NSES Content Standard B
Physical Science: Structure of atoms
Grades 9-12, page 178
Radioactive isotopes are unstable and undergo spontaneous nuclear reactions,
emitting particles and/or wavelike radiation. The decay of any one nucleus
cannot be predicted, but a large group of identical nuclei decay at a predictable
rate. This predictability can be used to estimate the age of materials
that contain radioactive isotopes.
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Benchmark 4D The Physical Setting: Structure
of Matter
Grades 9-12, page 80
The nucleus of radioactive isotopes is unstable and spontaneously decays,
emitting particles and/or wavelike radiation. It cannot be predicted exactly
when, if ever, an unstable nucleus will decay, but a large group of identical
nuclei decay at a predictable rate. This predictability of decay rate allows
radioactivity to be used for estimating the age of materials that contain
radioactive substances.