CHICO, a heavy ion detector for Gammasphere

A 4 pi position-sensitive heavy-ion detector system, CHICO, has been developed primarily for use in conjunction with the 4 pi gamma-ray facility, Gammasphere. The CHICO detector comprises an array of 20 Parallel Plate Avalanche Counters (PPACs) covering 12 degrees < theta < 85 degrees and 95 degrees < theta < 168 degrees and 280 degrees in phi. The PPACs have segmented delay-line cathode boards, measuring the polar scattering angle theta to 1 degrees, and segmented anodes, measuring the azimuthal angle phi with 9 degrees resolution, while measuring the time-of-flight difference with 500 ps resolution. For binary reactions the kinematics can be reconstructed from the measured information, allowing identification of the target- and projectile-like nuclei with a mass resolution of Delta m/m approximate to 5%. The measured masses, recoil velocities, and recoil angles allow correction for Doppler shift and assignment of individual gamma-rays to decay of the correct reaction product. This paper describes the design, operation and performance of the CHICO detector. The powerful combination of CHICO plus Gammasphere provides new research opportunities for the study of nuclear structure and reactions. (C) 2000 Elsevier Science B.V. All rights reserved.