Observation of energy-shifted gamma-ray absorption by 133Cs nucleus placed in finite space

We report the first reliable observation of the tiny shifts of energy levels of a nucleus placed between two parallel metallic plates. We observed the absorption of the 81 keV gamma ray from 133Cs induced by the β-decay of 133Ba in a *BaTiO3 compound. This Moessbauer experiment was carried out at 4.2 K with the absorber placed between two silicon plates with gold coating. The observed shifts are around 0.95 neV (equivalent to 0.007 mm/s) for the distance of about 2 mm between the two plates. (author)