Interactions of 100 MeV/nucleonAr40with uranium

Abstract

Fragments produced in the interactions of 100 MeV/nucleon ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ projectiles with a uranium target have been measured at energies from 10 to 130 MeV/nucleon at angles from 10° to 170°. Nuclei with charge $5\le Z\le 10$ were observed. The data can roughly be divided into two groups, corresponding to central and peripheral collisions. The central collision data can be fitted with a thermal model that uses two recoiling sources. The source velocities are consistent with the predictions of the fireball and target explosion models, but the source temperatures inferred from the data are higher than one would expect on the basis of energy and momentum conservation. These results are similar to those obtained in previous studies at beam energies of 400 and 500 MeV/nucleon. The data also follow the pattern of the universal curve of invariant cross section vs momentum observed at higher beam energies by Price et al. The projectile fragmentation data are also fitted by two thermal sources. There are indications that the observed temperatures are higher than one would expect on the basis of other projectile fragmentation studies. From this broad survey we conclude that although much of the spectrum can be described by falling exponentials in energy in the emitting frames, the observed spectrum is due to nonequilibrium sources since the temperatures derived from the slopes of the exponentials are greater than those we predict.