Reading Half Life Graphs

What is the half-life of iodine-131?

• 32 days
• 8 days
• 16 days
• 24 days

Tags

NGSS.HS-PS1-8

What is the Half life of this isotope?

• 5 seconds

• 10 seconds

• 15 seconds

• 20 seconds

Tags

NGSS.HS-PS1-8

What is the Half Life of this isotope?

• 3 days

• 5 days

• 8 days

• 10 days

Tags

NGSS.HS-PS1-8

What is the half-life of this sample?

Answer explanation

Our starting activity is 400 cpm, so we’re looking for the point where it hits 200 to find its half-life. By reading our graph, we can see that this is after 15 days, so the half-life is 15 days. 

Tags

NGSS.HS-PS1-8

What is the half-life of this sample?

Tags

NGSS.HS-PS1-8

What is the half life of this sample?

Tags

NGSS.HS-PS1-8

What is the half-life of this sample?

Tags

NGSS.HS-PS1-8

If someone started off with a kilogram sample of this material, calculate how many grams of it would be remaining after half an hour.

Give your answer to two decimal places.

Answer explanation

Half-life of 3 minutes so 10 half-lives in half an hour.

1000g > 500g > 250g > 125g > 62.5g > 31.25g > 15.625g > 7.8125g > 3.90625g > 1.953125g > 0.9765625g remaining after 30 minutes.

We only round our answer at the end to ensure we do not make errors.

0.98g

What is the half-life of this sample?

Tags

NGSS.HS-PS1-8

What would the activity of this sample be after 60 minutes?

Do not round your answer

Answer explanation

Our first step is to work out the half-life from the graph. Our starting activity is 500 cpm and we hit 250 cpm after 15 minutes. 

To work out the total number of half-lives we divide the total time by the length of each half-life to give us four total half-lives with a starting activity of 500cpm.

500 > 250 > 125 > 62.5 > 31.25 cpm