NUCLEAR CHEMISTRY nuclear chemistry/physic processes that occur in the NUCLEUS—these are not chemical reactions!
Dec 31, 2015
NUCLEAR CHEMISTRY
nuclear chemistry/physics:processes that occur in the NUCLEUS—these arenot chemical reactions!
Objectives
• What is radiation? Understand the meaning of terminology related to radioactivity.
• Know the three main types of nuclear radiation.
• Be able to write correct nuclear equations.
Radioactivity
• 1896: Henri Becquerel discovers that uranium affects photographic film.
• Marie Curie calls it radioactivity: the process of materials emitting “rays”
• radiation: the rays/particles given off by a radioactive source
• radioisotope: unstable isotope that emits radiation
Three Types of Radiation
• a: Alpha (helium nucleus emitted)
Total charge (subscript) and mass (superscript) must be conserved.
• b: Beta (electrons emitted as no → p+ + e-)
• g: Gamma (high energy EM radiation)
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714
10C N e
12
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24
01H H He n
Objectives
• Why do atoms decay? Understand the concept of nuclear stability.
• Be able to determine the type of radioactive decay based on various circumstances.
• Be able to determine the products of various transmutation reactions.
Nuclear Stability
• Protons repel, but the nuclear strong force holds p+ and no together.
• A stable p+ / no ratio is needed.
• Elements “decay” to make a stable ratio. 1:1
1:1.5
Transmutations
• transmutation: an atom is converted into a different atom (a different element)
• occurs through radioactive decay
*positron: positive electron (antimatter)*neutrino (v): may be massless
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24Ra R n H e alpha
712
612
10N C e v beta
512
612
10B C e v beta
(nucleus is too heavy)
(too many neutrons)
(too many protons)
Transmutations
• bombardment: particles collides with the nucleus to cause transmutations (like bowling!)
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24
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11N He O H
The discovery of the p+ and the no were achieved using bombardment.
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Rutherford
Objectives
• How long does it take for a nucleus to decay? Understand the concept of half-life.
• Simulate the radioactive decay of an imaginary radioisotope and determine the half-life of the isotope.
• Be able to make simple half-life calculations.
Half-Life
• half-life (T1/2): the time it takes for one-half of the nuclei of a radioisotope to decay to products
• 64 nuclei → 32 → 16 → 8 → 4 → 2 → 1
• If T1/2 = 200 years, it takes six half-lives (1200 years) to decay from 64 to 1.
Measuring Nuclear Decay
• Fermium has a half-life of 100.5 days. How much of a 5.2 mg sample of fermium will remain after 365 days?
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Objectives
• What is nuclear energy? Understand the processes of nuclear fission.
• Be able to discuss how various technologies employ nuclear fission.
• Be familiar with the process of nuclear fusion.
Nuclear Fission
• fission: the splitting of a large nucleus
• products have less mass than reactants
• mass is converted into energy (E=mc2)
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Nuclear Fission Power
• Nuclear power plants use controlled nuclear fission to release energy slowly.
• Heat creates steam that generates electricity.
The Fission A-Bomb
• The WWII bombs used uncontrolled nuclear fission.
• Material must have a critical mass to explode.
• Test bomb/Nagasaki: implosion of Pu-239
• Hiroshima: gun-type with U-235
Nuclear Fusion• nuclear fusion: small
nuclei combine and release much more energy than fission reactions.
• occurs in the sun and nuclear weapons
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24
10H He e v
Thermonuclear Weapons• Modern “nukes” use fission to start a fusion reaction.• 100 times more powerful than the A-bomb (1.2
megatons vs. 15 kilotons of TNT).