Precompound charged particle emission (PCE) - a mechanism beyond element production by complete fusion

Complete fusion reactions (xn-channels) using actinide targets are observed for values of the effective fission parameter x(eff) ∼ 0.80 in the sub-pb range of production cross sections. The elements produced at this limit are Z = 108-112. Beyond complete fusion, heavier elements might still be produced by reaction mechanisms releasing part of the nuclear charge before an equilibrated compound system might have been reached. Precompound Charged particle Emission (PCE) is proposed as a possible mechanism following complete fusion. A scheme delivering isotopes of elements Z = 110-115 is discussed, and experimental evidence for such a process is presented. Compound systems, the atomic numbers of which are smaller than in complete fusion reactions, might be produced in Ca48 induced reactions on actinides with larger cross sections than those at the limits of complete fusion. Besides complete fusion, the PCE-mechanism should be considered as an alternative to interpret the Ca48-induced reactions on actinides. (author)