NUMEC Criticality Dosimeter (ca. 1970s, 1980s)

This neat little item is a criticality dosimeter from the Nuclear Materials and Equipment Corporation (NUMEC) facility at Apollo, Pennsylvania where substantial quantities of enriched uranium and plutonium were handled. One of the more intriguing stories about this site is that during the 1960s it might have supplied the Israeli government with several hundred pounds of enriched uranium—enough to build an atomic bomb or two. At least that's what the FBI suspected.

The central barrel of the dosimeter contains a cadmium capsule (see photograph above) in which an indium foil wrapped around a copper cylinder is located.

The two ends of the dosimeter hold tiny (ca. 1 cm long) glass tubes which contain some sort of white powder, possibly aluminum or magnesium.

The radioactivity induced in these different materials by the neutrons released in a criticality accident can help determine the radiation dose. Indium is activated by 0.5 MeV neutrons while copper is activated by 12 MeV neutrons. The aluminum or magnesium, if that is what the white powder contains, would be activated by neutrons in the 3 to 6 MeV range.

Size: 5 1/4” long and 7/8” maximum diameter

Donated by Ray Vinton.