A pure sample of a known element has a very long half-life.
The diagram shows three electron energy levels of an atom.
A pure sample of a known element has a very long half-life. What measurement(s), together with the initial activity of the sample, must be made in order to measure the half-life of the element?
The activity of the sample after a given period of time.
The mass of the sample after a given period of time.
The activity and the mass of the sample after a given period of time.
The mass of the sample.