Abstract
A conventional lens spectrometer has been adapted to the measurement of high energy gamma-rays by detecting positron-electron pairs in coincidence. The source and converter are centered on the optic axis and the baffle system selects pairs of nearly equal energy. The detection method consists of dividing the focal circle of confusion in half and observing coincidences between particles entering these two regions. Statistically the components strike different areas in half the cases. The detectors are semicircular anthracene crystals connected by light pipes to 1P21 photomultiplier tubes. Pulses from these are fed through amplifiers to a coincidence circuit of 7×10−8 sec resolving time. The method has been tested by observing ``pair peaks'' due to the 2.76- and 2.62-Mev gamma-rays of Na24 and ThC″, respectively. The Po–Be reaction gamma-ray has been measured at 7.5 percent resolution and found to have an energy of 4.47±0.04 Mev. Using a proton beam from the Brookhaven electrostatic accelerator gamma-rays of 6.19±0.08 Mev and 7.13±0.12 Mev occurring in the F19(p,α)O16 reaction have been observed with this apparatus. The results on both Po–Be and the fluorine reaction are in agreement with previous measurements by other methods.
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