VIBRATIONS OF SURFACE ATOMS STUDIED BY NRRA

The motion of the target nuclei in the surface of a solid affects the shape of yield curves of narrow nuclear resonances. We measured yield curves for the 272 keV resonance in Ne-21(p,gamma)Na-22 with frozen ne on. The in-situ preparation of the targets and the measurements were c arried out under UHV conditions. The targets were cooled by a He evapo ration cryostat to temperatures below 10 K. This temperature could be maintained even with beam currents of about 1 mu A. The measurements w ere carried out with the 400 kV high energy resolution accelerator at the University of Munster. The measured yield curves showed a huge Lew is peak with a peak-to-plateau ratio of 2.5. The influence of atomic m otion on the width of the Lewis peak was calculated with two different theoretical models. The calculated values are in good agreement with the experimental width.