AAPT 2005 - AlbuquerqueAAPT 2005 - AlbuquerqueHoward Matis - hsmatis@lbl.govHoward Matis - hsmatis@lbl.gov11

ABC’s of RadiationABC’s of Radiation Howard MatisHoward MatisLawrence Berkeley National LaboratoryLawrence Berkeley National Laboratory

                                                                                                               

• • AAPT 2005 - AlbuquerqueAAPT 2005 - Albuquerque• Howard Matis - hsmatis@lbl.govHoward Matis - hsmatis@lbl.gov• 22• 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 Protons determine chemical propertiesRatio of neutrons to protons make a nucleus stable or unstablemake 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 Alpha - lose an alpha particle (a - helium nucleus)nucleus)Beta - emit a beta particle (b - electron or Beta - emit a beta particle (b - electron or anti-electron)anti-electron)Gamma - emit a gamma (g or photon or Gamma - emit a gamma (g or photon or light particle)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 Nucleus changes mass by four units and charge by two unitsunits

– Alpha particle easily stoppedAlpha particle easily stopped

– 4 x nucleon mass4 x nucleon mass

– +2 Charge +2 Charge

– BigBig

• 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 penetratingRadiation moderately penetrating

– +1 charge+1 charge

• Small electronSmall electron

•

• Gamma DecayGamma Decay• Nucleus changes energy level - emits gamma ray or Nucleus changes energy level - emits gamma ray or

photonphoton

• Nucleus stays the sameNucleus stays the same

– Very penetratingVery penetrating

– Very smallVery small

– NeutralNeutral

• Penetrating Properties of

• Ionizing Radiation

• Cosmic RaysCosmic RaysAnother form of RadiationAnother form of Radiation

• Comes from outside the earthComes from outside the earthParticles from the sunParticles from the sun

• Star dust - from supernova - exploding Star dust - from supernova - exploding starsstarsConsists of protons and neutronsConsists of protons and neutrons

•

• Sources of RadiationSources of Radiation

• Average radiation exposure in the United Average radiation exposure in the United States - 360 mrem Very location States - 360 mrem Very location dependentdependent

•

• Additional SourcesAdditional Sources• Plane travelPlane travel

• Living at high elevation - Albuquerque has 2x cosmic radiationLiving at high elevation - Albuquerque has 2x cosmic radiationSoilSoil

• 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 Use high exposure studies to determine radiation damagedamage

• Extrapolate from high exposure to low Extrapolate from high exposure to low

• Model assumes that body does not heal from radiation Model assumes that body does not heal from radiation exposureexposure

• Similar to calculating the risk of death from a pin prick by Similar to calculating the risk of death from a pin prick by extrapolating from a knife woundextrapolating from a knife wound

• Relative RiskRelative Risk1 in a million fatality1 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 steaks10 charbroiled steaks

• Smoking 1 cigaretteSmoking 1 cigarette