Nuclear Input Summary
(Conveners: Zs. Fulop, T. Rauscher)
(part of the presentation/discussion moved to the "Supernovae" section)
(some specific, important reactions are also covered in the "Stellar Evolution" section)
Presentations:
- New Instruments on the Horizon (Zs. Fulop)
--In the near future new facilities will be available with high intensity and/or
wide energy.
--FRANZ, the Frankfurt Neutron Source will use a high intensity 1.8-2.2 MeV
proton driver to produce neutrons with energies between 10-400keV.
http://exp-astro.physik.uni-frankfurt.de/franz/
--LUNA-MV, the upcoming high energy single ended underground accelerator at the Gran
Sasso Laboratory will have a terminal voltage of 3.5MV, extending the energies
reachable by the present 400kV LUNA-2 accelerator while keeping the high intensity of
alpha and proton beams. It is expected that by 2018 the first beam from LUNA-MV
will be available to study low energy alpha-induced reactions.
- Most recent Penning-trap and storage ring mass data for nuclear-astrophysics studies (K. Blaum)
--Discussing two types of facilities, storage ring (CSRe, Lanzhou) and Penning trap (ISOLTRAP, ISOLDE/CERN)
--CSRe: Beams: 56Ni, 78Kr, 86Kr, 112Sn; first measurements at proton drip line V-Se, Zr, Nb, Mo; Sp( 65As) = -90 (85) keV; remeasurements of some neutron-rich isotopes in the Ti-Cr region with improved precision. New data for nu-p process for Zr, Nb, Y isotopes to be published soon.
--ISOLTRAP: New data for Cd isotope chain across N=82, relevant for r-process.
- ab initio EOS (A. Schwenk)
--EOS is well constrained by ab initio calculations for neutron-rich conditions and nondegenerate conditions
especially interesting for mergers! General EOS band based on nuclear physics and observations; neutron star radius 9.7-13.9 km for M=1.4 Msun (±15%); Chiral EFT important for consistent neutrino-matter interactions;
Enhancement of neutrino bremsstrahlung at low densities.
--Chiral effective field theory: include long-range pion physics, few short-range couplings, fit to experiment once, systematic: can work to desired accuracy and obtain error estimates, consistent electroweak interactions and matching to lattice QCD. Frontier of ab-initio calculations at A~50.
--We provided representative equations of state: all EOS for cold matter in beta equilibrium should go through our band, constructed 3 representative EOS for users: soft, intermediate, stiff.
- EOS and supernovae (M. Hempel)
-- There are important constraints for the nuclear equation of state coming from systematics of nuclear masses, observations of neutron stars, heavy ion collision, other nuclear physics experiments, and also ab-initio theoretical nuclear physics.
-- Up to ~1.5 to 2 rho_0 the EOS is more or less under control, above our current ignorance leads to diverging results.
-- Regarding neutron star mergers and core-colapse supernovae, since a few years, we have a diversity of new EOS models available. They span the currently allowed range, whereas a few of them have nowadays to be considered as extreme cases, not compatible any more.
-- The community is just starting to study the impact of these models in supernovae and mergers. Due to the higher densities involved, the effects in neutron star mergers are more pronounced and better understood. Regarding the supernova mechanism, there is just a limited number of exploratory studies and still many open questions.
-- As a 'positive' example, constraints for the low-density symmetry energy can be used to limit the allowed range of nucleon interaction potentials, which in turn directly influence the asymptotic Ye of neutrino-driven winds.
-- Short and long term perspective: new observations (especially gravitational waves) could potentially pin down the zero temperature neutron star equation of state in the next years/decades. This will be extremely desirable for many different astrophysical scenarios. There are still additional aspects at finite temperature (thermal properties, correlations, light nuclei) important for supernovae but not relevant for neutron stars, which, however, can be addressed by heavy-ion collision experiments.
- fission and beta-decays in r-process (M. Eichler)
--Physics problem: R-process in binary compact mergers is characterised by very low Y_e. In this environment, seed nuclei can undergo fission several times before the r-process freeze-out, which means that fission treatment is an important part of network nucleosynthesis calculations. However, uncertainties in fission predictions (fission barriers, fragment mass distribution) are very large, with predictions of different model varying on a large scale.
--Present status: Recent, more elaborate fission fragment distributions lead to an improved agreement of the final abundances compared to the solar r-abundances around the second peak. However, these models take into account the experimentally proven fact that fission processes lead to the release of fission neutrons. In most low-Y_e nucleosynthesis calculations, the third r-process peak is shifted to heavier masses compared to the solar peak due to neutron captures after the r-process freeze-out. These neutrons are released only at and after the r-process freeze-out from fissioning nuclei.
--short-term aim / possibilities: An acceleration of beta-decay rates of the heaviest nuclei in the nuclear chart (Z>80) leads to a vastly improved abundance distribution concerning the third r-process peak and the rare earth peak. Due to the accelerated reaction flux, most fission neutrons are released before the freeze-out, in the context of (n,g)-(g,n) equilibrium. Therefore, there are less free neutrons available after the freeze-out to be captured by third peak material, leading to a smaller shift. The changes in beta-decays are well in line with recent half-life calculations performed by I. Panov.
--Long-term aim / possibilities: Experimental studies of beta-decay half-lives push more and more towards the neutron-rich part of the nuclear chart. These new experimental values help to test and constrain existing nuclear mass models and their extrapolations to "unknown" regions in the nuclear chart.
- Nuclear fission and beta-decays in the r-process (I. Panov)
The nucleosynthesis of the heavy nuclei in the r-process is rather complicated phenomena - not only due to the unknown detailes of the scenario, but also due to number of nuclear parameters of big number neutron rich nuclei, not measured experimentally. The parameters, like neutron cross-sections, beta-decay rates, probabilities of delayed processes and fission properties should be predicted theoretically.
Beta-decay rates is the important nuclear parameter, defining the rate of formation of new chemical element nuclei. The new data presented by Panov show the results of beta decay rates calculations and their comparison with experimental data. The advantage of the new results is the increasing of the accuracy for the short live neutron rich nuclei, which is important for the rates prediction for the nuclei, involved into the r-process. The comparison with existed RPA prediction show the close results for nuclei before lead and more fast rates for the nuclei beyond lead, that theoretically confirmed the artificially increased rates for these region, made before.
The calculated rates can be applied in nearest future for the r-process calculations and by previous evaluations should make better the agreement of theoretical yields with observations in the region of rare earth peak and probably third peak at the abundance curve.
The second point discussed by Panov was the answer of the question – how the predicted spontaneous fission rates can be checked during r-process modelling.
In the calculations of the r-process in scenario of NSM were applied 4 different sets of spontaneous fission rates, predicted by different models. In total, among different fission modes the influence of spontaneous fission on the formation of nuclei between 2nd and 3d peaks is small, but it was shown, that the yields of nuclei-cosmochronometers depend strongly from spontaneous fission rate.
It was shown, that only two sets of spontaneous fission rates, when applied to the r-process calculation can describe well the observational amounts of such a nuclei as 232Th, 234,235,238U and 244Pu. The other question which should be evaluated in nearest time – whether enough observable information to consider 244Pu as nucleus-cosmochronometer and form a new pairs for nuclear dating of Universe age?
- Neutrino oscillations (Wu):
-- physics problem: Many nucleosynthesis processes occur in the presence of strong neutrino flux, where the behavior of neutrino oscillations is complicated due to the neutrino-neutrino coherent forward scattering. However, this problem has to be addressed in order to know the yield of those nucleosynthesis processes.
-- present status: Simplified model for neutrino oscillations has been developed and used in the past decades. With those results, it suggests that
(1) neutrino oscillations have little impact on nu-p process in the neutrino driven wind.
(2) If ev sterile neutrinos exist, weak r process may be activated for early SN ejecta.
(3) may substantially change the nucleosyntheis outcome in the wind from the accretion disk.
-- short term aim/possibilities: Couple the neutrino interactions with the neutrino oscillation calculation; more realistic modelling (much better numerical method is needed); explore some fundamental issues (many particles, wave-packets...)
-- long term aim/possibilities: For SN, couple the neutrino oscillations with the hydrodynamic simulations; using neutrino signals as a probe for physics of hot & dense matter.
-Predictions of astrophysical reaction rates (T. Rauscher)
--Problems: Low energies, 0-10 MeV (reaction rates, mechanisms?), exotic Nuclei (properties needed for reactions,
6000 nuclei, 60000 reactions); Stellar Rates (thermal excitation, screening, β-decay in plasma); (De)population of isomers (26Al, 180Ta). Experiments can only provide limited information for reactions with intermediate and heavy nuclei due to thermal excitation (even at stability), theory necessary. Better exp constraints for light nuclei.
--Reaction Mechanisms: Dominating mechanism determined by nuclear level density at compound formation energy (low for magic nuclei and at driplines); Regimes: 1. Overlapping resonances: statistical model (Hauser-Feshbach), 2. Single resonances: Breit-Wigner, R-matrix; 3. Without or in between resonances: Direct reactions;
--Reaction theory is well-seasoned and tested but requires knowledge of nuclear properties which have to be predicted across the nuclear chart.
--Input for Hauser-Feshbach
Neutron widths: Spin, parity of ground state and low-lying excited states in target or final
nucleus, Optical neutron+(target) nucleus potential, Nuclear mass density distributions for certain optical potentials, Neutron separation energy (from mass differences);
Proton widths: Spin, parity of ground state and low-lying excited states in target or final
nucleus, Optical proton+(target) nucleus potential, Nuclear mass density distributions for certain optical potentials, Proton separation energy (from mass differences);
Alpha widths: Spin, parity of ground state and low-lying excited states in target or final
nucleus, Optical alpha+(target) nucleus potential, Nuclear mass density distributions for certain optical potentials, Alpha separation energy (from mass differences);
Photon (Gamma) Width: E1 strength function at about Sproj+Eproj-3 MeV (pygmy resonance?), Nuclear level density (or levels) at same energy, M1 strength functions;
Remark: large uncertainty for neutron captures (s-process and r-process) in low-energy tail of strength function.
--Input for Resonance Widths (Breit-Wigner)
Separation energies (from mass differences); Close to and within astrophysical energy window: Resonance energy and Resonance partial widths; If widths have to be calculated: Ground state and excited states in target and final nucleus (energies, spins, parities), Depending on type of calculated width, similar input as already listed for averaged widths, Spectroscopic factors
Remark 1: Uncertainty propagation from MC input variation provided already by STARLIB for lighter nuclei, Remark 2: Usually simple Breit-Wigner formula used or R-Matrix
--Input for Direct Capture
Separation energies (from nuclear mass differences), Spins, Parities, Energies of ground state and low-lying excited states in target and final nucleus, Spectroscopic factors
ATTENTION: Spectroscopic factors have also to be known for excited states in TARGET nucleus (usual spectroscopic factors are measured/calculated relative to target ground state)!
Effective interaction potential between projectile and target (perhaps calculated from nuclear mass density distribution) (This is not necessarily the same as the optical potential used in Hauser-Feshbach
theory but has to give total reaction cross section consistent with optical model).
--Discussion points:
---Propagation of nuclear uncertainties into final abundance uncertainties: first attempts made with Monte Carlo studies, large-scale studies planned.
---Development of global (ab initio or param.) predictions in the future? Identification of relevant key nuclei needed which help constrain theory developments; difficult to treat generally because there are many different nucleosynthesis processes and reaction mechanisms with different requirements.
---Experimental input needed for comparison to predictions