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Survey meters in radiation protection are hand-held ionising radiation measurement instruments used to check such as personnel, equipment and the environment for radioactive contamination and ambient radiation. The hand-held survey meter is probably the most familiar radiation measuring device owing to its wide and visible use.
The most commonly used hand-held survey meters are the scintillation counter, which is used in the measurement of alpha, beta and neutron particles; the Geiger counter, widely used for the measurement of alpha, beta and gamma levels; and the ion chamber, which is used for beta, gamma and X-ray measurements.
The instruments are designed to be hand-held, are battery powered and of low mass to allow easy manipulation. Other features include an easily readable display, in counts or radiation dose, and an audible indication of the count rate. This is usually the “click” associated with the Geiger type instrument, and can also be an alarm warning sound when a rate of radiation counts or dose has been exceeded. For dual channel detectors such as the scintillation detector it is normal to generate different sounds for alpha and beta. This gives the operator rapid feedback on both the level of radiation and the type of particle being detected. These features allow the user to concentrate on manipulation of the meter whilst having auditory feedback of the rate of radiation detected. [1]
Meters can be fully integrated with probe and processing electronics in one housing to allow single-handed use, or have separate detector probe and electronics housings, joined by a signal cable. This latter is preferred for checking of convoluted surfaces for radioactive contamination due to the ease of manipulating the probe.
The readout for alpha and beta radiation is normally in counts, whilst that for gamma and X-ray is normally in a reading of radiation dose. The SI unit for this latter is the sievert. There is no simple universal conversion from count rate to dose rate, as it depends on the particle type, its energy, and the characteristic of the sensor. Count rate therefore tends to be used as a value which has been calculated for a particular application for use as a comparator or against an absolute alarm threshold. A dose instrument may be subsequently used if a dose reading is required. To help with this some instruments have both dose and count rate displays.
Battery operated meters usually have a battery level check.
Survey meters can be ratemeters or scalers
In Radiation Protection, an instrument which reads a rate of detected events is normally known as a ratemeter, which was first developed by N.S.Gingrich et al. in 1936. [2] This provided a real-time dynamic indication of the radiation rate, and the principle has found widespread use in Health Physics and as radiation Survey meter.
An instrument which totalises the events detected over a time period is known as a scaler. This colloquial name stems from the early days of automatic counting, when a scaling circuit was required to divide down a high count rate to a speed which mechanical counters could register. This technique was developed by C E Wynn-Williams at The Cavendish Laboratory and first published in 1932. The original counters used the "Eccles-Jordan divider" circuit, today known as a flip flop. [3] This was before the era of electronic indicators, which started with the introduction of the Dekatron tube in the 1950s. [3] [4]
The user must have an awareness of the types of radiation to be encountered so that the correct instrument is used. A further complication is the possible presence of "mixed radiation fields" where more than one form of radiation is present. Many instruments are sensitive to more than one type of radiation; alpha and beta, or beta and gamma, for instance, and the operator must know how to discriminate between these. The necessary skills in using a hand-held instrument are not only to manipulate the instrument, but also to interpret results of the rate of radiation exposure and the type of radiation being detected.
For instance, a Geiger end-window instrument cannot discriminate between alpha and beta, but moving the detector away from the source of radiation will reveal a drop off in alpha as the detector tube must normally be within 10mm of the alpha source to obtain a reasonable counting efficiency. The operator can now deduce that both alpha and beta is present. Likewise for a beta/gamma geiger instrument, the beta may have an effect at a range in the order of metres, depending on the energy of the beta, which may give rise to the false assumption that only gamma is being detected, but if a sliding shield type detector is used, the beta can be shielded out manually, leaving only the gamma reading.
For this reason, an instrument such as the dual phosphor scintillation probe, which will discriminate between alpha and beta, is used where routine checking will come across alpha and beta emitters simultaneously. This type of counter is known as "dual channel" and can discriminate between radiation types and give separate readouts for each.
However, scintillation probes can be affected by high gamma background levels, which must therefore be checked by the skilled operator to allow the instrument to compensate. A common technique is to remove the counter from any proximity to alpha and beta emitters and allow a "background" count of gamma. The instrument can then subtract this in subsequent readings.
In dose survey work Geiger counters are often just used to locate sources of radiation, and an ion chamber instrument is then used to obtain a more accurate measurement owing to their better accuracy and capability of counting higher dose rates.
In summary, there are a variety of instrument features and techniques to help the operator to work correctly, but the use by a skilled operator is necessary to ensure reliable results. The UK Health and Safety Executive has issued a guidance note on selecting the correct instrument for the application concerned, and the care and use of such instruments. [1]
A Geiger counter is an electronic instrument used for detecting and measuring ionizing radiation. It is widely used in applications such as radiation dosimetry, radiological protection, experimental physics and the nuclear industry.
The Geiger–Müller tube or G–M tube is the sensing element of the Geiger counter instrument used for the detection of ionizing radiation. It is named after Hans Geiger, who invented the principle in 1908, and Walther Müller, who collaborated with Geiger in developing the technique further in 1928 to produce a practical tube that could detect a number of different radiation types.
A scintillation counter is an instrument for detecting and measuring ionizing radiation by using the excitation effect of incident radiation on a scintillating material, and detecting the resultant light pulses.
In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify ionizing particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a particle accelerator. Detectors can measure the particle energy and other attributes such as momentum, spin, charge, particle type, in addition to merely registering the presence of the particle.
Health physics, also referred to as the science of radiation protection, is the profession devoted to protecting people and their environment from potential radiation hazards, while making it possible to enjoy the beneficial uses of radiation. Health physicists normally require a four-year bachelor’s degree and qualifying experience that demonstrates a professional knowledge of the theory and application of radiation protection principles and closely related sciences. Health physicists principally work at facilities where radionuclides or other sources of ionizing radiation are used or produced; these include research, industry, education, medical facilities, nuclear power, military, environmental protection, enforcement of government regulations, and decontamination and decommissioning—the combination of education and experience for health physicists depends on the specific field in which the health physicist is engaged.
Radioactive contamination, also called radiological pollution, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids, or gases, where their presence is unintended or undesirable.
The measurement of ionizing radiation is sometimes expressed as being a rate of counts per unit time as registered by a radiation monitoring instrument, for which counts per minute (cpm) and counts per second (cps) are commonly used quantities.
The proportional counter is a type of gaseous ionization detector device used to measure particles of ionizing radiation. The key feature is its ability to measure the energy of incident radiation, by producing a detector output pulse that is proportional to the radiation energy absorbed by the detector due to an ionizing event; hence the detector's name. It is widely used where energy levels of incident radiation must be known, such as in the discrimination between alpha and beta particles, or accurate measurement of X-ray radiation dose.
The ionization chamber is the simplest type of gaseous ionisation detector, and is widely used for the detection and measurement of many types of ionizing radiation, including X-rays, gamma rays, alpha particles and beta particles. Conventionally, the term "ionization chamber" refers exclusively to those detectors which collect all the charges created by direct ionization within the gas through the application of an electric field. It uses the discrete charges created by each interaction between the incident radiation and the gas to produce an output in the form of a small direct current. This means individual ionising events cannot be measured, so the energy of different types of radiation cannot be differentiated, but it gives a very good measurement of overall ionising effect.
Gamma-ray spectroscopy is the qualitative study of the energy spectra of gamma-ray sources, such as in the nuclear industry, geochemical investigation, and astrophysics. Gamma-ray spectrometry, on the other hand, is the method used to acquire a quantitative spectrum measurement.
In the measurement of ionising radiation the counting efficiency is the ratio between the number of particles or photons counted with a radiation counter and the number of particles or photons of the same type and energy emitted by the radiation source.
Geiger counter is a colloquial name for any hand-held radiation measuring device in civil defense, but most civil defense devices were ion-chamber radiological survey meters capable of measuring only high levels of radiation that would be present after a major nuclear event.
Gaseous ionization detectors are radiation detection instruments used in particle physics to detect the presence of ionizing particles, and in radiation protection applications to measure ionizing radiation.
In health physics, whole-body counting refers to the measurement of radioactivity within the human body. The technique is primarily applicable to radioactive material that emits gamma rays. Alpha particle decays can also be detected indirectly by their coincident gamma radiation. In certain circumstances, beta emitters can be measured, but with degraded sensitivity. The instrument used is normally referred to as a whole body counter.
Nuclear MASINT is one of the six major subdisciplines generally accepted to make up Measurement and Signature Intelligence (MASINT), which covers measurement and characterization of information derived from nuclear radiation and other physical phenomena associated with nuclear weapons, reactors, processes, materials, devices, and facilities. Nuclear monitoring can be done remotely or during onsite inspections of nuclear facilities. Data exploitation results in characterization of nuclear weapons, reactors, and materials. A number of systems detect and monitor the world for nuclear explosions, as well as nuclear materials production.
Radiation monitoring involves the measurement of radiation dose or radionuclide contamination for reasons related to the assessment or control of exposure to radiation or radioactive substances, and the interpretation of the results.
The Royal Observer Corps (ROC) was a civil defence organisation operating in the United Kingdom between October 1925 and 31 December 1995, when the Corps' civilian volunteers were stood down.. Composed mainly of civilian spare-time volunteers, ROC personnel wore a Royal Air Force (RAF) style uniform and latterly came under the administrative control of RAF Strike Command and the operational control of the Home Office. Civilian volunteers were trained and administered by a small cadre of professional full-time officers under the command of the Commandant Royal Observer Corps; a serving RAF Air Commodore.
The CD V-700 is a Geiger counter employing a probe equipped with a Geiger–Müller tube, manufactured by several companies under contract to United States federal civil defense agencies in the 1950s and 1960s. While all models adhere to a similar size, shape, coloring and form-factor, there were substantial differences between various models and manufacturers over the years the CD V-700 was in production. Many of the earlier units required the use of now-obsolete high-voltage batteries, and were declared obsolete by the end of the 1970s.
A multichannel analyzer (MCA) is an instrument used in laboratory and field applications to analyze an input signal consisting of voltage pulses. MCAs are used extensively in digitizing various spectroscopy measurements, especially those related to nuclear physics, including various types of spectroscopy.
In particle physics, the coincidence method is an experimental design through which particle detectors register two or more simultaneous measurements of a particular event through different interaction channels. Detection can be made by sensing the primary particle and/or through the detection of secondary reaction products. Such a method is used to increase the sensitivity of an experiment to a specific particle interaction, reducing conflation with background interactions by creating more degrees of freedom by which the particle in question may interact. The first notable use of the coincidence method was conducted in 1924 by the Bothe–Geiger coincidence experiment.
Guidance on the Choice, Use and Maintenance ofHand-held Radiation Monitoring Equipment. - National Radiation Protection Board - UK, May 2001.