RCL Mark 2, Model 201 Proportional Counter (1950s)

This is a fast neutron detector produced by Radiation Counter Laboratories (RCL) of Skokie, Illinois. 

The tube is approximately 8 1/4 inches long and 1 7/8 inches in diameter. A brass evacuation tube can be seen projecting to the right from the brass chamber. The actual proportional counter chamber is 1.2 inches long, lined with 1/16 inch of polyethylene, and filled with methane at a pressure of 150 cm. It operated at 2100 volts. Fast neutrons knock protons off the polyethylene lining. The protons then ionize the methane fill gas to produce the signal.

The RCL detector designation is the Mark 2, Model 201, Serial 127. The "1" at the end of the model number (201) refers to the number of chambers housed in the unit. The Models 202 and 203 used two and three chambers respectively.

Reference

Atomic Energy Commission Radiation Measuring Instruments and Associated Components RIB-8 (Part 2) Supplement, July 1, 1954, page BP-A13A.