Half Life

What is Half-life?

• The amount of time it takes for some of the nuclei in a sample of the isotope to decay
• The amount of time it takes for half the electrons in a sample of the isotope to decay
• The amount of time it takes for half the nuclei in a sample of the isotope to decay
• the amount of time it takes to double the nuclei in a sample of the isotope to decay

Barium-122 has a half-life of 2 minutes. A fresh sample weighing 80 g was obtained. If it takes 10 minutes to set up an experiment using barium-122, how much barium-122 will be left when the experiment begins?

• 0.25g
• 2.5g
• 25g
• 80g

If 10 mg of iodine 131 is given to a patient, how much is left after 24 days? The half-life of iodine-131 is 8 days. Round to two decimal points. NO UNITS NEEDED

The half-life of strontium-90 is 25 years. How much strontium-90 will remain after 100 years if the initial amount is 4.0 g? Round to two decimal points. NO UNITS

The half-life of Zn-71 is 2.4 minutes. If 6.25 g of Zn-71 are needed for an experiment, how much should be prepared if it will take 9.6 minutes before the experiment can begin? (FIND M_i)

• 100.0g

• 50.0g

• 12.5g

• 8.5g

Barium-122 has a half-life of 2 minutes. If after 10 minutes a sample of 15.0 g is left, what mass must have been initially present?

• 30 g

• 480 g

• 240 g

• 120 g

What is the half-life of iodine-131?

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

If 10 mg of iodine 131 is left after 40 days how much must we have started with? The half-life of iodine-131 is 8 days. NO UNITS

The half life of isotope X is 2.0 years. How many years would it take for a 4.0 mg sample of X to decay and have only 0.50 mg of it remain?

• 6.0 years

• 3.0 years

• 8.0 years

• 2.0 years

Selenium-83 has a half-life of 25.0 minutes. How many minutes would it take for a 10.0 mg sample to decay and have only 1.25 mg of it remain?

• 3.0 minutes

• 25.0 minutes

• 75.0 minutes

• 250.0 minutes