Half-life

Half-life is a term used in pharmacology and nuclear physics to describe the time it takes for the amount of a substance undergoing decay to decrease by half. The term is commonly used in relation to radioactive decay, but can also be used to describe other types of decay, such as the loss of plasma from the body.

Pharmacology

In pharmacology, the half-life of a drug is the time it takes for the concentration of the drug in the body to be reduced by half. This is an important factor in determining the dosage and frequency of administration of a drug. The half-life of a drug can be affected by many factors, including the rate of absorption, distribution, metabolism, and excretion.

Nuclear Physics

In nuclear physics, the half-life of a radioactive substance is the time it takes for half of the atoms in a sample to decay. This is a measure of the stability of a radioisotope. The half-life of a radioisotope can range from fractions of a second to billions of years.

Calculation

The half-life of a substance can be calculated using the formula:

t_1/2 = ln(2) / λ

where:

t_1/2 is the half-life

ln(2) is the natural logarithm of 2 (approximately 0.693)

λ is the decay constant

See Also

• Decay constant
• Radioactive decay
• Pharmacokinetics

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