4π Si ball

The report addresses the developement of a 4π-type Si detector array, called Si crystal ball, designed for determination of the multiplicity of charged particles. The design requirements for the detector array are as follows: it should be possible to distinguish between output signals for proton and α particle; the detector system as a whole should be operable up to a counting rate of about 5x105 cps; the vacuum tank containing the detector array and target should be of a size that permits its accommodation in a spherical container with a diameter of 98 mm; the detector system should have a dodecahedron configuration consisting of pentagonal unit detectors; and the incident particles should not enter the detector system to allow heavy ions to damage the system. Each pentagonal unit detector has sides of 18 mm and a thickness of 178 μm. Tests are made to determine the performance of the Si crystal ball. Results show that its detection efficiency is 25 percent for 3p-channel gamma rays gated by 3p and 40 percent for 2p-channel gamma rays gated by 2p, which are about 20 and 10 times as high, respectively, compared to conventional detectors. (N.K.)