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ABC’s of Radiation Howard AAPT 2005 Matis - Albuquerque - [email protected] 1 Howard Matis Lawrence Berkeley National Laboratory • • • • • • AAPT 2005 - Albuquerque Howard Matis - [email protected] 2 What is a Nucleus? Quarks determine if proton or neutron • Neutrons • Protons • Protons determine chemical propertiesRatio of neutrons to protons make a nucleus stable or unstable • • • • Examples - Isotopes Uranium-238 (23892U) – • Uranium-235 (23592U) – – • 1 proton, 0 neutrons, mass 1 Deuterium (21D) – • 92 protons, 143 neutrons, mass 235 Hydrogen (11H) – • 92 protons, 146 neutrons, mass 238 1 proton, 1 neutron, mass 2 Tritium (31T) – 1 proton, 2 neutrons, mass 3 • Nuclear Stability • N = # of Neutrons • Z = # of Protons • White are the stable nuclei • For light nuclei, stable nuclei have N=Z • If too many protons, then a proton will turn into a neutron • If too many neutrons, a neutron will turn in a proton • • 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 Decay • Alpha particle or helium nucleus emitted • Nucleus changes mass by four units and charge by two units – Alpha particle easily stopped – 4 x nucleon mass – +2 Charge – Big • Beta Decay • Beta minus - neutron converts to electron and anti-neutrino • Beta plus - proton converts to a anti-electron and neutrino • Nucleus changes charge but not mass number – Radiation moderately penetrating – +1 charge • Small electron • • Gamma Decay • Nucleus changes energy level - emits gamma ray or photon • Nucleus stays the same – Very penetrating – Very small – Neutral • Penetrating Properties of • Ionizing Radiation • Cosmic Rays Another form of Radiation • Comes from outside the earth Particles from the sun • Star dust - from supernova - exploding stars Consists of protons and neutrons • • Sources of Radiation • Average radiation exposure in the United States - 360 mrem Very location dependent • • • Additional Sources Plane travel • Living at high elevation - Albuquerque has 2x cosmic radiation Soil • Medical x-rays • Occupational exposure • Is radiation bad for you? • Too difficult to directly measure risk of low level • Use high exposure studies to determine radiation damage • Extrapolate from high exposure to low • Model 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 wound • Relative Risk1 in a million fatality • 40 tablespoon peanut butter (aflotoxin) • 2 days in New York City (air quality) • • 3 mrem radiation (cancer) 1 mile on motorcycle (collision) • 300 miles in car (collision) • 10 charbroiled steaks • Smoking 1 cigarette
