Imaging and identification of relativistic projectile fragments with Lexan spectrometry

Abstract

We describe the method and some applications of Lexan spectrometry to the identification of nuclides produced in the fragmentation of relativistic heavy ions at the Lawrence Berkeley Laboratory Bevalac. Fragments emitted at 0° to the beam are deflected in a magnetic spectrometer and come to rest in a large stack of Lexan plastic detectors. Charge, mass, and energy are determined from measurements of range and lateral position in the stack and from etch pit lengths in two consecutive sheets. In favorable cases charge and mass can be determined from range and deflection alone without the necessity of etch pit measurements. The main advantage of the method is its large collecting power: fragments striking any portion of the 450 cm 2 detector surface are sufficiently focussed for their mass, charge, and energy to be identified. Unusual events such as the attachment of two electrons by a projectile nucleus can be observed.