H

Half-Life

A(t) = A₀e^(−λt); t½ = ln2/λ
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Quick Reference
Formula / NotationA(t) = A₀e^(−λt); t½ = ln2/λ
Also Known AsRadioisotope half-life, Decay half-life, Biological half-life

What is Half-Life?

The time required for half of the atoms in a radioactive sample to decay. Different radioactive isotopes have characteristic half-lives ranging from fractions of a second to billions of years. Half-life is also used in pharmacokinetics to describe drug elimination rates.

Formula & Notation

A(t) = A₀e^(−λt); t½ = ln2/λ

Other Names / Synonyms: Radioisotope half-life, Decay half-life, Biological half-life

Properties & Characteristics

Time for half of radioactive atoms to decay. First-order process — independent of initial amount. Each successive half-life reduces amount by 50%. After n half-lives: amount = A₀ × (1/2)^n. Radioactive half-lives range from 10⁻²¹ s (unbound neutron 614 s) to billions of years (U-238: 4.47×10⁹ yr). Pharmacokinetic half-life: time for drug concentration to halve in body.

Uses & Applications

Radiocarbon dating (C-14 t½ = 5730 yr, dates objects up to 50,000 yr). Geological dating (U-238/Pb-206, K-40/Ar-40). Medical radioisotopes: Tc-99m (6 hr, imaging), I-131 (8 days, thyroid treatment), F-18 (110 min, PET scan). Nuclear waste storage calculations. Pharmacokinetics and drug dosing interval design. Reactor fuel burnup calculations.

Safety Information

Short half-life isotopes have high activity (high radiation dose rate) but shorter environmental persistence. Long half-life isotopes (Pu-239: 24,100 yr, U-238: 4.47 billion yr) require permanent geological storage. Never dispose of radioactive materials in regular waste — specialized licensed disposal required. Dosimetry badges must be worn in radiation areas.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Half-Life
Formula A(t) = A₀e^(−λt); t½ = ln2/λ
Index All "H" terms
Synonyms Radioisotope half-life, Decay half-life, Biological half-life

Frequently Asked Questions

The time required for half of the atoms in a radioactive sample to decay. Different radioactive isotopes have characteristic half-lives ranging from fractions of a second to billions of years. Half-life is also used in pharmacokinetics to describe drug elimination rates.

More "H" Terms

1-Hexanol C6H14O 2-Hydroxyethyl methacrylate C6H10O3 4-Hydroxybenzaldehyde C7H6O2 Haber Process N₂ + 3H₂ ⇌ 2NH₃ | ΔH = −92 kJ/mol Hafnium Hf Half Cell Half Life Half-Cell E = E° − (RT/nF)lnQ Half-Reaction Halide X⁻ (e.g., F⁻, Cl⁻, Br⁻, I⁻) Halogen F₂, Cl₂, Br₂, I₂, At; Group 17; ns²np⁵ valence configuration Halogenation C-X + Cl₂/Br₂ (hv or AlCl₃) → C-X(halogen); EAS or radical pathway
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Editorial standards: Chemical data is sourced from peer-reviewed literature, CAS Registry, NIST WebBook, and PubChem. Safety information reflects guidance from OSHA, ECHA, and IAEA. For educational purposes only — always consult official SDS documentation and qualified professionals before handling chemicals.

AllChemicals.info — The Online Chemical Glossary | https://allchemicals.info/chemical/495-half-life

For educational purposes only. Verify all information before use.