Geiger counters

Radiation is around all of us, and most of it is natural. A Geiger counter is an instrument that detects it.

How one works

The US Nuclear Regulatory Commission (NRC) describes a Geiger counter as having two main parts: a sealed tube filled with gas, and a display. When radiation passes into the tube and strikes the gas, it knocks an electron away from an atom. A wire in the middle of the tube draws the electrons in, and a current runs through the wire.

The counter adds up these events. The NRC says these devices usually show the result as "counts per minute".

What its reading can and cannot tell you

A Geiger counter can tell you there is radiation around you. The NRC adds that it can't tell you where the radiation came from, what type it is or how much energy it carries.

The UK Health Security Agency (UKHSA) gives doses in a different unit, the millisievert (mSv). It says a millisievert is a measure of dose that allows for the different effects of different types of radiation, and for how they affect different parts of the body.

Where everyday radiation comes from

UKHSA says people in the UK receive on average about 2.6 mSv a year. The largest share comes from natural radiation in homes and workplaces. Many building materials hold low levels of natural radioactivity, and radon gas seeps from the ground into all buildings.

An earlier government page, from Public Health England, splits the total by source. About 84% comes from natural sources, about 16% from medical uses, and less than 1% from industry and weapons fallout together.

The same page says the radiation from sunlight, power lines, electrical equipment and mobile phone systems does not carry enough energy to ionise.

Radon at home and at work

UKHSA's UKradon service describes radon as a colourless, odourless radioactive gas. It forms from the small amounts of uranium found naturally in all rocks and soils.

To find a home's radon level, UKradon sends a home measurement pack with two detectors, one for the living area and one for a bedroom. The householder posts them back after three months, and the results arrive about four weeks later. The pack gives the yearly average level and shows whether it is above or below the Action Level.

The Health and Safety Executive (HSE) says breathing in radon is the second largest cause of lung cancer in the UK. Under UK regulations, it says, all employers must review the potential radon hazard in their premises.

Useful links