An angle-sensitive detection system for scattered heavy ions

A compact detection system for heavy ions scattered in collisions at the Coulomb barrier is presented. This system, consisting of four identical, low-pressure Parallel Plate Avalanche Counter (PPAC) modules with two sensitive layers each, was built to operate in an ultra-high-vacuum environment inside the EPoS II solenoid spectrometer at GSI Darmstadt. The detector covers polar angles between 20° and 70° with respect to the beam axis, and about 80% of 2π in azimuthal angle. Segmented cathodes and a delay-line read-out allow for a determination of both angles with a precision of δΘ≈0.7° in polar and δΦ≈1.5° in azimuthal angle, respectively. The system has been proven to be capable of handling instantaneous rates of up to 5×105 detected ions per second per module. It neither exhibits the degradation of detection efficiency nor loss in resolution over a 500 h period of a 6 MeV/u 238U+181Ta measurement at average luminosities of 8×1027 cm−2 s−1.