How is half-life defined?

How is half-life defined?

• A. The rate of heat production
• B. The number of protons in the nucleus
• C. The number of neutrons lost per decay
• D. The time it takes for half of a radioactive sample to decay

Answer: (D)

Half-life is the time required for half of the unstable nuclei in a radioactive sample to decay. For a given nuclide, this interval is a constant even if you start with more or less material, and it describes how quickly the sample loses undecayed nuclei over time, following exponential decay. It does not measure heat production, which is tied to the decay rate (activity); it doesn’t pertain to the number of protons in the nucleus (the element’s identity), nor to how many neutrons are lost per decay (that varies with the decay mode). So the best definition is the time it takes for half of the radioactive sample to decay. For example, with a half-life of one year, starting with 1000 nuclei leaves about 500 after one year, about 250 after two years, and so on.

Half-life is the time required for half of the unstable nuclei in a radioactive sample to decay. For a given nuclide, this interval is a constant even if you start with more or less material, and it describes how quickly the sample loses undecayed nuclei over time, following exponential decay. It does not measure heat production, which is tied to the decay rate (activity); it doesn’t pertain to the number of protons in the nucleus (the element’s identity), nor to how many neutrons are lost per decay (that varies with the decay mode). So the best definition is the time it takes for half of the radioactive sample to decay. For example, with a half-life of one year, starting with 1000 nuclei leaves about 500 after one year, about 250 after two years, and so on.