NEW FOCAL-PLANE DETECTOR SYSTEM FOR THE ROCHESTER RECOIL MASS-SPECTROMETER

A focal plane detector system has been developed for the Rochester Rec oil Mass Spectrometer. It consists of a parallel grid avalanche counte r (PGAC) backed by an ionization counter (IC). The PGAC is used to obt ain 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 w ith 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 resolv e 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).