Introduction to Nuclear Chemistry

© 2009, Prentice-Hall, Inc. The Nucleus Remember that the nucleus is comprised of the two nucleons, protons and neutrons. The number of protons is the atomic number. The number of protons and neutrons together is effectively the mass of the atom.

Radioactive Decay & Decay Products What makes a nucleus unstable and why do some isotopes undergo spontaneous decay, emitting nuclear decay products? Nuclear chemistry addresses the transformations and reactions that affect the nucleus of an atom, resulting in the change in identity of the element. Types of radioactive decay: – Alpha decay – Beta decay – Positron emission – Electron capture – Gamma rays

 -particles can be stopped by paper.  -particles require at least a cm of lead (Pb).  -particles require at least 10 cm of lead (Pb). Energy:  >  >  Natural Radioactivity

Penetrating Ability

© 2009, Prentice-Hall, Inc. Neutron-Proton Ratios Any element with more than one proton (i.e., anything but hydrogen) will have repulsions between the protons in the nucleus. A strong nuclear force helps keep the nucleus from flying apart. Neutrons play a key role stabilizing the nucleus. Therefore, the ratio of neutrons to protons is an important factor.

Band of Stability And Nuclear Decay Number of Neutrons, (N) Number of Protons (Z)

Band of Stability and Radioactive Decay Isotopes with low n/p ratio, below band of stability decay by positron emission or electron capture: (P  N) Isotopes with high n/p ratio, above the band of stability decay by beta decay (N  P) Isotopes with atomic numbers > 83 are beyond the band of stability.They decay by alpha decay, decreasing mass by 4 and atomic number by 2.

© 2009, Prentice-Hall, Inc. Radioactive Series Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation. They undergo a series of decays until they form a stable nuclide (often a nuclide of lead).

The Half-Life of an isotope is the time it takes for 1/2 a sample to decay from its initial amount. The rate of a nuclear transformation depends only on the “reactant” concentration. The decay and half-life for a nuclear reaction follows first order kinetics. Half-Life

After each successive half-life, one half of the original amount remains. Half-Life

Decay follows first order kinetics: The half-life of radioactive decay ist 1/2 = 0.693/k Kinetics of Radioactive Decay

Half- Life Calculations A sample of Radon-222 has an initial α-particle activity (A 0 ) of 7.0 x 10 4 dps ( disintegrations per second ). After 6.6 days, its activity (A t ) is 2.1 x 10 4 dps. What is the half-life of Radon-222? 1. solve for “k” 2. plug into half- life equation Answer: 3.8 days

Binding Energy Binding energy- the energy required to separate a nucleus into individual protons and neutrons. Mass is converted to energy in the formation of the nucleus based on Einstein’s equitation: E= mc 2 Binding energy increases with atomic number.

Binding Energy/Nucleon

Fission/Fusion Discussion of binding energy Discussion of fission & fusion for nuclear for energy source: tvvY tvvY

Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. 17% of the world’s energy comes from nuclear. Nuclear Fission & Power