CD V-700
The CD V-700 (often written as "CDV-700") is a Geiger counter employing a probe equipped with a Geiger–Müller tube, manufactured by several companies under contract to United States federal civil defense agencies in the 1950s and 1960s.
Even though large numbers have been sold off as surplus to civilian users, many remain in use with first responders and state emergency management agencies today.
Mounted to the top of the upper case is a carry handle in which the probe clips in for storage, a connector for a headphone and the control knob.
The inside of the unit contains high voltage electronics of up to 900 volts, so care is recommended when operating with the case open.
Unlike many newer devices of this type, the CD V-700s are not equipped with a visual or audible alarm for excessively high levels of radiation.
The choice of this tube is intended to strike a balance between sensitivity and ruggedness and detects gamma radiation at energy levels of between 20 and 1000 Kev.
High-radiation fields can saturate the Geiger tube, causing the meter to read a very low level of radiation (close to 0 R/h), thus inducing the user to erroneously believe conditions are safe when they are not.
The isotope varied with the maker; depleted or natural uranium was common, though the Instruction and Maintenance Manual for the Lionel Model 6B indicates that a "Radium D+E beta source" with an approximate half-life of 22 years is present under the nameplate.
This produced, at the time of installation on the machine, about 1–2 mR/hr adjacent to the source, a value which was clearly visible on the analog meter as well as audible via the headphones that accompanied the units.
[2] The units were calibrated at the factory, but this may drift over time and need to be recalibrated by means of an adjusting screw inside the case.
In their original Cold War application, the sensitive CD V-700s would be saturated and thus rendered useless by the high radiation levels expected after an exchange of nuclear weapons.
The CD V-700s main purpose was as a peacetime training instrument and for use in checking food and shelter entrances for low levels of fallout contamination.
[7] The kit, which was produced by Lionel Electronic Labs and EON Corporation, is designed to decrease the sensitivity of Model 6, 6A & 6B meters by ten times.
However, the 496 features a number of improvements over any of the older civil defense versions, including modernized electronics, a BNC connector or MHV connector for external probes, a built-in speaker with on-off knob, a built-in battery test circuit, and a meter face graduated in Counts Per Minute for use with various probes.
