Landsverk Model L-65 Indirect Reading Pocket Chambers (1950s and 1960s)
These indirect reading pocket dosimeters were manufactured by the Landsverk Electrometer Company of Glendale California. The earliest reference I have found for the Model L-65 is the May 1951 issue of Nucleonics, while the last reference is a 1968 company price list.
The following photograph shows an early version (ca. 1950s) of the L-65. It is 4" long and 0.5" in diameter, and its range is 0-200 mR. The barrel is polished bakelite and the protective cap for the charging contact is aluminum.
The company catalog states: "Model L-65 chambers are used in very large numbers in atomic production plants in the United States. It is also a standard model for laboratories, clinics, etc. This chamber provides much lower cost than film badges over a period of two years or more and it is much more accurate. Its energy dependence is less than 10% from Co-60 to 50 keV."
The following photograph shows a later version of the Model L-65. It is somewhat shorter than the earlier version, (3.5" vs 4") and it uses an aluminum rather than bakelite cap at the clip end of the dosimeter. The aluminum cap is stamped with the chamber exposure range and serial number. The latter information had been indicated on a paper label on the barrel of the earlier version of the chamber. Paper labels tend to deteriorate over time.
Landsverk always incorporated a groove around the aluminum cap used to protect the charging contact. The idea was that the person responsible for reading large quantities of these dosimeters could insert the groove into the slot of a tabletop jig and pull off (or put on) the cap while only using one hand.