In the course of the evolution of civilization, mankind has created a number of sources of radiation which contribute to radiation exposure of people. These include substances, medical equipments, consumer devices and building materials.
Sources of radiation that impact the average individual in industrialized countries include tobacco which contains thorium and uranium, televisions which emit x-rays, medical X-rays, smoke detectors which contain americium, and lantern mantles which contain thorium.
Modern medicine utilizes a large variety of radioactive isotopes which include: bismuth-213, cesium-137, carbon-11, chromium-51, cobalt-57, cobalt-60, copper-64, dysprosium-165, erbium-169, fluorine-18, gallium-67, gold-198, holmium-166, indium-111, iodine-123, iodine-125, iridium-192, iron-59, krypton-81, lutetium-177, nitrogen-13, oxygen-15, palladium-103, phosphorus-32, potassium-42, rhenium-188, rubidium-82, samarium-153, selenium-75, sodium-24, strontium-89, strontium-92, technetium-99, thallium-201, xenon-133 (5 d), ytterbium-169, and yttrium-90. These isotopes, with the exception of cesium, have half lives for seconds to days. They are used for diagnosis of many conditions, imaging of different parts of the body and treatment of a variety of disease.
Most building materials from natural sources contain small quantities of radium 226, uranium 238 and Thorium 232 as well as radionuclides which are the result of decay of these isotopes. Radon 22 and radon 220 are gases which are injected into the interior air of builds from the decay in the building materials.
Recycled industrial by-products contain radioactive isotopes which have been concentrated above normal background levels in industrial processes. These include coal ash from the burning of coal which is an additive in cement, coal slag is used in floors as an insulating fill, phosphogypsum which is a by-product of the production of phosphorous fertilizers and red mud which is a waste product in aluminum manufacture used in bricks, ceramics and tiles.
Some professions expose workers to radioactivity. Workers who mine uranium and process uranium are exposed to the natural radioactivity of uranium. Nuclear power plant workers and power plant inspectors can be exposed to uranium 235 and plutonium. Nuclear medicine technician can be exposed to any of the radioisotopes mentioned in the paragraph above on nuclear medicine. Radiography and X-ray technicians are exposed to x-rays.
During the period of atmospheric testing of nuclear bombs small particles form from some of the material of the bomb and disperse in the atmosphere. This dust is known as fallout and is dangerous because it contains long-lived radioactive isotopes such as stontium-90 and cesium-137. Testing at ground level or over water draws up large amounts of soil and/or water which contain elements that can be made radioactive by neutron activation from the explosion and add to the danger of the fallout. These include: antimony-131, barium-140, cerium-144, cesium-137, lanthanum-141, molybdenum-99, ruthenium-106, strontium-91, strontium-92, tellurium-132, tellurium-134, and zirconium-95.
When there are accidents at nuclear power plants, large amounts of radioactivity can be released into the environment. The workers and the people who live near the plant have the greatest initial exposure but winds and water currents can carry the radioactivity around the globe.
Nuclear power plants may release radioactivity from leaks or catastrophic failures such as Chernobyl and Fukushima. A great deal of the radioactivity from such events is in the form of radioisotopes of the noble gases chemically related to radon. These are quickly dispersed in the air and decay into inert isotopes rapidly. About one tenth of the radioactivity released is iodine-131. Cesium-137 and strontium-90 constituted about one half of one percent each. Iodine-131 is the most dangerous because it is taken up by the thyroid gland of mammals and can cause cancer.
Man-made radioactivity is a source of radiation exposure that varies a great deal more from place to place and person to person than the natural occurring radioactivity.