Radioactive decay is a spontaneous and ... It takes another two days for the count rate to halve again, this time from 40 Bq to 20 Bq. The half-life of this source is 2 days.

A radioactive isotope's nucleus is unstable and spontaneously decays, giving off radiation and changing into a different isotope. The rate at which nuclei decay is constant. Half-life describes ...

This rate of decay is constant for a given isotope, and the time it takes for one-half of a particular isotope to decay is its radioactive half-life. For example, about 1.5 percent of a quantity ...

A spontaneous process means that it is not possible to say which particular nucleus will decay ... count rate might get very small, it does not drop to zero completely. The half-life of ...