Civil defense Geiger counters
Most Geiger and ion-chamber survey meters were issued by governmental civil defense organizations in several countries from the 1950s in the midst of the Cold War in an effort to help prepare citizens for a nuclear attack.
Regardless of producer, most counters exhibit the same basic physical characteristics, albeit with slight variations between some production runs: a yellow case with black knobs and meter bezels.
The CD V-700 is a Geiger counter employing a probe equipped with a Geiger–Müller tube manufactured by several companies under contract to US federal civil defense agencies in the 1950s and 1960s.
The Federal Emergency Management Agency (FEMA) purchased a quantity of CD V-718s in the 1990s as a supplement to and partial replacement for the older meters in the inventory.
The CD V-718 differs from the military AN/VDR-2 primarily by being painted bright "civil defense" yellow instead of olive green and being graduated in Röntgens rather than Grays.
The CD V ion chamber units are now all approaching 50 years old at a minimum and that they contain parts that are sensitive to moisture, so relatively frequent calibration and inspection by an accredited and properly equipped facility is required to ensure reliable and accurate function.
This is a simple ion chamber radiological survey meter, specifically designed for high-radiation fields for which Geiger counters will give incorrect readings (see above).
They work by radiation penetrating the case of the unit and the enclosed ionization chamber to produce a visible reading between 0.1 R/h and 500 R/h (× 0.1, × 1, × 10, and × 100 scales).
A transistor oscillator coupled to a step-up transformer furnishes the necessary B current for the tube, with necessary rectifier diodes and filter capacitors.
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.
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.
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 defence instruments retained until 1982 or later were manufactured from 1953 to 1957, and required high voltage batteries which became obsolete after portable valve radios were superseded by transistor ones.
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.
Built by Plessey Controls, the Portable Dose Rate Meter (PDRM) 82 began to be issued in 1982 for civil defence, mainly the Royal Observer corps, with rollout completed in 1985.
The model is lightweight and water resistant, with an LCD display and a plastic case, along with miniature Geiger tube (shielded against beta particles), on a single, EMP-hardened, PCB.
It gave more accurate readings than previous models and due to the dry 'c'-cell torch batteries could be operated for up to 400 hours.
The fixed version had an external coaxial socket mounted on its rear that accepted a cable from the above ground ionisation detector under a green polycarbonate dome.
