Passage II

When the nucleus of an atom of a radioactive isotope undergoes certain types of decay, the atom transforms into an atom of a different isotope. An isotope's half-life is the time it takes for half of any given number of its nuclei to decay. An isotope's decay constant, λ, depends on the isotope's rate of decay. Table 1 gives the value of λ (in ) for 8 isotopes of different elements.

Figures 1 and 2 show, for each of 6 of the isotopes listed in Table 1, the change over time in the number of the nuclei remaining,, in a sample initially containing 1,000 of the nuclei.

(Note: In Figure 1, the unit of time is years; in Figure 2, the unit of tine is days.)