Excitation energy deposition from neutron multiplicity distributions for reactions induced with 30 A MeV 14N, 20Ne, 63Cu and 55 A MeV 4He

Abstract

Inclusive neutron multiplicity distributions have been measured for 30 A MeV 14N, 20Ne, 63Cu and 55 A MeV 4He beams incident on targets ranging from 12C to 238U. For the lightest targets, the distributions decrease approximately exponentially with increasing multiplicity. The heavier targets display an additional Gaussian component peaked at higher multiplicities, which is attributable to central collisions. In the latter cases, the most probable multiplicities, M n ∗ , have been extracted by fitting the data with a simple functional form. These multiplicities are compared to the predictions of the statistical model codes GEMINI and CASCADE using a massive transfer scenario to define the initial conditions. Reasonable agreement is obtained for systems with estimated excitation energies ≈ 100 MeV, but the calculations consistently overpredict the most probable multiplicities for more highly excited systems. Good agreement is observed between the experimental M n ∗ values and the predictions of the code EUGENE. However, this code gives M n ∗ values that are consistently lower than those predicted by other statistical model calculations. An alternative procedure is utilized to extract the amount of excitation energy of the composite system. In this approach, the input excitation energy in a standard model code is varied until the predicted M n ∗ value matches the experimental value. The resulting excitation energies follow systematic trends with the estimated momentum transfer and the N Z of the system. These patterns are also observed in reactions induced with other projectiles.