CHAPTER 16 SECTION 1 Radioactivity - Salem...

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Interactive Textbook 283 Atomic Energy

SECTION

1 RadioactivityAtomic Energy

Name Class Date

CHAPTER 16

After you read this section, you should be able to answer these questions:

• What are three types of radioactive decay?

• How does radiation affect living and non-living things?

• How do people use radioactive materials?

How Was Radiation Discovered?In 1896, a French scientist named Henri Becquerel per-

formed an experiment to test a hypothesis. He thought that certain materials made X rays when light shone on them.

To test his idea, he wrapped a photographic plate in black paper to protect it from sunlight. Then he placed a mineral that glows when it is exposed to light on top of the paper. Becquerel placed the photographic plate and the mineral in the sun. When he developed the plate, he saw an image of the mineral as shown below.

Sunlight could not pass through the paper. The image on the plate must have come from energy given off by the mineral.

When Becquerel tried to do the experiment again, the weather was cloudy, so he put his materials away in a drawer. He decided to develop the plate anyway and found a surprising result. Even without sunlight, an image of the mineral formed on the photographic plate. He repeated the test with the same result. He concluded that some kind of energy came from uranium, an element in the mineral.

The energy was nuclear radiation, high-energy parti-cles that come from the nuclei of some atoms. A scientist who worked with Becquerel, Marie Curie, named the pro-cess that causes nuclear radiation. That process is called radioactivity. It is also known as radioactive decay.

BEFORE YOU READ National Science Education StandardsPS 3a, 3e

STUDY TIPCompare In a table, list the types of radioactive decay, the particle given off, how pene-trating it is, and how it is useful.

READING CHECK

1. Identify What caused the image of the mineral in Becquerel’s experiment to form on the photographic plate?

2. Identify What is another name for radioactivity?



SECTION 1

Name Class Date

Radioactivity continued

What Are the Types of Radioactivity?The nuclei of some atoms are not stable. During radio-

active decay, an unstable nucleus changes and gives off particles and energy. There are three types of radioactive decay, called alpha, beta, and gamma.

ALPHA DECAY An alpha particle is made of two protons and two neu-

trons. The mass number of a nuclear particle or a nucleus is the sum of the numbers of protons and neutrons. The mass number of an alpha particle is 4 and its charge is 2�. An alpha particle is also labeled helium-4, because a helium-4 nucleus has two protons and two neutrons.

The release of an alpha particle from a nucleus is called alpha decay. When an alpha particle is released from a nucleus, it changes into the nucleus of another element. See the figure below.

Alpha Decay of Radium-226

Radium-226 Radon-222

Charge: 86�

Charge: 88�Charge: 2�

Alpha particle(helium-4)

EnergyMass number is conserved.226 � 222 � 4

Charge is conserved.(88�) � (86�) � (2�)

Many large radioactive nuclei break apart by releasing an alpha particle. When a nucleus emits an alpha particle, it becomes the nucleus of a different element because the new nucleus has a different number of protons. Radium-226 becomes radon-222.

The model of alpha decay in the figure shows two important facts about radioactive decay. The first is that mass is conserved. Radium-226 has the same mass as radon-222 plus helium-4.

The second fact is that charge is conserved. A radium nucleus has a charge of 88�. If you add the charge of radon, 86�, and an alpha particle, 2�, you get 88�.

READING CHECK

3. Describe What is an alpha particle made of? What is mass number?

Math Focus4. Determine If the mass number of radium were 228, what would be the mass number of the radon formed?

READING CHECK

5. Identify What is conserved by the radioactive decay process?



SECTION 1

Name Class Date


READING CHECK

6. Describe What happens to the mass of the nucleus that emits a beta particle?

Critical Thinking7. Infer What would have been the charge of the new nucleus formed if the beta particle had been a positron?

READING CHECK

8. Describe What are isotopes?

READING CHECK

9. Describe What are gamma rays?

BETA DECAYA beta particle is an electron or positron that is

released from an atomic nucleus. An electron has a charge of 1�. A positron has a charge of 1�. Both par-ticles have a mass that is very close to zero compared to the mass of a nucleus. That means the mass of a nucleus does not change when it emits a beta particle.

The beta decay shown in the figure below is the loss of an electron from a carbon-14 nucleus. During this kind of decay, one of the neutrons becomes a proton and an elec-tron leaves the nucleus. Mass and charge are conserved. The number of protons changes so the nucleus becomes a different element.

Carbon-14 Nitrogen-14

Beta particle (electron)

Energy

Charge: 6� Charge: 1�

Charge: 7�

Mass number is conserved.14 � 14 � 0

Charge is conserved.(6�) � (7�) � (1�)

Beta Decay of Carbon-14

Isotopes are atoms that have the same number of pro-tons but different number of neutrons. Different isotopes of an element can decay in different ways. A carbon-11 nucleus decays by emitting a positron. Again, the overall mass and charge do not change. The decay of carbon-11 creates a nucleus of boron-11, which has 5 protons and 6 neutrons.

GAMMA DECAYSome changes to a nucleus also emit energy in the

form of high-energy waves. These waves are called gamma rays. During gamma decay, particles in the nucleus move and change position, but there is no change of mass or charge. That means one element does not change into another. Gamma decay often occurs at the same time as alpha or beta decay.



SECTION 1

Name Class Date


How Does Radiation Affect Matter?Because the particles and rays of nuclear radiation

have a lot of energy, they can move through matter. As shown in the figure below, each type of radiation has a different ability to penetrate, or go through, matter. This penetration depends on charge and on mass.

Alpha particles have the most mass and charge so they tend to interact with atoms more easily. Alpha particles are stopped by a piece of paper or clothing. A beta parti-cle has almost no mass and a single charge. Clothing does not stop beta particles but about 3 mm of a metal such as aluminum can.

Gamma rays have no charge or mass. They pass through metals such as aluminum. Only very dense, thick materials can stop gamma rays. They can be blocked by a few centimeters of lead or a few meters of concrete.

Paper Aluminum Concrete

Radioactivematerial

Alphaparticles

Betaparticles

Gamma rays

Alpha particles have a greater charge and mass than beta particles and gamma rays do. Alpha particles travel about 7 cm through air and are stopped by paper or clothing.

Beta particles have a 1� or 1� charge and almost no mass. They are more penetrat-ing than alpha particles. Beta particles travel about 1 m through air but are stopped by 3 mm of aluminum.

Gamma rays have no charge or mass and are the most penetrating. They are blocked by very dense, thick materials, such as a few centimeters of lead or a few meters of concrete.

The Penetrating Abilities of Nuclear Radiation

When nuclear radiation hits atoms, atoms can lose electrons. Radiation can also break bonds between atoms. These changes can cause damage to matter. The amount and location of the changes depends on the type of radiation.

Gamma rays can cause changes deep inside mat-ter because they penetrate deeply. Beta radiation does not penetrate as far, so it causes damage closer to the surface. Alpha particles are much larger and have more charge than beta particles. Although they are easier to stop, alpha particles cause the most damage when they get inside matter.

READING CHECK

10. Explain Why are alpha particles less penetrating than beta particles?

STANDARDS CHECKPS 3e In most chemical and nuclear reactions, energy is transferred into or out of a system. Heat, light, mechanical motion, or electricity might all be involved in such transfers.

11. Describe How can gamma rays cause changes deep inside matter?

Say ItDescribe Research the effects of alpha, beta, and gamma radiation on a living cell. Describe to the class what each type can do to a cell.



SECTION 1

Name Class Date


DAMAGE TO LIVING MATTERRadiation can harm the cells of a living organism.

The damage is often similar to a burn caused by touch-ing something hot. A large exposure to radiation causes radiation sickness. The symptoms of this sickness include fatigue, loss of appetite, and hair loss. When blood cells are destroyed, radiation sickness can cause death.

Repeated exposure to radiation can damage many cells in the body. One of the effects of this damage can be can-cer. Many people who work near radiation wear badges that can warn them when radiation levels are too high.

DAMAGE TO NONLIVING MATTERRadiation can also damage nonliving matter. For

example, when electrons are knocked away from metal atoms, the metal becomes weaker. The metal structures in nuclear power plants must be tested often. Too much exposure to radiation can make them unsafe. Parts in spacecraft can be changed by radiation from the sun.

How Do People Use Radioactivity?Radiation can be harmful but it can also be useful in

industry, in medicine, and even in your home. Some smoke detectors use a tiny amount of radioactive material. It ionizes atoms in smoke and the ions turn on the alarm.

Radioactive materials can also be used as tracers. Tracers are radioactive elements whose paths can be fol-lowed through a process such as a chemical reaction.

RADIOACTIVITY IN HEALTH CAREDoctors use tracers to help find patient’s medical

problems. The figure below shows an image of a thyroid gland. The image shows parts of the gland are not work-ing correctly. Radioactive materials are also used to treat diseases, including cancer.

Radioactive iodine -131 was used to make this scan of a thyroid gland. The dark area shows the location of a tumor.

READING CHECK

12. Explain Why do people exposed to radiation regularly need to wear radiation badges?

READING CHECK

13. Describe What do tracers allow people to do?

TAKE A LOOK 14. Identify Circle the dark area in the thyroid shown in the fi gure.



SECTION 1

Name Class Date


RADIOACTIVITY IN INDUSTRYRadioactive isotopes are also used as tracers in industry.

The figure below shows a worker looking for leaks in pipes by tracing radioactive material in the pipe. Notice that he is wearing protective clothing so his cells are not exposed to radiation. Another way to use radiation is to look for flaws in metal objects. This is similar to the way a doctor uses an X-ray image to look at your bones.

Tracers are used to fi nd weak spots in materials and leaks in pipes. A Geiger counter is often used to detect the tracer.

Some space probes use radioactive isotopes for power. The energy given off as nuclei decay is converted to elec-trical power.

How Can Radiation Tell Us About the Past?In 1991, hikers in the Alps found a frozen body high in

mountains. Scientists used radioactivity to figure out that the Iceman, shown below, lived about 5,300 years ago.

The Iceman is a 5,300-year-old mummy. His are the best-preserved remains of a human from that time.

Every living thing has many carbon atoms. A small percentage of these atoms is radioactive carbon-14. This percentage does not change in a living organism because carbon atoms are constantly being replaced. When the organism dies, though, it no longer replaces atoms. As the radioactive isotope decays, the percentage of carbon-14 decreases. Scientists can figure out when the organism was alive by measuring how much carbon-14 remains.

READING CHECK

15. Identify What are two uses for tracers in industry?

READING CHECK

16. Identify What radioactive isotope of carbon is not re-placed after an organism dies?



SECTION 1

Name Class Date


Radioactive Decay and Half-LifeThe original sample con-tains a certain amount of radioactive isotope.

After ,one-half of the original sample has decayed, and half is unchanged.

After ,one-fourth of the original sample is still unchanged.

A STEADY DECAYEvery radioactive isotope decays at a particular rate,

called its half-life. As shown in the figure above, a half-life

is the amount of time that it takes for one-half the nuclei of a radioactive isotope to decay.

The half-life is the same for every sample of a particu-lar isotope. It is not affected by any conditions such as temperature and pressure. As shown in the table, half-lives range from part of a second to billions of years.

Examples of Half-lives

Isotope Half-life Isotope Half-life

Uranium-238 4.5 billion years Polonium-210 138 days

Oxygen-21 3.4s Nitrogen-13 10 min

Hydrogen-3 12.3 years Calcium-36 0.1s

FINDING AGEThe half-life of carbon-14 is 5,730 years. This rate is con-

stant. Scientists know what percentage of the carbon in the Iceman’s body was carbon-14 when he was alive. They mea-sured the number of decays per minute in a sample from his body. This showed what the percentage of carbon-14 is now.

A little less than half of the carbon-14 had decayed after his death. That means that not quite one half-life has passed since the Iceman walked in the mountains.

Carbon-14 can be used to find the age of objects up to 50,000 years old. After that, there is not enough carbon-14 left to make good measurements. To find the age of older things, scientists use isotopes with longer half-lives. For example, the half-life of potassium-40 is about 1.3 bil-lion years. It is used to find the age of dinosaur fossils. Isotopes with very long half-lives, such as uranium-238, are used to measure the age of Earth’s oldest rocks.

Math Focus17. Identify Fill in the blanks to identify which half-life (one, two, three, etc.) the sample has decayed through.

READING CHECK

18. Describe Why do scien-tists think that the Iceman is less than 5,730 years old?



Name Class Date

Section 1 Review NSES PS 3a, 3e

SECTION VOCABULARY

half-life the time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope

isotope an atom that has the same number of protons (or the same atomic number) as other atoms of the same element but has a differ-ent number of neutrons (and thus a different atomic mass)

mass number the sum of the numbers of protons and neutrons in the nucleus of an atom.

radioactivity the process by which an unstable nucleus gives off nuclear radiation

1. Compare Most atoms of uranium, which has 92 protons, are either uranium-235 or uranium-238. Compare the mass numbers and atomic numbers of these two isotopes of uranium. Recall, atomic number is the number of protons in the nuclei of elements.

2. Compare Use the information in this section to fill in the blank spaces in the comparison table below.

Types of Radiation

Name Form Mass Charge Penetrating power

particle (helium nucleus)

2+

Beta 0 medium

particle (positron)

0 1+ medium

energy

3. Make Inferences Nuclear radiation can be used to look for flaws in metal parts of bridges. The process is similar to using X rays to look at human bones. What type of radioactive decay would work best for this test? Explain your answer.

4. Evaluate Results A rock contains one-fourth of its original potassium-40. The half-life of potassium 40 is 1.3 billion years. What is the rock’s age?


Interactive Textbook Answer Key 87 Physical Science

Physical Science Answer Key continued

2. A strong acid has more molecules that break apart when you dissolve the acid in water than a weak acid does.

3. water and a salt

4. pH is the amount of hydronium ions in a solution.

5. Bases have high pH value, and acids have low pH.

6. acid rain

7. when a positive ion from a base combines with a negative ion from an acid

8. table salt and melting snow and ice

Review 1. In water, all the molecules of a strong acid

break apart and form hydronium ions. When a weak base is dissolved in water, only a few molecules break off to form hydroxide ions.

2. When an acid and base combine, there is a neutralization reaction. The hydrogen ions from the acid combine with the hydroxide ions from the base to form water and a salt.

3. Sodium hydroxide � hydrochloric acid water � sodium chloride

4. with pH paper or a pH meter

5. The pH would be around 9 because bases have high pH values. The stronger the base, the higher the pH value.

6. A pH value below 7 indicates an acid; the lower the number, the more acidic. This would be a bad place for fish to live, because the water is too acidic.

SECTION 4 ORGANIC COMPOUNDS 1. two or more carbon atoms linked to one

another

2. straight chain, branched chain, ring

3. organic compounds that contain only carbon and hydrogen

4. alkanes, alkenes, and alkynes

5. Saturated hydrocarbons have only single covalent bonds between carbon atoms. Unsaturated hydrocarbons have double or triple covalent bonds between carbon atoms.

6. carbohydrates, lipids, proteins, nucleic acids

7. biochemicals that are made of one or more simple sugar molecules

8. biochemicals that do not dissolve in water; store energy

9. biochemicals that are made of chains of building blocks called amino acids

10. biochemicals made up of nucleotides

11. all of the information that a body’s cells need to function

12. the information that the cell needs to build protein molecules

Review 1. Type of carbon

backboneDescription

Ring The chain of carbon atoms forms a ring.

Straight chain All carbon atoms are connected in a straight line.

Branched chain The chain of carbon atoms separates into different directions.

2. saturated compounds—alkanes,

unsaturated compounds—alkenes and alkynes

3. Type of biochemical Description

Proteins made of hundreds or thousands of amino acid molecules

Nucleic acids one of the functions is to store genetic information

Carbohydrates made of one or more simple sugar molecules

Lipids one of the functions is to store energy

4. DNA—contains the genetic material of a cell; RNA—contains the information that the cell needs to build protein molecules.

Chapter 16 Atomic EnergySECTION 1 RADIOACTIVITY 1. Energy came from the uranium.

2. radioactive decay

3. An alpha particle has two protons and two neutrons. Mass number is the sum of the protons and neutrons in a nuclear particle or in a nucleus.

4. 224

5. mass and charge

6. It stays the same.

7. 5+

8. atoms that have the same number of protons but different number of neutrons

9. high-energy waves

10. They have more mass and charge, so they tend to interact with atoms more easily.


Interactive Textbook Answer Key 88 Physical Science

Physical Science Answer Key continued

11. They penetrate matter deeply.

12. to warn them if they have been exposed to radiation harmful enough to damage cells

13. follow the path of a process

14. Dark area should be circled.

15. Check for leaks in pipes and flaws in metal objects.

16. carbon-14

17. one half-life, two half-lives

18. A little less than half of the carbon-14 had decayed after his death.

Review 1. The atomic number for both isotopes is 92.

The mass number of uranium-235 is 235, and the mass number of uranium-238 is 238.

2. First column, top to bottom: alpha, beta, gamma

Second column: particle (electron)

Third column, top to bottom: 4, 0

Fourth column, top to bottom: 1-, 0

Last column, top to bottom: low, high

3. Gamma rays would work because they have the most penetrating power and enough energy to pass through metal. Alpha and beta particles would be stopped by the metal parts.

4. One-fourth remaining indicates 2 half-lives or 2.6 billion years.

SECTION 2 ENERGY FROM THE NUCLEUS 1. A large nucleus splits into two smaller

nuclei, releasing energy.

2. Their difference is three because three neu-trons are also produced.

3. Some of the masses are changed into energy.

4. a continuous series of nuclear fission reactions

5. by keeping some of the neutrons from hit-ting a uranium nucleus

6. kinetic energy changed into mechanical energy, mechanical energy changed into electrical energy

7. An explosion can blow a large amount of radioactive fuel and waste into the atmosphere.

8. It has dangerous levels of radioactivity.

9. carbon dioxide

10. Two or more nuclei that have small masses combine to form a larger nucleus.

11. the core

12. Scientists cannot yet control the high tem-peratures well enough to use fusion.

Review 1. The neutrons come from the nucleus of

the atom that split. These neutrons continue the chain reaction by causing other fission reactions.

2. Without the control rods, an uncontrolled chain reaction could occur in the fuel and release energy too quickly or even cause an explosion.

3. Answers include: nuclear energy to heat energy, heat energy to mechanical energy, mechanical energy to electrical energy

The conversions are needed because we cannot use the nuclear or heat energy directly in homes and factories. The process changes energy that can be used at only one place to energy that can be delivered.

4. If a fusion power plant were to have an acci-dent, it would not release large amounts of radioactive material.

5. 244 � (144 � 3) � 97

Chapter 17 Introduction to ElectricitySECTION 1 ELECTRIC CHARGE AND STATIC ELECTRICITY 1. protons and electrons

2. Protons are positive in charge; electrons have a negative charge.

A “�” should be drawn next to the proton, and a “�” next to the electron in the figure.

3. Objects with the same charge repel each other.

4. They have opposite charges.

5. They would be neutral in charge and hang straight down.

6. amount of charge and distance between charges

7. an electric field

8. friction, conduction, induction

9. During conduction, charging is by direct contact. With induction, objects are charged without direct contact.

10. When you charge something, no charges are created or destroyed.

11. See if something is charged.

12. A “�” should be next to each leaf.

CHAPTER 16 SECTION 1 Radioactivity - Salem...

Documents

Transcript of CHAPTER 16 SECTION 1 Radioactivity - Salem...