EXCITATION FUNCTIONS FOR THE ($alpha$,$alpha$n) AND ($alpha$,2pn) REACTIONS ON Ce$sup 14$$sup 2$

Cross sections are measured radiochemically for the reactions Ce/sup 1// sup 4//sup 2/( alpha , alpha n)Ce/sup 1//sup 4//sup 2/ and Ce/sup 1//sup 4//sup 3/ at a heliumion energy of 16.8 to 40.1 Mev. The cross section for the ( alpha , alpha n) reaction begins to rise sharply at about 25 Mev and reaches a value of 69 plus or minus 5 mb at 40.1 Mev. The cross section for the ( alpha ,2pn) reaction begins to rise at about 32 Mev and reaches a value of 2.5 plus or minus 0.4 mb at 40.1 Mev. An upper limit of approximately 0.1 mb for the cross section for the reaction Ce/sup 1//sup 4//sup 2/( alpha , alpha p)La/sup 1//sup 4/ /sup 1/ in the energy range covered is also obtained. The results for the ( alpha , alpha n) and ( alpha , alpha p) reactions are discussed in terms of several mechanisms: compound nucleus formation and decay, knock-on, and direct inelastic scattering followed by neutron evaporation. The results seem to be most consistent with the last mechanism. The existence of a measurable cross section for the ( alpha ,2pn) reaction in this energy region suggests that the reactionmore » proceeds mainly by He/sup 3/ emission, probably by a stripping mechanism. The data reported are consistent with the hypothesis that in this energy range at most one particle is emitted as a result of direct interaction. (auth)« less