Impact of level densities and γ\gamma-strength functions on rr-process simulations

Studies attempting to quantify the sensitivity of the $r$-process abundances to nuclear input have to cope with the fact that the theoretical models they rely on, rarely come with confidence intervals. This problem has been dealt with by either estimating these intervals and propagating them statistically to the final abundances using reaction networks within simplified astrophysical models, or by running more realistic astrophysical simulations using different nuclear-physics models consistently for all the involved nuclei. Both of these approaches have their strengths and weaknesses. In this work, we use the reaction network code SkyNet to run $r$-process calculations for five trajectories using 49 different neutron-capture rate models. Our results shed light on the importance of taking into account shell effects and pairing correlations in the network calculations.Comment: 11 pages, 7 figure

Experimentally constrained 165,166Ho(n,γ)^{165,166}\text{Ho}(n,\gamma) rates and implications for the ss process

The $\gamma$-ray strength function and the nuclear level density of $^{167}$Ho have been extracted using the Oslo method from a $^{164}\text{Dy}(\alpha,p\gamma)^{167}$Ho experiment carried out at the Oslo Cyclotron Laboratory. The level density displays a shape that is compatible with %can be approximated with the constant temperature model in the quasicontinuum, while the strength function shows structures indicating the presence of both a scissors and a pygmy dipole resonance. Using our present results as well as data from a previous $^{163}\text{Dy}(\alpha,p\gamma)^{166}$Ho experiment, the $^{165}\text{Ho}(n,\gamma)$ and $^{166}\text{Ho}(n,\gamma)$ MACS uncertainties have been constrained. The possible influence of the low-lying, long-lived 6~keV isomer $^{166}$Ho in the $s$ process is investigated in the context of a 2~$M_\odot$, [Fe/H]=-0.5 AGB star. We show that the newly obtained $^{165}\text{Ho}(n,\gamma)$ MACS affects the final $^{165}$Ho abundance, while the $^{166}\text{Ho}(n,\gamma)$ MACS only impacts the enrichment of $^{166,167}$Er to a limited degree due to the relatively rapid $\beta$ decay of the thermalized $^{166}$Ho at typical $s$-process temperatures.Comment: 11 pages, submitted to Physical Reviews

Neutron Stars - Study of the Mass-Radius Relation and Mean-Field Approaches to the Equation of State

The structure and the relation between the total mass, the radius and the central energy density of a neutron star may be found by numerically solving a set of three coupled differential equations. One of these equations is the equation of state, relating the pressure to the energy density. In this thesis, after introducing some important concepts of general relativity, quantum mechanics, quantum field theory and thermal field theory, we will discuss the equation of state using different models. The first is the sigma-omega model, later expanded to include leptons and the rho meson in what in the literature is referred to as npe-mu matter. In the last part we also consider the shift in the vacuum energy due to the presence of matter. Some focus has been given to the first-order phase transition in neutron matter as conceived in the paper from Chin et al. (1974). Although unphysical, the theory behind the phase transition is a first step for understanding more complex phase transitions between hadronic and quark matter in hybrid stars

Perspectives and Trends in the History of Science

Perspectives and Trends in the History of Scienc

Indirect measurement of the (

Sensitivity studies of the i process have identified the region around 135I as a bottleneck for the neutron capture flow. Nuclear properties such as the Maxwellian-averaged cross section (MACS) are key to constrain the uncertainties in the final abundance patterns. With the Oslo method, we are able to indirectly measure such properties for the nuclei involved in this process. From the 124Sn(α, pγ)127Sb reaction data we extract the nuclear level density and γ-ray strength function for 127Sb. The level density at higher excitation energies is compatible with the constant-temperature model, while the γ-ray strength function presents features like an upbend and a pygmy-like structure below S n. From these two quantities we can calculate the MACS for the 126Sb(n, γ)127Sb reaction using the Hauser-Feshbach formalism, and constrain its uncerainties from the theoretical ones. Libraries such as JINA REACLIB, TENDL and BRUSLIB agree well with the experimental results, while ENDF/B-VIII.0 predicts a higher rate

Indirect measurement of the (

Sensitivity studies of the i process have identified the region around 135I as a bottleneck for the neutron capture flow. Nuclear properties such as the Maxwellian-averaged cross section (MACS) are key to constrain the uncertainties in the final abundance patterns. From the 124Sn(α, pγ)127Sb reaction we are able to indirectly measure the nuclear level density and γ-ray strength function for 127Sb using the Oslo method. From these two quantities we can calculate the MACS for the 126Sb(n, γ)127Sb reaction using the Hauser-Feshbach formalism, constrain its uncertainties and compare it to libraries such as JINA REACLIB, TENDL and BRUSLIB

Indirect measurement of the (n,γ)127Sb cross section

Nuclei in the 135I region have been identified as being a possible bottleneck for the i process. Here we present an indirect measurement for the Maxwellian-averaged cross section of 126Sb(n,γ). The nuclear level density and the γ-ray strength function of 127Sb have been extracted from 124Sn(α,pγ)127Sb data using the Oslo method. The level density in the low-excitation-energy region agrees well with known discrete levels, and the higher-excitation-energy region follows an exponential curve compatible with the constant-temperature model. The strength function between Eγ≈1.5–8.0 MeV presents several features, such as an upbend and a possibly double-peaked pygmy-like structure. None of the theoretical models included in the nuclear reaction code talys seem to reproduce the experimental data. The Maxwellian-averaged cross section for the 126Sb(n,γ)127Sb reaction has been experimentally constrained by using our level-density and strength-function data as input to talys. We observe a good agreement with the jina reaclib, tendl, and bruslib libraries, while the endf/b-viii.0 library predicts a significantly higher rate than our results