VIBRATIONS OF SURFACE ATOMS STUDIED BY NRRA

Abstract 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 21 Ne(p,γ) 22 Na with frozen neon. The in-situ preparation of the targets and the measurements were carried out under UHV conditions. The targets were cooled by a He evaporation cryostat to temperatures below 10 K. This temperature could be maintained even with beam currents of about 1 μA. The measurements were carried out with the 400 kV high energy resolution accelerator at the University of Munster. The measured yield curves showed a huge Lewis peak with a peak-to-plateau ratio of 2.5. The influence of atomic motion 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.