SPEED OF RESPONSE OF SOME CRITICALITY DETECTORS

The Appendix B published with ANSI 8.3 in both the present and previous editions, contains a calculation example for distance of coverage of a CAAS. In it, a trip point multiplication factor of 2500 is included to address system under response to a short pulse of radiation. While the text describes this to accommodate needle response, it might seem that this would be unnecessary with modern circuitry. An investigation of the response of some radiation detectors used in alarm systems shows some fundamental effects still make such a consideration necessary. Outputs and alarms from an ionization chamber system are examined for response to a fast pulse reactor,and some. gamma detectors response to pulse radiation are examined including GM and scintillation detectors, and an ionization chamber. In addition, time to alarm by typical personal alarming dosimeters is determined by exposure to step - increase radiation and pulse radiation. This type of commercial instrument has been considered f or the application as a portable criticality alarm as addressed in section 4.4.2 of ANSI 8.3- 1997. There are variations in alarm signal activation delay depending on the amount of signal processing involved, with the greatest delay from those using digital data processing