The time for half of an isotope to decay to its stable form is called its:

1. Radioactive decay is described statistically rather than one atom at a time. 2. The time it takes for half of the original concentration of an isotope to decay back to its more stable form is called its half-life. 3. For carbon-14 that period is approximately 5,730 years. 4. Mass number and atomic number count particles instead of measuring time. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 2 'The Chemical Foundation of Life', sections 2.1-2.3_