SPNDs with Prompt Response

Neutron-sensitive self-powered detectors with prompt response operate on a different principle than rhodium and vanadium SPNDs. The emitter, in this case, absorbs a neutron and emits gammas at the time of capture. It is these capture gammas that are responsible for the signal, and since they are only emitted at the time of the neutron capture, the detector response is instanta- 

Consider, then, a cobalt SPND (Fig. 14.30). Most of the capture gammas traverse the emitter, the insulator, and the collector without an interaction. Those that do interact produce electrons through the photoelectric or Compton reactions. As these fast electrons travel, they produce an outward flow of charge that generates a current. Because relatively few gammas interact, the sensitivity of a cobalt detector is lower than that of either rhodium or vanadium detectors (see Table 14.6). 

The Co detector has one undesirable characteristic due to the product of the neutron capture. That product is °Co, a j8 emitter with a 5.3-year half-life. The betas from Co produce a background signal that builds up with exposure. A way to suppress this background, using platinum shields, has been reported by Goldstein and Todt.  

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