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.)

9. Based on Table 1 and Figure 1, if a sample initially contains 1,000 Ti-44 atoms, the number of Ti-44 atoms in the sample 20 yr later will most likely be:

Answer and Explanation

Your Answer is

Correct Answer is C

Explanation

First, through table 1, we can see that the λ of Ni is smaller than the λ of Sr and smaller than the λ of H;

Looking at figure 1 again, it is found that as the λ of the isotope becomes larger and larger, the ordinate of each line is also decreasing;

The λ of Ti in the title is between Ni-63 and Sr-90, so when the time is 20 yr, its corresponding Nt is also between Ni-63 and Sr- Between Nt of 90, that is about 600-900