PHOTOFISSILITY OF TH-232 MEASURED WITH TAGGED PHOTONS FROM 250 TO 1200 MEV

The photofission cross section of Th-232 was measured in the energy ra nge 250-1200 MeV using a monochromatic tagged photon beam and a parall el-plate avalanche detector. The Th-232 nuclear photofissility was obt ained by measuring simultaneously and in the same energy range the pho tofission cross section of U-238 and assuming a photofissility equal t o one for U-238. It was found that, contrary to the case for heavier a ctinides, the Th-232 photofissility value does not saturate up to 1200 MeV. Rather, it lies between 0.6 and 0.8, and shows a weak energy dep endence: it increases by about 15% over an interval of 1 GeV. A compar ison of these experimental findings with the predictions of an intranu clear-cascade Monte Carlo calculation is given.