Handbook of Radon. Glossary.

This Glossary is not comprehensive. It is intended only as an aid for readers who never studied science. Many terms used in the Handbook are included.

actinide a small group of elements with high atomic number, including uranium, plutonium and americium.

active system a radon removal system that relies on electrical power or other man-made energy source for its operation.

ALARA As Low As Reasonably Achievable - social and economic factors being taken into account. A principle often quoted to justify expenditure to reduce radiation dose, but with the qualification removed.

alpha particle the nucleus of a helium atom, a sub-atomic particle emitted from some large nuclei when they undergo radioactive decay. Very poorly penetrating in matter, but with a high index of harm per unit of energy. (see quality factor).

atom once thought of as the smallest amount of matter that could not be divided further, now recognised as the smallest amount of matter having the characteristics of a chemical element.

attached fraction applied to radon daughters to describe the fraction of daughters that have become attached to smoke or dust particles.

Becquerel French scientist who discovered radioactivity in 1896 whilst experimenting with uranium salts. The becquerel (Bq) is now the standard unit for activity: one becquerel is one atomic transformation per second.

BEIR as in the BEIR IV report, the term signifies the committee of the US National Academy of Sciences dealing with Biological Effects of Ionising Radiation. The risk factor commonly used for radon of 0.035 deaths per sievert derives from this committee, and from work of ICRP, whose estimates range to 0.05 cancer deaths per sievert for a population of all ages.

beta particle a positively or negatively charged subatomic particle of low mass: positron or electron.

Bq/m³(Bq.m^-3)The recognised units for expressing radon concentration (activity concentration) in air. Not yet widely used in the USA.

BRE Building Research Establishment. Until recently primarily a research based body and part of the DOE.

collective dose dose totalled for a population. For example the collective dose from radon in the UK is calculated from 57 million people times 1.2 mSv each (on average), giving 68400 Sv per year. If the BEIR IV figure of 0.035 deaths per sievert is applied, the prediction is 2400 deaths annually from radon related lung cancer. Collective dose may easily be calculated for counties or other regions once average indoor radon levels are known.

cosmic radiation a stream of high energy subatomic particles received from the sun and from outer space. The dose from these increases with altitude because there is less absorption by the atmosphere. Typical exposure is 0.2 to 0.3 mSv annually, rising to nearly 2 mSv annually in the world's highest cities.

Curie Husband and wife team of scientists (Pierre and Marie). Received Nobel prizes for discovering radium and polonium. The curie is still used as a unit of radioactivity, but is being replaced by the becquerel. One curie is 3.7 x 10¹⁰ events per second.

discounting part of economics and a way of expressing that benefits in the future may be worth less than those in the present, expressed in monetary terms. Parameters such as Net Present Value and Internal Rate of Return are related to Discount Rate, a notional rate of interest on investments.

DOE Department of Environment (UK) or Department of Energy (USA).

dose general term for quantity of radiation, often used to mean effective dose equivalent.

early effects a term used to describe death or injury from exposure to ionising radiation where the effect occurs days or weeks after exposure, rather than years or decades later. Only large doses of radiation received over a short time produce early effects, and the severity of the effect is linked to dose. The threshold for onset of mild early effects such as nausea is about 0.5 Sv. However, larger doses from radon over a year produce no early effects. If received in a short time 50 Sv may kill quickly.

economics A pseudo-science popular in the twentieth century. Economic theories were proven correct by selected events. Theories were never disproved by unforeseen events.

EEDC equilibrium equivalent decay product concentration, being the amount of each product necessary to produce the same PAEC as the mixture of decay products that is actually present. Units are Bq/m³, or equivalent.

effective dose equivalent absorbed dose corrected for both type of radiation and sensitivity of the irradiated tissue. May be thought of as a normalised index of potential harm from ionising radiation. Often abbreviated simply to 'dose'.

EPA A large government body in the USA, based in Washington DC. EPA is responsible for a wide range of environmental matters and has many Divisions.

epidemiology a branch of statistics and medical science concerned with discovering and quantifying the relation between causes and (medical) effects often in cases where no causal link is immediately apparent.

equilibrium factor, (F) the ratio of the EEDC to the existing radon activity concentration. Usually has a value of between 0.2 and 0.6 in houses.

GAC granular activated charcoal, often used to remove radon from water.

Gray Scientist who helped develop medical uses of radiation. The gray is now the standard unit of absorbed dose expressed in J/kg. 1 Gy = 100 rad.

half-life The time taken for the activity of a radioactive species to reduce to half its initial value.

HMIP A part of the DOE in England concerned primarily with pollution from industry, but having the policy remit for some matters connected with ionising radiation.

ICRP International Commission on Radiological Protection. An unincorporated organisation whose aims are to develop an international consensus on the risks from radiation and appropriate safety levels. It has been said that if ICRP did not exist it would be necessary to invent it.

ionising radiation Types of radiation that have sufficient energy to produce ionisation within matter. Examples are alpha particles, beta particles, gamma rays and neutrons, as distinct from visible light, infra-red light and radio waves.

late effects sometimes called delayed effects. A term used to describe the onset of cancers or hereditary defects in future generations years or decades after exposure to radiation. These are stochastic processes - governed by chance - and the severity of a cancer or defect is not linked to the dose received. Only the chance of occurrence is so determined.

LET linear energy transfer, used in the context of low and high LET radiation. High LET radiation such as alpha particles imparts energy to tissue within a short distance, and may therefore produce more concentrated damage. Related to quality factor.

leukaemia a group of rare cancers, sometimes described as cancer of the blood. Some types occur in children and some are linked with exposure to radiation, and perhaps to radon.

mSv millisievert: the recommended unit for expressing radiation dose, usually as effective dose equivalent.

NRPB National Radiological Protection Board in the UK. Advisors to the government on radiation and the risks factors from radiation.

occupational exposure exposure to ionising radiation occurring at a place of work by virtue of one's job.

PAEC potential alpha energy concentration, a measure of the total alpha particle energy that will be emitted by a mixture of radon daughters during their decay. Expressed in joules per cubic metre (J/m³).

pascal usually seen as Pa, a unit of pressure or pressure difference. One Pa is a very small pressure and can be measured only with sensitive equipment. 101,325 Pa equal one atmosphere.

passive system a radon removal system or technique that does not rely on electricity or other external motive power for its operation.

picocurie per litre (pCi/l) activity concentration of radionuclide(s), similar to becquerel per cubic metre.

plate-out the deposition and attachment of radon daughters onto walls, floors, etc., thus rendering them relatively harmless.

plutonium a radioactive element very rare in nature but produced in nuclear reactors from uranium and used in nuclear weapons and some types of nuclear power stations. It has acquired a reputation for toxicity that verges on the irrational.

ppb parts per billion (one thousand million). A billion is 1,000,000,000.

ppm parts per million.

premature deaths deaths that occur before they need have done. Avoidable premature deaths are those that might have been prevented by (for example) safety precautions being observed, diseases being diagnosed earlier, or exposure to known dangerous substances such as radon avoided or minimised.

quality factor a number usually 1 to 20 to express the different amounts of potential harm to a person caused by unit dose of different types of radiation. Alpha particles have the highest quality factor usually taken as 20, and meaning that the transfer of a given amount of energy to tissue by alpha particles is 20 times as damaging biologically as the same energy absorbed from gamma radiation. Much higher values than 20 have been suggested for alpha particles in induction of leukaemias.

QALY Quality Adjusted Life Year. A parameter used to rationalise the benefit from different medical treatments or procedures, so as to calculate relative cost-benefit. Similar to Well Year in the USA.

rad old unit for absorbed dose, now replaced by the gray.

radioactivity term used to describe the property of radionuclides of emitting ionising radiation, and of transmuting to other elements.

radon A radioactive gas formed from radium, usually in the earth. Harmful primarily by inhalation of its daughter products. Atomic mass of 222.

radon daughters the atoms of solids such as polonium, bismuth and lead formed when radon undergoes radioactive decay. Often airborne for part of their lives, they can be inhaled and deposited onto lung tissue, and may thus induce lung cancer.

radon progeny radon daughters.

radionuclide an unstable or radioactive nuclide that decays emitting ionising radiation.

radiophobia a term coined to describe the tendency to blame radiation (radioactivity) for any or all ills suffered by people exposed to fallout from Chernobyl or other nuclear incidents. A result probably of psychological trauma combined with inadequate information, secrecy, and mistrust of official statistics.

radium radioactive element of mass 226 and the immediate precursor to radon. Formed from uranium (via intermediate elements) but sometimes found isolated from it in nature owing to very different chemical properties. One of the first radioactive elements to be discovered. Half life of 1622 years.

rbe relative biological effectiveness. Similar to quality factor.

rem roentgen equivalent man. An old unit for dose equivalent and equal to 0.01 Sv or 10 mSv. One rem produces the same biological effect as one roentgen of hard x-rays per kilogram of tissue. A sudden dose of 5000 to 10,000 rem (50 to 100 Sv) is sufficient to kill through damage to the central nervous system.

risk the probability of injury or harm occurring.

risk factor risk per unit dose, usually as deaths per sievert or cancers per sievert.

Roentgen (Rontgen) German scientist who discovered x-rays in 1895. The roentgen is an obsolete unit for an amount of ionising radiation expressed by way of electrical charge produced in air.

Sellafield a nuclear complex in north-west England previously called Windscale and the location in 1952 of the UK's worst nuclear accident. The site now houses facilities for storing and reprocessing nuclear waste. Although synonymous with fears about plutonium, leukaemia and contamination of beaches, the discharges from Sellafield are now at a very low level.

Sievert Scientist who worked with radiation. The sievert is now the standard unit for dose equivalent, but usually as millisievert (1/1000 of a sievert). 1 Sv = 100 rem.

stack effect a term used to describe the gentle buoyancy pressures that are responsible for warm air rising up chimneys and for radon being drawn into houses during cold weather. The pressures involved in the stack effect in houses are typically 0.1 to 5 Pa.

synergism where two or more causes of an effect act together in some way to produce a risk factor greater than the sum of the individual factors. Examples are the enhanced risks from radon and smoking and from asbestos and smoking.

thoron one of the less common isotopes of radon with mass 220 rather than 222. Its half-life is less than a minute.

unattached fraction applied to radon daughters to describe the fraction of daughters that have not yet attached themselves to a smoke or dust particle. Unattached daughters have high mobility and, it is thought, are potent in causing lung cancer if inhaled.

uranium primordial radioactive element having long-lived isotopes and occurring in rocks and soils as typically a few ppm, or 5 to 50 Bq/kg. A precursor to radium, and therefore to radon.

WL Working Level. A unit dating from study of radon in mines, it is a measure of the energy of alpha particle decays in air, applied to radon daughters only.

WLM Working Level Month. A unit of exposure to radon daughters, one WL for 173 hours.

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