Basics of Measuring Radiation with Different Types of Monitors
Understanding How Radiation is Measured with Geiger Counter and Scintillation Crystal Technology.
The Sensing Element is The Heart of The Detector!
There are primarily two types of detector sensor technologies that are used.
- Geiger Mueller (GM) tube sensing element. are used in most Portable Hand Held Survey Detectors to locate radiation. They detect alpha, beta, X-rays and gamma radiation.
- Scintillation Crystal are the sensing element that connected to a photomultiplier are used in applications that demand spectrum analysis and great sensitivity. They can be used to identify specific radioactive isotopes when used with spectrometry software. Normally they are used with lead shielding to reduce background radiation. In turn, they are heavier and less portable to the often-used lead-shielding component. They detect gamma radiation, not beta or alpha radiation.
Geiger Mueller Tube Technology And Very Portable Hand Held Survey Detectors
The Geiger–Müller tube (or GM tube) is the heart of most radiation detectors. It is the sensing element of the Radiation Monitor used for the detection of ionizing radiation – found in alpha, beta, and gamma and X- Ray particles. It is the most widely used detector for radiation survey measurement.
GM tubes are filled with an inert gas such as helium, neon, or argon. As ionized particles hit the tube area, two electrodes transmit the conductive number of interactions occurring as “counts.” These counts are then displayed and often stored in various Radiation Detector instruments with specialized features.
The GM tube is manufactured in various sizes in the shape of either a tube or mica windowed ‘pancake’. The size and shape are a factor in the quality of detection, the larger the size and surface area, determines the sensors ability to sense radiation in any given area. Geiger Counters International offers detector models with your choice of “basic cylinder” tube or better sensitive “pancake” GM tube.
Standard Geiger Mueller Tubes
Standard Sensitivity -– Detects Alpha, Beta, and Gamma Radiation including X Rays from the Gamma Spectrum.
Our Handheld Instruments for Radiation Surveys models that use this type of GM tube are the RadAlert™ and CRM100™
2” Pancake GM (Geiger Mueller) Tube
Best Sensitivity – the “Gold- Standard “in GM Technology. It detects Alpha, Beta, and Gamma Radiation and X Rays.
Our Handheld Instruments for Radiation Surveys models that use the 2” Pancake GM tube with mica windows are the improved INSPECTOR ALERT™ and the Revolutionary New ONYX™.
Many individuals, hospitals, laboratories and public safety programs use the cost effective Inspector Alert ™or ONYX™ or bGeigei Nano Kit because of its better sensitivity, data functions and ability to detect all four major types (alpha, beta, gamma and X-ray) of radiation.
Basics of Measuring Radiation Measurement Values
Values on our radiation monitors are displayed in both mrem/hr and µSv/h. The µSv (microSievert) is an internationally accepted unit for tissue dosage. Much of contemporary literature on the subject refers to the REM (Roentgen Equivalent Man). REM’s are converted to Sieverts at the following ratios:1 rem = 0.01 Sv = 10 mSv = 10,000 µSv 1 mrem = 0.001 rem = 10 uSv
Our radiation monitors can be switched from uSv/hr (Sievert) to mR/hr (REM) or from Counts per Minute(CPM) to Counts per Second (CPS)
Understanding the differences between Sievert, MilliSievert and MicroSievert/hr, also the Becquerel , and Counts per Minute(CPM)
The Sievert is named after Rolf Maximilian Sievert, a Swedish medical physicist renowned for work on radiation dosage measurement and research into the biological effects of radiation.
‘Biological effect” then connects with the term effected radiation (the effect of the radiation on human tissue) or radiation “ Dose” or Dose Equivalent. Dose Equivalent is measured in the now international standard “Sievert (Sv)”.
In the USA it is often still referred to as “Rem”(R). 1 sievert = 100 rem.
Since one Sievert represents a massive dose, most measurements are done in either millisieverts (mSv = 1/1000th of a Sievert) or, more commonly, microsieverts (uSv = one millionth of a Sievert). Radiation monitors often offer values in microsieverts uSV/hr (or mR/hr)
For example, the CRM 100™, RadAlert™, Inspector Alert™ and Onyx™ radiation monitors measure in values of uSv/hr or mR/hr. (as well as counts per minute/second).
Radiation dose depends on three factors: the strength of the radiation source, the distance you are from it, and the duration of the exposure.
The effects of radiation on human beings are somewhat unpredictable, but around half of those exposed to 4 Sieverts or 4,000 mSV will die. It is 100% lethal when exposure is 10 Sieverts.
The average exposure from all radiation sources for a member of the public is approximately 0.26 uSv/hr (one quarter of one millionth of a sievert). The average dose received by nuclear workers is in the 3-25 uSv/hr range.
Radiation data is often reported in uSv/hr (microSieverts per hour) or mSv/hr (milliSieverts per hour) or most often as just “mSv.” So mSv/hr indicates rate. It’s like driving a car at 50 kilometers per hour. In one hour the car has gone 50 kilometers. If you are exposed to 1 mSv (one milliSievert) per hour for one hour, you will get a dose of 1 mSv. Or 1000 uSv (microSievert) per hour for one hour you will get a dose of 1000uSV.
As it applies to organisms, including the human species, DNA appears to be uniquely affected by a cumulative radiation dose. If the dose is too much over a given period of time there is less likelihood that the DNA will be repaired, creating the effect of increased percentage of disease and mutation of the cells.
And then there is value known as Becquerel. The Becquerel is named after Henri Becquerel, who shared a Nobel Prize with Pierre and Marie Curie in 1903 for their work in discovering radioactivity.
The amount of radioactivity in a given volume of air, water or tissue is generally expressed in Becquerel (Bq). One Becquerel means one disintegration (radiation event) takes place every second. It is a value that is used for measurement of radiation in food or water.
If a sample of water contains 10,000 Becquerel of a certain isotope per cubic centimeter it means every second 10,000 radioactive events are happening in that sample.
Disintegrations per minute (dpm) is a measure of the intensity of the source of radioactivity, and its International System of Units (SI) is Becquerel. It is not be confused with cpm (counts per minute). Becquerel is the strength of the source of radiation, but cpm is the number of counts received by an instrument from that source.
The efficiency and its relative position of the radiation detector (e.g. scintillation counter) to the source of radiation must be accounted for when relating cpm to dpm. Dpm is the number of decayed atoms, not the number of atoms that have been measured as decayed by the device.
All radiation monitors including the ones we offer are limited by its sensor (including sensor material and surface area) measure in counts per minute or counters per second relative to that particular device.
So again, the “pancake” GM sensor value will be different than the Standard GM value due its surface area of the mica window tube. And the Scintillation Crystal is very sensitive but also shares a relative value.
It is important to understand the capabilities of the detector and the characteristics of the radiation. Alpha radiation is considered to be 20 times more harmful than beta, gamma, x radiation. It is also not detected by many instruments. The same holds true for beta radiation. So dose and dose rate are often under estimated.
Quick terminology guide:
Dose Equivalent is measured in Sievert (Vs.) (also Rem in the U.S.)
Activity (quantity) is measured in Becquerel (also Curies in the U.S.)
Absorbed Dose is measured in gray (Gy) (Rads in the U.S.)
Converting between Conventional Units (used in U.S.) and SI Units (used in Japan and Europe)
To convert millirems (mrem) to microsieverts (uSv) multiply by 10.
To convert microsieverts to millirem multiply by 0.1
1 Sievert (Sv) = 1,000 millisieverts (mSv) = 1,000,000 microsieverts (μSv)
1 Sievert = 100 rem
1 Becquerel (Bq) = 1 disintegration per second (dps)
1 curie = 37,000,000,000 Becquerel = 37 Gigabecquerels (GBq)
1 gray (Gy) = 100 rad
1 rad = 10 milligray (mGy)
Helpful online unit converters:
Dose Equivalent Units Converter (Sv-rem)
Activity Unit Converter (Bq-Ci)
A guide to terminology about radiation exposure From MIT:
It is Important to Explore the Different Features of Your Radiation Device and Understand How to Change Units of Measurement and Establish the Background Radiation with the Timer Features.
Study the Power Point presentation and manuals.
Please click below to download one of the following PowerPoint training presentations.
- Radiation Basics (PPT: 928KB)
- How to Use the Radalert 100™ (PPT: 7.6MB)
- How to Use the Inspector Alert™ (PPT: 8MB)
Manuals: Please click below to display each guide or manual.
Common Procedures to Measure Radiation With The Inspector Alert™
The following sections give instructions for several commonly- used procedures. With any procedure, the user must determine the suitability of the instrument or procedure for that application.
Establishing the Background Count
Normal background radiation levels vary at different locations, even in different areas of the same room. To accurately interpret the readings you get on the Inspector Alert, it is a good idea to establish the normal background radiation level for each area you plan to monitor. You can do this with a timed count. Use the following steps to get a ten-minute average.
- With the Inspector Alert operating, set the Mode switch to Total/Timer.
- Set the Timer switch on the end panel to Set. Unless you have previously changed it, the display reads 00:01, which means one minute.
- Press the + button nine times. The display should read 00:10, for ten minutes.
- Set the Timer switch to On. The Inspector Alert beeps three times and starts counting. If you want to see how much of the ten minutes remains, set the Timer switch to Set. The display counts down from ten minutes to zero. For example, if the display says 00:03, seven minutes have passed and three minutes remain. Reset the switch to On to return to the radiation level display.
- At the end of the ten minutes, the Inspector Alert beeps three times, and repeats the beeping several times. Note the total reading.
- To find the average counts per minute and dose rates, divide the total by ten (the number of minutes) or hold down the set button.
A ten-minute average is moderately accurate. You can repeat it several times and see how close the averages are. To establish a more accurate average, take a one-hour timed count. If you need to determine whether there is prior contamination, take averages in several locations and compare the averages.
Environmental Area Monitoring
You can keep the Inspector Alert in CPM or mR/hr mode whenever you want to monitor the ambient radiation, and look at it from time to time to check for elevated readings. You can also use Alert mode to warn you if the radiation increases above the alert level.
If you suspect an increase in ambient radiation, use the timer to take a five or ten minute count, and compare the average to your average background count. If you suspect an increase that is too small to detect with a short timed reading, you can take a longer count (for example 6, 12, or 24 hours).
Checking for Surface Contamination
To check a surface, hold the Inspector Alert with the alpha window facing and close to the surface. If you want to find out if a surface is slightly radioactive, place the Inspector Alert next to it and take a timed count or a longer accumulated count.
CAUTION: Never touch the GM sensor to a surface that may be contaminated. You may contaminate the instrument.
Remember to DOCUMENT OR RECORD YOUR RESULTS
SEE ALSO OUR FAQ SECTION
Can your Geiger-Mueller (GM) tube radiation monitors detect radioactivity in food and water?
What type of radiation does CRM 100™, RadAlert™, Inspector Alert™ and Onyx™ detect?
What type of radiation does the G-Explorer NaI scintillation Crystal?
What is radiation?
What is background radiation?
What are alpha, beta, gamma and X-ray radiation?
What are some of the specific isotopes found in alpha, beta and gamma radiation?
Properly Analyse Radioactive Samples
Marco Kaltofen, PE explains how citizens scientists can properly, collect, document, package and ship radiation samples. In this video, he also demonstrates how he analyzes radioactive samples in his lab.
Hot Particles & Measurement of Radioactivity (Arnie Gundersen & Marco Kaltofen
Arnie Gundersen and Marco Kaltofen talk about how to measure radiation in the environment.