AAPT Albuquerque Howard Matis - 1 ABC’s of Radiation Howard Matis Lawrence Berkeley National Laboratory

AAPT AlbuquerqueAAPT Albuquerque Howard Matis - Matis - 2 What is a Nucleus?What is a Nucleus? Quarks determine if proton or neutronQuarks determine if proton or neutron NeutronsNeutrons ProtonsProtons Protons determine chemical propertiesRatio of neutrons to protons make a nucleus stable or unstableProtons determine chemical propertiesRatio of neutrons to protons make a nucleus stable or unstable

Examples - IsotopesExamples - Isotopes Uranium-238 (23892U) –92 protons, 146 neutrons, mass 238 Uranium-235 (23592U) –92 protons, 143 neutrons, mass 235 – Hydrogen (11H) –1 proton, 0 neutrons, mass 1 Deuterium (21D) –1 proton, 1 neutron, mass 2 Tritium (31T) –1 proton, 2 neutrons, mass 3

Nuclear StabilityNuclear Stability N = # of NeutronsN = # of Neutrons Z = # of ProtonsZ = # of Protons White are the stable nucleiWhite are the stable nuclei For light nuclei, stable nuclei have N=ZFor light nuclei, stable nuclei have N=Z If too many protons, then a proton will turn into a neutronIf too many protons, then a proton will turn into a neutron If too many neutrons, a neutron will turn in a protonIf too many neutrons, a neutron will turn in a proton

How Does it Decay?How Does it Decay? Alpha - lose an alpha particle (a - helium nucleus) Beta - emit a beta particle (b - electron or anti-electron) Gamma - emit a gamma (g or photon or light particle)Alpha - lose an alpha particle (a - helium nucleus) Beta - emit a beta particle (b - electron or anti-electron) Gamma - emit a gamma (g or photon or light particle)

Alpha DecayAlpha Decay Alpha particle or helium nucleus emittedAlpha particle or helium nucleus emitted Nucleus changes mass by four units and charge by two unitsNucleus changes mass by four units and charge by two units –Alpha particle easily stopped –4 x nucleon mass –+2 Charge –Big

Beta DecayBeta Decay Beta minus - neutron converts to electron and anti-neutrinoBeta minus - neutron converts to electron and anti-neutrino Beta plus - proton converts to a anti-electron and neutrinoBeta plus - proton converts to a anti-electron and neutrino Nucleus changes charge but not mass numberNucleus changes charge but not mass number –Radiation moderately penetrating –+1 charge Small electronSmall electron

Gamma DecayGamma Decay Nucleus changes energy level - emits gamma ray or photonNucleus changes energy level - emits gamma ray or photon Nucleus stays the sameNucleus stays the same –Very penetrating –Very small –Neutral

Penetrating Properties of Ionizing Radiation

Cosmic Rays Another form of RadiationCosmic Rays Another form of Radiation Comes from outside the earth Particles from the sunComes from outside the earth Particles from the sun Star dust - from supernova - exploding stars Consists of protons and neutronsStar dust - from supernova - exploding stars Consists of protons and neutrons

Sources of RadiationSources of Radiation Average radiation exposure in the United States mrem Very location dependentAverage radiation exposure in the United States mrem Very location dependent

Additional SourcesAdditional Sources Plane travelPlane travel Living at high elevation - Albuquerque has 2x cosmic radiation SoilLiving at high elevation - Albuquerque has 2x cosmic radiation Soil Medical x-raysMedical x-rays Occupational exposureOccupational exposure

Is radiation bad for you?Is radiation bad for you? Too difficult to directly measure risk of low levelToo difficult to directly measure risk of low level Use high exposure studies to determine radiation damageUse high exposure studies to determine radiation damage Extrapolate from high exposure to lowExtrapolate from high exposure to low Model assumes that body does not heal from radiation exposureModel assumes that body does not heal from radiation exposure Similar to calculating the risk of death from a pin prick by extrapolating from a knife woundSimilar to calculating the risk of death from a pin prick by extrapolating from a knife wound

Relative Risk1 in a million fatalityRelative Risk1 in a million fatality 40 tablespoon peanut butter (aflotoxin) 40 tablespoon peanut butter (aflotoxin) 2 days in New York City (air quality) 2 days in New York City (air quality) 3 mrem radiation (cancer) 3 mrem radiation (cancer) 1 mile on motorcycle (collision) 1 mile on motorcycle (collision) 300 miles in car (collision) 300 miles in car (collision) 10 charbroiled steaks 10 charbroiled steaks Smoking 1 cigarette Smoking 1 cigarette