpha, n) and (alpha, xn) reactions is analyzed. Next the uncertainties are determined from a variation of the a-nucleus potential which is the all-dominant parameter for the astrophysical Z -> Z + 2 reaction rate.Results: It is found that the r-process flow towards nuclei with larger Z is essentially influenced only by the alpha-nucleus potential whereas the other ingredients of the statistical model play a very minor role. This finding is based on the fact that the flow towards larger Z depends on the sum over all (alpha, xn) cross sections, which is practically identical to the total alpha-induced reaction cross section.Conclusions: alpha-nucleus potentials play an important role under certain r-process conditions because the flow towards larger Z depends sensitively on the total alpha-induced reaction cross section. The uncertainty of the reaction rate is about a factor of two to three at higher temperatures and exceeds one order of magnitude at very low temperatures.

α-decay properties of the yet unknown nucleus ^296118 are predicted using the systematic behavior of parameters of α-nucleus double-folding potentials. The results are Q_α = 11.655 ± 0.095 MeV and T_1/2 = 0.825 ms with an uncertainty of about a factor of 4.

The doubly magic nucleus 16O has a small neutron-capture cross section of just a few tens of microbarns in the astrophysical energy region. Despite this, 16O plays an important role as a neutron poison in the astrophysical slow neutron capture (s) process due to its high abundance. We present in this paper a re-evaluation of the available experimental data for 16O()17O and derive a new recommendation for the Maxwellian-averaged cross sections between kT = 5 and 100 keV. Our new recommendations are lower up to kT = 60 keV compared to the previously recommended values but up to 14% higher at kT = 100 keV. We explore the impact of this different energy dependence on the weak s-process during core helium burning (kT = 26 keV) and shell carbon burning (kT = 90 keV) in massive stars where 16O is the most abundant isotope.

In this work we present the experimental details and the results of the α scattering measurement on 64 Zn performed at the Atomki cyclotron, at energies close to the Coulomb barrier (12.08 MeV and 16.15 MeV).A comparison of the cross sections to different global α-nucleus potential predictions is also presented.Inelastic scattering cross sections leading to the first few excited states of 64 Zn were also determined.Total cross sections important for the statistical model are also derived and compared with the available experimental data.

A simple reduction scheme using so-called reduced energies E-red and reduced cross sections sigma(red) allows the comparison of heavy-ion-induced reaction cross sections for a broad range of masses of projectile and target and over a wide energy range. A global behavior has been found for strongly bound projectiles whereas much larger reduced cross sections have been observed for weakly bound and halo projectiles. It has been shown that this simple reduction scheme works also well for alpha-particle-induced reactions on heavy target nuclei, but very recently significant deviations have been seen for alpha + S-33 and alpha + Na-23. Motivated by these unexpected discrepancies, the present study analyses alpha-induced reaction cross sections for targets with masses A approximate to 20-50. The study shows that the experimental data for a-induced reactions on nuclei with A approximate to 20-50 deviate slightly from the global behavior of reduced cross sections. However, in general the deviations evolve smoothly towards lower masses. The only significant outliers are the recent data for S-33 and Na-23 which are far above the general systematics, and some very old data may indicate that Ar-36 and Ar-40 are below the general trend. As expected, also the doubly magic Ca-40 nucleus lies slightly below the results for its neighboring nuclei. Overall, the experimental data are nicely reproduced by a statistical model calculation utilizing the simple a-nucleus potential by McFadden and Satchler. Simultaneously with the deviation of reduced cross sections sred from the general behavior, the outliers Na-23, S-33, Ar-36, and Ar-40 also show significant disagreement between experiment and statistical model calculation.