Ionizing Nuklear Radiation Detection Circuits Technologies

OddMix.com - Technology Note - TN110501 - Karl Nagy

Figure 1. Radiation Detector Victoreen CDV-715 Front View [8 KB]
Figure 1. Radiation Detector Victoreen CDV-715 Front View

The recent tragedy in Japan demonstrated that nuklear accidents - even with the best of planning - are just waiting to happen. And with potentially life threatening radiactive fallout and rain as well as radon gas emissions are infiltrating into many houses. As a result public interest is justifiably high about affordable radiation detectors - Figure 1.

There are three major types of nuclear radiation that is potentially endangering our life and commonly found in the environment. These three fundamental major types of radiations are the alpha, the electron or beta rays and the gamma particle radiation. Of these three the gamma rays are the most damaging and difficult to stop.

Beta particles are light, highly energetic electrons, while alpha rays are heavy charged particles. Because both alpha and beta rays are charge carriers, they are both deflected by magnetic field. Gamma rays are comprised of heavy, charge-less particles that are not deflected by magnetic fields.

Figure 2. Radiation Detector Ionization Chamber at Left [10 KB]
Figure 2. Radiation Detector Ionization Chamber at Left

Based on the way the radiation interacts with the environment, two major classes of detectors are known and available for use. These two groups are the direct and indirect effect detectors. Direct detectors are usually produce electrical or light impulses when receiving radiation. In this major direct effect group we have the gas ionization detectors like the Geiger-Muller or G-M tube and the ionization chamber detectors Figure 2, scintillation and the newer solid state detectors.

The second group contains the dosimeters, TL [Thermo Luminescent] detectors, trace detectors and other additional detectors based on more esoteric technologies.

Figure 3. Photomultiplier Tube Type 931A Sylvania [6 KB]
Figure 3. Photomultiplier Tube Type 931A Sylvania

Sensitive radiation detectors are not that easy to construct thus the entire instrumentation field is little changed over half a century. The stagnation is attributable to the one sided, foolish "secrecy" practiced by most government around the planet. Those agents of retarded technologies hushed up any little thing whatever, that had to do with nuclear detection and measurements. As a result of that stagnation, all we have to work with is the same old - and very tired - workhorses. The most ancient is the well known and widely used major radiation sensor is the ionized gas type G-M tube that date back to 1928. Other, often used sensors are the ion chamber, solid state sensors and some scintillation detectors.

Available G-M tubes are mostly surplus that was manufactured long ago by now defunct, extinct vacuum tube factories. Two major types of G-M tubes were made; the end, or the side sensitive types. Tubes with a Mylar or mica end window are sensitive enough for alpha radiation measurements but - long term - those tubes that using them don't seal and last as well as units using all glass enclosures.

Either type G-M tubes requires high voltage power supplies for their operation. Usually the higher of this voltage the higher is the tube's sensitivity. Operating voltage for G-M tubes are in the range of 500 to 1,000 V DC [Direct Current]. The generation and the handling of this high voltage is often a problem so contemporary circuits often use some other type of sensor - like scintillating crystals. Unfortunately they are convenient, but not the most sensitive.

Scintillating crystals are difficult to come by and they often used along with photomultiplier tubes Figure 3. Photomultipliers are also requires precisely regulated high voltages for their operation.

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