Influence of atomic excitation processes on yield curves of narrow nuclear resonances

Atomic excitation and ionization processes affect the shape of yield curves of narrow nuclear resonances obtained with high beam energy resolution. Yield curves for the narrow resonances in the 21Ne+p reaction at Ep=126, 272 and 291 keV and for the Ep=309 keV resonance in 23Na+p were measured with very low target densities (i.e., with thin targets fulfilling atomic single collision conditions). The ionization probabilities of K and L electron shells were determined at an impact parameter close to zero. Collision spectra were measured which provide information on the energy loss integrated over all impact parameters in a single collision. From an analytical description for the thin-target yield curve and the experimental collision spectra, the experimental thick-target yield curves with an intense Lewis peak could be reproduced with a Monte Carlo computer simulation.