Energy Spectra of Fragments from Silver and Uranium Bombarded with5.0 GeV Protons

Abstract

In this third paper in a series in which the characteristics of nuclear fragments produced in the interaction of 5 GeV protons with Ag and U targets were studied by means of dE/dx-E measurements with semiconductor detector telescopes new information was obtained on the energy spectra of light fragments. One set of measurements on fragments from a Ag target involved the use of a two-element telescope incorporating a {Delta}E detector as thin as 16 {micro}m. A new algorithm for processing the {Delta}E and E data to extract particle identification was developed and the resulting particle spectra showed superior resolution for the elements from Li(Z = 3) to S (Z = 16). Segments of the energy spectra of each of these elements were measured at 20{sup o} and, for many of them, also at 45{sup o}, 90{sup o}, 135{sup o} and 160{sup o} to the beam direction. By use of 3-element telescopes and absorbers the high energy part of the energy spectrum for isotopes of He, Li, Be, B, and C ejected from Ag and U targets was measured at 20{sup o}. The measurements extended beyond 300 MeV for {sup 6}Li and {sup 7}Li and to 400 MeV for {sup 7}Be. A distinct high-energy component was found in these cases. The suitability of nuclear evaporation as a description of the emission of the low-energy fragments was tested with two simple theoretical models, one specifying isotropic fragment emission from a moving nucleus at a fixed nuclear temperature and one specifying isotropic fragment emission from a set of moving nuclei with a Maxwellian distribution of excitation energies and forward momenta. The second could describe rather well all the 90{sup o} data, provided a Coulomb barrier 0.4 that of the classical tangent spheres barrier was used. However, the measured intensity in the forward direction was much higher than predicted. Neither evaporation calculation was able to describe the highest energy part of the spectra, and the conclusion was drawn that these particles must be produced in the initial high-energy cascade.