Generally, more massive nuclides tend to be more unstable to alpha decay. For example, the most stable isotope of uranium, 238U, has an alpha decay half-life of 4.5 x 109 y. The most stable isotope of plutonium is 244Pu with an 8.0 x 107 y half-life, and for curium we have 248Cm and 3.4 x 105y. When half of an original sample 238U has decayed, what fraction of the original sample of

(a) Plutonium and

(b) Curium is left?