Photofission of ²⁷Al nucleus in the quasi-deuteron region of photonuclear absorption

Quasi-monochromatic photon beams of 108 MeV Compton-edge energy produced in the ROKK-1M facility at the storage ring VEPP-4M (BINP, Novosibirsk) and makrofol sheets as fission track detectors were used to measure the photofission yield of ²⁷Al. The fission yield was found to be (160±55) µb. From this result and previously measured ²⁷Al photofission yield at ~79 MeV end-point energy with the LADON apparatus, the trends of fission cross section and fissility have been obtained in the incident photon energy range ~40-110 MeV. The present results and data for other intermediate-mass nuclei obtained with the same methodology indicate an increase of fissility with decreasing Z²/A as predicted by the liquid drop model for fissioning systems lighter than ~Ag.