Radioactive decay is the loss of elementary particles from an unstable nucleus, ultimately changing the unstable element into another more stable element.

There are five types of radioactive decay: alpha emission, beta emission, positron emission, electron capture, and gamma emission.

Each type of decay emits a specific particle which changes the type of product produced.

In solids, atoms move via diffusion, driven by concentration gradients, as described by Fick's first law; the proportionality constant in this case is D, the diffusivity.

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chemical kinetics: the rate equation, order of reaction, and rate laws for zeroth, first, and second order reactions, temperature dependence of rate of reaction, catalysts, Fick's first law and steady-state diffusionsteric hindrance, cisplatin, first-order, second-order, zero-order, half-life, radioactive decay, reaction rate, chemical kinetics, rate of reaction, products, reactants, rate constant, rate equation, activation energy, Arrhenius equation, activated complex, decomposition reaction, nuclear decay, linearizing function, least-squares fitting, integral method, differential method, catalysis, reaction coordinate diagram, adsorb, desorb, selectivity, catalyst, inhibitor, diffusion, mass transport, mass flow rate, flux, Fick's first law, concentration gradient, diffusivity, concentration profile, oxidation, reduction) are inversely proportional to concentration.

To determine the order and rate constant of an unknown system, integral and differential methods can be used to linearize experimental data measuring concentration over time.Catalysts affect reaction rates by adsorbing, aligning, or otherwise physically manipulating reactants, changing the activation energy of a reaction.Reaction rates are also limited by mass transport of reactants and products.For information on each type of decay, read the page Decay pathways.In terms of entropy, radioactive decay can be defined as the tendency for matter and energy to gain inert uniformity or stability.For elements, uniformity is produced by having an equal number of neutrons and protons which in turn dictates the desired nuclear forces to keep the nuclear particles inside the nucleus.