An Introduction to Radiation Detection Instruments 1950 Armed Forces Special Weapons Project

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Originally a public domain film, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.

The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

https://en.wikipedia.org/wiki/Geiger_counter

Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/

A Geiger counter is an instrument used for detecting and measuring ionizing radiation. Also known as a Geiger–Muller counter (or Geiger–Müller counter), it is widely used in applications such as radiation dosimetry, radiological protection, experimental physics, and the nuclear industry.

It detects ionizing radiation such as alpha particles, beta particles, and gamma rays using the ionization effect produced in a Geiger–Müller tube, which gives its name to the instrument...

The original detection principle was realized in 1908, at the Victoria University of Manchester, but it was not until the development of the Geiger–Müller tube in 1928 that the Geiger counter could be produced as a practical instrument. Since then, it has been very popular due to its robust sensing element and relatively low cost. However, there are limitations in measuring high radiation rates and the energy of incident radiation...

A Geiger counter consists of a Geiger–Müller tube (the sensing element which detects the radiation) and the processing electronics, which displays the result.

The Geiger–Müller tube is filled with an inert gas such as helium, neon, or argon at low pressure, to which a high voltage is applied. The tube briefly conducts electrical charge when a particle or photon of incident radiation makes the gas conductive by ionization. The ionization is considerably amplified within the tube by the Townsend discharge effect to produce an easily measured detection pulse, which is fed to the processing and display electronics. This large pulse from the tube makes the Geiger counter relatively cheap to manufacture, as the subsequent electronics are greatly simplified. The electronics also generate the high voltage, typically 400–900 volts, that has to be applied to the Geiger–Müller tube to enable its operation. To stop the discharge in the Geiger–Müller tube a little halogen gas or organic material (alcohol) is added to the gas mixture.

Readout

There are two types of detected radiation readout: counts or radiation dose. The counts display is the simplest and is the number of ionizing events detected displayed either as a count rate, such as "counts per minute" or "counts per second", or as a total number of counts over a set time period (an integrated total). The counts readout is normally used when alpha or beta particles are being detected. More complex to achieve is a display of radiation dose rate, displayed in a unit such as the sievert which is normally used for measuring gamma or X-ray dose rates. A Geiger–Müller tube can detect the presence of radiation, but not its energy, which influences the radiation's ionizing effect. Consequently, instruments measuring dose rate require the use of an energy compensated Geiger–Müller tube, so that the dose displayed relates to the counts detected. The electronics will apply known factors to make this conversion, which is specific to each instrument and is determined by design and calibration.

The readout can be analog or digital, and modern instruments offer serial communications with a host computer or network.

There is usually an option to produce audible clicks representing the number of ionization events detected. This is the distinctive sound normally associated with handheld or portable Geiger counters...

Limitations

There are two main limitations of the Geiger counter. Because the output pulse from a Geiger–Müller tube is always of the same magnitude (regardless of the energy of the incident radiation), the tube cannot differentiate between radiation types. Secondly, the inability to measure high radiation rates due to the "dead time" of the tube. This is an insensitive period after each ionization of the gas during which any further incident radiation will not result in a count, and the indicated rate is, therefore, lower than actual. Typically the dead time will reduce indicated count rates above about 104 to 105 counts per second depending on the characteristic of the tube being used. While some counters have circuitry which can compensate for this, for accurate measurements ion chamber instruments are preferred for high radiation rates...