Landsverk Model L-64 Roentgen Meter

Manufactured by the Landsverk Electrometer Company (ca. 1960) and intended for the measurement of X-rays and gamma rays. 

It is actually a modified version of a Lauritsen electroscope with the sensing element (a quartz fiber) connected to a socket into which one of several interchangeable chambers can be inserted. Each chamber is intended for a particular exposure range: 0-1 mR up to 0-1000 R. The unit also has a set of plastic build-up sleeves that are used to attain electronic equilibrium with high energies radiation (e.g., Co-60).

When used, the quartz fiber as seen through the eyepiece is adjusted to the zero position on the 100 division scale. The selected chamber is then inserted into the socket and charged. After charging, the chamber is removed and exposed in the radiation field being measured. After the exposure, the chamber is again inserted into the socket of the L-64 and the position of the fiber is recorded. If, for example, the fiber is at 50 on the 100 division scale with the 0-1 mR chamber, the exposure was 0.5 mR.