Question

If the half-life of a radioisotope is 10,000 years, the amount remaining after 20,000 years is

none
half
a fourth
double

answer is c

Answer 1

Considering the half-life of 10,000 years, after 20,000 years we will have a fourth of the remaining amount.

Step-by-step explanation:

The half-time is the time a radioisotope takes to decay and lose half of its mass. Therefore, we can make the following scheme to know the amount remaining after a period of time:

Time_________________ Amount

t=0_____________________x

t=10,000 years____________x/2

t=20,000 years___________x/4

During the first 10,000 years the radioisotope lost half of its mass. After 10,000 years more (which means 2 half-lives), the remaining amount also lost half of its mass. Therefore, after 20,000 years, the we will have a fourth of the initial amount.