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Civil defense Geiger counters

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Most Civil Defense Geiger Counters were issued by the United States Civil Defense during the 1960s in the midst of the Cold War in an effort to help prepare citizens for a nuclear attack. Although referred to as geiger counters, most CD devices were radiological survey meters capable of measuring only high levels of radiation that would be present after a nuclear event.

Manufacturers

CD meters were produced by a number of different firms under contract. Victoreen, Lionel, Electro Neutronics, Nuclear Measurements, Chatham Electronics, International Pump and Machine Works, Universal Atomics, Anton Electronic Laboratories; Landers, Frary, & Clark; El Tronics, Jordan, and Nuclear Chicago are among many of the manufacturers contracted.Regardless of producer, all counters exhibit the same basic characteristics, albeit with slight variations between some production runs: a yellow case with black knobs and meter bezels. All meters had a "CD" sticker on the side of the case.

Models

CD Counters came in a variety of different models, each with specific capabilities:

CDV-700

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 uranium oxide-glazed red 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

CDV-715

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!

CDV-717

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.

CDV-720

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.

Kearny Fallout Meter

Another meter of note is the Kearny Fallout Meter. The plans for this meter were published in Appendix C of Nuclear War Survival Skills by Cresson Kearny from research performed at Oak Ridge National Laboratory. It was designed to be able to be constructed from household materials by someone with moderate mechanical ability on the eve of an attack. The plans are presented in a newspaper printable format.

Other countries

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.

British civil defense instruments

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.

Contamination Meter No. 1

The first large scale British civil defense issue was the geiger counter 'Contamination Meter No. 1', of 1953 [1]. It had 0 - 10 mR/hour range with external probe and headphones. This was designed to use two 120 volt batteries, although those retained until the 1980s had an inverter and used four 1.5 volt standard batteries or a mains electricity supply. There was also a Mk 2 model which used rubber connectors and cable for the probe unit, compared to the Larkspur style ones of the 1st model.

Radiac Survey Meter

The British 'Radiac Survey Meter No 2' [2] date's from 1953-6, and required obsolete 15 and 30 volt high voltage batteries in addition to a 1.5 volt standard cell (which powers the valve heaters and light bulb). There was also a training unit [3] which measured 0-300 mR, and ran on four 30V cells plus one 1.5V for the filaments. This meter used a large GM tube as opposed to the ion chamber of the RSM No 2.

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.

PDRM82

In 1982 the British PDRM82 was issued for civil defense. This 'Tricorder'-design PDRM82 [4] is lightweight with an LCD display and a plastic case and has all the electronics including miniature geiger tube (shielded against beta particles) on a single, EMP-hardened, PCB. It was designed by Plessey to use three standard 1.5 volt cells, and is microprocessor controlled with digital readout.

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.

Quartz Fibre Dosimeter Chargers

The 1958-9 'Quartz Fibre Dosimeter Chargers, No. 1 and 2' were retained until the early 1990s as they do not require batteries at all (they incorporate a simple handle-driven generator). A later British civil defence dosimeter charger was developed by R. A. Stephen Ltd and manufactured from 1967-88, and uses a single 1.5 volt cell. It is similar to American dosimeter chargers.

See Also

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