Large nuclear scattering effects in antiproton transmission through polymer and metal-coated foils
K. Nordlund, M. Hori, Dage Sundholm
Abstract
We simulate the deceleration and transmission of antiprotons with keV-scale kinetic energies through polymer foils using a molecular dynamics approach, which includes a model of nuclear stopping based on the attractive interaction potentials between antiprotons and target atoms calculated by quantum chemical methods. Antiprotons scatter into larger angles with higher cross sections than protons. This causes a significant fraction of antiprotons to annihilate in the foil instead of emerging with energies of a few keV, especially when coatings of materials with high atomic number are applied to the surfaces. The simulation results are in good agreement with data from two experiments that involved pulsed antiproton beams with incident energies between 63 keV and 122 keV that traverse polymer foils with thicknesses of $\ensuremath{\approx}1.3$ $\ensuremath{\mu}\mathrm{m}$ and 1.8 $\ensuremath{\mu}\mathrm{m}$. The 25-nm-thick layers of Ag on the latter foil reduced the transmission of antiprotons. The results will be utilized to design the degrader foils in laser spectroscopy experiments of antiprotonic helium atoms and experiments involving Penning traps that are carried out at the ELENA facility of CERN.