209x\ngular distributions, energy spectra, and absolute cross sections have been measured for alpha particles emitted in the bombardment of Au 197 and Bi 209 by C 12 , N 14 , and O 16 projectiles at bombarding energies of 10.5 Mev/nucleon and for the C+Bi reaction at reduced energies of 8.7 and 7.1 Mev/nucleon. Angular distributions and absolute cross sections have also been measured for protons from the C+Bi and O+Bi reactions at bombarding energies of 10.5 Mev/nucleon. It was found that, from the angular distributions and energy spectra, it was possible to separate the contributions from direct and evaporation processes. The direct alpha particle results suggest that the principal direct process involved is the breakup of the incident projectile in an interaction with the surface of the target nucleus. At the 10.5 Mev/nucleon bombarding energies the cross sections for the emission of direct protons and direct alpha particles are found to be about 10% and 25-35%, respectively, of the calculated total reaction cross sections. The evaporation cross sections depend strongly on the excitation energy available in the compound system. The evaporation energy spectra can be fitted by an expression of the form exp(-E a /T) and the results yield an average level density parameter, # = 22=1=2 Mev -1 , for these reactions.

Neutron-induced fission cross sections on 235 U and 235 U m targets in the incident neutron energy range E n ϭ0.1-2.5 MeV have been deduced from surrogate 234 U(t,p f ) measurements. The surrogate (t,p f ) reaction is used to populate the same compound system as the (n, f ) reaction before fission, and modeling is used to compensate for the difference in population mechanisms. The calculations presented in this paper improve on previous results by incorporating realistic angular momentum and parity distributions for the (t,p) channel, and by updating transmission-coefficient values used in the neutron-capture and emission contributions that compete with the fission process. The results are generally reliable within the 10% systematic uncertainties of the (t,p f ) data.

Neutron-induced fission cross sections have been extracted for targets of 240,241,243 Pu, 234,236,237,239 U, and 231,233 Th from E n ϭ100 keV to Ϸ2.5 MeV using surrogate (t,p f ) fission-probability data and a detailed statistical model to compensate for the difference between neutron-induced and (t,p) reactions. This paper extends the results of previous work on the 235 U(n, f ) cross section, which serves as a proof-of-principle study. The (n, f ) cross sections are compared to earlier estimates based on the same surrogate data, but obtained using a more simplistic approach. The cross sections are also compared to accepted values where direct measurements exist and are consistently accurate to within 20% below E n Ϸ0.5 MeV and 10% at higher energies. The case of the 237 U(n, f ) cross section, simulated from surrogate (t,p f ) data, is investigated in greater detail to reconcile contradictory measurements in the literature.

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Proton and deuteron distributions from 11.6A GeV/c Au ϩ Au collisions measured by the E802 Collaboration in experiment E-866 are presented. The invariant yield of protons and deuterons is studied as a function of the transverse mass for different cuts of rapidity and centrality. At low m t Ϫm 0 the proton and deuteron invariant spectra deviate from a single exponential shape. The average m t as function of centrality and rapidity is used to explore the effect of collective transverse flow in the reaction. The ratio of the deuteron to squared proton yield as a function of transverse momentum, rapidity, and centrality is used to probe the coalescence model of deuteron production. This ratio is constant as a function of rapidity only for the most central cuts and decreases with the centrality for every rapidity cut. The ratio of the differential cross section of the deuteron to the squared differential cross section of the proton, for the most central cut, is not constant as a function of m t Ϫm 0 . ͓S0556-2813͑99͒04911-0͔ PACS number͑s͒: 25.75.Dw, 25.75.Ld

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