New focal plane detector system for the rochester recoil mass spectrometer

A focal plane detector system has been developed for the Rochester Recoil Mass Spectrometer. It consists of a parallel grid avalanche counter (PGAC) backed by an ionization counter (IC). The PGAC is used to obtain the horizontal and vertical position of the incident particles and also to provide a fast timing signal. The PGAC has an active area of 5.1 cm x 5.1 cm. The IC consists of three charge collecting anodes (2.0 cm, 6.2 cm, 21.6 cm long) and provides nuclear charge identification and a total energy measurement. Both the PGAC and the IC are filled with isobutane as the counter gas. The intrinsic position resolution of the PGAC was determined to be 0.9 mm (FWHM). The IC is able to resolve neighboring nuclear charges for light ions with energies as low as 0.7 MeV/u. The nuclear charge resolution of the IC for heavy ions with IC energies below 0.7 MeV/u was found to be 1.3 e (FWHM).