Radiometric Dating

Radiometric Dating

Open Ended

How are you feeling about nuclear decay reaction equations?

General Steps

• Identify the Isotope being used

• Identify the length of one half-life for that PARENT isotope

• Identify the percentage or fraction of the PARENT isotope remaining in the substance

• Determine how many half-lives a substance has experienced based on the remaining PARENT isotope

• Figure out the amount left or the time passed based on the amount of half lives

Example #1

• The half-life of Carbon-14 is 5730 years before it turns into Nitrogen-14 gas. If 1/8th of a sample is left as Carbon-14, how old is the sample?

• 1.) Isotope = Carbon-14

• 2.) Half-life of Carbon-14 = 5730 years

• 3.)  Remaining parent = ⅛

• 4.) ⅛ of sample =  3 half-lives

• 5.) 3 x 5730 years = 17190 years

• ANSWER = The sample is 17190 years old

Example #2

• If an object is 500 grams and only 125 grams are the unstable isotope radium-226, which has a half-life of 1600 years, how old is the object?

• 1.) Isotope = Radium-226

• 2.) Half-life of radium-226 = 1600 years

• 3.) Remaining parent = 125/500 = .25 = 25% = ¼

• 4.)  ¼ of sample = 2 half lives

• 5.) 2 x 1600 years = 3200 years

• ANSWER = The object is 3200 years old.

Multiple Choice

If a sample starts with 100 atoms of an unstable atom, how much will be left after 2 half-lives?

• 75

• 50

• 25

• 20

Multiple Choice

If there is 25 atoms left from a 100 atom sample of an isotope with a half life of 100 years, how old is the sample?

• 500 years

• 200 years

• 100 years

• 50 years

• 25 years

Multiple Choice

A radioactive element has a half-life of 2 days. How many half-lives would it experience at 6 days?

• 5

• 4

• 3

• 2

• 1

Multiple Choice

A radioactive element has a half-life of 2 days.

What percentage would remain radioactive after 6 days?

• 100%

• 75%

• 50%

• 25%

• 12.5%

Multiple Choice

A radioactive element has a half-life of 2 days. If the original mass was 120 grams, how much would have decayed after 6 days?

• 240 grams

• 120 grams

• 60 grams

• 30 grams

• 15 grams

Open Ended

Where are you having problems with these equations?