Heavy-ion Compound-nucleus Formation

Heavy-ion reactions will be considered only briefly here, dividing them into (1) heavy-ion compound-nucleus formation and (2) other reactions. 

The first predicament may be illustrated by a reaction attempted by Sikke-land and by Gvozdev et aV using the present generation of accelerator, namely 

The second problem, that of low excitation of the compound nucleus, stems from what Swiatecki calls the brittleness of superheavy nuclei. They can withstand only a small amount of distortion from the spherical shape, and any appreciable deformation invariably involves a lowering of the fission barrier. Heavy-ion reactions are particularly bad in this respect as a large amount of vibrational and rotational energy can be involved. Moretto has considered the question quantitatively. It is also treated extensively by Lefort who concludes that projectiles with Z between 35 and 40 (Br to Zr) on to targets of Th, U, or Pu show most promise. Greiner argues that excitation will be minimized if the nuclei involved are hard , that is relatively incompressible, as would occur with closed-shell magic nuclei, when the amount of coulombic interaction in the fusion reaction would be small. Kr, with 50 neutrons, is an attractive candidate. 

If target and projectile are of similar mass, with Z between 50 and 65, then it is thought that the excitation energy of the compound nucleus can be controlled by a careful choice of projectile energy. This has been called inverse fission or the cold nucleus reaction. Natowitz has calculated cross- 

It is thus clear that even if only a small fraction of the nuclei formed were deactivated to the ground state rather than undergoing fission, then appreciable quantities of superheavy atoms could be formed. 

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