Nuclear stopping power of antiprotons

Abstract

The slowing down of energetic ions in materials is determined by the nuclear and electronic stopping powers. Both of these have been studied extensively for ordinary-matter ions. For antiprotons, however, there are numerous studies of the electronic stopping power, but none of the nuclear stopping power. Here, we use quantum-chemical methods to calculate interparticle potentials between antiprotons and different atoms, and derive from these the nuclear stopping power of antiprotons in solids. The results show that the antiproton nuclear stopping powers are much stronger than those of protons, and can also be stronger than the electronic stopping power at the lowest energies. The interparticle potentials are also implemented in a molecular dynamics ion range calculation code, which allows us to simulate antiproton transmission through degrader foil materials. Foil transmission simulations carried out at experimentally relevant conditions show that the choice of antiproton-atom interaction model has a large effect on the predicted yield of antiprotons slowed down to low (a few keV) energies.

Large nuclear scattering effects in antiproton transmission through polymer and metal-coated foils

“…Nevertheless it has been predicted that the S p n contribution is larger than the value for protons and becomes an important energy-loss mechanism at E k ≤ 1 keV (Fig. 1) [28,29,[46][47][48]. Past theoretical [28][29][30][31][32][33]47] and experimental [46,49] studies of the nuclear stopping power have primarily concentrated on H, H 2 , or He gas targets.…”

“…Antiprotons arriving with small impact parameters relative to an atom follow complex trajectories that curve toward the nucleus with larger scattering angles θ (see Fig. 2(a)) and cross sections [48] compared to protons that are deflected in the opposite direction along approximately hyperbolic trajectories in the repulsive protonnucleus potential [28,29]. Similarly to the kinematics in elastic neutron moderation, the antiproton tends to lose the largest kinetic energy ∆E per elastic collision with a target of similar mass, such as a hydrogen atom (Fig.…”

“…2(b)). Collisions with heavier atoms involve larger cross sections and scattering angles, but lower ∆E-values that are kinematically allowed [48]. An experimental indication of E k = 1-10 keV antiprotons reflecting off of an Al wall [50] has been interpreted in terms of consecutive Rutherford scatterings with multiple scattering angles between 10 • and 40 • .…”

Directional dependency of electronic stopping in nickel, projectile’s excited charge state and momentum transfer

“…There are two main contributions to the stopping power phenomena: (i) electronic stopping power S e [12][13][14][15][16] which is mainly due to electronic excitations of the target electrons and (ii) nuclear stopping power S n [17][18][19][20] which is due to the elastic collision of the projectile with the target nuclei, where energy is dissipated as lattice defects or vibrations. Our discussion in this paper focuses on the first category of electronic stopping and pertains to the regime in which the phenomena occur a e-mail: correaa@llnl.gov (corresponding author) in the femtosecond time scale, with explicit simulation of electron dynamics.…”

Ab Initio Prediction of a Negative Barkas Coefficient for Slow Protons and Antiprotons in LiF

“…So far we concentrated on the electronic contribution. Recently, Nordlund and co-workers [45] showed that there also exists a proton-antiproton asymmetry for the nuclear stopping power S n . We therefore implemented their FIG.…”