Accurate stopping power calculations for antiprotons and protons

© Published under licence by IOP Publishing Ltd. The convergent close-coupling method is applied to calculate antiproton and proton stopping cross sections for atomic and molecular targets. Excellent agreement with experimental measurements is obtained for antiprotons in helium while unexpectedly large disagreement is found for the hydrogen molecule, which is inconsistent with very good agreement between our ionisation cross section and the experiment

Trojan Horse as an indirect technique in nuclear astrophysics. Resonance reactions

The Trojan Horse method is a powerful indirect technique that provides information to determine astrophysical factors for binary rearrangement processes $x + A \to b + B$ at astrophysically relevant energies by measuring the cross section for the Trojan Horse reaction $a + A \to y+ b + B$ in quasi-free kinematics. We present the theory of the Trojan Horse method for resonant binary subreactions based on the half-off-energy-shell R matrix approach which takes into account the off-energy-shell effects and initial and final state interactions.Comment: 6 pages and 1 figur

Astrophysical 3He(α,γ)7Be and 3H(α,γ)7Li direct capture reactions in a potential-model approach

The astrophysical 3He(α,γ)7Be and 3H(α,γ)7Li direct capture processes are studied in the framework of the two-body model with potentials of a simple Gaussian form, which describe correctly the phase shifts in the s, p, d, and f waves, as well as the binding energy and the asymptotic normalization constant of the ground p3/2 and the first excited p1/2 bound states. It is shown that the E1transition from the initial s wave to the final p waves is strongly dominant in both capture reactions. On this basis the s-wave potential parameters are adjusted to reproduce the new data of the LUNA Collaboration around 100 keV and the newest data at the Gamov peak estimated with the help of the observed neutrino fluxes from the sun, S34(23+6−5keV)=0.548±0.054 keV b for the astrophysical Sfactor of the capture process 3He(α,γ)7Be. The resulting model describes well the astrophysical Sfactor in the low-energy big-bang nucleosynthesis region of 180–400 keV; however, it has a tendency to underestimate the data above 0.5 MeV. The energy dependence of the S factor is mostly consistent with the data and the results of the no-core shell model with continuum, but substantially different from the fermionic molecular dynamics model predictions. Two-body potentials, adjusted for the properties of the 7Be nucleus, 3He+α elastic scattering data, and the astrophysical S factor of the 3He(α,γ)7Bedirect capture reaction, are able to reproduce the properties of the 7Li nucleus, the binding energies of the ground 3/2− and first excited 1/2− states, and phase shifts of the 3H+α elastic scattering in partial waves. Most importantly, these potential models can successfully describe both absolute value and energy dependence of the existing experimental data for the mirror astrophysical 3H(α,γ)7Licapture reaction without any additional adjustment of the parameters

Calculation of Energy and Angular Distributions of Electrons Produced in Intermediate-Energy p + H₂ Collisions

We extend the two-centre wave-packet convergent close-coupling approach to doubly differential ionisation in proton collisions with H2 to intermediate projectile energies. The results for the doubly differential cross section at projectile energies from 48 to 200 keV are presented as a function of the energy and angle of emitted electrons. We consider a wide range of emission angles from 10 to 160∘, and compare our results to experimental data, where available. Excellent agreement between the presented results and the experimental data was found, especially for emission angles less than 130∘. For very large backward emission angles our calculations tended to slightly overestimate the experimental data when energetic electrons are ejected and the doubly differential cross section is very small. This discrepancy may be due to the large uncertainties in the experimental data in this region and the model target description. Overall, the present results show significant improvement upon currently available theoretical results and provide a consistently accurate description of this process across a wide range of incident energies

Close-coupling approach to antiproton-impact breakup of molecular hydrogen

An ab initio time-dependent convergent close-coupling approach to describing antiproton collisions with molecular hydrogen or the hydrogen molecular ion has been developed. The approach accounts for all possible orientations of the molecular target. Averaging over the molecular orientations is performed fully analytically. For the molecular hydrogen target calculated orientation-averaged total cross sections for single ionization and proton production are compared with several experiments over the energy range of 1-2000 keV. Results for single ionization are in good agreement with experiment, except for the region around the experimental maximum. For proton production reasonable agreement with experiment is observed above 40 keV

Antiproton-impact ionization of Ne, Ar, Kr, Xe, and H2O

We calculate antiproton-impact total single ionization of Ne, Ar, Kr, Xe, and H2O using a time-dependent convergent close-coupling approach. The Ne, Ar, Kr, and Xe atom wave functions are described in a model of six p-shell electrons above a frozen Hartree-Fock core with only one-electron excitations from the outer p shell allowed. For treating the water molecule we use a neonization method recently proposed by Montanari and Miraglia [J. Phys. B: At. Mol. Opt. Phys. 47, 015201 (2014)], which describes the ten-electron water molecule as a dressed Ne-like atom in a pseudospherical potential. In the present work the target states of noble gas atoms and water are obtained using a Laguerre basis expansion. For the noble gas atoms there is reasonably good agreement with the calculated single-ionization cross sections