How to Read a Geiger Counter

A Geiger counter detects ionizing radiation such as beta and gamma particles, and some models also detect alpha particles. The primary component of the Geiger counter is a tube filled with a gas that conducts electricity when struck by radiation. This allows the gas to complete an electrical circuit. This typically includes moving a needle and making an audible sound. Geiger counters can measure radiation in a variety of units, depending on the application.

Difficulty:

Moderate

Instructions

1. Measure radiation with sound. Geiger counters usually have a speaker that makes a "click" each time it detects a particle. This method measures alpha and beta particles in counts per minute (CPM) such that a high CPM sounds like radio static.

2. Obtain a visual display of the CPM value. Some Geiger counters also translate the CPM value into a visual representation, such as an LED display or meter.

3. Define the roentgen equivalent in rem. This is a unit of radiation dose given as r = WR where r is the radiation in rems, W is the biological efficiency of the radiation and R is the absorbed radiation in roentgens. Rem is not an exact measure of the radiation itself; rather it is a measure of the effect that radiation has on the human body.

4. Measure radiation in millirems. Geiger counters in the United States typically measure radiation in millirems (mR), since the rem is a large unit of radiation for most purposes. By comparison, the normal background radiation is about 100 mR per year.

5. Convert radiation in units of CPM to radiation in units of mR. Geiger counters commonly use a conversion ratio of 1,000 CPM = 1 mR. This conversion ratio is not exact due to the definition of the rem.

Tips & Warnings

• The maximum recommended dosage of radiation is 5,000 mR/year for radiation workers in the United States and 200 mR/year for non-workers.

References

• Mineralab

Resources

• Read this Article in Spanish