Specifications
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Geiger counters can detect the four main types of ionizing radiaon: 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 radiaon. Gamma and x-rays are measured in milliroentgens per
hour (mR/hr), microsieverts (µSv/hr), or millisieverts (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 plasc case or the side of the tube can be
sensed through the window.
Try not to touch the instrument to any suspected radioacve substance.
Although some beta and most gamma radiaon can go through protecve gear, try to avoid skin contaminaon
and ingeson. When you leave a radioacve area, remove any protecve outerwear and dispose of it properly.
If you think you have been contaminated, as an addional precauon, shower and consult a physician.
How to Determine Alpha, Beta, or Gamma source.
To determine whether the radiaon detected is alpha, beta, or gamma, hold the instrument toward the source.
Alpha: If there is no indicaon through the back of the case (the side of the tube), posion the window close
to but not touching the source. If there is an indicaon, it is alpha, beta, or low energy gamma. If a sheet of
paper placed between the window and the source stops the indicaon, it is most likely alpha. To avoid parcles
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
indicaon stops, decreases, or changes, it is most likely beta radiaon. Most common isotopes emit both beta
and gamma radiaon. This is why the indicaon would decrease or change but not stop.
The non-occupaonal dose limits set by the government is 100 mR above background annually.
It is up to the individual to decide what a safe radiaon level is. It will be dierent depending on the
individual and their knowledge of radiaon and its aects. Radiaon levels will vary according to locaon and
circumstances. As an example; if your background level is 25 CPM (counts per minute) where you live, when
you y in an airplane at 30,000 feet your rate meter may measure 200 CPM (.2 mR) for 2 to 5 hours. That is 8
mes your normal background radiaon on the ground, but it is only for a limited amount of me.
When measuring radiaon in an emergency response situaon, it is good to have something to compare your
readings to. Taking a background radiaon level reading in your area before a radiaon event will help you
determine if you have an elevated level of radiaon and whether or not to stay in that locaon. Background
radiaon is naturally occurring radiaon that is always present. It includes high energy gamma rays from the
sun and outer space and alpha, beta, gamma radiaon emied from elements in the earth. Using a rate meter,
you can determine your normal background radiaon levels.
Gamma and X-Rays: If there is an indicaon of radioacvity, 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 indicaon,
the source is eming primarily gamma radiaon.