half life

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By Dorothy Burford

Half-life Review

What is half-life and how is it calculated?

Half-life

• It is the time taken for a radioactive isotope to decay to half its original value.

• Time can be seconds, minutes, hours, weeks, months or years

• It varies depending on the isotope

Fill in the Blanks

Half-life is the period of time it takes for an isotope to decay to

its original value

Multiple Choice

What is an isotope?

• one of several forms of the same atoms; same number of protons but have different number of neutrons

• a particle that has no charge and is located in the nucleus of an atom.

• energy in the form of waves or particles that is emitted from an object and travels through space or air

Multiple Choice

Geologist use the time it takes for a radioactive isotope to decay to half its original mass called a___________.

• radioactive decay

• isotope

• half-life

• carbon dating

Half-life

Radon-222 decays with a half-life of 3.82 days. If an initial sample of the element contains 1000 atoms, how much remains after 15.28 days?

Half-life = 3.82 days

# of half-lives = 15.28/3.82 = 4

1000--> 500 --> 250-->125-->62.5 atoms

62.5 atoms remains after 4 half-lives.

Multiple Choice

What is the only difference between two different isotopes of the same element?

• Number of neutrons

• Number of protons

• Number of electrons

• Size of atom

Multiple Select

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?

What do we need to know to answer this question? (Check all that applies)

• the half-life for the given sample

• the number of half-lives passed based on the total time

• to multiply by 2

• if alpha decay occurs

Multiple Choice

If 20 mg of iodine-131 is given to a patient, how much is left after 32 days? The half-life of iodine-131 is 8 days.

• 32

• 1.25

• 10

• 2.5

Multiple Choice

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

Multiple Choice

You have 100 grams of radioactive C-14. The half life of C-14 is 5730 years.

How many grams are left after 1 half life?

• 100g

• 50g

• 25g

• 2g