What is the term for the amount of time it takes for half of the atoms in a radioactive sample to decay?

What is the term for the amount of time it takes for half of the atoms in a radioactive sample to decay?

• A. Activation energy
• B. Decay constant
• C. Half life
• D. Activity

Answer: (C)

Half-life is the time required for half of the undecayed nuclei in a radioactive sample to decay. If you start with N0 atoms, after one half-life you’d have N0/2 remaining; after two half-lives, N0/4, and so on. The decay follows an exponential law, N(t) = N0 e^{-λ t}, where λ is the decay constant. The two quantities connect through t1/2 = ln(2)/λ. This means the concept directly measures how long it takes for the population of undecayed atoms to drop by 50%. Activation energy and activity describe different ideas: activation energy is an energy barrier to reaction, and activity is the rate of decays per second, which scales with the number of undecayed nuclei, not the time for half to decay.

Half-life is the time required for half of the undecayed nuclei in a radioactive sample to decay. If you start with N0 atoms, after one half-life you’d have N0/2 remaining; after two half-lives, N0/4, and so on. The decay follows an exponential law, N(t) = N0 e^{-λ t}, where λ is the decay constant. The two quantities connect through t1/2 = ln(2)/λ. This means the concept directly measures how long it takes for the population of undecayed atoms to drop by 50%. Activation energy and activity describe different ideas: activation energy is an energy barrier to reaction, and activity is the rate of decays per second, which scales with the number of undecayed nuclei, not the time for half to decay.