Chapter Menu Section 21.1Section 21.1Types of Radioactivity Section 21.2 Section 21.2 Nuclear...

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Chapter Menu

Section 21.1 Types of Radioactivity

Section 21.2 Nuclear Reactions and Energy

Section 21.3 Nuclear Tools

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Section 21.1

Types of Radioactivity

• Analyze common sources of background radiation.

• Compare and contrast alpha, beta, and gamma radiation.

• Apply the concept of half-life of a radioactive element.

Section 21.1


photosynthesis: the process used by certain organisms to capture energy from the Sun

Section 21.1


radioactivity

alpha particle

beta particle

Alpha, beta, and gamma radiation are three types of radiation emitted as unstable nuclei decay into stable nuclei.

gamma ray

half-life

Section 21.1

Discovery of Radioactivity

• Henri Becquerel discovered that uranium compounds spontaneously give off radiation.

Section 21.1

Discovery of Radioactivity (cont.)

• Marie and Pierre Curie concluded that a nuclear reaction was taking place within the uranium atoms.

• Radioactivity is the spontaneous emission of radiation by an unstable atomic nucleus.

Section 21.1

Nuclear Notation

• Nuclear reactions are different from other types of reactions.

Section 21.1

Nuclear Notation (cont.)

• Nuclear reactions involve the protons and neutrons found in the nucleus.

• When writing nuclear equations, it is important to indicate the isotopes of the given elements.

Section 21.1

Radioactive Decay

• Isotopes of atoms with unstable nuclei are called radioisotopes.

• Unstable nuclei emit radiation to attain more stable atomic configurations in a process called radioactive decay.

Section 21.1

• There are three types of nuclear radiation: alpha, beta, and gamma.

• Alpha radiation consists of streams of alpha particles (α), which are helium nuclei consisting of two protons and two neutrons.

Radioactive Decay (cont.)

Section 21.1

• Alpha radiation is not very penetrating—a single sheet of paper will stop an alpha particle.


Section 21.1

• Whenever beta decay occurs, transmutation of elements occurs.

• Beta radiation is a stream of fast moving particles with greater penetrating power—they can only be stopped by stacked sheets of metal, blocks of wood, or heavy clothing.


• A beta particle is a high-energy electron with a 1– charge and is written as

Section 21.1

• A gamma ray (γ) is a high-energy form of electromagnetic radiation without mass or charge.

• Gamma rays are more difficult to stop than alpha or beta particles.


Section 21.1

• Gamma rays almost always accompany alpha and beta radiation.

• During gamma decay, only energy is released.

• Gamma radiation is often omitted from nuclear equations because it does not affect mass number or atomic number.


Section 21.1

• Determining mode of decay

– Both the atomic number and mass number decrease = alpha decay

– Mass number stays the same and atomic number increases = beta decay

– No change to mass number or atomic number = gamma radiation


Section 21.1

• There are several methods used to detect radiation.

– photographic film

– scintillation counters

– A Geiger counter detects ionizing radiation, which is radiation energetic enough to ionize matter with which it collides.


Section 21.1

• The rate of spontaneous nuclear decay cannot be changed.

• Radioactive decay rates are measured in half-lives.

• The half-life is the time it takes for half of a given amount of a radioactive isotope to undergo decay.

Half-Life and Radioisotope Dating

Section 21.1

Half-Life and Radioisotope Dating (cont.)

Section 21.1

• Four different isotopes are commonly used for dating objects: carbon-14, uranium-238, rubidium-87, and potassium-40.

• Carbon-14 dating is commonly used to measure the age of fossils.

• To date objects that are more than 60,000 years old, carbon-14 dating cannot be used since there is very little carbon left to measure.

Half-Life and Radioisotope Dating (cont.)

Section 21.1

Section Assessment

Which is not a type of nuclear radiation?

A. alpha

B. beta

C. gamma

D. omega

Section 21.1

Section Assessment

Why do radioisotopes emit radiation?

A. to balance charges in the nucleus

B. to release energy

C. to attain more stable atomic configuration

D. to gain energy

End of Section 21.1

Section 21.2

Nuclear Reactions and Energy

• Compare and contrast nuclear fission and nuclear fusion.

• Demonstrate equations that represent the changes that occur during radioactive decay.

• Trace the operation and structure of a fission reactor.

Section 21.2


half-life: the time it takes for half of a given radioactive isotope to decay (into a different isotope or element)

Section 21.2


nuclear fission

nuclear reactor

nuclear fusion

deuterium

tritium

Fission and fusion release tremendous amounts of energy.

Section 21.2

The Power of the Nucleus

• Nuclear reactions involve enormous energy changes.

• Albert Einstein was the first scientist to realize the enormous amount of potential energy available in matter and related it in the equation, E = mc2.

Section 21.2

Nuclear Fission

• Nuclear fission is the splitting of an atomic nucleus into two or more smaller fragments, accompanied by a large release of energy.

Section 21.2

Nuclear Fission (cont.)

• Nuclear power plants use fission to produce electricity by striking uranium-235 with neutrons.

– Fission of an atom of uranium-235 releases two neutrons.

– Each of those neutrons can split an atom of uranium, which releases more neutrons.

– The self-sustaining process is called a chain reaction.

Section 21.2


Section 21.2


• A sample that has enough fissionable material to sustain a chain reaction has critical mass.

• A sample that does not have fissionable material to sustain a chain reaction has subcritical mass.

Section 21.2


• If there is a much greater amount of material present, called supercritical mass, the chain reaction quickly escalates, an explosion occurs, and an enormous amount of energy is released at once.

– Atomic bomb

Section 21.2


Section 21.2

• A nuclear reactor is a device that is used to extract energy from a radioactive fuel.

• Breeder reactors produce more fuel than they consume.


Section 21.2


Section 21.2

• Although nuclear reactions do not produce pollutants such as carbon dioxide and acidic sulfur and nitrogen compounds, nuclear reactors do form highly radioactive waste that is hard to dispose of safely.


Section 21.2

• Nuclear fusion is the process of combining two or more nuclei to form a larger nucleus.

• The enormous amount of energy that is generated by fusion reactions in the Sun sustains all life on Earth.

Nuclear Fusion

Section 21.2

• In one common fusion reaction, two different isotopes of hydrogen combine to form helium and a neutron.

Nuclear Fusion (cont.)

Section 21.2

• The isotope of hydrogen with a mass number of 2 that is one of the reactants is called deuterium (D).

• The hydrogen isotope with a mass number of 3 is called tritium (T).


Section 21.2

• Fusion has several advantages over fission.

– Lightweight isotopes are abundant.

– Fusion products are not radioactive.

– Fusion reactions are easier to control.


Section 21.2

• Problems with fusion

– Fusion requires extremely high energies to initiate and sustain a reaction.

– Any material used to contain the reaction would melt at the temperatures necessary to trigger nuclear fusion.


Section 21.2

• Tokamak reactors are most promising reactor type but still need to overcome engineering issues to produce energy.


Section 21.2

Section Assessment

The hydrogen isotope which is often used in nuclear fusion reactions and has a mass number of 3 is called:

A. deuterium

B. tritium

C. alpha

D. beta

Section 21.2

Section Assessment

The self-sustaining process in a nuclear fission is called a ___.

A. fusion

B. catalyst

C. chain reaction

D. half-life

End of Section 21.2

Section 21.3

Nuclear Tools

• Distinguish the biological effects of radiation and the units used to measure levels of exposure.

• Illustrate medical and nonmedical uses for radioactivity.

Section 21.3

Nuclear Tools

nuclear fusion: the process in which two or more nuclei combine to form a larger nucleus

Section 21.3

Nuclear Tools

gray

sievert

Radiation has many useful applications, but it also has harmful biological effects.

Section 21.3

Medical Uses of Radioisotopes

• When used safely, radiation can be very useful.

• Radioisotopes can trace and identify abnormalities in the body, and are widely used in diagnosis to generate images of organs and glands.

Section 21.3

Nonmedical Uses of Radioisotopes

• If a radioisotope is substituted for a nonradioactive isotope of the same element in a chemical reaction, all compounds formed from that element in a series of steps will also be radioactive.

Section 21.3

Nonmedical Uses of Radioisotopes (cont.)

• A radiotracer is a radioactive isotope that emits non-ionizing radiation and is used to track the pathways of the compound.

Section 21.3

Nonmedical Uses of Radioisotopes (cont.)

• Gamma radiation can be used to sterilize food and surgical instruments.

• Irradiation can extend the shelf life of food so it can be stored for long periods of time without refrigeration.

Section 21.3

Sources of Radioisotopes

• Using nuclear chemistry, scientists can produce elements artificially.

– Some are produced as by-products in nuclear reactors.

– Most are made by bombarding nuclei with small particles that have been accelerated to high speeds.

Section 21.3

Problems Associated with Radioactivity

• Small amounts of radioactive elements, known as background radiation, are found almost everywhere on Earth.

Section 21.3

• Exposure to radioactive elements can be hazardous to your health.

• Because it can result in the formation of ions, nuclear radiation is also known as ionizing radiation.

• The more energy radiation has, the more dangerous it tends to be.

Problems Associated with Radioactivity (cont.)

Section 21.3

• A gray is the unit used to measure the received dose of radiation.

• A sievert is the unit of radiation equal to one gray multiplied by a factor that assesses how much of the radiation striking tissue is actually absorbed by the tissue and so is a measure of how much biological damage is caused.


Section 21.3


Section 21.3

• Other sources of radiation for most people include:


– medical radiation, such as X-rays

– exposure to cosmic rays from living at a higher altitude or taking frequent trips in airplanes

– cigarette smoke

Section 21.3

• 80% of radioactive waste is generated in hospitals.


• Scientists are researching new recycling and disposal technologies to deal with the nuclear waste.

Section 21.3

Section Assessment

Which is a better unit for measuring how much biological damage has been caused by an exposure to radiation?

A. gray

B. sievert

Section 21.3

Section Assessment

Most radioactive waste is generated by:

A. nuclear reactors

B. industrial processes

C. hospitals

D. pollution

End of Section 21-3

Resources Menu

Chemistry Online

Study Guide

Chapter Assessment

Standardized Test Practice

Image Bank

Concepts in Motion

http://www.glencoe.com/

Study Guide 1

Key Concepts

• Nuclear reactions involve protons and neutrons.

• Radioactivity can be detected and measured using film and instruments, including Geiger and scintillation counters.

• The half-life of a radioactive element is the time it takes for one-half of the nuclei in a sample to decay.

Study Guide 2

Key Concepts

• Nuclear reactions convert a small mass into a large amount of energy, according to Einstein’s equation E = mc2.

• Critical mass is the minimum mass of a sample of fissionable material necessary to sustain a nuclear chain reaction.

• Uranium-235 undergoes a fission chain reaction in a nuclear reactor, which converts some of the released energy into electricity.

• Fusion in the Sun provides energy for life on Earth.

Study Guide 3

Key Concepts

• Radioactive tracers have uses such as tracking compounds in an organism and charting the movement of pollutants.

• Radiation therapy involves selectively killing rapidly dividing cancer cells by targeting them with radiation.

• Gamma radiation can be used to irradiate food to keep it from spoiling.

• Most radiation exposure comes from natural sources.

Chapter Assessment 1

____ is the spontaneous emission of radiation by an unstable atomic nucleus.

A. Radioactivity

B. Fission

C. Fusion

D. Nuclear decay


When writing nuclear equations, it is important to indicate the ____ of the given elements.

A. protons

B. neutrons

C. electrons

D. isotopes


Whenever beta decay occurs, what process also occurs?

A. alpha radiation

B. gamma radiation

C. transmutation of elements

D. a chemical change


Alpha particles pass through matter more readily than beta particles.

A. true

B. false


What kind of decay causes both the atomic number and mass number to decrease?

A. alpha

B. beta

C. gamma radiation

STP 1

The rate of spontaneous nuclear decay cannot be changed.

A. true

B. false

STP 2

Which isotope is commonly used to determine the age of fossils?

A. potassium-40

B. rubidium-87

C. uranium-238

D. carbon-14

STP 3

___ is the splitting of an atomic nucleus into two or more smaller fragments, accompanied by a huge release of energy.

A. Carbon-14 dating

B. Nuclear fission

C. Nuclear fusion

D. Potential energy

STP 4

The detonation of an atomic bomb involves ___.

A. critical mass

B. subcritical mass

C. supercritical mass

STP 5

Humans are constantly being bombarded by radiation.

A. true

B. false

IB Menu

Click on an image to enlarge.

CIM

Table 21.1 Comparison of Chemical and Nuclear Reactions

Figure 21.13 Nuclear Fission

Figure 21.14 Chain Reaction

Figure 21.15 Nuclear Power Plant

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