TOTAL PHOTOABSORPTION CROSS-SECTIONS FOR H-1, H-2, AND HE-3 FROM 200 TO 800 MEV

The total photoabsorption. cross sections for H-1, H-2, and He-3 have been measured for incident photon energies ranging from 200 to 800 MeV . The He-3 data are the first for this nucleus. By using the large acc eptance detector DAPHNE in conjunction with the tagged photon beam fac ility of the MAMI accelerator in Mainz, cross sections of high precisi on have been obtained. The results show clearly the changes in the nuc leon resonances in going from H-1 to He-3. In particular, for the D-13 region the behavior for He-3 is intermediate between that for H-1, H- 2, and heavier nuclei. This will provide a strong constraint to the th eories that are presently being developed with a view to explaining th e apparent ''damping'' of higher resonances in heavy nuclei.