Uranium target fragmentation by intermediate and high energy 12C and 20Ne ions.

Abstract

Target fragment formation cross sections for nuclides with 24\ensuremath{\le}A\ensuremath{\le}237 have been measured for the interaction of 1.0, 3.0, 4.8, and 12.0 GeV $^{12}\mathrm{C}$ and 8.0 and 20.0 GeV $^{20}\mathrm{Ne}$ with $^{238}\mathrm{U}$. Fragment isobaric yields were deduced from these data. The light fragment (A60) yields increase rapidly with increasing projectile energy until 4 to 8 GeV with only smaller increases in yield with increasing projectile energy beyond this consistent with the origin of these fragments in a high deposition energy process. The yields of n-rich fragments (80\ensuremath{\le}A\ensuremath{\le}145) are energy independent from 1--20 GeV consistent with their origin in low energy fission of a uranium-like species. The n-deficient fragments (80\ensuremath{\le}A\ensuremath{\le}145) have excitation functions consistent with their origin in either a deep spallation or high energy fission process. (At a $^{12}\mathrm{C}$ projectile energy of 1.0 GeV, the n-deficient fragments appear to originate primarily from a fission rather than a spallation process.) The excitation functions of the heavy fragments with 60\ensuremath{\le}A\ensuremath{\le}200 are similar to those of the light fragments. No large yields of these fragments were observed for any system studied, contrary to a previous report. Both the intranuclear cascade model and the nuclear firestreak model satisfactorily predict the observed yields of fragments with A>60, indicating that the general pattern of yields of these fragments is governed by the excitation energy deposited in the nucleus during the first step of the reaction and the geometry of the collision.