Americium-243 Has a Decay Constant Of $9.39 \times 10 ^ { - 5 }$

Americium-243 has a decay constant of $9.39 \times 10 ^ { - 5 }$ years $- 1$ . How long will it take for a sample of americium-243 to lose one-third of its nuclei?

A) $2960 \mathrm {~s}$
B) $10.6 \times 10 ^ { 3 } \mathrm { y }$
C) $7.84 \times 10 ^ { 3 } \mathrm { y }$
D) $4.32 \times 10 ^ { 3 } \mathrm { y }$
E) $6.44 \times 10 ^ { 3 } \mathrm { y }$