Victoreen Model 287 Minometer (ca. 1940s)
This is a Model 287 "Minometer" (serial number 816) charger-reader manufactured by the Victoreen Instrument Company of Cleveland, Ohio. Quoting a 1947 product description "The minometer has been designed to measure stray radiation as well as extremely small X-ray and gamma ray quantities. The instrument consists essentially of a string electrometer and a small ionization chamber designed in the shape of a fountain pen for carrying in the coat pocket. The value of the ionization chamber, as well as the scale supplied with the instrument, is 0.2 r which is twice the accepted quantity estimated for a daily tolerance dose."
The photo to the right shows the Minometer with an indirect reading pocket chamber positioned for charging or reading.
The exposure (in mR) was determined by measuring the decrease in charge in the condenser chamber as a result of the radiation exposure. The condenser chambers that the Minometer charged and read were used for personnel monitoring. Because the exposure could not be determined without the Minometer, the chambers were referred to as indirect reading pocket dosimeters.
The Minometer appears to have been developed sometime in the late 1930s while the example on display probably dates from the late 1940s.
There are two possible reasons that the scale read 0-200mR. The first is that this would place the daily tolerance dose of 100 mR in the middle of the scale. The other possible reason is that making the chamber any more sensitive would require increasing the size of the chamber to the point where it would not conveniently fit in a pocket.
The photograph to the right shows the identification plate on the end of the Minometer's base and an indirect reading pocket chamber with the protective cap for the charging contact removed.
Case: 8" long x 4" wide x 6" high
Weight: 6 pounds
Power: 110 volt 60 cycle
Donated by the Victoreen Instrument Company courtesy of John Pobicki.
- Atomic Energy Commission Radiation Instrument Catalog No. 2, 1950, Page AE-2A.
- Product description, Nucleonics November 1947, Page 77.
- Davis, DM, Gupton, ED, and Hart, JC. Applied Health Physics Radiation Survey Instrumentation, ORNL-332 (rev), Jan. 1, 1954.