A focal-plane detector for the recoil mass spectrometer of the Institute of Atomic Physics

Available as short communication only. A focal-plane detector for the recoil mass spectrometer has been conceived and developed. It consists of a 14 x 14 cm2 position-sensitive parallel-plate avalanche counter (PS - PPAC); it has three electrodes: two anode wire planes each with 140 wires stretched in the x and y directions and a common cathode foil between them at a distance of 2.0 mm from the anodes. The anode wires consists of 20 μm gold-plated tungsten wires with 1 mm spacing; the cathode is made of 1.3 μm thick Mylar foil aluminized on both sides. To extract the position information each anode wire is connected to one of the two delay lines fixed on the x and y anode frames. Each delay line is made of 14 integrated circuits and has a total delay of 280 ns. A typical response of the PS - PPAC exposed to a 5.5 MeV α-source is presented. For this measurement the detector was filled with heptane (10 torr). A peak corresponds to each of the anode single wire and the resolution is determined by the wire separation. The peak-to-valley ratio is 15 with is comparable with the focal-plane detector for Recoil Mass Spectrometer of Laboratori Nazionali di Legnaro. (Author) 1 Fig., 2 Refs