The Basics of Radiation Detection
|For a list of common terms and definitions, please visit the Health Physics Society's "Radiation Terms, Definitions and Fact Sheets" page on their website, RadWaste.org. For information about State Radiation Protection Programs, click here to see a list by state from the CRCPD.|
|A Brief Overview of Radiation Detection
All of the instruments are most accurate for Cesium 137 and isotopes of similar energies. Some isotopes detected relatively well are Cobalt 60, Technicium 99M, Phosphorous 32, Strontium 90, and many forms of Radium, Plutonium, Uranium, and Thorium. Some forms of radiation are very difficult or impossible for a Geiger tube to detect. Tritium is a byproduct of a nuclear reactor and is used in research. The beta emissions from Tritium are so weak that there are very few instruments that are capable of detecting it. More sophisticated equipment is needed for the measurement of environmental samples, such as radioactivity in milk, produce, soil, etc., unless you are looking for gross contamination. The radiation from some isotopes can cause a Geiger tube to overexcite and indicate a higher level of radiation than is actually present. Americium 241 is an example of this phenomenon. Americium 241 is used in some smoke detectors and many different types of industrial density and flow meters. Unless you know exactly what you are measuring and understand the limitations of detection instruments, it is possible to draw misleading conclusions from your readings. We design our instruments to detect the broadest range of ionizing radiation possible and still be affordable. The full spectrum of ionizing radiation cannot be measured by one single instrument. Everyone agrees that radioactive materials can be dangerous. We encourage you to seek out other sources of information.
Are any of your products suitable for neutron detection? Not currently. Neutrons are too high of an energy and too fast for standard GM tubes to detect. Neutrons need to be slowed down in order to detect them using a (BF3) boron trifluoride (uses a neutron to alpha particle conversion to get a measurement)or a High Pressure Helium 3 probe (uses a neutron to positron conversion to get a measurement).
Can your instruments detect microwaves? No. Our instruments detect ionizing radiation. Microwaves are non-ionizing radiation. DO NOT PLACE OUR INSTRUMENTS IN A MICROWAVE AS IT MAY DAMAGE THE INSTRUMENT OR THE MICROWAVE OVEN.
Can your instruments detect Radon? Technically, you can use the kusnetz method or the tsivoglou method with our instruments for radon detection, however, these tests should be preformed by a trained professional. There are much more practical commercially available tests for detecting radon. These are available at many home improvement stores, or you can contact your local RSO or Radiological Health Department for more information.
|Common Conversions and Prefixes|
1 µCi = 37 kBq
1 mCi = 37 MBq
1 Bq = 27 pCi
370 MBq = 10 mCi
1 µSv = 0.1 mrem
SI Unit Prefixes
Roentgen, represented by "R", is the unit of measurement that indicates the charge produced in air by x or gamma rays, whereas SI Units are n terms of coulombs per kilogram of air (C kg-1).
1R = 2.58 X 10-4 C kg-1
Radiation Absorbed Dose and KERMA (Kinetic Energy Released in Material)
100 rad = 1 gray (Gy) 0.01 Gy = 1 rad
Radiation Dose Equivalent
100 rem = 1 sievert (Sv) 0.01 Sv = 1 rem
1 disintigration per second = 1 becquerel (Bq)
2.7 X 10-11 curie (Ci) = 1 Bq
Emergency Response and Preparedness Since the event of September 11, we have had an increased amount of calls from individuals wanting to be informed if a radiation event takes place. Radiation is a scary topic for most individuals, but some basic knowledge will help in determining what action to take when exposed to radiation in an emergency response situation.
The types of radiation encountered during such an event are alpha, beta, and gamma. Alpha and beta are particles and gamma is a ray/photon. A piece of paper can stop alpha and a few millimeters of aluminum foil can stop most betas. We say most beta energies because there are high energy betas that are more penatrable. Most people consider alpha and beta not to be of a concern; however, these particles can be ingested or inhaled and cause damage to the body. There are high and low levels of gamma, but the primary concern with gamma radiation is the amount of time you are exposed to it.
There are two types of monitoring devices that are applicable in an emergency response to radiation. One is a rate meter/general purpose Geiger counter. This type of instrument shows the rate that the radiation is being received. The other is a dosimeter. A dosimeter shows the amount/dose being received.
When measuring radiation in an emergency response situation, it is good to have something to compare your readings to. Taking a background radiations level in your area before a radiation event, will help you determine if you have a radiation elevation and whether or not to stay in that location. Background radiation is naturally occurring radiation that is always present. It includes; high energy gamma rays from the sun and outer space and alpha, beta, gamma radiation emitted from elements in the earth. Using a rate meter, you can determine what your normal background is.
It is up to the individual to decide what a safe radiation level is because it differs depending on the individual and their knowledge of radiation and its affects. As an example; say your background level is 25 CPM (counts per minute) where you live. When you fly in an air plane at 30,000 feet your rate meter is getting 200 CPM for anywhere between 2 to 5 hours. That is 8 times what your normal background is on the ground, but it is for a limited amount of time. There are non-occupational dose limits set by the government which is 100 mR per year above background per year.
What we suggest for a good emergency response kit for radiation is a general purpose Geiger counter like the Monitor 4, a carbon fiber dosimeter such as the PEN200 and a Charger to reset the dosimeter. There are electronic dosimeters, however, if you are in the blast zone of a nuclear bomb the pulse of the bombs render most electronic inoperable but the carbon style dosimeters will still operate.
How far away from a source can I detect it if it is shielded? Generally, our instruments will detect radiation up to 18 -24 inches through sheilding.
How often do you recommend that your instruments need to be calibrated? We recommend yearly calibrations, although our instruments hold a stable calibration and rarely need adjusting.
Possible Household Sources of Radiation
Taking Measurements Geiger counters can detect the four main types of ionizing radiation: alpha, beta, gamma, and x-rays. Some detect only gamma and x-rays. Our instruments are calibrated to Cesium 137, but also serve as excellent indicators for many other sources of ionizing radiation. Gamma and x-rays are measured in milli-Roentgens per hour (mR/hr), micro-Sieverts (µSv/hr), or milli-Sieverts (mSv/hr). Alpha and beta are measured in counts per minute (CPM) or counts per second (CPS).
The window of the GM tube is very thin mica. This mica window is protected by a screen. Some levels of alpha, low energy beta, gamma, and x-rays that cannot penetrate the plastic case or the side of the tube can be sensed through the window.
Try not to touch the instrument to any suspected radioactive substance.
Although some beta and most gamma radiation can go through protective gear, try to avoid skin contamination and ingestion. When you leave a radioactive area, remove any protective outerwear and dispose of it properly. If you think you have been contaminated, as an additional precaution, shower and consult a physician.
To determine whether the radiation detected is alpha, beta, or gamma, hold the instrument toward the source.
Alpha: If there is no indication through the back of the case (the side of the tube), position the window close to but not touching the source. If there is an indication, it is alpha, beta, or low energy gamma. If a sheet of paper placed between the window and the source stops the indication, it is most likely alpha. To avoid particles falling into the instrument, do not hold the source above the window.
Beta: Place a piece of aluminum about 1/8 inch (3 mm) thick between the instrument and the source. If the indication stops, decreases, or changes, it is most likely beta radiation. Most common isotopes emit both beta and gamma radiation. This is why the indication would decrease or change but not stop.
The non-occupational dose limits set by the government is 100 mR per year above background per year.
It is up to the individual to decide what a safe radiation level is. It will be different depending on the individual and their knowledge of radiation and its affects. Radiation levels will vary according location and circumstances. As an example; if your background level is 25 CPM (counts per minute) where you live, when you fly in an airplane at 30,000 feet your rate meter may measure 200 CPM (.2 mR) for 2 to 5 hours. That is 8 times your normal background radiation on the ground, but it is only for a limited amount of time.
When measuring radiation in an emergency response situation, it is good to have something to compare your readings to. Taking a background radiation level reading in your area before a radiation event will help you determine if you have an elevated level of radiation and whether or not to stay in that location. Background radiation is naturally occurring radiation that is always present. It includes; high energy gamma rays from the sun and outer space and alpha, beta, gamma radiation emitted from elements in the earth. Using a rate meter, you can determine your normal background radiation levels.
For a good emergency response kit for radiation we recommend a general purpose Geiger counter (like the Monitor 4), a carbon fiber dosimeter (such as the PEN200) and a Charger to reset the dosimeter. There are electronic dosimeters, however, if you were in the blast zone of an atomic bomb the pulse of the bomb would make most electronic equipment inoperable. The carbon style dosimeters will still operate.
Gamma: If there is an indication of radioactivity, it is most likely gamma or high energy beta. Low energy gamma and x-rays (10-40 keV) cannot penetrate the side of the GM tube, but may be detected through the window.
If you perform the alpha/beta test above and there is no change or only a very slight change in the indication, the source is emitting primarily gamma radiation.
What is a Typical Geiger Counter?
What is the MARSSIM method?
What types of radiation do your instruments detect?
Glossary of TermsAlpha: Positively charged particles emitted from the nucleus of an atom. Alpha particles are relatively large, and very heavy. Due to this strong (+) charge and large mass, an alpha particle cannot penetrate far into any material. A sheet of paper or an inch of air can usually stop most alpha particles.
Background Radiation: Naturally occurring radiation is always present, it includes high energy gamma rays from the sun and outer space and alpha, beta, and gamma radiation emitted from elements in the earth.
Beta Particles: Negatively charged particles emitted from an atom. Beta particles have a mass and charge equal to that of an electron. They are very light particles (about 2,000 times less mass than a proton) and have a charge of -1. Because of their light mass and single charge, beta particles can penetrate more deeply than alpha particles. A few millimeters of aluminum will stop most beta particles.
Bq (Becquerels): A quantity of radioactivity in which one atom is transformed per second. 1 dps (one disintegration per second).
CPM (counts per minute): The unit of measurement usually used to measure alpha and beta radiation.
Gamma Rays: Short wavelength electromagnetic radiation higher in frequency and energy than visible and ultraviolet light. Gamma rays are emitted from the nucleus of an atom. These high energy photons are much more penetrating than alpha and beta particles.
Ion: An atomic particle, atom, or molecule that has acquired an electrical charge, either positive or negative, by gaining or losing electrons.
Ionization: The process by which neutral atoms of molecules are divided into pairs of oppositely charged particles known as ions.
Ionizing Radiation: Radiation capable of producing ionization by breaking up atoms or molecules into charged particles called ions.
Radiation: The emission and propagation of energy through space or through matter in the form of particles or waves.
Roentgen (rent-gen): A basic unit of measurement of the ionization produced in air by gamma or x-rays. One Roentgen (R) is exposure to gamma or x-rays that will produce one electrostatic unit of charge in one cubic centimeter of dry air. One thousand milliroentgen (1,000 mR)= 1R.
Radionuclide: The naturally occurring or artificially produced radioactive form of an element.
Sievert: A unit of dose equivalent. 1 Sv= 100 roentgens, 10 µSv/hr = 1 milliroentgen/hr. (µSv micro-Sievert, micro is one millionth, milli is one thousandth.)
X-Rays: Electromagnetic radiation (photons) of higher frequency and energy than visible and ultraviolet light, usually produced by bombarding a metallic target with high speed electrons in a vacuum. X-rays are photons emitted by interactions involving orbital electrons rather than atomic nuclei. X-rays and gamma rays have the same basic characteristics. The only difference between them is their source of origin.
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