The CDV-700 is an actual geiger counter with a geiger tube. Detects beta radiation and gamma radiation with the detecting wand's beta shield open, or gammas only when the shield is closed. Used to detect low levels of radiation, but must be used in conjunction with a survey meter (below) in high-radiation areas. High-radiation fields can saturate the geiger tube, causing the meter to read a very low level of radiation (close to 0R/hr) causing the user to believe it is safe when it is not. Maximum reading of 50mR/hr. In rare cases, this particular counter was modified to detect alpha radiation in addition to betas and gammas.
The CDV-700 also came with a "check source", a bit of a radioactive isotope under a sticker on the side of the unit. The isotope varied with the maker; depleted or natural uranium was common. This produces about 1-2 mR/hr adjacent to the source, a value which is clearly visible on the analog meter as well as audible via the headphones that accompanied the units. This is about 100 x background levels of radiation, and similar to the near-field from an red (uranium oxide glazed) Fiestaware saucer.
The CDV-700, as a true Geiger Counter, is capable of measuring these ambient environmental levels; the ionization-chamber detectors listed below will not register any activity unless a major radiological incident (e.g., nuclear fallout, spent (but not new) reactor fuel-rods, industrial radiography source leakage) occurs.
The CDV-700 came in 8 models: CD V-700 Model 1, CD V-700 Model 2, CD V-700 Model 3, CD V-700 Model 4, CD V-700 Model 5, CD V-700 Model 6, CD V-700 Model 6A, and CD V-700 Model 6B
By far the most popular meter on the market today. This is the simplest radiological survey meter, specifically designed for high-radiation fields for which geiger counters will give incorrect readings (see above). Survey meters do not read alpha or beta radiation. They work by radiation penetrating the case of the unit and the enclosed ionization chamber to produce a visible reading between .1R/hr and 500R/hr. If you can get this unit (or any other like it) to react to any source of radiation evacuate the area immediately!
Similar to the CDV-715, this unit reads from .1R/hr to 500R/hr. It is also a survey meter with an ionization chamber, however this unit's chamber is detachable for hanging outside your shelter or basement. When used, the ionization chamber would be inserted into a yellow anti-contamination bag, tied off, and hung outside a bomb shelter to measure radioactivity levels from a safe distance. An extension coaxial cord, typically stored inside the unit, is then run from the outdoor chamber to the indoor meter. The coaxial spool is used to prop the meter up for reading. This would allow those hiding to wait until outside radiation levels have fallen to a "safe" level before emerging. When using the extension cord, a slight delay in measurement readings occurs, however this is not really an issue as outdoor radiation levels are unlikely to change quickly.
This is a survey meter with a twist. Similar to the CDV-715, the CDV-720 is a fixed-position ionization chamber survey meter. Unlike any other survey meter, however, this unit has a movable beta shield on the bottom of the unit for detecting high levels of beta radiation. When slid to the open position, beta particles are allowed to directly penetrate the ionization chamber. With the beta shield closed, only gammas can penetrate both the shield and ionization chamber. This meter also reads from .1R/hr to 500R/hr.
The United States manufactured approximately 500,000 geiger counters. Britain manufactured about 20,000 of each of its major types, and is second after the U.S. Some instruments were also manufactured by other countries in smaller numbers.
The American instruments dating from the Kennedy administration era were designed to use low voltage transistor electronics, and the batteries are still available today. However, most British civil defense instruments retained until 1982 or later were manufactured from 1953-7, and required high voltage batteries which became obsolete after portable valve radios were superseded by transistor ones.
All British civil defense instruments were jointly designed by the Home Office and the Ministry of Defense, and were also a military issue.
These meters were favoured as they had been tested on fallout in Australia after Operation Buffalo nuclear tests, and were retained until 1982 by commissioning a manufacturer to regularly produce special production runs of the obsolete batteries.
The UK's Royal Observer Corps initially used the RSM No 2 as its prime radiation detector until it was replaced by the specially designed 'Fixed Survey Meter' which used the same obsolete high voltage batteries as the RSM. The ROC retained the RSM No 2 for use during external 'post attack' mobile monitoring surveys.
For use by the Royal Observer Corps the instrument was also provided in the fixed version designated the PDRM82(F). The fixed version had an external coaxial socket mounted on its rear, that accepted a cable from the above ground ionisation detector under a polycarbinate dome. For training purposes timed simulated readings could be fed to the meter from an Eprom.