Three-Body Photodisintegration ofHe3

The ${\mathrm{He}}^3(\gamma , n)2p$ cross section has been measured in 1-MeV steps from threshold to 30 MeV using the National Bureau of Standards betatron and a ${\mathrm{He}}^4$ cryostat to produce a 40-${\mathrm{cm}}^3$ liquid-${\mathrm{He}}^3$ target. The measured cross section shows a broad peak between 14 and 20 MeV with a maximum cross section at about 0.90 mb. The cross section and bremsstrahlung-weighted cross section integrated up to 28 MeV give 12.1±10% MeV mb and 0.68±10% mb, respectively. Theoretical calculations of the three-body photodisintegration cross section overestimate the experimental cross section by factors of 3 to 10.