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Peter Mohr

Publications and source records attributed to Peter Mohr.

At least 19 recordsLinked to original sources
arXiv2026

Nuclear Physics of X-ray Bursts

Thermonuclear X-ray bursts from the surface of accreting neutron stars are the most common astrophysical explosions in our galaxy. They provide a unique window into the physics of neutron stars, the physics of matter under extreme conditions, and the physics of astrophysical thermonuclear explosions. X-ray bursts are powered by a broad range of nuclear reactions that need to be understood to interpret observations. The relevant nuclei are mostly neutron deficient and unstable, and thus experimental information and theoretical understanding is limited and an active area of research in nuclear science. We review the current status of the nuclear physics of X-ray bursts, with special emphasis on new experimental and theoretical information on a large number of reaction rates. As such we provide an overview of the broad experimental and theoretical methods currently used to advance the nuclear physics of X-ray bursts. The new information is used to update the public JINA REACLIB database with 32 new reaction rates based on experimental information, and a new dataset of theoretical statistical model reaction rates where no experimental information is available. Using several models for X-ray bursts that are powered by mixed hydrogen and helium burning, we take advantage of the updated nuclear data to review the current understanding of the nuclear reaction sequences in such X-ray bursts, the modeling of light curves, and predictions of the composition of nuclear ashes.

astro-ph.HE↗
arXiv2026

The 2025 Evaluation of Experimental Thermonuclear Reaction Rates (ETR25)

This work describes the formalism for estimating thermonuclear reaction rates for astrophysical applications, emphasizing modern statistical approaches such as Monte-Carlo sampling and Bayesian models. We discuss related topics including the calculation of resonance energies from nuclear Q values, indirect estimates of particle partial widths, and matching of reaction rates at elevated temperatures to statistical-model results. We have evaluated available experimental data on cross sections, resonance energies and strengths, partial widths, life-times, spin-parities, and spectroscopic factors. Based on these results, we have estimated numerical values of 78 experimental charged-particle thermonuclear reaction rates for target nuclei in the A = 2 to 40 mass region, for temperatures ranging from 1 MK to 10 GK. For each reaction, three rate values are provided: low, median, and high, corresponding to the 16th, 50th, and 84th percentiles, respectively, of the cumulative reaction rate probability density distribution. Additionally, we present the factor uncertainty of each rate at each temperature grid point. These results enable users to sample the reaction rate probability density in nucleosynthesis calculations, facilitating uncertainty estimates of nuclidic abundances. The rates presented here refer to their laboratory values. For use in stellar model simulations, these values need to be corrected for the effects of thermal excitations of the interacting nuclei. For each reaction, we include graphs that illustrate the fractional contributions to the overall reaction rate along with the associated uncertainty. These visuals are designed to assist both stellar modelers and nuclear experimentalists by identifying the primary sources of rate uncertainty at specific stellar temperatures. A graphical comparison with earlier Monte-Carlo rates is also provided.

astro-ph.SR↗
arXiv2024

CODATA Recommended Values of the Fundamental Physical Constants: 2022

We report the 2022 self-consistent values of constants and conversion factors of physics and chemistry recommended by the Committee on Data of the International Science Council (CODATA). The recommended values can also be found at physics.nist.gov/constants. The values are based on a least-squares adjustment that takes into account all theoretical and experimental data available through 31 December 2022. A discussion of the major improvements as well as inconsistencies within the data is given.

hep-ph↗
arXiv2020

Yrast band in the heavy $N = Z$ nucleus $^{88}$Ru: $α$-cluster approach

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 $\otimes$ $α$) structure. Contrary, the yrast bands in neighboring $N \ne Z$ 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.

nucl-th↗
arXiv2020

Comment on "Observation of annual modulation by $γ$ rays from ($α$,$γ$) reactions at the Soudan Underground Laboratory"

Tiwari {\it et al.}\ have identified an annual modulation of the $γ$-ray flux at the Soudan Underground Laboratory which is strongly correlated to the radon concentration. The $γ$-ray flux results from ($α$,$γ$) reactions which are induced by the $α$ activity of radon and its daughters. Unfortunately, the quantitative analysis of the $γ$-ray flux is based on unrealistic ($α$,$γ$) cross sections, and thus the calculated $γ$-ray fluxes are not reliable.

nucl-th↗
arXiv2019

Cross sections at sub-Coulomb energies: full optical model vs.\ barrier transmission for $^{40}$Ca + $α$

Cross sections for $^{40}$Ca + $α$ at low energies have been calculated from two different models and three different $α$-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 using a complex nuclear potential. The excitation functions from barrier transmission are smooth whereas the excitation functions from the optical model show a significant sensitivity to the chosen imaginary potential. Cross sections far below the Coulomb barrier are lower from barrier transmission than from the optical model. This difference is explained by additional absorption in the tail of the imaginary part of the potential in the optical model. At higher energies the calculations from the two models and all $α$-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 $^{40}$Ca + $α$ at low energies is clearly confirmed in the present analysis for the simple barrier transmission model and for the full optical model calculation.

nucl-th↗
arXiv2019

Direct capture cross section of $^{9}$Be(n,$γ$)$^{10}$Be

The cross section of the $^{9}$Be(n,$γ$)$^{10}$Be reaction was calculated in the direct capture model. All parameters of the calculations were adjusted to properties of the $^{9}$Be + 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.

nucl-th↗
arXiv2018

Revised Cross Section of the $^{13}$C($α$,n)$^{16}$O reaction between 5 and 8 MeV

As suggested in a Comment by Peters, Phys.\ Rev.\ C {\bf 96}, 029801 (2017), a correction is applied to the $^{13}$C($α$,n)$^{16}$O data of Harissopulos {\it et al.}, Phys.\ Rev.\ C {\bf 72}, 062801(R) (2005). The correction refers to the energy-dependent efficiency of the neutron detector and appears only above the ($α$,n$_1$) threshold of the $^{13}$C($α$,n)$^{16}$O reaction at about $E_α\approx 5$ MeV. The corrected data are lower than the original data by almost a factor of two. The correction method is verified using recent neutron spectroscopy data and data from the reverse $^{16}$O(n,$α$)$^{13}$C reaction.

nucl-ex↗
arXiv2017

$α$-cluster states in $^{46,54}$Cr from double-folding potentials

$α$--cluster states in $^{46}$Cr and $^{54}$Cr are investigated in the double-folding model. This study complements a recent similar work of Souza and Miyake \cite{Sou17} 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 $^{46}$Cr and $^{54}$Cr. The $α$-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 $^{50}$Ti is found.

nucl-th↗
arXiv2017

Uncertainty of the astrophysical $^{17,18}$O($α$,n)$^{20,21}$Ne reaction rates and the applicability of the statistical model for nuclei with $A \lesssim 20$

Background: The ($α$,n) and ($α$,$γ$) reactions on $^{17,18}$O have significant impact on the neutron balance in the astrophysical $s$-process. In this scenario stellar reaction rates are required for relatively low temperatures below $T_9 \lesssim 1$. Purpose: The uncertainties of the $^{17,18}$O($α$,n)$^{20,21}$Ne reactions are investigated. Statistical model calculations are performed to study the applicability of this model for relatively light nuclei in extension to a recent review for the $20 \le A \le 50$ mass range. Method: The available experimental data for the $^{17,18}$O($α$,n)$^{20,21}$Ne reactions are compared to statistical model calculations. Additionally, the reverse $^{20}$Ne(n,$α$)$^{17}$O reaction is investigated, and similar studies for the $^{17}$F mirror nucleus are provided. Results: It is found that on average the available experimental data for $^{17}$O and $^{18}$O are well described within the statistical model, resulting in reliable reaction rates above $T_9 \gtrsim 1.5$ from these calculations. However, significant experimental uncertainties are identified for the $^{17}$O($α$,n$_0$)$^{20}$Ne(g.s.) channel. Conclusions: The statistical model is able to predict astrophysical reaction rates for temperatures above 1 GK with uncertainties of less than a factor of two for the nuclei under study. An experimental discrepancy for the $^{17}$O($α$,n)$^{20}$Ne reaction needs to be resolved.

nucl-th↗
arXiv2017

Adaptive User Perspective Rendering for Handheld Augmented Reality

Handheld Augmented Reality commonly implements some variant of magic lens rendering, which turns only a fraction of the user's real environment into AR while the rest of the environment remains unaffected. Since handheld AR devices are commonly equipped with video see-through capabilities, AR magic lens applications often suffer from spatial distortions, because the AR environment is presented from the perspective of the camera of the mobile device. Recent approaches counteract this distortion based on estimations of the user's head position, rendering the scene from the user's perspective. To this end, approaches usually apply face-tracking algorithms on the front camera of the mobile device. However, this demands high computational resources and therefore commonly affects the performance of the application beyond the already high computational load of AR applications. In this paper, we present a method to reduce the computational demands for user perspective rendering by applying lightweight optical flow tracking and an estimation of the user's motion before head tracking is started. We demonstrate the suitability of our approach for computationally limited mobile devices and we compare it to device perspective rendering, to head tracked user perspective rendering, as well as to fixed point of view user perspective rendering.

cs.HC↗
arXiv2016

$α$-decay properties of $^{296}118$ from double-folding potentials

$α$-decay properties of the yet unknown nucleus $^{296}$118 are predicted using the systematic behavior of parameters of $α$-nucleus double-folding potentials. The results are $Q_α= 11.655 \pm 0.095$ MeV and $T_{1/2} = 0.825$ ms with an uncertainty of about a factor of 4.

nucl-th↗
arXiv2016

$\mathbfα$-induced reaction cross sections in the mass range $\mathbf{A \approx 20 - 50}$: a critical review

In a recent review it was shown that the cross sections of $α$-induced reactions in the $A \approx 20 - 50$ 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 $σ_{\rm{red}}$ and reduced energies $E_{\rm{red}}$ was used. Four outliers were identified: $^{36}$Ar and $^{40}$Ar with unusally small cross sections and $^{23}$Na and $^{33}$S with unusually large cross sections. New data for $^{23}$Na 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 $E_{\rm{red}}$ is presented.

nucl-th↗
arXiv2016

Role of ($α$,n) reactions under $r$-process conditions in neutrino-driven winds revisited

Background: The astrophysical $r$-process occurs in an explosive astrophysical event under extremely neutron-rich conditions, leading to (n,$γ$)-($γ$,n) equilibrium along isotopic chains which peaks around neutron separation energies of a few MeV. Nuclei with larger $Z$ are usually produced by $β^-$-decay, but under certain conditions also $α$-induced reactions may become relevant for the production of nuclei with $Z+2$. Purpose: The uncertainties of the reaction rates of these $α$-induced reactions are discussed within the statistical model. As an example, $α$-induced ($α$,n) and $(α$,$x$n) reaction cross sections for the neutron-rich $^{86}$Se nucleus are studied in detail. Method: In a first step, the relevance of ($α$,n) and $(α$,$x$n) reactions is analyzed. Next the uncertainties are determined from a variation of the $α$-nucleus potential which is the all-dominant parameter for the astrophysical $Z \rightarrow Z+2$ reaction rate. Results: It is found that the $r$-process flow towards nuclei with larger $Z$ is essentially influenced only by the $α$-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 ($α$,$x$n) cross sections which is practically identical to the total $α$-induced reaction cross section. Conclusions: $α$-nucleus potentials play an important role under certain $r$-process conditions because the flow towards larger $Z$ depends sensitively on the total $α$-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.

nucl-th↗
arXiv2016

Comment on "Structure effects in the $^{15}$N(n,$γ$)$^{16}$N radiative capture reaction from the Coulomb dissociation of $^{16}$N"

In their recent study Neelam, Shubhchintak, and Chatterjee have claimed that "it would certainly be useful to perform a Coulomb dissociation experiment to find the low energy capture cross section for the reaction" $^{15}$N(n,$γ$)$^{16}$N. However, it is obvious that a Coulomb dissociation experiment cannot constrain this capture cross section because the dominating branchings of the capture reaction lead to excited states in $^{16}$N which do not contribute in a Coulomb dissociation experiment. An estimate of the total $^{15}$N(n,$γ$)$^{16}$N cross section from Coulomb dissociation of $^{16}$N requires a precise knowledge of the $γ$-ray branchings in the capture reaction. Surprisingly, the calculation of Neelam, Shubhchintak, and Chatterjee predicts a strongly energy-dependent ground state branching of the order of 0.05\% to 0.6\% at energies between 100 and 500 keV which is almost 2 orders of magnitude below calculations in the direct capture model. Additionally, this calculation of Neelam, Shubhchintak, and Chatterjee deviates significantly from the expected energy dependence for $p$-wave capture.

nucl-th↗
arXiv2016

Nucleosynthesis of $^{92}$Nb and the relevance of the low-lying isomer at 135.5 keV

Background: Because of its half-life of about 35 million years, 92Nb is considered as a chronometer for nucleosynthesis events prior to the birth of our sun. The abundance of 92Nb in the early solar system can be derived from meteoritic data. It has to be compared to theoretical estimates for the production of 92Nb 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 92Nb is analyzed. The thermal coupling between the ground state and the isomer via so-called intermediate states affects the production and survival of 92Nb. Method: The properties of the lowest intermediate state in 92Nb 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 92Nb are calculated as a function 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 92Nb in any explosive production scenario and almost 100% survival of 92Nb in its ground state. However, the strong coupling leads to a temperature-dependent effective half-life of 92Nb which makes the 92Nb survival very sensitive to temperatures as low as about 8 keV, thus turning 92Nb at least partly into a thermometer. Conclusions: The low-lying isomer in 92Nb does not affect the production of 92Nb 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 92Nb after its synthesis in supernovae which are the most likely astrophysical site for the nucleosynthesis of 92Nb.

nucl-th↗
arXiv2016

Re-evaluation of the $^{16}$O($n$,$γ$)$^{17}$O cross section at astrophysical energies and its role as neutron poison in the $s$ process

The doubly-magic nucleus $^{16}$O has a small neutron capture cross section of just a few tens of microbarn in the astrophysical energy region. Despite of this, $^{16}$O plays an important role as 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 $^{16}$O($n,γ$)$^{17}$O and derive a new recommendation for the Maxwellian-averaged cross sections (MACS) between $kT$= 5$-$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- ($kT$= 26 keV) and shell carbon burning ($kT$= 90 keV) in massive stars where $^{16}$O is the most abundant isotope.

astro-ph.SR↗
arXiv2015

Broad levels in $^{17}$O and their relevance for the astrophysical s-process

Levels in $^{17}$O affect the astrophysical s-process in two opposite ways. The neutron production is enhanced by resonances in the $^{13}$C($α$,$n$)$^{16}$O reaction at excitation energies around 7 MeV in $^{17}$O, and the number of available neutrons is reduced by low-lying resonances in the $^{16}$O($n$,$γ$)$^{17}$O reaction corresponding to levels in $^{17}$O with excitation energies of $4-5$ MeV. The present work uses the $^{19}$F($d$,$α$)$^{17}$O reaction to determine absolute widths of the relevant levels in $^{17}$O. The results improve the uncertainties of the previously adopted values and resolve a discrepancy between recent studies for the $1/2^+$ level close to the threshold of the $^{13}$C($α$,$n$)$^{16}$O reaction. In addition, improved excitation energies and widths are provided for several states in $^{17}$O up to excitation energies close to 8 MeV.

nucl-ex↗