A helical cathode position sensitive proportional counter system for use in a broad range spectrograph

Abstract

A 40 cm helical cathode position sensitive gas counter (Helix) has been developed for use with an Enge split-pole spectrograph. The detector consists of three separate sections: the position and ΔE proportional counters and a total energy ( E) plastic scintillator. These detectors provide the signals for position information, particle identification and background suppression (when operated in a coincidence mode). The plastic scintillator is used for particle identification when detecting Z = 1 ions and provides energy resolutions of about 5%. For Z≥2 ions either the ΔE or the position counter is used. Inherent spatial resolution of <0.3 mm is deduced for the Helix detector from X-ray bench tests. Spectrograph results for the normal solid angle of 1.4 msr and for particles incident at 45° show total resolutions of ∼0.5 mm for deuterons and tritons. Energetic, lightly ionizing protons give 0.6–0.7 mm resolutions due mainly to the energy loss straggling limit (0.4–0.5 mm). The detector has operated reliably for two years. Construction details and operational characteristics are given along with examples of experiments in which the Helix detector has proven useful.