The new p-process database of KADoNiS

The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars) project is an online database (www.kadonis.org) for cross sections relevant to the s-process and the p-process. The first version was an updated sequel to the previous Bao et al. [1] compilations from 1987 and 2000 for (n; g) cross sections relevant to Big Bang and s-process nucleosynthesis. The first update, KADoNiS v0.2, was published in 2006 [2]. It contained mainly Maxwellian averaged (n; g) cross sections relevant to the s-process, and some experimental charged particle induced reaction relevant to the p-process. After that a second update was presented in 2009 [3]. Recently, we started to collect and review all existing experimental data relevant for p-process nucleosynthesis and to provide a user-friendly database based on the KADoNiS framework. The p-process part of the KADoNiS database is currently being extended and will include all available experimental data from (p; g), (p;n), (p;a), (a,g), (a;n) and (a; p) reactions in or close to the respective Gamow window

The “Beta-Delayed Neutrons at RIKEN” project (BRIKEN): conquering the most exotic beta-delayed neutron-emitters

Among the main missions of modern radioactive isotope facilities is the exploration of properties of yet unknown isotopes on the neutron-rich side of the chart of nuclides. However, going more neutron-rich also means that the neutron separation energy decreases until it reaches the dripline at Sn = 0 MeV. If the neutron separation energy gets lower than the ß-decay energy window (Qß value), a new decay mechanism can occur: the emission of neutrons after ß-decay. These “ß-delayed neutron” (ßn) emitters play a crucial role in nuclear structure, nuclear astrophysics, and for nuclear reactor applications.Postprint (published version

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

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(n, γ)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

Recent Efforts in Data Compilations for Nuclear Astrophysics

Some recent efforts in compiling data for astrophysical purposes are introduced, which were discussed during a JINA-CARINA Collaboration meeting on "Nuclear Physics Data Compilation for Nucleosynthesis Modeling" held at the ECT* in Trento/ Italy from May 29th- June 3rd, 2007. The main goal of this collaboration is to develop an updated and unified nuclear reaction database for modeling a wide variety of stellar nucleosynthesis scenarios. Presently a large number of different reaction libraries (REACLIB) are used by the astrophysics community. The "JINA Reaclib Database" on http://www.nscl.msu.edu/\~nero/db/ aims to merge and fit the latest experimental stellar cross sections and reaction rate data of various compilations, e.g. NACRE and its extension for Big Bang nucleosynthesis, Caughlan and Fowler, Iliadis et al., and KADoNiS. The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars, http://nuclear-astrophysics.fzk.de/kadonis) project is an online database for neutron capture cross sections relevant to the s process. The present version v0.2 is already included in a REACLIB file from Basel university (http://download.nucastro.org/astro/reaclib). The present status of experimental stellar $(n,\gamma)$ cross sections in KADoNiS is shown. A "high priority list" for measurements and evaluations for light charged-particle reactions set up by the JINA-CARINA collaboration is presented. The central web access point to submit and evaluate new data is provided by the Oak Ridge group via the http://www.nucastrodata.org homepage. "Workflow tools" aim to make the evaluation process transparent and allow users to follow the progress.Comment: Proceedings 10th Int. Symp. on Origin of Matter and Evolution of Galaxies OMEG07, Sapporo/ Japan, December 4-7 200

Uncertainty Quantification of Mass Models using Ensemble Bayesian Model Averaging

Developments in the description of the masses of atomic nuclei have led to various nuclear mass models that provide predictions for masses across the whole chart of nuclides. These mass models play an important role in understanding the synthesis of heavy elements in the rapid neutron capture ($r$-) process. However, it is still a challenging task to estimate the size of uncertainty associated with the predictions of each mass model. In this work, a method to quantify the mass uncertainty using \textit{ensemble Bayesian model averaging} (EBMA) is introduced. This Bayesian method provides a natural way to perform model averaging, selection, calibration, and uncertainty quantification, by combining the mass models as a mixture of normal distributions, whose parameters are optimized against the experimental data, employing the Markov chain Monte Carlo (MCMC) method using the No-U-Turn sampler (NUTS). The average size of our best uncertainty estimates of neutron separation energies based on the AME2003 data is 0.48 MeV and covers 95% of new data in the AME2020. The uncertainty estimates can also be used to detect outliers with respect to the trend of experimental data and theoretical predictions.Comment: 12 pages, 6 figure

First determination of ß -delayed multiple neutron emission beyond A=100 through direct neutron measurement: the P2n value of Sb 136

Background: ß-delayed multiple neutron emission has been observed for some nuclei with A=100, being the 100Rb the heaviest ß2n emitter measured to date. So far, only 25P2n values have been determined for the ˜300 nuclei that may decay in this way. Accordingly, it is of interest to measure P2n values for the other possible multiple neutron emitters throughout the chart of the nuclides. It is of particular interest to make such a measurement for nuclei with A>100 to test the predictions of theoretical models and simulation tools for the decays of heavy nuclei in the region of very neutron-rich nuclei. In addition, the decay properties of these nuclei are fundamental for the understanding of astrophysical nucleosynthesis processes, such as the r-process, and safety inputs for nuclear reactors.Postprint (published version

Measurement of the stellar Ni 58 (n,γ) Ni 59 cross section with accelerator mass spectrometry

The Ni58(n,γ)Ni59 cross section was measured with a combination of the activation technique and accelerator mass spectrometry (AMS). The neutron activations were performed at the Karlsruhe 3.7 MV Van de Graaff accelerator using the quasistellar neutron spectrum at kT=25 keV produced by the Li7(p,n)Be7 reaction. The subsequent AMS measurements were carried out at the 14 MV tandem accelerator of the Maier-Leibnitz Laboratory in Garching using the gas-filled analyzing magnet system (GAMS). Three individual samples were measured, yielding a Maxwellian-averaged cross section at kT=30 keV of (σ)30keV = 30.4 (23)syst(9)stat mbarn. This value is slightly lower than two recently published measurements using the time-of-flight (TOF) method, but agrees within the uncertainties. Our new results also resolve the large discrepancy between older TOF measurements and our previous value

Presolar Silicon Carbide Grains of Types Y and Z: Their Molybdenum Isotopic Compositions and Stellar Origins

We report Mo isotopic compositions of 37 presolar SiC grains of types Y (19) and Z (18), rare types commonly argued to have formed in lower-than-solar metallicity asymptotic giant branch (AGB) stars. Direct comparison of the Y and Z grain data with data for mainstream grains from AGB stars of close-to-solar metallicity demonstrates that the three types of grains have indistinguishable Mo isotopic compositions. We show that the Mo isotope data can be used to constrain the maximum stellar temperatures (TMAX) during thermal pulses in AGB stars. Comparison of FRUITY Torino AGB nucleosynthesis model calculations with the grain data for Mo isotopes points to an origin from low-mass (~1.5-3 Msun) rather than intermediate-mass (>3-~9 Msun) AGB stars. Because of the low efficiency of 22Ne({\alpha},n)25Mg at the low TMAX values attained in low-mass AGB stars, model calculations cannot explain the large 30Si excesses of Z grains as arising from neutron capture, so these excesses remain a puzzle at the moment.Comment: The Astrophysical Journal (Accepted

First results from the HENSA/ANAIS collaboration at the Canfranc Underground Laboratory

The HENSA/ANAIS collaboration aims for the precise determination of the neutron flux that could affect ANAIS-112, an experiment looking for the dark matter annual modulation using NaI(Tl) scintillators. In this work, the first measurements of the neutron flux and Monte Carlo simulations of the neutron spectrum are reported.Peer ReviewedPostprint (published version