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RadioactiveElements
Part 1Jan 2, 2013
Radioactivity: An Imbalance of Forces in the Nucleus
Radioactivity: An Imbalance of Forces in the Nucleus
Radioactivity: An Imbalance of Forces in the Nucleus
• Forces dependent on distance• SO.. Larger nuclei are less stable
• Neucleons less effective in holding nucleus together
• Electrical (repulsive) forces have greater impact
Types of Radioactive Particles
Alpha Particles – 2 protons and 2 neutrons
Beta Particles – split 1 neutron into 1 proton and 1 electron
Gamma Particles – emits a photon
Half Life: Measures Decay Rate
Half life refers to amount of time it takes for ½ of the radio active sample to decay
Half life for a particular isotope is always the same
Half Life
Half life measures decay rateEx. Every1620 years ½ of a sample of
radium-226 will have decayed.
Start1620 years
3240 years
6480 years
RadioactiveElements
Part 2Jan 4, 2013
Half-life: Exponential Decay
Decay of 238U: Natural Decay Chain
Decay of 238U: Natural Decay Chain decays, through alpha-emission, with a half-life of 4.5 billion years to thorium-234 which decays, through beta-emission, with a half-life of 24 days to protactinium-234 which decays, through beta-emission, with a half-life of 1.2 minutes to uranium-234 which decays, through alpha-emission, with a half-life of 240 thousand years to
thorium-230 which decays, through alpha-emission, with a half-life of 77 thousand years to radium-
226 which decays, through alpha-emission, with a half-life of 1.6 thousand years to radon-
222 which decays, through alpha-emission, with a half-life of 3.8 days to polonium-218 which decays, through alpha-emission, with a half-life of 3.1 minutes to lead-214 which decays, through beta-emission, with a half-life of 27 minutes to bismuth-214 which decays, through beta-emission, with a half-life of 20 minutes to polonium-214 which decays, through alpha-emission, with a half-life of 160 microseconds to lead-210 which decays, through beta-emission, with a half-life of 22 years to bismuth-210 which decays, through beta-emission, with a half-life of 5 days to polonium-210 which decays, through alpha-emission, with a half-life of 140 days to lead-206, which is
a stable nuclide.
Types of Radioactive Particles
Alpha Particles – 2 protons and 2 neutrons
Beta Particles – split 1 neutron into 1 proton and 1 electron
Gamma Particles – emits a photon
Types of Radioactive Particles
Alpha Particles – 2 protons and 2 neutrons• Lowest Energy
• Still fast enough to do damage• Easily stopped
• Relatively large size and mass• Large enough to do damage• Easily stopped
• +2 Charge. • Tends to pick up electrons
& convert to Helium
Types of Radioactive Particles
Alpha Particles
Emits: 2 p + 2 n
Example:Uranium-238 Thorium-234 + Helium-4
Element Atomic #(# protons)
Mass # (# p + # n)
# neutrons
Uranium 92 238 146
Thorium 90 234 144
Helium 2 4 2
Types of Radioactive Particles
Beta Particles - 1 n 1 p + 1 e- (emits e-)• Higher Energy
• Harder to stop than α particle• Becomes part of material when stopped
Types of Radioactive Particles
Beta Particles
Loses: 1 nGains: 1 pEmits: 1 e-
Example: Thorium -234 Protactinium – 234 + electron
Element Atomic #(# protons)
Mass # (# p + # n)
# neutrons
Thornium 90 234 144
Protactinium 91 234 143
Types of Radioactive Particles
Gamma Particles – emits a photon• Highest Energy
• Can do significant damage• Hard to stop
• No charge• Doesn’t combine with other materials
• No mass• Hard to stop