A broad-range detector system with large geometric efficiency for heavy-ion reaction studies

A detector module sensitive to heavy ions, capable of covering a very large solid angle, and having a broad dynamic range in energy and atomic number has been designed and tested. It is tapered, has a pentagonal cross section and has been constructed to permit close-packing in a spherical array with a minimum of inactive area. The detector consists of a radial-field drift chamber for Bragg-curve spectroscopy, followed by a thin fast-plastic scintillator laminated to a thick slow-plastic scintillator for light-ion detection; the two scintillators are read together in phoswich Δ E - E mode. Mixed-mode operation is also possible, with the drift chamber serving as a ΔE counter and the fast plastic scintillator providing an energy signal. Tests with a beam of 145 MeV ²⁸Si ions have shown that for 83% geometric efficiency (active/total solid angle) the Bragg curve spectrometer gives Δ Z Z {reversed tilde equals} 5% at Z = 12 and Δ E E {reversed tilde equals} 6% for silicon ions depositing 100 MeV in the detector. Mixed mode operation has 70% geometric efficiency with a measured Δ Z Z {reversed tilde equals} 5% for Z = 8. Phoswich mode operation also has 70% geometric efficiency and gives Δ Z Z {reversed tilde equals} 6% for Z = 2; isotopic identification of light ions is unambiguous.