Nucleosynthesis In X-ray Bursts Research Articles

The rate of the astrophysical 48Cr(p,γ)49Mn reaction and its influence on the potential A = 48 waiting point in the rp process

We have performed a detailed γ-ray spectroscopy study of the nucleus, 49Mn, using the GRETINA tracking array and FMA recoil separator. With this powerful new setup, low-spin excited states, which are most relevant for astrophysical processes, have been identified for the first time, including four proton-unbound levels, corresponding to key astrophysical resonances in the 48Cr(p,γ)49Mn reaction. Of these four levels, two were found to dominate the 48Cr(p,γ)49Mn reaction for temperatures, T = 0.2 − 1.4 GK, and uncertainties in the rate have been reduced by more than 3 orders of magnitude. Specifically, γ decays were observed from 1/2+ and 3/2− excited states at Ex = 2570.9(26) keV and 2595.8(21) keV, corresponding to an ℓ = 0 and ℓ = 1 resonance in the 48Cr + p system at Er = 482.9(84) keV and 507.9(83) keV, respectively. Present simulations of Type-I X-ray burst nucleosynthesis indicate that the newly defined 48Cr(p,γ) reaction rate is sufficiently fast to drive the flow of material towards higher masses in such environments. Consequently, despite the relatively long half life of 48Cr, we now do not expect a strong waiting point in the rp process at A = 48.

Study of the ^{22}Mg Waiting Point Relevant for X-Ray Burst Nucleosynthesis via the ^{22}Mg(α,p)^{25}Al Reaction.

The ^{22}Mg(α,p)^{25}Al reaction rate has been identified as a major source of uncertainty for understanding the nucleosynthesis flow in Type-I x-ray bursts. We report a direct measurement of the energy- and angle-integrated cross sections of this reaction in a 3.3-6.9MeV center-of-mass energy range using the MUlti-Sampling Ionization Chamber (MUSIC). The new ^{22}Mg(α,p)^{25}Al reaction rate is a factor of ∼4 higher than the previous direct measurement of this reaction within temperatures relevant for x-ray bursts, resulting in the ^{22}Mg waiting point of x-ray burst nucleosynthesis flow to be significantly bypassed via the (α,p) reaction.

Machine learning approach to pattern recognition in nuclear dynamics from the ab initio symmetry-adapted no-core shell model

A novel machine learning approach is used to provide further insight into atomic nuclei and to detect orderly patterns amidst a vast data of large-scale calculations. The method utilizes a neural network that is trained on ab initio results from the symmetry-adapted no-core shell model (SA-NCSM) for light nuclei. We show that the SA-NCSM, which expands ab initio applications up to medium-mass nuclei by using dominant symmetries of nuclear dynamics, can reach heavier nuclei when coupled with the machine learning approach. In particular, we find that a neural network trained on probability amplitudes for $s$-and $p$-shell nuclear wave functions not only predicts dominant configurations for heavier nuclei but in addition, when tested for the $^{20}$Ne ground state, it accurately reproduces the probability distribution. The nonnegligible configurations predicted by the network provide an important input to the SA-NCSM for reducing ultra-large model spaces to manageable sizes that can be, in turn, utilized in SA-NCSM calculations to obtain accurate observables. The neural network is capable of describing nuclear deformation and is used to track the shape evolution along the $^{20-42}$Mg isotopic chain, suggesting a shape-coexistence that is more pronounced toward the very neutron-rich isotopes. We provide first descriptions of the structure and deformation of $^{24}$Si and $^{40}$Mg of interest to x-ray burst nucleosynthesis, and even of the extremely heavy nuclei such as $^{166,168}$Er and $^{236}$U, that build upon first principles considerations.

An implantation Diamond detector as a beam monitor for an intense radioactive ion beam

We present the characterization of a Diamond detector and its response as a beam rate monitor with full stopping of radioactive ion beams of high intensity. The detector has been implemented in the VAMOS focal plane at GANIL and utilised in conjunction with AGATA and MUGAST detector systems. In the present experiment, for the first time, the beam has been fully stopped, rather than being recorded by a transmission detector. The Diamond detector has been tested for use as a particle counter for monitoring a high intensity, radioactive ion beam in the study of the alpha transfer reaction 7Li(15O,t)19Ne. The present experiment, which took place in July 2019, has used a 15O radioactive beam with a high intensity of 107 particles per second due to the weak reaction population and it has been measured using the VAMOS spectrometer and the AGATA and MUGAST arrays. Detailed monitoring of beam intensities in the range of 106 – 107 particles per second is particularly challenging in radioactive ion beam experiments. Thus, the chosen method involves the diamond detector due to its sub-nanosecond response time as well as its radiation hardness. The study of the alpha transfer reaction 7Li(15O,t)19Ne will be performed to determine the radiative alpha capture rate on 15O which is a key breakout route from the Hot-CNO cycle which leads to a explosive nucleosynthesis in X-ray bursts.

Accurate mass measurements of exotic nuclei with the CSRe in Lanzhou

With the successful commissioning of the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou accurate mass measurements of short-lived nuclides became possible by employing isochronous mass spectrometry. A series of experiments have been carried out in the past few years using projectile fragmentation of 78Kr, 86Kr, 58Ni, and 112Sn beams. Masses of 16 nuclides have been obtained for the first time. The mass data have been used as an input for dedicated nuclear structure and astrophysics studies, providing for instance new insights into the rp-process of nucleosynthesis in X-ray bursts. Here we review the so far conducted experiments and the main results, as well as outline the plans for future experiments.

Studying X-ray Burst Nucleosynthesis in the Laboratory

Type I X-ray bursts are the most common explosions in the Galaxy; however, the nucleosynthesis that occurs during the thermonuclear runaway and explosion is poorly understood. In this proceedings we discuss current experimental efforts and techniques that are being used to study X-ray burst nucleosynthesis in the laboratory. Specifically, radioactive ion beam techniques that have recently been developed have allowed the study of some of the most important (α, p) reactions in X-ray bursts for the first time.

Direct radiative proton capture 23Al(p,γ)24Si studied via one-proton nuclear breakup of 24Si

We present the results of an experimental work that studied the direct component of the radiative proton capture reaction 23Al(p,γ)24Si for its relevance in X-ray burst nucleosynthesis. The experiment was performed at GANIL using one-proton nuclear breakup reaction at intermediate energies to determine the Asymptotic Normalization Coefficient (ANC) of the system 24Si→23Al + p. Using the ANC, we evaluated the corresponding astrophysical S factor and reaction rate.

The Effects of Variations in Nuclear Processes on Type I X‐Ray Burst Nucleosynthesis

Type I X-ray bursts are violent stellar events that take place in the H/He-rich envelopes of accreting neutron stars. We have investigated the role played by uncertainties in nuclear processes on the nucleosynthesis accompanying these explosive phenomena. Two different approaches have been adopted, in the framework of postprocessing calculations. In the first one, nuclear rates are varied individually within uncertainties. Ten different models, covering the characteristic parameter space for these stellar events, have been considered. The second, somewhat complementary approach involves a Monte Carlo code in which all nuclear rates are randomly varied within uncertainty limits simultaneously. All in all, about 50,000 postprocessing calculations, with a network containing 606 nuclides (H to 113Xe) and more than 3500 nuclear processes, have been performed in this work. A brief comparison between both procedures is outlined together with an overall account of the key nuclear reactions whose uncertainties have the largest impact in our X-ray burst nucleosynthesis studies.

The effects of variations in nuclear processes on type I X-ray burst nucleosynthesis

The effects of variations in nuclear processes on type I X-ray burst nucleosynthesis

Stellar Reactions with Short-Lived Nuclei:17F(p,α)14O

A method has been developed that can provide beams of many short-lived nuclei of interest in nucleosynthesis along the $\mathrm{rp}$ process path. With a ${}^{17}\mathrm{F}$ beam $({T}_{1/2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}64\mathrm{s}$) the excitation function of the ${}^{17}\mathrm{F}(p,\ensuremath{\alpha}{)}^{14}\mathrm{O}$ reaction was measured to determine properties of excited states in ${}^{18}\mathrm{Ne}$. These states influence the rate of the ${}^{14}\mathrm{O}(\ensuremath{\alpha},p{)}^{17}\mathrm{F}$ reaction which is important for understanding energy generation and nucleosynthesis in x-ray bursts. The present direct measurements yield a pattern of resonances and cross sections which differ substantially from previous estimates.

CURRENT QUESTS IN NUCLEAR ASTROPHYSICS AND EXPERIMENTAL APPROACHES

▪ Abstract This review summarizes current problems and questions in experimental nuclear astrophysics. It focuses on the present need for experimental data, emphasizing novel methods and approaches. Starting with an overview on nuclear energy generation and nucleosynthesis in an astrophysical plasma, the discussion concentrates on crucial problems related to the various aspects of stellar evolution, from the hydrostatic stage through the advanced burning scenarios up to and including the supernova explosion mechanism. Innovative experimental approaches are needed to pursue the associated questions in stellar nucleosynthesis. Particular emphasis is given to the potential use of radioactive ion beams and their importance for characterizing explosive nucleosynthesis in X-ray bursts and supernovae.

The endpoint of the rp-process

The endpoint of rp-process nucleosynthesis in X-ray bursts determines the fuel consumption, the energy generation, and the abundance pattern of the produced nuclei. To investigate the time structure of rp-process nucleosynthesis, we used a nuclear reaction network including nuclei from H to Sn. We found that if 2p-capture reactions are included, the synthesis of nuclei heavier than Kr proceeds faster than previously thought. Therefore, in most X-ray bursts large amounts of nuclei in the A=80–100 region are expected to be produced. With an escape factor of about 1%, X-ray bursts could account for the large observed solar system abundances of the light p-nuclei like 92Mo and 96Ru that cannot be produced sufficiently in other p-process scenarios.