L.S. El-Mekkawi, O.M. El-Bakly

Hot Laboratory Centre, Atomic Authority of Egypt.

The present work considers that nuclei may contain a quantum system of two packed clusters. The deuteron which is considered as a two body problem was solved as the case of lightest clusters.

The photofission cross section has been estimated for deuteron in the energy range 2.35-450 Mev. The results of calculation give a curve with two peaks. One peak has a cross section 3.2 m. barn at energy 4.4. Mev. and another peak has a cross section 0.081 m. barn at energy 280 Mev.

The results agree well with experimental data.

For heavy fissionable nuclei 233-U, 235-U and 239-Pu, the disturbance of the system of two packed clusters may show a release of a saturated quantum shell. At a certain energy threshold gamma rays can resolve two equal clusters, if a quantum shell, with the higher quantum number of the bigger cluster, leaves cluster motion.

It was shown that photofission may originate from the substates of quantum system of clusters, when a ray resolves them. The number of final fission states is that of the order of the disturbed shell, in case of main resolution of both clusters. But when the ray resolves the equal cluster substates, the number of final fission states is the number of substates of the disturbed shell.

The number of channels released from packed cluster system is in excellent agreement with number of fission product chains. Relation of thresholds allows energy of shell release. The two modes of fission give close agreement with experiments and explain the low energy bump in photofission cross sections.