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Radiation Objectives Understand the concepts of ½ life and ½ thickness in radiation Differentiate between fusion and fission Describe the processes involved in radioactive decays (alpha, beta, and gamma)
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Elementary Particle Properties
Particle Symbol Charge Weight Weight Ratio (e-) proton p amu heavy electron e amu light neutron n amu heavy 1 Atomic Mass Unit (amu) = 1.66 x grams Atoms are electrically neutral with no net charge. Ions are atoms that have been stripped of one or more of their electrons and have a net charge.
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Isotopes Identical Chemical Properties, Different Atomic Weight
Difference = presence of number of neutrons in the nucleus Hydrogen = amu ISOTOPE Constituents Atomic Mass Occurrence H 1 proton 1 electron amu % Deuterium 1 proton 1 electron amu % 1 neutron Tritium 1 proton 1 electron amu % 2 neutrons
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Isotope Designations Hydrogen 11H 1 proton, 0 neutrons
Helium He 2 protons, 2 neutrons Uranium U 92 protons, 143 neutrons neutron 10n proton 11p electron 0-1e
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Radiation Three types of Nuclear Radiation.
Revealed by their deflection in a magnetic field as neutral, charged negative or charged positive.
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Radioactive Particles
Alpha a Ejection of 2 protons and 2 neutrons from an unstable nucleus. 42He = a Beta b Ejection of an electron from an unstable nucleus as part of the decay of a neutron e = b Gamma g Atomic nucleus transition, yielding high energy photons.
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AZX Nuclear Reactions 22688Ra 22286Rn + 42He
Note that the numbers all add-up (conservation of particles). AZX A nucleons Total particles in nucleus = Z protons Number of protons =
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Alpha Decay Alpha a = 42He 22688Ra 22256Rn + 42He
Parent Ra Radium Daughter Rn Radon Radiation 42He a 22688Ra Rn He Most of the energy is with the lighter particle, in this case the alpha particle.
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Beta Decay Beta b = 0-1e 10n 11p + 0-1e
The decay of a neutron into a proton and electron.
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Beta Decay Beta b = 0-1e 10n 11p + 0-1e
The decay of a neutron into a proton and electron. 146C 147N + 0-1e (Radioactive Carbon) 9038Sr Y + b
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Gamma Radiation Gamma g E = h f 8738Sr* 8738Sr + g
Very high energy photons are emitted from the nucleus. Excess radiation emitted from an excited nucleus…. 8738Sr* Sr + g Excess radiation emitted as part of another process…. 6027Co Ni + b + g
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Radioactive Decay If you start out with a sample of parent atoms (No),
after some time there will be fewer because of radioactive decay into the daughter atoms.
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Shielding We can detect the radiation from a radioactive source.
Say we get X counts/minute (cpm). Geiger Counter
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Shielding We can shield the source with various
materials to test their usefulness in protecting against the radiation. Geiger Counter
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Half Thickness Half Thickness: The thickness of a material needed to
cut the count rate by 1/2. If a 4 inch thickness of lead, drops a count rate from 1000 cpm to 500 cpm, the half thickness must be 4 inches.
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Half Thickness Half Thickness: The thickness of a material needed to
cut the count rate by 1/2. If 12 inches of wood, drops a count rate from 2000 cpm to 125 cpm, the half thickness must be 3 inches.
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Shielding Efficiency a b g Cotton Fabric Wood Lead
g’s are the most penetrating type of radiation.
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Nuclear Energy Generation
Hydrogen Fusion Binding Energy/nucleon Fission Uranium Iron Atomic Mass Number
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