0000000000200920
AUTHOR
Michael Wiescher
rp-process nucleosynthesis at extreme temperature and density conditions
We present nuclear reaction network calculations to investigate the influence of nuclear structure on the rp-process between Ge and Sn in various scenarios. Due to the lack of experimental data for neutron-deficient nuclei in this region, we discuss currently available model predictions for nuclear masses and deformations as well as methods of calculating reaction rates (Hauser-Feshbach) and beta-decay rates (QRPA and shell model). In addition, we apply a valence nucleon (NpNn) correlation scheme for the prediction of masses and deformations. We also describe the calculations of 2p-capture reactions, which had not been considered before in this mass region. We find that in X-ray bursts 2p-c…
Comparison of electromagnetic and nuclear dissociation of Ne-17
8 pags., 10 figs., 3 tabs.
The astrophysical implications of low-energy resonances in 22Ne + α
Abstract The 22 Ne( 6 Li, d) α-transfer reaction has been used to search for α-unbound levels in 26 Mg of importance for resonant α-capture on 22 Ne in stellar helium burning. To determine the resonance strengths of the observed states the 22 Ne(α, n) 25 Mg reaction was investigated in the energy range between 600 and 900 keV. One resonance was identified and its strength determined. The astrophysical implications of the present results are discussed.
Neutron capture cross section measurements for nuclear astrophyisics at CERN n_TOF
A series of neutron capture cross section measurements of interest to nuclear astrophysics have been recently performed at n_TOF, the neutron spallation source operating at CERN. The low repetition frequency of the proton beam driver, the extremely high instantaneous neutron flux, and the low background conditions in the experimental area are optimal for capture cross section measurements on low-mass or radioactive samples. An overview of the measurements performed during the two experimental campaigns in 2002 and 2003 is presented with special emphasis on the measurement of the capture cross sections of the Os isotopes relevant for the cosmochronology based on the Re/Os clock. http://www.s…
Helium burning of22Ne
The22Ne(α, γ)26Mg and22Ne(α, n)25Mg reactions were investigated forE α(lab) from 0.71 to 2.25 MeV. Neon gas enriched to 99% in22Ne was recirculated in a differentially pumped gas target system of the extended type. Theγ-ray transitions were observed with Ge(Li) detectors and the neutrons with3He ionization chambers. A previously known resonance at ER(lab)=2.05 MeV was verified and 15 new resonances were found in the energy range covered, with the lowest at ER(lab)=0.83 MeV. Information on resonance energies, widths, strengths,γ-ray branching ratios, as well asJ π assignments, is reported. The energy range investigated corresponds to the important temperature range ofT 9 from 0.3 to 1.4 (109…
Study of the β-delayed neutron decay of 17C and 18C
Abstract The β-delayed neutron decays of 17C and 18C have been studied using a time-of-flight array with a high detection efficiency. The 17C and 18C ions were produced by fragmentation of an E A = 69 MeV 22Ne beam. Transitions to several neutron unbound states have been observed for the first time for both decays with total branching ratios of (10.8 ± 2.2)% and (21.4 ± 4.4)%. Half-lives of 193 ± 6 ms and 92 ± 2 ms were found for 17C and 18C, respectively. The results are compared with previous measurements of the β-decays and with shell-model calculations.
Nuclear physics far from stability and explosive nucleosynthesis processes
In this paper, we discuss the astrophysically relevant nuclear-physics input for a selected set of explosive nucleosynthesis scenarios leading to rapid protonand neutron-capture processes. Observables (like,e.g., luminosity curves or abundance distributions) witness the interplay between nuclear-structure aspects far from β-stability and the appropriate astrophysical environments, and can give guidance to and constraints on stellar conditions and/or key features of reaction and decay data for radioactive isotopes.
Study of the $^{15}$O(2p, γ )$^{17}$Ne cross section by Coulomb dissociation of $^{17}$Ne for the rp process of nucleosynthesis
Acta physica Polonica / B 45(2), 229 - 234 (2014). doi:10.5506/APhysPolB.45.229
The triple-alpha-reaction at low temperatures.
We have studied the triple-α-reaction at low temperatures which is of importance on accreting white dwarfs and neutron stars. Although we have improved a recent investigation of Nomoto, Thielemann and Miyaji on several points, we find a reaction rate for the relevant temperature range (T=107−108K) which is rather similar to the previous result. In particular, our improved study confirms that helium might be ignited on accreting white dwarfs at temperaturesT≦4.107 K.
Interpretation of the SolarCa48/Ca46Abundance Ratio and the Correlated Ca-Ti Isotopic Anomalies in the EK-1-4-1 Inclusion of the Allende Meteorite
$\ensuremath{\beta}$-delayed neutron-emission probabilities of neutron-rich S to K isotopes are calculated with nuclear-structure effects taken into account. These results strongly affect predictions made in high-neutron-density astrophysical scenarios for isotopic abundances of several elements. In particular, it is demonstrated that the solar abundance ratio $^{48}\mathrm{Ca}$/$^{46}\mathrm{Ca}$ as well as the correlated Ca and Ti isotopic anomalies can be explained by the same nucleosynthesis process.
Experimental study of the 15O(2p, γ)17Ne cross section by Coulomb Dissociation for the rp process
6th Nuclear Physics in Astrophysics Conference (NPA), Lisbon, Portugal, 19 May 2013 - 24 May 2013; Journal of physics / Conference Series 665, 012046 (2016). doi:10.1088/1742-6596/665/1/012046
Neutron capture cross sections for neutron-rich isotopes
Average continuum (Hauser-Feshbach) and resonance (Breit-Wigner) neutron capture rates for neutron-rich isotopes, determined on the basis of recent experimental nuclear physics input parameters, are compared to earlier theoretical reaction rates commonly used in astrophysical model computations.
Measurement of the 151Sm n,gamma 152Sm cross section at n_TOF
The 151 Sm(n, γ ) 152 Sm cross section, which is important for the interpretation of the 151 Sm branching as an s -process thermometer, was measured from 1 eV up to 1 MeV at the innovative n_TOF facility at CERN. Based on these data, the Maxwellian-averaged cross section at k T = 30 keV is found to be 3100±160 mb. This value can be used to constrain the thermodynamical conditions in Asymptotic Giant Branch (AGB) stars during He-shell burning.
Nucleosynthesis of proton-rich nuclei. Experimental results on the rp-process
Experience NSCL; International audience; We report in this study the nuclear properties of proton-rich isotopes located along the rp-process path. The experiments have recently been performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The level properties above the proton separation energy of the nuclei 30S, 36K and 37Ca were measured with precision of < 10 keV. This will allow a reduction in the determination of the astrophysical (p, ) reaction rate under rp-process conditions.
Coulomb dissociation of P 27 at 500 MeV/u
J. Marganiec et al. ; 15 págs.; 14 figs.; 6 tabs.
The endpoint of the rp-process
Abstract 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 92 Mo and 96 Ru t…
Reaction Rates in the RP-Process and Nucleosynthesis in Novae
Nuclear structure information available on proton rich unstable nuclei were used to evaluate thermonuclear reaction rates in the rp-process in explosive hydrogen burning. These rates were applied in a systematic analysis for a variety of temperature conditions, appropriate to nova explosions, to study nucleosynthesis for isotopes of Ne Na Mg Al Si. The results are discussed in comparison with recent observations of elemental abundances in nova ejecta.
The neutron long counter NERO for studies of neutron emission in the r-process
Abstract The neutron long counter NERO was built at the National Superconducting Cyclotron Laboratory (NSCL), Michigan State University, for measuring β -delayed neutron-emission probabilities. The detector was designed to work in conjunction with a β -delay implantation station, so that β decays and β -delayed neutrons emitted from implanted nuclei can be measured simultaneously. The high efficiency of about 40%, for the range of energies of interest, along with the small background, are crucial for measuring β -delayed neutron emission branchings for neutron-rich r-process nuclei produced as low intensity fragmentation beams in in-flight separator facilities.
Measurements of the 90,91,92,94,96 Zr n, gamma cross-sections at n_TOF
Neutron capture cross sections of the 90,91,92,94,96Zr have been measured over the energy range from 1 eV to 1 MeV at the spallation neutron facility n TOF at CERN in 2003. The innovative features of the neutron beam, in particular the high instantaneous flux, the high energy resolution and low background, together with improvements of the neutron sensitivity of the capture detectors make this facility unique for neutron-induced reaction cross section measurements with much improved accuracy. The preliminary results of the Zr measurements show capture resonance strengths generally smaller than in previous measurements. Peer Reviewed
Coulomb and nuclear excitations of narrow resonances in 17Ne
Physics letters / B 759, 200 - 205 (2016). doi:10.1016/j.physletb.2016.05.073
Properties ofNe22(α,n)25Mg resonances
The $^{22}\mathrm{Ne}$(\ensuremath{\alpha},n${)}^{25}$Mg reaction has been investigated in the energy range ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}^{\mathrm{lab}}$=0.73--2.10 MeV using high-resolution $^{3}\mathrm{He}$ ionization chambers. Sixteen resonances have been observed in the three neutron channels to the ground state and the first two excited levels of $^{25}\mathrm{Mg}$. From the analysis of neutron angular distributions, spin and parity assignments could be made for eight resonances. Furthermore, partial widths as well as absolute cross sections have been obtained yielding resonance strengths for the observed levels. The role of the $^{22}\mathrm{Ne}$(\ensuremath{\alpha},n) …