LVIII. The lifetime of the 200 kev excited state of19F

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Abstract
Experiments to determine the magnetic moment of the 800 kev excited state of 19F (see Phillips and Jones 1956 and Lehmann, Leveque and Fiehrer 1955, and Treacy 1955) have made it, necessary to know the lifetime of the state more accurately than previously determined (Jones, Phillips Johnson and Wilkinson 1954, and Thirion, Barnes and Lauritsen 1954). The experimental arrangement used was similar to that of Bell, Graham and Petch (1952) as shown in fig. 1. The counters were sodium iodide crystals 2 in. × 2 in. × 1 in. in size, optically coupled to EMI 6262 photomultipliers. The collectors of these were connected to limiters for the fast coincidence circuit, and proportional pulses were taken from the twelfth dynodes. The resolving time of the fast coincidence unit was 45 millimicroseconds in one series of runs, and 80 millimicroseconds in another. The proportional pulses from the counters were fed to single channel kick sorters, set for the counter A to accept the photopeak of a 1·36 Mev gamma ray, and the counter B the photopeak of a 200 kev gamma ray. The outputs of the single channel kicksorters, and of the fast coincidence unit, were connected to a triple coincidence circuit of resolving time about one microsecond. This ensures that each counter counts only one gamma, ray.

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