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.
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.
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 interv…
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 dispo…
The formula or notation for Half-Life is: A(t) = A₀e^(−λt); t½ = ln2/λ
