To determine how much thorium-229 remains after 14,680 years, we can use the concept of half-lives.
The half-life of thorium-229 is 7340 years. After each half-life, the quantity of the substance is reduced by half.
First, we calculate how many half-lives fit into 14,680 years:
\[ \text{Number of half-lives} = \frac{14,680 \text{ years}}{7340 \text{ years/half-life}} \approx 2 \]
Now that we know that 14,680 years is approximately 2 half-lives, we can calculate the remaining amount of thorium:
Starting amount: 0.25 grams
After the first half-life (7340 years): \[ 0.25 , \text{g} \div 2 = 0.125 , \text{g} \]
After the second half-life (14,680 years): \[ 0.125 , \text{g} \div 2 = 0.0625 , \text{g} \]
Therefore, after 14,680 years, 0.0625 grams of thorium-229 will remain.
The correct response is: A 0.0625g
1 answer