Complete calculation of evaluated Maxwellian-averaged cross sections and their errors for s-process nucleosynthesis (original) (raw)
Present contribution represents a significant improvement of our previous calculation of Maxwellian-averaged cross sections and astrophysical reaction rates. Addition of newlyevaluated neutron reaction libraries, such as ROSFOND and Low-Fidelity Covariance Project, and improvements in data processing techniques allowed us to extend it for entire range of sprocess nuclei, calculate Maxwellian-averaged cross section uncertainties for the first time, and provide additional insights on all currently available neutron-induced reaction data. Nuclear reaction calculations using ENDF libraries and current Java technologies will be discussed and new results will be presented.
Springer Proceedings in Physics, 2019
We investigated the impact of uncertainties in neutron-capture and weak reactions (on heavy elements) on the s−process nucleosynthesis in low-mass stars using a Monte-Carlo based approach. We performed extensive nuclear reaction network calculations that include newly evaluated temperature-dependent upper and lower limits for the individual reaction rates. Our sophisticated approach is able to evaluate the reactions that impact more significantly the final abundances. We found that β-decay rate uncertainties affect typically nuclides near s-process branchings, whereas most of the uncertainty in the final abundances is caused by uncertainties in neutron capture rates, either directly producing or destroying the nuclide of interest. Combined total nuclear uncertainties due to reactions on heavy elements are approximately 50%.
Nuclear Physics of the s Process
Publications of the Astronomical Society of Australia, 2008
Starting from a sketch of the s-process concept formulated 50 years ago, the nuclear physics data for s-process calculations are briefly reviewed with emphasis on the status of neutron capture cross sections and beta decay rates. Accurate and comprehensive experimental data are mandatory as direct input for s-process calculations as well as for improving the complementary information from nuclear theory. The current challenges of the field are discussed in the light of new or optimized methods and state-of-theart facilities, indicating the potential for accurate measurements and the possibility to study cross sections of radioactive isotopes. These opportunities will be considerably enriched by the enormous improvements provided by new facilities.
Impact of nuclear mass measurements in the vicinity of 132Sn on the r-process nucleosynthesis
HNPS Advances in Nuclear Physics
Nuclear masses are a key aspect in the modelling of nuclear reaction rates for the r-process nucleosynthesis. High precision mass measurements drastically reduce the associated uncertainties in the modelling of r-process nucleosynthesis. We investigate the impact of nuclear mass uncertainties on neutron-capture rates calculations using a Hauser – Feshbach statistical code in the vicinity of 132Sn. Finally, we study the impact of the propagated neutron-capture reaction rates uncertainties on the r-process nucleosynthesis. We find that mass measurements with uncertainties higher than 20 keV affect the calculation of reaction rates. We also note that modelling of reaction rates can differ for more than a factor of two even for experimentally known nuclear masses.
Experimental Studies of Nuclear Physics Input for \(\gamma \)-Process Nucleosynthesis
Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016), 2017
The predictions of reaction rates for the γ process in the scope of the Hauser-Feshbach statistical model crucially depend on nuclear physics input-parameters as optical-model potentials (OMP) or γ-ray strength functions. Precise cross-section measurements at astrophysically relevant energies help to constrain adopted models and, therefore, to reduce the uncertainties in the theoretically predicted reaction rates. During the last years, several cross-sections of charged-particle induced reactions on heavy nuclei have been measured at the University of Cologne. Either by means of the in-beam method at the HORUS γ-ray spectrometer or the activation technique using the Cologne Clover Counting Setup, total and partial cross-sections could be used to further constrain different models for nuclear physics input-parameters. It could be shown that modifications on the α-OMP in the case of the 112 Sn(α,γ) reaction also improve the description of the recently measured cross sections of the 108 Cd(α,γ) and 108 Cd(α,n) reaction and other reactions as well. Partial cross-sections of the 92 Mo(p, γ) reaction were used to improve the γ-strength function model in 93 Tc in the same way as it was done for the 89 Y(p,γ) reaction.
montage: AGB Nucleosynthesis with Full s-Process Calculations
Publications of the Astronomical Society of Australia, 2009
We present montage, a post-processing nucleosynthesis code that combines a traditional network for isotopes lighter than calcium with a rapid algorithm for calculating the s-process nucleosynthesis of the heavier isotopes. The separation of those parts of the network where only neutron-capture and beta-decay reactions are significant provides a substantial advantage in computational efficiency. We present the yields for a complete set of s-process isotopes for a 3 M⊙, Z = 0.02 stellar model, as a demonstration of the utility of the approach. Future work will include a large grid of models suitable for use in calculations of Galactic chemical evolution.
ND2007, 2007
The paper deals with the investigation of the uncertainty associated to the calculation of activation and transmutation cross sections for neutron and proton induced reactions. Results of the calculations performed by means of the TALYS code and the ALICE/ASH code with different models for the description of the nuclear level densities have been extensively compared with EXFOR experimental data. Statistical deviation factors quantifying the discrepancy between experimental and theoretical results have been obtained, which can be used to define appropriate models for the nuclear reaction cross section calculation for different mass range of target nuclei. Furthermore, experimental data have been also compared against the most modern nuclear data files in order to investigate the gain in accuracy one should expect from the evaluation work with respect to the data obtained via nuclear model calculation.
Impacts of nuclear-physics uncertainties in the s-process determined by Monte-Carlo variations
arXiv (Cornell University), 2018
The s-process, a production mechanism based on slow-neutron capture during stellar evolution, is the origin of about half the elements heavier than iron. Abundance predictions for s-process nucleosynthesis depend strongly on the relevant neutron-capture and β-decay rates, as well as on the details of the stellar model being considered. Here, we have used a Monte-Carlo approach to evaluate the nuclear uncertainty in s-process nucleosynthesis. We considered the helium burning of massive stars for the weak s-process and low-mass asymptotic-giant-branch stars for the main s-process. Our calculations include a realistic and general prescription for the temperature dependent uncertainty for the reaction cross sections. We find that the adopted uncertainty for (n, γ) rates, tens of per cent on average, effects the production of s-process nuclei along the line of β-stability, and that the uncertainties in β-decay from excited state contributions, has the strongest impact on branching points.
Current quests in nucleosynthesis: Present and future neutron-induced reaction measurements
2014
We present some open questions in nucleosynthesis focused on the measurement of relevant neutron capture cross-sections and on new experimental methods. We review the recent 63 Ni(n,γ) experiment carried out at the n_TOF facility at CERN and its astrophysical implications as well as future experiments and opportunities at n_TOF. We argue some improvements in the measurement of cross-sections by activation arising from a new method for the generation of stellar neutron spectra. We show preliminary results of the experimental validation of the method. We discuss the astrophysical implications of the 181 Ta(n,γ) stellar cross-section measured with this method. Finally, we describe challenging experiments consisting of in situ radioactive ion beams and stellar neutron beams.
Sensitivity studies for r-process nucleosynthesis in three astrophysical scenarios
In rapid neutron capture, or r-process, nucleosynthesis, heavy elements are built up via a sequence of neutron captures and beta decays that involves thousands of nuclei far from stability. Though we understand the basics of how the r-process proceeds, its astrophysical site is still not conclusively known. The nuclear network simulations we use to test potential astrophysical scenarios require nuclear physics data (masses, beta decay lifetimes, neutron capture rates, fission probabilities) for all of the nuclei on the neutron-rich side of the nuclear chart, from the valley of stability to the neutron drip line. Here we discuss recent sensitivity studies that aim to determine which individual pieces of nuclear data are the most crucial for r-process calculations. We consider three types of astrophysical scenarios: a traditional hot r-process, a cold r-process in which the temperature and density drop rapidly, and a neutron star merger trajectory.
THE SENSITIVITY OF r-PROCESS NUCLEOSYNTHESIS TO THE PROPERTIES OF NEUTRON-RICH NUCLEI
Fission and Properties of Neutron-Rich Nuclei, 2013
About half of the heavy elements in the Solar System were created by rapid neutron capture, or r-process, nucleosynthesis. In the r-process, heavy elements are built up via a sequence of neutron captures and beta decays in which an intense neutron flux pushes material out towards the neutron drip line. The nuclear network simulations used to test potential astrophysical scenarios for the r-process therefore require nuclear physics data (masses, beta decay lifetimes, neutron capture rates, fission probabilities) for thousands of nuclei far from stability. Only a small fraction of this data has been experimentally measured. Here we discuss recent sensitivity studies that aim to determine the nuclei whose properties are most crucial for r-process calculations.
Compound-nuclear reaction cross sections from surrogate measurements
Reviews of Modern Physics, 2012
Nuclear reaction cross sections are important for a variety of applications in the areas of astrophysics, nuclear energy, and national security. When these cross sections cannot be measured directly or predicted reliably, it becomes necessary to develop indirect methods for determining the relevant reaction rates. The surrogate nuclear reactions approach is such an indirect method. First used in the 1970s for estimating ðn; fÞ cross sections, the method has recently been recognized as a potentially powerful tool for a wide range of applications that involve compound-nuclear reactions. The method is expected to become an important focus of inverse-kinematics experiments at rareisotope facilities. The present paper reviews the current status of the surrogate approach. Experimental techniques employed and theoretical descriptions of the reaction mechanisms involved are presented and representative cross section measurements are discussed.
Determination of the neutron-capture rate of C17 for r -process nucleosynthesis
Physical Review C, 2017
With the R 3 BLAND setup at GSI we have measured exclusive relative-energy spectra of the Coulomb dissociation of 18 C at a projectile energy around 425 AMeV on a lead target, which are needed to determine the radiative neutron-capture cross sections of 17 C into the ground state of 18 C. Those data have been used to constrain theoretical calculations for transitions populating excited states in 18 C. This allowed to derive the astrophysical cross section σ * nγ accounting for the thermal population of 17 C target states in astrophysical scenarios. The experimentally verified capture rate is significantly lower than those of previously obtained Hauser-Feshbach estimations at temperatures T9 ≤ 1 GK. Network simulations with updated neutron-capture rates and hydrodynamics according to the neutrino-driven wind model as well as the neutron-star merger scenario reveal no pronounced influence of neutron capture of 17 C on the production of second-and third-peak elements in contrast to earlier sensitivity studies.
Compound-nuclear reaction cross sections via Surrogate measurements
… Symposium on Nuclear …, 2006
Indirect methods play an important role in the determination of nuclear reaction cross sections. Often the cross section needed for a particular application cannot be measured directly since the relevant energy region is inaccessible or the target is too short-lived. This is particularly true for many reactions of interest to astrophysics. An innovative indirect approach to compoundnuclear reactions has recently been used to obtain cross sections for neutron-induced fission for various actinide targets via "Surrogate" reactions [1 -5]. In the present paper we will discuss the feasibility of using the Surrogate approach for neutron-capture reactions at low energies, relevant to the astrophysical s process. In particular, applications involving mass 90-100 nuclei will be discussed.
(n,γ) cross-sections of light p nuclei: Towards an updated database for the p process
2018
Abstract.: The nucleosynthesis of elements beyond iron is dominated by the s and r processes. However, a small amount of stable isotopes on the proton-rich side cannot be made by neutron capture and is thought to be produced by photodisintegration reactions on existing seed nuclei in the so-called "p process”. So far most of the p-process reactions are not yet accessible by experimental techniques and have to be inferred from statistical Hauser-Feshbach model calculations. The parametrization of these models has to be constrained by measurements on stable proton-rich nuclei. A series of (n,γ) activation measurements on p nuclei, related by detailed balance to the respective photodisintegrations, was carried out at the Karlsruhe Van de Graaff accelerator using the 7Li(p, n) 7Be source for simulating a Maxwellian neutron distribution of kT = 25keV. We present here preliminary results of our extended measuring program in the mass range between A = 74 and A = 132, including first e...
Nucleosynthesis at the termination point of the s process
Physical Review C, 2004
Stellar cross sections of importance with respect to the termination of the s-process reaction chain have been determined for the two cases, 208 Pb͑n , ␥͒ 209 Pb and 209 Bi͑n , ␥͒ 210 Bi g , yielding kT = 30 keV values of ͗v͘ / v T = 0.31± 0.2 mb and 2.54± 0.14 mb, respectively. The measurements were carried out by activation of Pb and Bi samples in a quasistellar neutron spectrum using gold as a cross section standard. With this technique the uncertainties reported in previous works could be considerably reduced. The measurements are complemented by a discussion of the recycling at the termination point of the s-process neutron capture chain in a 3M ᭪ and ͓Fe/ H͔ = −1.3 asymptotic giant branch star. At this metallicity, AGB stars give rise to the maximum production of s-process lead. The sensitivity of the isotopic lead abundances is discussed with respect to the remaining cross section uncertainties. The information obtained in this work is also of relevance for an assessment of the ␣ activity due to a buildup of 210 Po in Pb/ Bi cooled fast reactor systems.
We present calculations of neutron thermal cross sections, Westcott factors, resonance integrals, Maxwellianaveraged cross sections and astrophysical reaction rates for 843 ENDF materials using data from the major evaluated nuclear libraries and European activation file. Extensive analysis of newly-evaluated neutron reaction cross sections, neutron covariances, and improvements in data processing techniques motivated us to calculate nuclear industry and neutron physics quantities, produce s-process Maxwellian-averaged cross sections and astrophysical reaction rates, systematically calculate uncertainties, and provide additional insights on currently available neutron-induced reaction data. Nuclear reaction calculations are discussed and new results are presented. 0.4pt0.4pt 0pt0.4pt
Physical Review C, 2021
We present a detailed account of neutron capture experiments of astrophysical relevance on 78,80,84,86 Kr(n, γ) reactions at the border between weak and main s process. The experiments were performed with quasi-Maxwellian neutrons from the Liquid-Lithium Target (LiLiT) and the mA-proton beam at 1.93 MeV (2-3 kW) of the Soreq Applied Research Accelerator Facility (SARAF). The setup yields high-intensity ≈40 keV quasi-Maxwellian neutrons (3-5 ×10 10 n/s) closely reproducing the conditions of s-process stellar nucleosynthesis. A sample of 100 mg of atmospheric, pre-nuclear-age Kr gas contained in a Ti spherical shell was activated in the LiLiT neutron field. The abundances of long-lived Kr isotopes (81,85g Kr) were measured by atom counting via atom trap trace analysis (ATTA) at Argonne National Laboratory and low-level counting (LLC) at University of Bern. This work is the first measurement of a nuclear cross section using atom counting via ATTA. The activities of short-lived Kr isotopes (79,85m,87 Kr) were measured by γ-decay counting with a high-purity germanium detector. Maxwellian-averaged cross sections for s-process thermal energies are extracted. By comparison to reference values, our nucleosynthesis network calculations show that the experimental cross sections have a strong impact on calculated abundances of krypton and neighboring nuclides, in some cases improving agreement between theory and observations.