Khan Academy on a Stick
Radioactive decay

Types of Decay
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Alpha, Beta, Gamma Decay and Positron Emission

HalfLife
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Introduction to halflife

Exponential Decay Formula Proof (can skip, involves Calculus)
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Showing that N(t)=Ne^(kt) describes the amount of a radioactive substance we have at time T. For students with background in Calculus. Not necessary for intro chemistry class.

Introduction to Exponential Decay
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Introduction to Exponential Decay

More Exponential Decay Examples
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A few more examples of exponential decay.