A Geiger counter is a device which can accurately measure the radiation being given off within a certain area or from a specific object. Based around a Geiger–Müller tube which responds to ionizing radiation, the Geiger counter provides a relatively inexpensive way to measure alpha, beta, and gamma radiation. There are good reasons to know exactly what kind of radiation is in the area around you. Some examples include mining, excavating, visiting known radioactive locations, and early detection of Radon related radiation in your home.
It is important to know what these different kinds of radiation are in order to understand the best uses of a Geiger counter.
Alpha radiation is when a radioactive atom ejects a particle consisting of two protons without neutrons or electrons. Alpha radiation changes the emitting nucleus into one with a lower atomic number. As an example, uranium-238 decays into thorium-236 by way of alpha radiation. Alpha particles are by far the largest of any radiation and can be blocked by a single piece of paper.
Beta radiation is when one of a radioactive atom’s neutrons ejects a particle consisting of a single electron. The result is that the neutron is converted into a proton, which increases the atomic number of the element. As an example, carbon-14 decays into nitrogen-14 by way of beta radiation. Beta particles are the second largest in radiation emissions, though still much smaller than alpha particles. These can be blocked by sufficiently thick wood or about 1/8″ thick aluminum.
Gamma radiation is electromagnetic radiation, as opposed to strict particle radiation. It does not change the mass or charge of the atom which emits it. Gamma radiation is often associated with alpha or beta radiation, as it results from an atom’s need to relieve stored energy from other types of radioactive decay. Gamma radiation and x-radiation are essentially the same thing and can be blocked by lead.
Radiation is quite literally all around us, forming a feature known as “background radiation.” The average global individual is exposed to about 2.4 millisieverts (mSv) per year from natural sources. By law in the US, the maximum allowable dose for radiation workers is 50 mSv. A person generally exhibits symptoms of radiation sickness when exposed to 400 mSv within a short time. For reference purposes, the observed radiation inside a nuclear power plant can be .130 microsieverts (µSv) per hour, culminating in an annual dosage of 1.13 mSv per year.
Geiger counters consist three major parts: the Geiger–Müller tube for detection, a visual display, and an audio readout. Different models will measure radiation in milli-Roentgens per hour or µSv per hour (depending on preference) via the visual display. The audio readout is the portion which makes the famous clicking sound that many people are familiar with. Slow, periodic clicking generally indicates safety. If the clicking increases to a rapid pace or sounds more like static fuzz there is likely a dangerous amount of radiation nearby.
In application, Geiger counters can provide a useful purpose. Improperly sealed basements can become home to deposits of radon gas. This can become dangerous over time if the concentration of radon builds. Higher concentrations will expose anyone living in the home to increased radiation levels. Mineral hobbyists can find out if their favorite digging site or pieces are giving them extra doses of radiation. This is of particular interest in areas with higher granite concentrations. Other collectors may find mild radiation in older items like jewelry, watches, and pottery.
An effective way of testing whether a given object is emitting radiation is to note the levels of background radiation in a given area, then move the counter closer to the source in question without pointing the detector at the supposed source. If the radiation levels increase, the source is likely emitting gamma or high energy beta radiation. Next, insert a 1/8″ piece of aluminum between the counter and source. If the reading decreases, it is beta radiation. If no radiation is noticed through the housing of the counter, use the detector to look for increases. By inserting foil or paper between the source and detector, you will be able to determine if the source is beta or alpha radiation respectively.