RADIOACTIVITY

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RADIOACTIVITY

RADIOACTIVITYAssociated with nuclear weapons/power stations, but naturallypresent in air, soil and waterRadioactive elements (radionuclides/isotopes) can be placedin 3 general categories:1. Primordial, prior to Earth’s formation, e.g. Ur 2382. Cosmogenic, formed from cosmic ray interactions, e.g. Be3. Anthropogenic, enhanced/formed from human activity, e.g.I 131


Anthropogenic activity: ca. 100 yearsWilhelm Roentgen (1845-1923):Discovered X-rays 1895Observed that rays originating fromcathode ray tube able to penetrate paperAntoine Becquerel (1852-1908)Found spontaneous emission of radiationfrom material, later demonstrated thatradiation consisted of charged particles


Ernest Rutherford (1871-1937):Named & characterised particlesof the atom responsible forradiation. Calculated decay ofradioactive substances, explainedconcept of half-life. Split the atom.Marie & Pierre Curie (1867-1934;1859-1906)Studied Ur ore, coined term‘radioactivity’. Isolated elementspolonium and radium.Marie Curie – initiated researchinto use of R to treat cancer


Albert Einstein- influential in encouragingdevelopment of atom bombBomb used in warfare at Hiroshima andNagasaki (Japan) 1945.Hiroshima: estimated 80,000 peopledied initially, with 60,000 more inlater monthsNagasaki: estimated 39,000 peoplekilled outright, 75,000 believed tohave died in later years


Atomic structure Normally, + charge =-chargeChemical/physicalreactions can causeatom to lose or gainelectronsLithium atom


Atomic massAtomic no.No. protons determinesatomic numberE.g. atom with 6protons, 6 neutrons = C• Atoms of same element – have same no. protons, neutronsvary• Variants – isotopes, same chemical properties, differentnuclear mass• 99% C - C 12 : 1% C – 7 neutrons, C 13• K – 19 protons, 20 neutrons = K 39 : 19 protons, 21 neutrons =K 40 .• Instability leads to emission of particles, = radioactivity


PENETRATING POWER OFRADIATIONSlow, loseenergy overshort distanceForm ofelectromagnetic radiation


Time for half of a givenmaterial to decay from currentformRadioactivity inverselyproportional to ½ life. Short ½life – high radioactivity.


Assumed after the passage of 10 half-lives, that radioactivityof an isotope is not significantly different to backgroundE.g. P 32 – half life of 14 days:If held under shielded conditions, could be disposed of withnormal refuse after 140 days.Disposal of radioactive waste dictated by half-life of longestlived isotopeLow-level waste – secured in concrete, buried in trenchesMedium/high level – long-term storage, deep undergound


80% humanexposure fromnatural sourcesRadon54%


TOXICITYAll radioactive emissions dangerous. Electrons removed fromatoms, can result in cell death or cell mutation - cancers95% external radioactive material can be removed by washingIngested material: treatment has to reduce absorption,enhance excretionIncludes stomach pumping, laxatives,blocking/dilution/mobilizing agents such as potassium iodideor ammonium chlorideBiochemical properties of radioactive elements important -Follow same biochemical pathways as stable isotopesI in thyroid glandStrontium 90 follows Ca pathwayCaesium 137 follows potassium pathways


CHERNOBYL April 1986


135 000 people evacuatedRadiation exposure 100x greater than Hiroshima bomb3 people died immediately, 28 emergency workers within 3 monthsEstimated >70% radiation fell over BelarusCHERNOBYL


Increases inthyroid cancerparticularlyprevalentLack of public information at time judgedto increase incidence of psychologicaldisordersLittle consensus in estimates concerningultimate impact on human health


2006: Chernobyl & theEnvironmentOnce humans evacuated, existinganimal populations increased, e.g.elkPreviously absent animals returnedor introduced:e.g. Lynx, eagle owl, great whiteegret, Przewalski's horse. Footprintsof brown bear observedLevels of radioactivity high in tissues, DNA mutations frequentSome scientists report no evidence of effects on physiology orreproduction


TOXICITY OF OTHER ATMOSPHERIC POLLUTANTSCO 2SO 2 , CO 2PM, PAHCO, CO 2 ,HC, NO 2 ,PAH, PMTCDD,CO 2PM, PAHNO, CO 2SO 2 , PM, PAHWasteincineration(incl. chlorinated solvents orplastics)Coal (incl. S impuritiesGasPetrolDiesel fuel


5 major pollutants account for 98% air pollutionCarbon monoxide (CO) 52%Hydrocarbons (HC) 12%Nitrogen oxide (NO) 6%Sulphur oxides/sulphur dioxide (SO 2 ) 18%Particulate matter (PM) 10%Climatic conditions can alter composition of air pollution andlead to smog• Photochemical: high levels ozone, NO, HC. Cause – carexhaust gases and bright sunlight• Reducing: high levels PM, SO 2 . Cause: incompletecombustion, fog, cool temperatures


Carbon monoxide:Responsible for ca. 100 fatalities per year in UKBinds to haemoglobin to form carboxyhaemoglobinand blocks O 2 carrying capacity of bloodCauses tissue damage& acidosis(arises from build-upof lactic acid viaanaerobic respiration)On-roadVehicles (60%)Metal (3%)processingOther5%Non-roadengines/vehicles19%Miscellaneous8%Combustion5%


Nitrogen oxides: Nitric oxide (NO), nitrogen dioxide (NO 2 )Both toxic, originate from burning of fossil fuelsNitrogen oxides – can form acid derivatives and contribute toacid rainNO:interferes withphotosynthesisNO 2 :Causes leaf necrosis.Lung irritantCombustionelectrical utility(28%)On-roadvehicles(30%)Other5%Combustion(5%)Non-roadengines/vehicles19%Combustionindustrial (13%)


Sulphur dioxideOriginates mostly from burning coalContributes to acid rain via formation of acid derivativesCombustionindustrial(17%)Combustionelectricalutility(67%)Combustion(4%)Other7%MetalProcessing(3%)Non-roadengines/vehicles(2%)


Hydrocarbons/volatile organic compoundsThose contributing to atmospheric pollution are smallmolecules (


Particulate matterWidely variable compositionParticles < 10 micrometres diameter known as PM10s, emittedfrom car exhaustsNon-roadengines/vehicles15%Combustion (15%)Miscellaneous(19%)Other industrialprocesses(13%)Other(32%)Combustionindustrial (7%)

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