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.• Understand the concept of penetration power.

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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Radiation Problems

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Penetration Power

Objectives

• Why do atoms decay? Understand the concept of nuclear stability and be able to determine the type of radioactive decay for various isotopes.

• Be able to determine the products of various transmutation reactions.

Nuclear Transformations• Protons repel, but

the nuclear strong force can hold p+ and no together.

• Neutrons are needed to supply this force, but a stable p+ to no ratio is necessary.

• Elements “decay” to create a stable ratio.

Transmutations

• transmutation: an atom is converted into a different atom (of a different element)

• radioactive decay

*positron: positive electron (antimatter)*neutrino (v): may be massless

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(nucleus is too heavy)

(too many neutrons)

(too many protons)

Decay Series

Transmutations

• bombardment: particles collide with the nucleus to cause transmutations (like bowling!)

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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.

Nuclear Fission

• fission: the splitting of a large nucleus into smaller fragments

• the products have less mass than the 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.

Fission Reactor Core

Three-Mile Island

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 more energy than fission reactions.

• The energy (E=mc2) is mostly in the form gamma rays, positrons, and neutrinos.

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Thermonuclear Weapons• Modern “nukes” use fission to start a fusion reaction.• These weapons are about 100 times more powerful

than the A-bomb (1.2 megatons vs. 15 kilotons of TNT).