Great Ideas in Science: Lecture 7 – Nuclear Reactions Professor Robert Hazen PROV 301 Great Idea: Nuclear energy arises from the conversion of mass into energy.
Nuclear Reactions Key Idea: Nuclear reactions result from the rearrangement of an atom’s protons and neutrons (i.e. the nucleus) Key Words: Proton Neutron Nucleus Isotope Radioactivity Nuclear Fission Nuclear Fusion
The Building Blocks of Matter Of what is matter made? Atoms Nuclei and electrons Quarks
A Hierarchy of Scientific Ideas Fact (a confirmed observation) Hypothesis (an educated guess) Law (a predictive mathematical description of nature) Theory (a well established explanation of nature)
Key Words About Atoms Atom: Any object with a nucleus and electrons Element: An atom with a known number of protons (the atomic number) Ion: An electronically-charged atom with a different number of protons (+) and electrons (-) Isotope: An element with a known number of neutrons
The Structure of the Atom Electrons in shells (energy levels) Negatively charged Shift during chemical reactions
The Structure of the Atom Electrons in shells (energy levels) Negatively charged Shift during chemical reactions Central dense nucleus Composed of protons and neutrons Positively charged Nucleus - Stays put in chemical reactions
Isotopes: Hydrogen & Carbon H-1 – 1 proton H-2 – 1 p & 1 neutron (Deuterium) H-3 – 1 p & 2 n (Tritium) C-12 – 6p & 6n C-13 – 6p & 7n C-14 – 6p & 8n (radioactive) For any given element the number of protons is fixed
Four Fates of Isotopes An isotope may be stable An isotope may be radioactive An isotope may be split apart by fission An isotope may combine with another by fusion
Chart of the Isotopes (Z vs. N)
Stable Isotopes 99.999+% of all the atoms around us Examples are carbon-12 and carbon-13 Different isotopes don’t affect chemical reactions. Used in scientific research to track chemical reactions (2 ways) As tracers Fractionation
Four Fates of Isotopes An isotope may be stable An isotope may be radioactive An isotope may be split apart by fission An isotope may combine with another by fusion
Radioactivity or Radioactive Decay (three kinds) The spontaneous emission of an energetic particle by a nucleus Alpha radiation Beta radiation Gamma radiation
Most Kinds of Isotopes are Radioactive STABLE RADIOACTIVE
Alpha Radiation Atom spontaneously loses 2 protons and 2 neutrons (= a Helium-4 nucleus)
Alpha Radiation Atom spontaneously loses 2 protons and 2 neutrons (= a Helium-4 nucleus) Uranium-238 Thorium-234 + 2n + 2p
Beta Radiation One neutron spontaneously becomes a proton plus an electron Thorium-234 Proactinium-234
Gamma Radiation Atom spontaneously emits a gamma ray (electromagnetic radiation) Uranium-238* Uranium-238 + γ
Gamma Radiation Atom spontaneously emits a gamma ray (electromagnetic radiation) Uranium-238* Thorium 234 + γ
SUMMARY: The Three Kinds of Radioactive Decay Alpha Decay Release of α particle with 2 protons and 2 neutrons Beta Decay Neutron becomes a proton Emission of electron (β-ray) Gamma Radiation Electromagnetic radiation
Radioactivity and Health Ionization Stripping off electrons Long-term effects Cancer Birth defects Alpha Beta Gamma
Half-Life The average time for decay of ½ batch of radioactive isotopes Wide range of half-lives
Radiometric Dating Measure the half-life of the isotope. Estimate how much was there at first. Measure what’s left now. Carbon-14: Half-life = 5730 years
Radiometric Dating Applications to geology Need longer half-lives Uranium, potassium
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Radioactive Decay Chain (radon)
Four Fates of Isotopes An isotope may be stable An isotope may be radioactive An isotope may be split apart by fission An isotope may combine with another by fusion
Nuclear Fission (Splitting) Fission = Splitting of nucleus A nuclear reactor converts mass to energy
Nuclear Fission (Splitting)
Nuclear Fission – The Atom Bomb Hiroshima – August 6, 1945
Nuclear Fission – The Atom Bomb
Yucca Mountain, Nevada (NIMBY)
Yucca Mountain, Nevada (NIMBY)
Four Fates of Isotopes An isotope may be stable An isotope may be radioactive An isotope may be split apart by fission An isotope may combine with another by fusion
Nuclear Fusion (Fusing) Hydrogen atoms combine to form helium Some mass is converted into energy
Nuclear Fusion – Hydrogen Bomb
Nuclear Fusion – Hydrogen Bomb
Stars are Giant Fusion Reactors http://www.earth.northwestern.edu/people/seth/107/Solar/Image12.gif
Fates of Stars
Benefits of Isotopes Stable Isotopes Radioactive Isotopes Medical Research Environmental Tracers Radioactive Isotopes Medical diagnosis Cancer treatments Environmental tracers Age Determination Nuclear fission Power generation Nuclear Fusion The Sun