Tracerlab Model TGC 315 Annular GM (1960s)
In the late 1940s and early 1950s, prior to the development of liquid scintillation counters, the main options for counting liquid samples were the use of dipping counters, Marinelli beakers, and the annulus tubes of the sort shown here. An annulus (jacketed) tube consists of a central thin-walled glass GM tube surrounded by an outer glass jacket (which served the same role as a Marinelli beaker). The water to be analyzed was fed into the lower of the two openings on the jacket. The sample might remain stationary in the annulus or it could flow continuously through the tube during the count. Annulus tubes were used for analyzing gas samples as well as liquid samples.
The photograph to the right shows a Model TGC 315 annular GM tube manufactured by Tracerlab of Waltham, Massachusetts.
Size: 6 1/2" high, 1 1/4" diameter
Wall: 30 mg/cm² glass
Jacket volume: ca. 30 ml
Gas: Neon (?), halogen quenched
Cathode: Inner surface of glass wall coated conductive film (tin?)
Operating voltage: 600 volts
Base: 4 prong
Tracerlab Bulletin J-27, June 1968, Glass Wall, Halogen Quenched "Flow Around" GM Tube.