The Henson Electroscope is a pioneers instrument
dedicated to the measurement of radiation. Designed by Charlie
Lauritsen around ~1937 and produced by Fred Henson Company of
Pasadena, it became immensely popular. It had both the sensitivity
required for use in the laboratory and the portability that
allowed it to serve as a type of survey instrument, at a time
no true survey instruments were commercially available.
The incident radiation produces ionize atoms
in the chamber volume, which creates a current flow. Consequently
the charge on the electrode decreases. Due to this decrease,
the quartz fiber moves and its deflection can be projected by
a light source to a calibrated scale through an objective lens.
Since the deflection of the quartz fiber is proportional to
the current flowing through the chamber, therefore it is a measure
of the dose delivered by the radiation. Upon full discharge,
the electroscope charged again, applying a voltage through a
Such instruments were built at Chalk River Laboratory
sometime around 1945. Originally designed for gamma-emitting
samples, but this device was used to measure beta-emitting samples
being inserted into a hemispherical chamber via a sliding drawer.
Spy story from the 1940's: