Published on February 15, 2014
Nuclear Reactions • Nuclear reactions change an atom’s nucleus. • 3 Types of radiation are produced from nuclear reactions: alpha, beta & gamma. –Alpha: positive –Beta: negative –Gamma: no charge
• Strong nuclear force: force that holds the protons together in the nucleus • Neutrons add a strong nuclear force to a nucleus, which keeps the protons from breaking the nucleus apart. • All nuclei with atomic numbers >83 are radioactive.
• Beyond 20 protons, nuclei need many more neutrons than protons to be stable. • Nuclei can become unstable if there are too many or too few neutrons. • Isotopes that are much heavier or much lighter than the most common isotope are likely to be radioactive.
Alpha Particles • An alpha (α) particle has 2 neutrons & 2 protons and is identical to a He-4 nucleus.
Beta Particle • a neutron changes into a proton & electron. • The proton stays in the nucleus & the electron/beta particle is propelled out of the nucleus. • Beta particle = electron
Gamma Ray • Gamma radiation has no particles. • Most dangerous type of radiation • Emitted from the nuclear bomb
Nuclear Fission • When certain elements are struck with neutrons, the nucleus can split into smaller fragments. – Only occurs in Uranium-235 & Plutonium-239 – Creates a chain reaction that releases an immense amount of energy • ~2 lbs of U-235 creates as much energy as 20,000 tons of dynamite – Nuclear bombs use fission – Nuclear Power Plants use fission to heat water
Nuclear Fusion • When 2 or more atoms combine to create one atom • Occurs in stars, like our sun – Hydrogen atoms fuse to make helium atoms – When stars run out of hydrogen, they start to die • Creates more energy than fission reactions • Extremely high temperatures are needed to create a fusion reaction – We have not been able to attain temperatures hot enough for us to use nuclear fusion as a power source on Earth
Half-Life • Every radioactive sample decays at a certain rate • A half-life is the time required for half of the atoms in the sample to decay into products – Half-lives can range from fractions of a second to billions of years – Half-lives of: • Radon-222: 3.8 days • Carbon-14: 5730 years • Uranium-235: 700,000,000 years
Calculating Half-Lives amount _ of _ time _ elapsed length _ of _ halflife number _ of _ halflives • The half-life of Carbon-14 is 5730 years. How many half-lives elapse after 17,190 years? • How many grams of C-14 is left after 3 halflives if it started off with 100 grams? • Starting with 80 grams, how many half-lives have elapsed if you end with 5 grams?
• What is the half-life of a 100 g sample of N16 that decays to 12.5 g in 21.6 seconds? • If an 800 g sample of technetium-99 decays to 100 g in 639,000 years, what is its halflife? • A 208 g sample of sodium-24 decays to 13 g of sodium-24 within 60 hours. What is the half-life of this isotope? • The half-life of Au-198 is 2.7 days. How much of a 300g sample will be left after 10.8 days?
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