Devices are available to measure radiation, from expensive Geiger Counters to smartphone apps. There are several different units used. Some areas or items have naturally high radiation levels which confuse readings. It’s difficult for an amateur to work out how dangerous a source might be.

Curies and Becquerel

A curie (C) is the original unit used to describe the intensity of radioactivity. It is based on the physical properties of radioactive material, as the dangers of exposure were not well understood at the time. One curie is the radioactivity of a single gram of radium.

A microcurie is a millionth of a curie and a picocurie is a trillionth. Thirty seven billion becquerel (Bq) equal one curie. A becquerel is thus about 27 picocuries (pCi). Modern convention has replaced the curie as a unit with becquerels. As these are tiny, measurements are often given in kilobecquerels (1000 Bq) or megabecquerels (1,000,000 Bq).

The unit is named after the French scientist who discovered radioactivity, Antoine-Henri Becquerel.  It describes one atomic disintegration per second. These disintegrations release energetic particles, which are the basis of radioactivity. The process is called decay.

Alpha particles are the largest, the same size as a helium atom. Beta particles are smaller, but can be stopped by a shield only a few millimeters thick. Gamma rays, a sort of proton, can penetrate up to two feet of concrete.

Skin and clothes protect against the larger particles. If radioactive atoms enter the body, however, these particles will hit cells directly during decay. A nuclear incident distributes these atoms in the air, water and food.

Radioactive material presents two types of hazard. There is the danger of being too close to an emitting source, and the risk of ingesting small fragments of it. This risk increases dramatically if the source explodes. Nuclear fallout is the resultant dust.

Although the luminous properties of radium and other elements were exploited for various gadgets, the dangers of emitting sources are now recognised. The public are unlikely to come into contact with them, except during medical treatments.

X-rays and radiotherapy both use radiation. A means of measuring the risks to patients and staff was needed. New systems were explored, designed to express the biohazard aspect, the actual damage done to living tissues.

Part Two ‘Roentgens, Rads and Rems’ to follow

© E J Walker 2014