Development of a Two-dimensional Angular-correlation-of-annihilation-radiation Apparatus Using Position Sensitive Photomultiplier Tubes

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The proposed development of an original, new-type two-dimensional angular-correlation-of-annihilation-radiation (2D-ACAR) apparatus has been successfully accomplished.The machine is already in practical use. At present the detectors are placed at 5m away from the sample. The angular resolution for a sample of size 2mm is 1.1x10^<-3>mc.The characteristic features of the new apparatus are as follows :(1) It is an original, new type of 2D-ACAR apparatus, making use of position senseitive photomultiplier tubes developed by HAMAMATSU.Arrays of 2.2mm x 2.2mm x 15mm BGO scintillator crystal blocks are coupled with the photomultiplier tubes.(2) The methods for the detection of the gamma ray incident position, the data processing system, and the detectors position control system are all simple.(2a) The gamma ray incident position is determined simply by analyzing the 8 outputs from the resister chains conected to the multi-wire anodes of the photomultiplier tubes by CAMAC ADC and then processing them by a personal computer.(2b) The translational and rotational motions of the detecters are driven by individual servo-motors controlled by the same personal computer. This gets rid of large arms otherwise necessary to keep the detectors directly face the sample regardless of their positions. The armless system make it easy to change the detector arrangement.(3) A variable magnetic field up to <plus-minus>2T can be applied to the sample by an electromagne