Target mass dependence of neutron emission in collisions with 35 MeV/nucleon 14N ions.

Abstract

Energy and angular distributions of neutrons emitted from collisions of 35 MeV/nucleon /sup 14/N ions with carbon, nickel, and holmium nuclei were measured. The neutrons were in coincidence with Li, Be, B, or C fragments at angles from 7/sup 0/ to 23/sup 0/ in the plane of the neutron detectors and at 15/sup 0/ out of this plane. Using fragment velocity bins of width corresponding to E/A = 7 MeV, we find the shapes of the neutron spectra above 15 MeV to be similar for the different targets for a given coincident fragment species, velocity bin, and angle. The cross sections are discussed in terms of moving thermal sources. In all cases the velocity and temperature parameters of the intermediate rapidity source are consistent with E/A = 8.5 +- 2.5 MeV and T = 9 +- 2.5 MeV, respectively. In agreement with a simple stripping-pickup model, the associated neutron multiplicities of this source decrease approximately linearly with the velocity of the coincident light fragments for fragment angles less than or equal to15/sup 0/. Using the model to compute the mass of the source, we find that, with some fluctuations, these multiplicities are proportional to the mass. Also, the linear relationshipmore » is approximately the same for the three targets. The temperature parameters of the target-like source are between 1 and 3.5 MeV for all three targets, while the associated neutron multiplicities increase considerably with target mass. For colinear neutron-fragment coincidences for a given projectile-like isotope, the neutron multiplicities associated with the projectile-like source are about the same for all three targets, indicating that the average excitations of the parent fragments are similar.« less