# Question #72f8f

Jun 21, 2016

One sixteenth part.

#### Explanation:

Half life means that half of the number of atoms you start with has decayed (i.e. emitted radiation):

Iodine 131 has a half life of $8$ days, so $32$ days is four half lifes:

• 1 half life = 1/2 left
• 2 half lifes = 1/4 left
• 3 half lifes = 1/8 left
• 4 half lifes = 1/16 left

For more complex calculations you can use the equation:

$N \left(t\right) = N \left(0\right) \cdot {0.5}^{\frac{t}{T}}$

In which $N \left(0\right)$ is the number of atoms you start with, and $N \left(t\right)$ the number of atoms left after a certain time $t$ for a nuclide with a half life of $T$.