Direct Reading Pocket Dosimeter (ca. 1932)

This direct reading pocket dosimeter was hand-built by Charlie Lauritsen sometime around 1932. Lauritsen gave it to Robley Evans who was one of Robert Millikan's graduate students at Caltech at that time. Dr. Evans donated it to the ORAU collection.

Charlie Lauritsen is credited with having designed the first direct reading pocket dosimeters and this is the oldest example in existence.

Direct reading dosimeters (often two) are typically worn in a shirt pocket, much like a fountain pen. The wearer determines their exposure by looking through the lens (upper left corner in the photo) and reading the position of a moving line (the shadow of a quartz fiber) on a small scale. In more modern devices, the scale usually indicates exposures between 0 and 200 mR (or mrem). The scale in this example reads from 0-50 with no units indicated.

The following selected quotes are from a December, 1932 U.P. press release describing events at a two-day meeting of the American Physical Society in Pasedena, California.

“As a safeguard for those who work around sources of short wave radiation, such as X-ray tubes, Dr. Charles C. Lauritsen of the California Institute of Technology has developed a portable roentgen-meter. . . The invention of Caltech’s noted X-ray authority, compact and convenient, resembles a fountain pen.” “Inside this little gadget, which the worker carries at all times, is a small ionization chamber, electroscope and microscope mounted within an aluminum housing.”

Donated by Robley Evans.