Knowing the radiation levels in their immediate environment is crucial for everyone who works with or around radiation. Radiation detectors of various kinds are mostly used to do this. Finding the right detector for the task at hand and making the most of using that detector can both benefit from having a basic awareness of the many types of detectors available and how they operate.
“GEIGER COUNTERS,” a notation
Many people prefer to lump them all together under the phrase “Geiger counters” when thinking of radiation detection, a mistake that is actively pushed by well-liked TV shows and motion pictures. Geiger Mueller (G-M) tubes are one of the most used forms of radiation detectors, however the general term “Geiger Counter” isn’t necessarily the most applicable. It is applicable to a very particular kind of detector and, often, to a particular use for that detector. Typically, the type of detector element used or the application involved are used to classify radiation detection systems. The terms “Ion Chamber,” “Survey Meter,” “Contamination Meter,” and “Frisker Probe” are sometimes used to describe instruments. The legitimate use of the term “Geiger Counter” has been so extensively corrupted by popular culture that using it rarely gives enough information about the gadget in question.
DETECTORS OF FIRST RADIATION
Scientists have been looking for techniques to gauge and observe the radiation emitted by the materials they work with since since the earliest radiation tests conducted by Roentgen and Becquerel. A photographic plate was one of the first tools for gathering any kind of data from radioactivity. A photographic plate would be positioned in a radioactive beam’s or material’s path or vicinity. Because of the radiation exposure, the plate would have spots or be fogged when it was developed. A similar technique was employed in 1896 by Henri Becquerel to prove the presence of radiation.
The electroscope was another widely used early detector. These made use of a pair of gold leaves that, when exposed to radiation, ionized and became charged, causing them to repel one another. This made it feasible to measure radiation more sensitively than was dependably achievable with photographic plates. They were an important instrument for early radioactivity experiments since they could be set up to measure alpha or beta particles depending on how the gadget was setup.
The spinthariscope was an intriguing early invention developed to measure the precise individual particles or rays being released by a radioactive substance rather than a more general measurement of a radioactive environment. The Crookes Tube was created by William Crookes, who also created the Crookes Screen, which Wilhelm Roentgen used to discover X-Rays. The Crookes Screen employed a little amount of a radioactive chemical close to the zinc sulfide screen at the end of a tube with a lens at the other end. Each contact between the zinc sulfide and the released alpha particles would cause a brief flash of light. This was one of the earliest methods of measuring the rate of decay, albeit a rather laborious one because it required scientists to work in shifts, actually counting the light bursts. The spinthariscope underwent a rebirth as an instructional tool later in the 20th century, although it was not very useful as a long-term radiation detection method. Future radiation detection methods would benefit from particular materials’ propensity to emit light when exposed to radiation.
The use of these pioneering tools—along with several others, like cloud chambers—helped researchers better comprehend radiation’s fundamental concepts and undertake significant experiments that laid the groundwork for later advancements. The creation of novel radiation detectors, many of which are still in use today, such as G-M Tubes, Ion Chambers, and Scintillators, was part of this.
WHERE/WHEN RADIATION DETECTORS ARE REQUIRED
Understanding how and where a detector will be used is crucial to selecting the right one. Different detector types are needed for different settings and applications since they may all be tailored to perform certain tasks. Measurement, protection, and search are three main categories into which the uses for radiation detecting instruments can be divided.
When there is a known presence of radioactive materials that needs to be monitored, radiation measurement tasks are used. This kind of detection aims to raise awareness. knowledge of the size of a radioactive field that has already formed, the limits of a radioactive region, or even just the spread of radioactive contamination. These are places where radiation is anticipated, or at the very least thought to be plausible. The demands placed on detectors in these environments are special, frequently necessitating relatively higher measurement ranges or modifications to specifically search for one type of radiation.
In that it frequently takes place in an environment where radiation is anticipated to be present, radiation protection is comparable to radiation measuring applications. The objectives are different, though. The objective of radiation measuring settings is to track radioactivity itself and be aware of changes, boundaries, etc. Monitoring people is the aim of radiation protection. The most prevalent example of this is radiation dosimetry, where workers in the medical field, the nuclear sector, and numerous other occupationally exposed workers all over the world wear radiation badges. The significance of this is that it offers protection from the most damaging effects of radiation exposure through awareness. A wearer can stay informed about how much radiation they’ve been exposed to and how that corresponds to potential health effects, and they can adjust their behavior, position, or schedule accordingly.
Since radiation is not anticipated in the area and there is a desire to keep things that way, radiation search is different from the other two fundamental categories of radiation detection applications. Radiation search has a particular set of requirements to reflect the fundamentally different situations in which it occurs, and is primarily the purpose of radiation security officers, first responders, or organizations like customs & border inspectors. The requirement for very sensitive detectors arises from the focus on smaller, hidden radioactive sources or materials. Since only a small subset of radioactive isotopes are typically of concern, it is crucial to be able to identify those that are present for valid reasons such as medical treatment or merely an accumulation of a naturally occurring radioactive substance. This is where spectroscopy comes in very handy.
These three groups and the various jobs that fall under them aid in identifying the best equipment or detector for the job.
TYPES
According to the particular requirements of the equipment, three types of detectors are most frequently employed when referring to radiation detection instruments. These three types of detectors are solid state, gas-filled, and scintillators. Each one is suited to their own particular roles because of a variety of talents and flaws.
FUEL FILLED
Gas-filled detectors, the original kind of radiation detector, are among the most widely used. Although there are several types of gas-filled detectors, they all operate according to the same general principles. The gas in the detector reacts to radiation by becoming ionized, and the electrical charge that results from this reaction is measured by a meter.
Ionization chambers, proportional counters, and Geiger-Mueller (G-M) tubes are the several varieties of gas-filled detectors. The applied voltage across the detector, which defines the sort of response that the detector will register from an ionization event, is the primary factor that distinguishes these various types.
CHAMBER OF ION
Ionization Chambers, or Ion Chambers, are at the low end of the voltage scale for detectors that are filled with gas. They work at low voltage, thus the detector only records measurements from the “primary” ions—a pair of ions formed by the interaction of a radioactive photon with a positively charged ion and a free electron in the reaction chamber. As a result, the measurement the detector takes is directly related to the quantity of ion pairs produced. This is especially helpful for tracking how much of a dose is absorbed over time. Due to the fact that they don’t experience any of the problems with dead time that other detector types can, they are also useful for measuring high-energy gamma rays.
Ion cambers cannot be utilized for spectroscopy because they are unable to distinguish between different types of radiation. They may also have a tendency to cost more than alternative options. They are useful detectors for survey meters despite this. They are frequently used in laboratories to create calibration reference standards.
PROPORTIONAL
The proportional (or gas-proportional) counter is the next voltage level up for gas-filled detectors. They are often designed so that, throughout the majority of the chamber, they function much like an ion chamber, producing ion pairs as a result of radiation interactions. But because of their high voltage, the ions “drift” toward the anode of the detector. The voltage rises as the ions go closer to the detector anode until they reach a point where a “gas amplification” effect happens.
Gas amplification is the process by which the first ions formed in a reaction with a photon of radiation set off additional ionization processes, increasing the output pulse strength as measured across the detector. The number of initial ion pairs generated, which correlates to the energy of the radioactive field it is interacting with, determines the size of the ensuing pulse.
The fact that proportional counters respond differently to various energies and can thus distinguish between various forms of radiation they come into contact with makes them extremely helpful for particular spectroscopic applications. This sort of detector is extremely important as a contamination screening detector since it is highly sensitive and effective at alpha and beta detection and discrimination.
G.M. Tube
The Geiger-Mueller tube, which gave rise to the term “Geiger Counter,” is the final significant class of gas-filled detectors. They differ from other detector types in that each ionization reaction, regardless of whether it is a single particle contact or a greater field, generates a gas-amplification effect across the whole length of the detector anode while operating at a considerably higher voltage than other detector types. They can therefore only actually be used as basic counters to measure count rates or, with the right algorithms, dosage rates.
A G-M needs to be “reset” to its initial condition following each pulse. Quenching is used to accomplish this. By momentarily reducing the anode voltage on the detector after each pulse, you may achieve this electronically and allow the ions to recombine back into their inert condition. This can also be done chemically using a quenching gas like halogen, which takes in the extra photons produced by an avalanche of ions without getting ionized.
At greater exposure rates, G-M tubes may have “dead time,” which is the lag between the pulse cascade and when the gas may return to its initial state and be prepared to detect another pulse. This is due to the lengthy reaction that G-M tubes encounter with each radiation pulse. Calibration or algorithms built into the detection instruments themselves that “compute” what the additional pulses would be based on the measurement data already collected can be used to account for this.
Leave A Comment