7.2 AND 7.3HALF LIFE AND NUCLEAR REACTIONS

HALF LIFE

• Half lives can be used to compare the rate of radioactive decay for an isotope

• A shorter half life means a faster decay rate• Radioactive decay rates all follow a pattern called a decay curve

CARBON DATING

• In carbon dating, we measure the radioactivity in plants or animals and how it has changed

• This is due to the fact that all organisms contain carbon• We use carbon dating by measuring the ratio between carbon-14 and

carbon-12 in their system• Carbon-14 atoms decay without being replaced after death and carbon-

12 atoms stay constant• Using this process we determine the age of an organism

RADIOACTIVE DECAY

• Radioactive decay can be compared using a quantity called half life • A half life is equal to the amount of time required for half the

amount of the nuclei in a sample to decay

USING A DECAY CURVE

• A decay curve the curved line on a graph showing the rate at which a radioisotope decays

• Graphing the rate of decay of any radioisotope will look the same

VIDEO!

COMMON ISOTOPE PAIRS

• Isotopes that undergo radioactive decay are called Parent isotope• The stable product of this process is called the daughter isotope • Each isotope can be used in radio carbon dating, but the range will

be different

NUCLEAR FISSION

• This is the process where one massive nucleus splits into two smaller nuclei, subatomic particles and a huge amount of energy

NUCLEAR FUSION

• This is the process where two smaller nuclei join together to make one massive nucleus• This reaction is found in the Sun• When two nuclei combine they release a huge amount of

energy

QUIZ !

1. What is a half life?

2. Radioactive decay rates all follow what?

3. What do all organisms contain?

4. What are the 2 isotopes that are necessary for carbon dating?

5. Which isotope stays constant even after death?

6. What does carbon dating determine?

7. What do all decay graphs all have in common?

8. Isotopes that undergo radioactive decay are called what?

9. What kind of nuclear reaction is found in the Sun?

10. The splitting of one massive nucleus into two smaller ones is what?

ANSWERS TO THE QUIZ

1. A half life is the amount of time required for half the nuclei in a sample to decay.

2. A similar pattern called a decay curve.

3. Carbon.

4. Carbon-12 and Carbon-14.

5. Carbon-12

6. The age of a sample.

7. The graphs all look the same.

8. The parent isotope.

9. Nuclear Fusion.

10. Nuclear Fission.