Nuclear Research Corporation SM-5A (ca. 1954)
This is a curious animal. The 1954 Atomic Energy Commission supplement to their Radiation Measuring Instruments compendium described it as follows: "Portable ratemeter with thin wall geiger tube for laboratory monitoring, prospecting, or personnel monitoring." They also commented that the probe "is conveniently placed inside cabinet for ease of handling and protection."
I say it is a curious instrument because there is blacked out text on the side of the instrument (and in the Instruction Manual) that originally read "CD-V-700." In addition, the General Description in the manual says the following of the SM-5A: "This instrument is especially intended for civil defense use, for monitoring personnel, food and water, and for other applications where low-level measurements must be made."
My guess is that Nuclear Research Corporation had, or was just about to, started production of the SM-5A when the FCDA announced that it was seeking bids to manufacture CD V-700 GM detectors for the U.S. civil defense program. In response, the company might have begun referring to the SM-5A as the CD V-700 and submitted the instrument to the FCDA for evaluation. The FCDA might then have rejected the SM-5A for this purpose thus forcing the company to remove any indications from the instrument and the associated literature that it was a CD V-700. That's pure speculation of course. There are two schematics in the Instruction Manual. One is dated December 1952, and the other is dated June 1953.
The above photo shows the probe removed from its storage housing inside the instrument case.
Detector: Glass-walled GM tube (Raytheon CK 1043). Wall thickness is 30 mg/cm2.
Range: 0-0.5, 0-5.0, 0-50 mR/h
Audio: Headphones, no speaker
Size: Approximately 5” x 9” x 5”
Weight: ca. 6 lbs.
- One mercury cell pack
- One 67.5 volt battery
- Two 22.5 volt batteries
- Nuclear Research Corporation Instruction Manual for Radiation Survey Meter SM-5A. No date, but contains schematics dated 1952 and 1953. This manual can be downloaded from the Museum Library.
- Atomic Energy Commission. Radiation Measuring Instruments RIB (Part 2) Supplement, page SGM-94A, July 1, 1954.