Many shorter-half-life and therefore more intensely radioactive isotopes have not decayed out of the terrestrial environment because they are still being produced.
Examples of these are radium-226 (a decay product of uranium-238) and radon-222 (a decay product of radium-226).
Gaseous ionization detectors use the ionizing effect of radiation upon gas-filled sensors.
In these areas it can represent a significant health hazard.Concentrations over 500 times higher than the world average have been found inside buildings in Scandinavia, the United States, Iran, and the Czech Republic.It can be inhaled into the lungs, along with its decay products, where it will reside for a period of time after exposure.In addition, the earth, and all living things on it, are constantly bombarded by radiation from outer space. Detectable amounts occur naturally in soil, rocks, water, air, and vegetation.
From these sources it can be inhaled and ingested into the body.
In Europe, the average natural background exposure by country ranges from under 2 m Sv annually in the United Kingdom to more than 7 m Sv annually in Finland, as shown in.
The biggest source of natural background radiation is airborne radon, a radioactive gas that emanates from the ground.
This radiation primarily consists of positively charged ions ranging from protons to iron and larger nuclei derived from sources outside of our solar system.
This radiation interacts with atoms in the atmosphere to create an air shower of secondary radiation, including x-rays, muons, protons, alpha particles, pions, electrons, and neutrons.
Potassium-40 (with a half-life of 1.25 billion years) is at about eight percent of its original activity.