Calculating Half Life

What is the half-life of a radioactive isotope?

• The time it takes for the number of nuclei to remain constant

• The time it takes for the number of nuclei to double

• The time it takes for the number of nuclei to halve

• The time it takes for the number of nuclei to triple

Tags

NGSS.HS-PS1-8

If a sample starts with 1,000 undecayed nuclei and after 20 minutes it has 500 undecayed nuclei, what is the half-life?

• 10 minutes

• 20 minutes

• 30 minutes

• 40 minutes

What is the count rate after 45 days for a radioactive isotope with a half-life of 15 days and an initial count rate of 200 counts per second?

• 50 counts per second

• 100 counts per second

• 12.5 counts per second

• 25 counts per second

Tags

NGSS.HS-PS1-8

What is the relationship between the rate of decay and the length of the half-life?

• The rate of decay is directly proportional to the length of the half-life

• The rate of decay is unrelated to the length of the half-life

• The rate of decay is equal to the length of the half-life

• The rate of decay is inversely proportional to the length of the half-life

Tags

NGSS.HS-PS1-8

What can half-life be used for?

• To determine the number of nuclei in a sample

• To predict when a nucleus will decay

• To solve problems related to radioactive isotopes

• To measure the rate of decay

What does a longer half-life indicate?

• faster rate of decay

• doubling rate of decay

• slower rate of decay

• constant rate of decay

Tags

NGSS.HS-PS1-8

How can you determine the half-life of a radioactive isotope?

• By calculating the count rate

• By measuring the decay rate

• By counting the number of nuclei

• By analyzing a graph

Tags

NGSS.HS-PS1-8

What is the count rate after 30 days for a radioactive isotope with a half-life of 10 days and an initial count rate of 500 counts per second?

• 250 counts per second

• 125 counts per second

• 31.25 counts per second

• 62.5 counts per second

Tags

NGSS.HS-PS1-8

What is the relationship between decay and half-life?

• Decay is the process by which half-life occurs

• Decay is the process that determines the length of half-life

• Decay is unrelated to half-life

• Decay is the result of half-life

Tags

NGSS.HS-PS1-8

After the third half-life, how much of the sample is left?

• 1/2

• 1/3

• 1/16

• 1/8