Radioactivity in the Environment

1 Radioactivityin the EnvironmentNo. 6 in a series of essays on Radioactivity produced by the Royal Society of Chemistry, Radiochemical Methods GroupRoyal Society of Chemistry, Registered Charity Number 207890 Every person, animal and objectpresent on our planet Earth issubjected to radiation and mayindeed contain it. We cannot seeit, smell it or feel it, but it is withus at all times. What is thisradiation? Where does it comefrom? What sort of radiation isit?RadiationRadiation is measured in terms of its ef-fects on people and materials. Radiationssuch as ultra violet, infra-red, microwavesetc. are not considered here but only thoseemitted by radioactive materials. Theseare known as ionising radiations. For manthe unit used to measure ionising radia-tion dose is the millisievert (mSv). Radia-tion from radioactive materials can be inthe form of three main types namely:-1) Alpha particles which are positivelycharged helium nuclei, which are of verylow penetration and hence do not giverise to a measurable external radiationdose but can give higher doses when in-corporated into the body by inhalation ) Beta particles which are equivalent toelectrons.

2 These can give an external dose,particularly those of high energy whichwill penetrate through two cm of ) Gamma-rays. These are very penetrat-ing passing through up to 6m of are equivalent to low Radioactivity levels in Bq per Kgare:-Soil (Berkshire) 1,000 Human Body4,000 Coffee1,000 Brazil Nuts460 Tea (Indian)630 Fertiliser2,200 Grass (Dried)600 Coal (UK)3001 Bq is one disintegration per characteristics of variousionising radiationsLet us consider the source of this radia-tion and its variation within the SourcesCosmic radiationThis is gamma radiation which has ema-nated from the sun and other terrestrialbodies and travelled to our planet. On itsjourney it has not had to pass through anysubstantial matter only space. Hence it cantravel large distances without being ab-sorbed. Once the radiation reaches our at-mosphere it begins to be absorbed by theair, thus reducing the radiation level on theground.

3 The radiation dose will be higherif you live or work at any altitude and willbe highest for people in aircraft or and soil contain uranium, thoriumand potassium. The former two are partof an elaborate decay scheme producing arange of radioactive elements which emitalpha, beta and gamma radiation . Potas-sium has a naturally occurring isotope,potassium-40 which emits beta andgamma radiation . All of these give rise tobackground radiation which will varyfrom to per annum de-pending on where you live in the UK. Thehighest radiation areas are those in whichthe underlying rocks are granite such asDevon & Cornwall and parts of buildings in which we work, study,play and live have all been constructed ofmaterials which contain Radioactivity thatis uranium, thorium and potassium. Inaddition wood and any other materialwhich at one time was living will containcarbon-14.

4 This is a very weak beta emit-ter and does not give a measurable will return to this radionuclide whenconsidering the dating of ancient air which we breath also contains ra-dioactive material which will give both anexternal dose to our bodies as a whole andan internal dose to our lungs. The majorradionuclides are of radon gas; radon-222which is produced from the decay of ura-nium and radon-220 from the decay of Decay SeriesThorium Decay Series Beta (b) Particle emitted Alpha (a) Particle emittedWe have already seen that both uraniumand thorium are present in rocks, soil andbuilding materials. The level of these ra-don isotopes in the air will depend on thequantity of uranium and thorium in theground and the degree to which they canescape from the ground. Both gases alsoemanate from building materials. Hencelevels inside buildings can be higher par-ticularly if there is poor ventilation and thegases are trapped.

5 This radiation dose canvary from to in normal buildings and other confinedspaces where the gases cannot disperse thelevels may be even carbon dioxide in the air we breathcontains carbon-14 a weak is produced in the upper atmo-sphere by the interaction of cosmic rayswith nitrogen-14. The radioactive isotopecarbon-14 hence enters every carbon cycleinvolving living organisms. It is subse-quently trapped when organisms die andit is a measure of its decay which allowsus to perform carbon Radioactivity present in air or moreimportantly the ground and soil maytransfer into food grown on it. Some of thefood producing the highest concentra-tions of Radioactivity are tea, coffee andBrazil nuts. The dose to man will vary de-pending on the quantities consumed andthe rate at which the body excretes the X-ray equipment used by hospitalsand dentists is the best known source ofmedical radiation .

6 Nowadays hospitalsuse a wide range of radioactive materialsfor diagnostic as well as therapeutic pur-poses. Examples of radioactive nuclidesused are Iodine-131, Iodine-129 and Tech-netium-99. Besides giving a dose whenadministered, the hospital, like all otherestablishments handling radioactive ma-terial, has an authorisation to dischargesmall quantities to the local will add to background sources of radiation account forapproximately 95% of the average dose tothe public from artificial (man-made) a result of nuclear weapon testingin the past our atmosphere containsradioactive material primarily Caesium-137 and Strontium-90 which can bedetected in current rainfall and ispresent in sea-water and soils. The initialexplosions transferred radioactive Royal Society of Chemistry, Registered Charity Number 207890debris to the upper stratosphere fromwhere it will take decades to return toearth.

7 This is the reason why radioactiv-ity from weapon testing is still measur-able in rainfall. Levels were substantiallyincreased as a result of the Chernobyl ac-cident, but these have now mainly beendeposited on the ground and form partof the ground source as these dischargeswere confined to low indicated earlier many hospitals andindustries are permitted to discharge ra-dioactive material to the Environment ina controlled and monitored include the discharges from thenuclear power industry. Coal-fired sta-tions also emit natural Radioactivity re-leased through the burning of coal, whichare not routinely monitored, but can beestimated from known concentrations inthe coal. This latter source produces 25%of the total dose from all UK ExposureNowadays many people are exposed toradiation as a result of their work not justin the nuclear power industry but in hos-pitals, industry, universities, armed ser-vices, civil aviation and there are consumer productswhich contain radioactive material.

8 Lu-minous watches and clocks originallycontained radium-226 but are now morelikely to contain tritium (which is hydro-gen-3) a very weak beta-emitter. Smokedetectors contain americium-241. Gasmantles contain thorium oxide. You maylike to think of other examples. Be care-ful though as we may have included somecommon items in the sections on build-ings and food DoseThe average annual dose to each personin the UK is of which (85%)arises from the natural background. Theremaining (15%) comes fromartificial Radioactivity and (14%)of this is from medical applications. Notethat these are average figures and will varyfrom person to contributions to the averageannual dose in the UK of sources found in common useRoyal Society of ChemistryRadiochemical Methods GroupBurlington HousePiccadillyLondonW1V 0 BNTel: 0171 437 865 Fax: 0171 734 1227 The background radiation from theground can vary by a factor of three andthat from air by a factor of six.

9 Informa-tion on radiation doses from all the abovesources can be obtained from the NationalRadiological Protection Board (NRPB)which was specifically set up by the Gov-ernment to advise it on the levels of radia-tion in the UK and the potential effect onman. For example the NRPB has a continu-ing programme to measure radon gases can participate in this prog-ramme for relatively little cost. Affectedareas where more than I % of homes haveindoor radon concentrations above 200 Bqper cubic metre are shown in the illustra-tion. The NRPB recommend that annualexposure to radon gas should not exceedl0mSv in existing buildings. This is basedon their concepts of safe levels of radia-tion and you will note that this is a lothigher than the average background radia-tion and therefore considerably greaterthan artificial radiation discharged as aresult of industrial applications and powerproduction in this now you should be able to answer allthe questions posed in the introductionand you have obtained some informationof all kinds of Radioactivity in our is a fact of life.

10 The radiationgiven off by artificial radioactive materi-als is no different from natural average the highest dose to man resultsfrom natural radiation . Radiological pro-tection methods have over the years de-veloped to keep doses to man as low asreasonably practicable . This has allowedus to reap some of the benefits from bothnatural and artificially produced radioac-tive Areas. Affected areas where more than I% of homeshave indoor radon concentrations above 200Bq per cubic metre.