The primary purpose of the Model CD V-750 was to charge civil defense dosimeters (CD V-138, 730, 740, and 742). By charge, we mean adjust the dosimeter so that the quartz fiber, visible through the eyepiece as a fine line running vertically across the scale, is set at zero. The CD V-750 could also be used to read the dosimeters if insufficient light was available - quite possible in an emergency situation.
cdv_750_742_1 cdv_750_742_2 cdv_750_742_3 cdv_750_742_4
The key features of the CD V-750 were the charging contact (protected by a dust cap attached to the case via a bead chain) and the control knob for adjusting the charge.
cdv_750_742_5 cdv_750_742_6 cdv_750_742_7 cdv_750_742_8
The model I have and that can be seen in the pictures above is 5b. Earlier models had a lever that pushed towards the lower left was used to provide the charge (The mechanical energy generated by pumping the lever is converted into electrical energy. Those units also had a battery, but only to power the light used to illuminate the dosimeter scale). The 5b and newer units use the battery energy for the charge as well, with a small invertor that boosts the 1.5V from the D cell battery to aprox 57Volts.

The CDV-742 Radiological Dosimeters are electrostatic devices used for measuring an
accumulated dose (over a period of time) of radiation. The civil defense dosimeters are a standard dosimeter design. This same type of dosimeter would be used anywhere people would have to measure their accumulated radiation dose. The electrostatic type of dosimeter is charged with a dosimeter charger (pictured above). This charger, charges the inner chamber of the dosimeter tube with a high voltage charge which zeros the dosimeters hair like crystal in the viewing scale. When ionizing gamma radiation passes through the dosimeter it discharges it causing the hair like crystal to move up scale resulting in a reading of the accumulated dose received by the dosimeter.

The inside of a dosimeter pen contains a capacitor (charged with the charger/CDV-750), an electroscope (the quartz fibre), lenses to focus the light to allow observations via the eyepiece and finally a scale (working as an overlay on top of the quartz fibre shadow):
And yet more in-detail diagrams:
dosimeter1 dosimeter2


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