The radioactive In116 produced by the In115(n,γ ) In116 reaction has been utilized in a simple personnel monitoring device at the ORGDP for several years as a method for estimating the total radiation dosage received in the event of a possible accidental nuclear reaction. A 1-gm indium foil is placed in a standard plastic security badge; after a suspected exposure to an accidental burst, this foil is monitored by a β-γ survey meter, and the reading obtained used to determine the estimated dosage. A time-after-exposure correction factor is also used. For calibration of indium foil, an exposure to a light-water moderated critical reactor of highly enriched uranyl fluoride was evaluated and the results are indicated briefly. An instantaneous exposure of about 60 mrad is detectable immediately after an exposure even with the unsplit badges and one of about 120 mrad is detectable an hour after the occurrence.