The energy lost by α -particles from 241Am in Al, Cu, Sn, and Au films: Measurements with 0.7% accuracy and first-principles calculations

Abstract

The energies lost, ΔE1, by the α-particles from 241Am in Al, Cu, Sn, and Au metallic targets have been measured. The films are not thin enough to extract a stopping cross section because they have to withstand the independent determination of their mass thickness ρx0=Δm/ΔA through their weights Δm and surfaces ΔA. The systematic uncertainties on ΔE1 (including the ones on ρx0) are estimated to be 0.6–0.7%. The largest contribution of 0.33% comes from the long-term stability of the electronics. The uniformity and purity of the targets have smaller impacts. The effect of the former, in particular, is attenuated by the diameter of the collimator of 6.5mm. A correction for the average track inclination of 0.1% is applied. All the runs lasted enough to reduce the combined statistical errors to ≈0.1%, which becomes irrelevant for the comparison with theory. The largest deviation of the experimental ΔE1 from the predictions of ASTAR is −0.3% for Cu. The situation is less regular for SRIM with a discrepancy of up to −2.0% also for Cu. First-principles calculations without any free parameters have also been carried out within the shellwise local plasma approximation (SLPA-LM). This formalism relies exclusively on fundamental atomic properties not directly related to particle stopping.