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Activation techniques were used to measure more than 30 excitation functions for single and multiple nucleon and/or a particle emission for d + ""Zn, "Y with Ed =9 -26 MeV and 'He+""Cu, "Nb with E('He) = 10-44MeV. The excitation functions are generally in agreement with the results of a combined equilibrium and preequilibrium hybrid model calculation applying initial exciton numbers n, =3 for d and n0=4 for He reactions. The composite system "Ga has been produced via d + "Zn and 'He+ "Cu at excitation energies between 22 and 36 MeV. An entrance channel dependence shows up in the yields for single pand n-emission when compared iu the double ratio R = [o('Hey}/o('He, n}]/[o(d p}/o(d, n}] It . approaches a value of about 2,indicating enhanced p emission for the He-induced reaction. This value disagrees with the equilibrium isospin formalism and is best reproduced by initial particle exciton numbers n 0 =n,"=1.5 for d and n, =2.5, n, "=1.5 for He projectiles, indicating conservation of charge asymmetry in the entrance channel. Isomeric ratios have been measured for "Y(d,2n)"Zr and "Nb('He~n)" "Tc (x = 1,2, 3). Calculations with a full statistical model fail to reproduce o. /cr as well as cr, and cr for reasonable values of the spin cutoff parameter. Inclusion of a preequilibrium decay mode improves the fit, in particular if the angular momentum depletion of the composite system due to preequilibrium decay is increased over that of the equilibrium decay at the same channel energy. NUCLEAR REACTIONS '6 Zn, Y(d, gyp ga), 8~=9-26 MeV, ' Cu, Nb( He, xnypzof), E3 =10-44 MeV, x~4, y &1, z &2; measured~(E) by acti-He vation, enriched targets. Statistical model analysis including preequilibrium decay, deduced reaction mechanism, charge asymmetry conservation, spin depletion.

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The excitation functions of 51V [(α, xn), x = 1.3; (α, p3n); (α, α3n) (α, 2α)] and 59Co[(α, 2n); (α, αxn); x = 1, 2] reactions were measured up to 50 MeV by the stacked-foil activation technique and high-resolution Ce(Li)–HPGe spectroscopy method. Of these 51V(α, xnypzα) reactions were studied for the first time with better accuracy than earlier measurements, which were done with a poor resolution scintillation–Ge(Li) detectors some 20 years ago. In the case of 59Co, existing data show large discrepancies at low energy. Comparisons are presented with the prediction of hybrid and exciton models. While for the (α, xn) type of reactions, reasonably explainable pre-equilibrium contributions are found, there seem to be indications of direct inelastic scattering effects in the (α, αxn) type of reactions.

Charged particles from protons up to projectile particles were measured from the systems Ne+ 'V and ' N+ Fe at 530 MeV bombarding energy forming the same composite "As . The data show entrance channel effects with respect to spectral distributions and fragment abundances. The data analysis in terms of different models indicates a common reaction mechanism for all particles produced.PACS number(s): 23.70. +j, 25.70.z

A microscopic exciton model has been developed which describes the time evolution of a highly excited nucleus through a series of binary collisions creating additional particle-hole pairs. Starting from an arbitrary exciton density distribution, the spectral shapes of the succeeding stages are generated through recursion relations which keep track of the "exciton flux" explicitely. The computer code BEEFALO provides particle spectra and average life times of the successive stages. The results are compared with the predictions of other preequilibrium models using "equal probability" density distributions. The controversy about the use of single particle or n-exciton state life times has been resolved by showing that both approaches lead to the same particle spectra if proper book-keeping is made through appropriate recursion relations.

Using the activation method, the cross-section for the following reactions on molybdenum were measured employing the mixed powder technique and Ge(Li) gamma-ray spectroscopy: 94Mo(n, 2n)93mMo, 3.5 i 0.5 mbarn; "Mo(n, 2n)'"Mo, 19 f 3 mbarn; 9zMo(n, 226 i 11 mbarn; looMo(n,p)'OOm~Nb, 9 f 1 mbarn; 98Mo(n,p)98Nb, 10 f 1 mbarn; 9 7 M ~( n , p ) 9 7 " b , 5 t 1 mbarn; 9 6 M ~( n , p ) 9 6 N b , 12 f 2 mbarn; '*Mo(n, a)89mZr, 2.1 t 0.5 mbarn; and 92Mo(n, a)s9m+gZr; 24 -r 6 mbarn; the neutron energy was 14.2 i 0.2 MeV.The experimental cross-sections were compared with the predictions of evaporation model and of different versions of pre-equilibrium model. The master equation approach appears to give satisfactory results.

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