11

Clip

1 . Differentiate among alpha and beta particles and gamma radiation .2 . Differentiate between fission and fusion .3 . Explain the process half-life as related to radioactive decay . 4. Describe nuclear energy , its practical application as an alternative energy source , and its potential problems.

22

Radioactivity is the spontaneous disintegration of atomic nuclei. The nucleus emits α particles, ß particles, or electromagnetic rays during this process.

Radioactivity is the spontaneous disintegration of atomic nuclei. The nucleus emits α particles, ß particles, or electromagnetic rays during this process.

After decaying, radioactive atoms “change” into other atoms

33

Clip

• Why does the atom do this?– the nucleus of an atom attempts to become

more stable

• In some instances, a new element is formed and in other cases, a new form of the original element, called an isotope, appears. – this process of change is often referred to as

the decay of atoms.

• The rate of Radioactive decay is described in half-liveshalf-lives.

44

Energy is released during Energy is released during radioactive decayradioactive decay

55

Types of Nuclear Types of Nuclear RadiationRadiation

• When an unstable nucleus decays, particles and energy are given off from the decaying nucleus.

• α and β radiation is in the form of particles

• γ radiation is in the form of waves-kind of like light but higher frequency

66

77Nuclear Decay

Neutron decays into a proton

2 protons & 2 neutrons

• Alpha particles consist of two protonstwo protons and two neutronstwo neutrons, identical to the nucleus of a helium atom.

• A sheet of paper or a person’s surface layer of skin will stop them.

• Alpha particles are only considered hazardous to a person’s health if they are ingested or inhaled and thus come into contact with sensitive cells such as in the lungs, liver and bones.

88

99

• Beta particlesBeta particles are electrons emitted from are electrons emitted from the nuclei of many fission products.the nuclei of many fission products.

•They can travel a few feet in air but can usually be stopped by clothing or a few centimeters of wood.

•They are considered hazardous mainly if ingested or inhaled, but can cause radiation damage to the skin if the exposure is large enough.

•Unstable Neutron decays into a proton.

1100

1111

• Gamma rays are a form of electromagnetic radiation (like light, radio, and television) that

come from the nucleus of a radioactive atom.– Occurs when an unstable nucleus emits electromagnetic

radiation. The radiation has no mass, and so its emission does not change the element.

– They penetrate matter easily and are best stopped by water or thick layers of lead or concrete.

– Gamma radiation is hazardous to people inside and outside of the body.

•However, gamma radiation often accompanies alpha and beta emission, which do change the element's identity.

•Gamma rays have the lowest ionizing power, but the highest penetrating power.

1122

1133

Biological Effects of Radiation:Biological Effects of Radiation:Ionizing radiation causes

physical damage to cells and DNA.

Radiation can excite DNA and result in the destruction on the

DNA backbone.

At high doses of radiation (10,000 - 15,000 rads), death

occurs in a few hours because of neurological and cardiovascular

breakdown (Central Nervous Syndrome).

1144

Biological Effects of Biological Effects of Radiation:Radiation:

Medium doses, 500 - 1200 rads, causes deathcauses death to occur in a

few days because of the destruction of the

gastrointestinal mucosa.

Lower doses, 250 - 500 rads, causes death to occur after

several weeks due to damage of the blood forming organs (hematopoietic syndrome).

1144

Medicine•For example, radiation and radioactive radioactive tracerstracersare used to diagnose and treat medical problems.

•A radioactive tracer is a radioactive isotope that is added to a substance so that the substance can be detected later.

•Radioactive tracers are used to locate tumors, to study the functioning of a particular organ, or to monitor the flow of blood.

•For example, radioactive iodine-131 is used to diagnose thyroid problems.

•Radiation therapyRadiation therapy used to treat cancer may involve the use of implanted radioactive isotopes such as gold-198 or iridium-192.

Radiation is used positively in a variety of ways1155

Industry•Manufacturers can also use radiation to check the thickness of metal containers by measuring the amount of radiation that passes through. •Small amounts of radioactive isotopes, like magnesium-28, can be introduced in a water source to determine the flow of underground water or to determine if an underground water system is leaking.•Radioactive isotopes are even used in smoke alarms.smoke alarms.

1166

Generate electrical powerGenerate electrical powerNuclear fission is used to Nuclear fission is used to generate electricity as an generate electricity as an alternative energy source.alternative energy source.

DatingDatingEven the age of fossils or Even the age of fossils or

rocks can be determined by rocks can be determined by using radioactive isotopes.using radioactive isotopes.

1177

Fission and FusionFission Fusion

Splitting a nucleus Combining of two nuclei.

1188

•Nuclear power can come from the fissionfission of uranium, plutonium or thorium or the fusion of hydrogen into helium.

•Today it is almost all uranium.

•The fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal.

1199

Issues for Fission Power PlantsIssues for Fission Power Plants

•Need for a spent fuel disposaldisposal facility and a decommissioning plan •Use of large amounts of water for

cooling purposes (if wet cooling towers are used) –thermal pollution

•Biological impactsBiological impacts on the ocean due to thermal discharge (if seawater

cooling is used) •Public safety safety concerns

2200 Clip

FUSIONFUSION•A fusion reaction occurs when nuclei of light

elements, specifically hydrogen and its isotopes (deuterium, or "heavy water," and tritium), are

forced together at extremely high high temperaturestemperatures and densities until they fuse into nuclei of heavier elements and release enormous

amounts of energy. •If fusion is to yield net energy, the fuel must be heatedheated in the form of plasma (a highly ionized

gas) to a very high temperaturetemperature and the plasma must then be held together for a sufficiently long

time such that the number of fusion reactions occurring releases more energy than was

required to heat the fuel.

2211

Half Life is the amount of time it takes for half of the nuclei in a sample to decay

Mass

(kg)

2222

mass numbermass number

• Carbon occurs naturally in three Carbon occurs naturally in three isotopes.isotopes.

• All of these atoms have the same All of these atoms have the same number of protons but different number of protons but different

numbers of neutrons.numbers of neutrons.• The number of neutrons and The number of neutrons and

protons determines the mass, so protons determines the mass, so the masses are different.the masses are different.

• 1414C is radioactive.C is radioactive.

14C12C13C

14C

• Radioactive 14C acts chemically just like 12C, so it becomes incorporated into plants an animals.

• When the animal/plant dies the 14C begins to decay into 14N at a know rate, so we can determine how long ago the organism died.

• This is called Carbon Dating.• It’s only good for about 50,000

years.

25g

• The half life of 14C is 5,730 years.

• If a sample originally contained 100 g, how much would be left

after 11,460 years?

50g

2266

Older Dating MethodsOlder Dating Methods• The isotopes 235U and

238U can be used to date objects billions of years old.

• 235U has a half life of 704 million years.

• 238U has a half life of 4.5 billion years.

• Mainly used for rocks.

Geiger Counter

• Used to measure radiation.

• The more intense the radiation the more “clicks”.