Uses of RadioactivityUses of Radioactivity

Nuclear FissionNuclear Fission

The The splittingsplitting of the nucleus of a large of the nucleus of a large atom into atom into twotwo or or moremore fragments fragments

It produces additional It produces additional neutronsneutrons and lots of and lots of energyenergy

Fission can cause Fission can cause chain reactionschain reactions – a – a reaction in which a change in a single reaction in which a change in a single molecule makes many molecules change.molecule makes many molecules change.

Critical MassCritical Mass – the minimum mass of a – the minimum mass of a fissionable isotope that provides enough fissionable isotope that provides enough neutrons to maintain a chain reactionneutrons to maintain a chain reaction

Figure 11 on page 654

Chain Reactions are used Chain Reactions are used in Nuclear Reactorsin Nuclear Reactors

Nuclear FusionNuclear Fusion

The The combinationcombination of the nuclei of of the nuclei of small atoms to form a larger small atoms to form a larger nucleusnucleus

This process also creates This process also creates energyenergy.. The The sunsun uses nuclear fusion to uses nuclear fusion to

generate heat and light.generate heat and light.

Half-Life and Geologic Half-Life and Geologic DatingDating Half-lifeHalf-life is the time required for is the time required for halfhalf of of

a sample of radioactive substance to a sample of radioactive substance to disintegratedisintegrate by radioactive decay or by radioactive decay or natural processes.natural processes.

So every time the “half-life time” So every time the “half-life time” passes, passes, halfhalf of the parent substance of the parent substance ((original original substance) has turned into substance) has turned into the daughter substance (the daughter substance (newnew substance)substance)

1.00 mg

I53

131

A look at half lifeA look at half lifeIodine-131 has a half-life of 8.02 days. So after 8.02 days, half of the Iodine-131 will have decayed to Xenon-131

0.00 days

0.500 mg

I53

131

0.750 mg

Xe54

131

0.875 mg

Xe54

131

0.125 mg I53

131

8.02 days 16.04 days 24.06 days

0.250 mgI

53

131

0.500 mg

Xe54

131

0 half-lives 1 half-lives 2 half-lives 3 half-lives

Example ProblemsExample Problems

Assuming a half life of 1599 years, how Assuming a half life of 1599 years, how many years will be needed for the many years will be needed for the decay of 15/16 of a given amount of decay of 15/16 of a given amount of radium-226.radium-226.

The half-life of radon-222 is 3.824 days. The half-life of radon-222 is 3.824 days. How much time must pass for one- How much time must pass for one-fourth of a given amount of radon to fourth of a given amount of radon to remain.remain.

The half-life of polonium is 3.0 minutes. The half-life of polonium is 3.0 minutes. If you start with 16 mg of polonium-218, If you start with 16 mg of polonium-218, how much time must pass for only 1.0 how much time must pass for only 1.0 mg to remain.mg to remain.

Geologic DatingGeologic Dating

As you can guess, we can use half-life As you can guess, we can use half-life and radioactive decay to determine and radioactive decay to determine the the geologic agegeologic age of materials. of materials.

Example: An ancient artifact is found Example: An ancient artifact is found to have a ratio of carbon-14 to to have a ratio of carbon-14 to carbon-12 that is one-eighth of the carbon-12 that is one-eighth of the ratio of carbon-14 to carbon-12 found ratio of carbon-14 to carbon-12 found in a similar object today. How old id in a similar object today. How old id this artifact? (C-14 has a half life of this artifact? (C-14 has a half life of 5715 years).5715 years).

Other uses of Nuclear Other uses of Nuclear ChemistryChemistry

Smoke DetectorsSmoke Detectors Art ForgeriesArt Forgeries Medicinal ReasonsMedicinal Reasons

– X-raysX-rays– PET scans (Positron Emission PET scans (Positron Emission

Tomography)Tomography)

Even though radiation Even though radiation can be helpful, it can be can be helpful, it can be dangerousdangerous

LargeLarge doses of radiation in a doses of radiation in a shortshort period of period of time or time or smallsmall doses of radiation over doses of radiation over longlong periods of time can lead to:periods of time can lead to:– Decrease in white blood cellsDecrease in white blood cells– NauseaNausea– Loss of hairLoss of hair– UlcersUlcers– Internal bleedingInternal bleeding– DeathDeath