25.1 Nuclear Radiation > Chapter 25

25.1 Nuclear Radiation >

25.1 Nuclear Radiation

25.2 Nuclear Transformations 25.3 Fission and Fusion 25.4 Radiation in Your Life

In 1896, the French chemist Antoine Becquerel made an accidental discovery. • He was studying the ability of uranium salts that had been exposed to sunlight to fog photographic film plates. • During bad weather, when Becquerel could not expose a sample to sunlight, he left the sample on top of the photographic plate. • When he developed the plate, he discovered that the uranium salt still fogged the film.

Two of Becquerel’s associates were Marie and Pierre Curie. • The Curies were able to show that rays emitted by uranium atoms caused the film to fog. • Marie Curie and her husband Pierre shared the 1903 Nobel Prize in physics with Becquerel for their pioneering work on radioactivity.

Marie Curie used the term radioactivity to refer to the spontaneous emission of rays or particles from certain elements, such as uranium. • The rays and particles emitted from a radioactive source are called nuclear radiation.

Radioactivity, which is also called radioactive decay, is an example of a nuclear reaction. • Nuclear reactions begin with unstable isotopes, or radioisotopes. • Atoms of these isotopes become more stable when changes occur in their nuclei. • The changes are always accompanied by the emission of large amounts of energy.

Unlike chemical reactions, nuclear reactions are not affected by changes in temperature, pressure, or the presence of catalysts. Also, nuclear reactions of a given radioisotope cannot be slowed down, sped up, or stopped.

Radioactive decay is a spontaneous process that does not require an input of energy. • If the product of a nuclear reaction is unstable, it will decay too. • The process continues until unstable isotopes of one element are changed, or transformed, into stable isotopes of a different element. • These stable isotopes are not radioactive.

Why do unstable isotopes undergo nuclear reactions?

Unstable isotopes undergo nuclear reactions so that they may be changed, or transformed, into stable isotopes.

Types of Radiation What are three types of nuclear radiation? Radiation is emitted during radioactive decay. Three types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation.

Characteristics of Some Types of Radiation Mass Common Penetrating Type Consists of Symbol Charge (amu) source power Low Alpha Alpha particles 4 Radium- a, 2 He 2+ 4 (0.05 mm radiation (helium nuclei) 226 body tissue) Moderate Beta Beta particles Carbon- b, 0 e 1– 1/1837 (4 mm body radiation (electrons) –1 14 tissue) High-energy Very high Gamma electromagnetic g 0 0 Cobalt-60 (penetrates radiation radiation body easily)

Alpha Radiation Some radioactive sources emit helium nuclei, which are also called alpha particles. • Each alpha particle contains two protons and two neutrons and has a double positive charge.

4 • An alpha particle is written 2 He or a. – The electric charge is usually omitted.

11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 25.1 Nuclear Radiation > Types of Radiation Alpha Radiation The radioisotope uranium-238 emits alpha radiation and is transformed into another radioisotope, thorium-234.

238 U Radioactive 234 Th + 4 He (a emission) 92 decay 90 2 Uranium-238 Thorium-234 Alpha particle

Alpha Radiation When an atom loses an alpha particle, the atomic number of the product is lowered by two and its mass number is lowered by

four. 238 234 4 92 U → 90 Th + 2 He • In a balanced nuclear equation, the sum of the mass numbers (superscripts) on the right must equal the sum on the left. • The same is true for the atomic numbers (subscripts).

Alpha Radiation Because of their large mass and charge, alpha particles do not travel very far and are not very penetrating. • A sheet of paper or the surface of your skin can stop them. • But radioisotopes that emit alpha particles can cause harm when ingested. – Once inside the body, the particles don’t have to travel far to penetrate soft tissue.

Beta Radiation An electron resulting from the breaking apart of a neutron in an atom is called a beta particle. • The neutron breaks apart into a proton, which remains in the nucleus, and a fast-moving electron, which is released.

1 1 0 0 n → 1 p + –1 e Neutron Proton Electron (beta particle)

Beta Radiation

1 1 0 0 n → 1 p + –1 e Neutron Proton Electron (beta particle) The symbol for the electron has a subscript of –1 and a superscript of 0. • The –1 represents the charge on the electron. • The 0 represents the extremely small mass of the electron compared to the mass of a proton.

Beta Radiation Carbon-14 emits a beta particle as it decays and forms nitrogen-14. 14 14 0 6 C → 7 N + –1 e (b emission) Carbon-14 Nitrogen-14 Beta particle (radioactive) (stable) • The nitrogen-14 atom has the same mass number as carbon-14, but its atomic number has increased by 1. • It contains an additional proton and one fewer neutron.

Beta Radiation A beta particle has less charge than an alpha particle and much less mass than an alpha particle. • Thus, beta particles are more penetrating than alpha particles. – Beta particles can pass through paper but are stopped by aluminum foil or thin pieces of wood.

Beta Radiation Because of their opposite charges, alpha and beta radiation can be separated by an electric field.

• Alpha particles move toward the negative plate. • Beta particles move toward the positive plate. • Gamma rays are not deflected.

Gamma Radiation A high-energy photon emitted by a radioisotope is called a gamma ray. • The high-energy photons are a form of electromagnetic radiation. • Nuclei often emit gamma rays along with alpha or beta particles during radioactive decay. 230 226 4 90 Th → 88 Ra + 2 He + g Thorium-230 Radium-226 Alpha Gamma particle ray

234 234 0 90 Th → 91 Pa + –1 e + g Thorium-234 Protactinium Beta Gamma -234 particle ray

Gamma Radiation Gamma rays have no mass and no electrical charge. • Emission of gamma radiation does not alter the atomic number or mass number of an atom.

Gamma Radiation Because gamma rays are extremely penetrating, they can be very dangerous. • Gamma rays pass easily through paper, wood, and the human body. • They can be stopped, although not completely, by several meters of concrete or several centimeters of lead.

Gamma rays can be dangerous because of their penetrating power. What property determines the relative penetrating power of electromagnetic radiation?

The wavelength and energy of electromagnetic radiation determine its relative penetrating power. Gamma rays have a shorter wavelength and higher energy than X-rays or visible light.

Three types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation.

24 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 25.1 Nuclear Radiation > Glossary Terms • radioactivity: the process by which nuclei emit particles and rays • nuclear radiation: the penetrating rays and particles emitted by a radioactive source • radioisotope: an isotope that has an unstable nucleus and undergoes radioactive decay • alpha particle: a positively charged particle emitted from certain radioactive nuclei; it consists of two protons and two neutrons and is identical to the nucleus of a helium atom • beta particle: an electron resulting from the breaking apart of neutrons in an atom • gamma ray: a high-energy photon emitted by a radioisotope 25 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 25.2 Nuclear Transformations >

Chapter 25 Nuclear Chemistry

25.1 Nuclear Radiation

25.2 Nuclear Transformations

25.3 Fission and Fusion 25.4 Radiation in Your Life

What is the source of radon in homes? Radon may accumulate in a basement that is not well ventilated. Test kits are available to measure the levels of radon in a building.

Nuclear Stability and Decay What determines the type of decay a radioisotope undergoes?

The nuclear force is an attractive force that acts between all nuclear particles that are extremely close together, such as protons and neutrons in a nucleus.

• At these short distances, the nuclear force dominates over electromagnetic repulsions and holds the nucleus together.

The stability of a nucleus depends on the ratio of neutrons to protons. • This graph shows the number of neutrons vs. the number of protons for all known stable nuclei.

The stability of a nucleus depends on the ratio of neutrons to protons. • The region of the graph in which these points are located is called the band of stability.

The stability of a nucleus depends on the ratio of neutrons to protons. • For elements of low atomic number (below about 20), this ratio is about 1. • Above atomic number 20, stable nuclei have more neutrons than protons.

A nucleus may be unstable and undergo spontaneous decay for different reasons. The neutron-to-proton ratio in a radioisotope determines the type of decay that occurs.

33 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Nuclear Stability and 25.2 Nuclear Transformations > Decay Some nuclei are unstable because they have too many neutrons relative to the number of protons. • When one of these nuclei decays, a neutron emits a beta particle (fast-moving electron) from the nucleus. – A neutron that emits an electron becomes a proton.

1 1 0 0 n 1 p + –1 e

– This process is known as beta emission. – It increases the number of protons while decreasing the number of neutrons.

Radioisotopes that undergo beta emission include the following.

66 66 0 29 Cu 30 Zn + –1 e

14 14 0 6 C 7 N + –1 e

Other nuclei are unstable because they have too few neutrons relative to the number of protons. • These nuclei increase their stability by converting a proton to a neutron. – An electron is captured by the nucleus during this process, which is called electron capture.

59 0 59 28 Ni + – 1 e 27 Co

37 0 37 18 Ar + – 1 e 17 Cl

A positron is a particle with the mass of an electron but a positive charge. 0 • Its symbol is +1 e. • During positron emission, a proton changes to a neutron, just as in electron capture.

8 8 0 5 B 4 Be + +1 e

15 15 0 8 O 7 N + +1 e – When a proton is converted to a neutron, the atomic number decreases by 1 and the number of neutrons increases by 1.

Nuclei that have an atomic number greater than 83 are radioactive. • These nuclei have both too many neutrons and too many protons to be stable. – Therefore, they undergo radioactive decay. • Most of them emit alpha particles. – Alpha emission increases the neutron-to-proton ratio, which tends to increase the stability of the nucleus.

In alpha emission, the mass number decreases by four and the atomic number decreases by two.

226 222 4 88 Ra 86 Rn + 2 He

232 228 4 90 Th 88 Ra + 2 He

Recall that conservation of mass is an important property of chemical reactions. • In contrast, mass is not conserved during nuclear reactions. • An extremely small quantity of mass is converted into energy released during radioactive decay.

Half-Life How much of a radioactive sample remains after each half-life?

A half-life (t 1) is the time required for one- half of the nuclei2 in a radioisotope sample to decay to products. After each half- life, half of the original radioactive atoms have decayed into atoms of a new element.

Comparing Half-Lives Half-lives can be as short as a second or as long as billions of years.

Half-Lives of Some Naturally Occurring Radioisotopes Isotope Half-life Radiation emitted Carbon-14 5.73 × 103 years b Potassium-40 1.25 × 109 years b, g Radon-222 3.8 days a Radium-226 1.6 × 103 years a, g Thorium-234 24.1 days b, g Uranium-235 7.0 × 108 years a, g Uranium-238 4.5 × 109 years a

Comparing Half-Lives • Scientists use half-lives of some long-term radioisotopes to determine the age of ancient objects. • Many artificially produced radioisotopes have short half-lives, which makes them useful in nuclear medicine. – Short-lived isotopes are not a long-term radiation hazard for patients.

Radiocarbon Dating Plants use carbon dioxide to produce carbon compounds, such as glucose.

• The ratio of carbon-14 to other carbon isotopes is constant during an organism’s life. • When an organism dies, it stops exchanging carbon with the environment and its radioactive 14 6 C atoms decay without being replaced. • Archaeologists can use this data to estimate when an organism died.

Exponential Decay Function You can use the following equation to calculate how much of an isotope will remain after a given number of half-lives. 1 n A = A  0 2 • A stands for the amount remaining.

• A0 stands for the initial amount. • n stands for the number of half-lives.

Exponential Decay Function

1 n A = A  0 2

• The exponent n indicates how many times A0 1 must be multiplied by 2 to determine A.

Exponential Decay Function This table shows examples in which n = 1 and n = 2.

Decay of Initial Amount (A0) of Radioisotope Half-Life Amount Remaining 1 0 0 A0 × ( 2 ) = A0 1 1 1 1 A0 × ( 2 ) = A0 × 2 1 2 1 1 2 A0 × ( 2 ) = A0 × 2 × 2

48 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 25.2 Nuclear Transformations > Transmutation Reactions For thousands of years, alchemists tried to change lead into gold. • What they wanted to achieve is transmutation, or the conversion of an atom of one element into an atom of another element. Transmutation can occur by radioactive decay, or when particles bombard the nucleus of an atom. • The particles may be protons, neutrons, alpha particles, or small atoms.

Ernst Rutherford performed the earliest artificial transmutation in 1919. • He bombarded nitrogen gas with alpha particles. 14 4 18 7 N + 2 He 9 F Nitrogen-14 Alpha Fluorine-18 particle • The unstable fluorine atoms quickly decay to form a stable isotope of oxygen and a proton.

18 17 1 9 F 8 O + 1 p Fluorine-18 Oxygen-17 Proton

Rutherford’s experiment eventually led to

the discovery of the proton. 1 1 P Proton

4 14 18 17 2He 7 N 9 F 8 O Alpha Nitrogen Unstable Oxygen particle atom fluorine atom

• He and other scientists noticed a pattern as they did different transmutation experiments. Hydrogen nuclei were emitted. • Scientists realized that these hydrogen nuclei (protons) must have a fundamental role in atomic structure.

James Chadwick’s discovery of the neutron in 1932 also involved a transmutation experiment.

• Neutrons were produced when beryllium-9 was bombarded with alpha particles. 9 4 12 1 4 Be + 2 He 6 C + 0 n Beryllium-9 Alpha Carbon-12 Neutron particle

Elements with atomic numbers above 92, the atomic number of uranium, are called transuranium elements.

• None of these elements occurs in nature. • All of them are radioactive. • All transuranium elements undergo transmutation.

Transuranium elements are synthesized in nuclear reactors and nuclear accelerators. • Reactors produce beams of low- energy particles. • Accelerators are used to increase the speed of bombarding particles to very high speeds.

– The European Organization for Nuclear Research, CERN, has a number of accelerators. The figure at right shows CERN’s largest accelerator.

• When uranium-238 is bombarded with the relatively slow neutrons from a nuclear reactor, some uranium nuclei capture these neutrons. The product is uranium-

239. 238 1 239 92 U + 0 n 92 U • Uranium-239 is radioactive and emits a beta particle. The other product is an isotope of the artificial radioactive element neptunium (atomic number 93).

239 239 0 92 U 93 Np + –1 e • Neptunium is unstable and decays, emitting a beta particle and a second artificial element, plutonium (atomic number 94). 239 239 0 93 Np 94 Pu + –1 e

Scientists in Berkeley, California, synthesized the first two artificial elements in 1940. • Since that time, more than 20 additional transuranium elements have been produced artificially.

The neutron-to-proton ratio in a radioisotope determines the type of decay that occurs.

After each half-life, half of the original radioactive atoms have decayed into atoms of a new element.

Transmutation can occur by radioactive decay, or when particles bombard the nucleus of an atom.

57 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 25.2 Nuclear Transformations > Glossary Terms • nuclear force: an attractive force that acts between all nuclear particles that are extremely close together, like protons and neutrons in a nucleus • band of stability: the location of stable nuclei on a neutron-vs.-proton plot • positron: a particle with the mass of an electron but a positive charge • half-life: the time required for one-half of the nuclei of a radioisotope sample to decay to products • transmutation: the conversion of an atom of one element to an atom of another element • transuranium elements: any elements in the periodic table with atomic number above 92, the atomic number of uranium 58 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 25.2 Nuclear Transformations > BIG IDEA

Electrons and the Structure of Atoms

• Unstable atomic nuclei decay by emitting alpha or beta particles. • Often gamma rays are emitted.

Chapter 25 Nuclear Chemistry

25.1 Nuclear Radiation 25.2 Nuclear Transformations

25.3 Fission and Fusion

25.4 Radiation in Your Life

Nuclear Fission

What happens in a nuclear chain reaction?

In a chain reaction, some of the emitted neutrons react with other fissionable atoms, which emit neutrons that react with still more fissionable atoms.

When the nuclei of certain isotopes are bombarded with neutrons, the nuclei split into smaller fragments.

• This process is called fission.

62 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 25.2 Nuclear Transformations > Nuclear Fission The figure below shows how uranium-235 breaks into two smaller fragments of roughly the same size when struck by a slow-moving neutron. Neutron 91 36Kr Krypton-91

1 3 0 n

235 236 U 92 U 92 142 Uranium-235 Uranium-236 56Ba (fissionable) (very unstable) Barium-142 • More neutrons are released by the fission. • These neutrons strike the nuclei of other uranium-235 atoms, which causes a chain reaction.

Nuclear fission can release enormous amounts of energy. • The fission of 1 kg of uranium-235 yields an amount of energy equal to that produced when 20,000 tons of dynamite explode. • An atomic bomb is a device that can trigger an uncontrolled nuclear chain reaction.

Nuclear reactors use controlled fission to produce useful energy. • The reaction takes place within uranium- 235 or plutonium-239 fuel rods. • A coolant absorbs heat produced by the controlled fission reaction and transfers the heat to water, which changes to steam. • The steam drives a turbine, which drives a generator that produces electricity.

Nuclear reactors use controlled fission to produce useful energy.

Neutron Moderation Nuclear moderation is a process that slows down neutrons so the reactor fuel can capture them to continue the chain reaction. • Moderation is necessary because most of the neutrons produced move so fast that they would pass right through a nucleus without being captured. • Water and carbon in the form of graphite are good moderators.

Neutron Absorption To prevent the chain reaction from going too fast, some of the slowed neutrons must be trapped before they hit fissionable atoms. • Neutron absorption is a process that decreases the number of slow-moving neutrons.

Neutron Absorption Control rods, made of materials such as cadmium, are used to absorb neutrons. • When control rods extend almost all the way into the reactor core, they absorb many neutrons and fission occurs slowly. • As the rods are pulled out, they absorb fewer neutrons and the fission process speeds up.

Neutron Absorption Control rods, made of materials such as cadmium, are used to absorb neutrons. • If the chain reaction were to go too fast, heat might be produced faster than the coolant could remove it. • Ultimately, a meltdown of the reactor core might occur.

Nuclear Waste Fuel rods from nuclear power plants are one major source of nuclear waste. • The fuel rods are made from a fissionable isotope, either uranium-235 or plutonium-239. • During fission, the amount of fissionable isotope in each rod decreases. • Eventually the rods no longer have enough fuel to ensure that the output of the power station remains constant.

Nuclear Waste Spent fuel rods are classified as high-level nuclear waste. • All nuclear power plants have holding tanks, or “swimming pools,” for spent fuel rods. • Water cools the spent rods and also acts as a radiation shield to reduce the radiation levels.

Nuclear Waste Spent fuel rods are classified as high-level nuclear waste. • At some nuclear power plants, the storage pool has no space left. • Finding appropriate storage sites is difficult because high-level waste may need to be stored for a long time. – Plutonium-239, for example, will not decay to safe levels for 20,000 years.

How does the fission of a uranium-235 nucleus cause a chain reaction?

When slow-moving neutrons bombard uranium- 235, the atom splits and releases more neutrons. These neutrons then collide with more uranium atoms, and so on.

74 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 25.2 Nuclear Transformations > Nuclear Fusion How do fission reactions and fusion reactions differ? The energy emitted by the sun results from nuclear fusion. • Fusion occurs when nuclei combine to produce a nucleus of greater mass. • In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei. • The reaction also produces two positrons.

Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split apart and form smaller nuclei. • However, fusion reactions occur only at very high temperatures—in excess of 40,000,000°C.

In a chain reaction, some of the emitted neutrons react with other fissionable atoms, which emit neutrons that react with still more fissionable atoms.

Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split apart to form smaller nuclei.

77 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 25.2 Nuclear Transformations > Glossary Terms • fission: the splitting of a nucleus into smaller fragments, accompanied by the release of neutrons and a large amount of energy • neutron moderation: a process used in nuclear reactors to slow down neutrons so the reactor fuel captures them to continue the chain reaction

• neutron absorption: a process that decreases the number of slow-moving neutrons in a nuclear reactor; this is accomplished by using control rods made of a material such as cadmium, which absorbs neutrons • fusion: the process of combining nuclei to produce a nucleus of greater mass

Electrons and the Structure of Atoms

• During fission and fusion, atoms change their chemical identity as the number of protons in their nuclei change. • In fission, large nuclei split into two or more smaller nuclei. • In fusion, smaller nuclei combine to form larger nuclei at extremely high temperature and pressure.

Chapter 25 Nuclear Chemistry

25.1 Nuclear Radiation 25.2 Nuclear Transformations 25.3 Fission and Fusion

25.4 Radiation in Your Life

How does a smoke detector work? A typical household smoke detector contains a small amount 241 of americium, 95 Am, in the form of AmO2. Americium-241 is a radioisotope.

Detecting Radiation What are three devices used to detect radiation?

Radiation emitted by radioisotopes has enough energy to knock electrons off some atoms of a bombarded substance, producing ions. • The radiation emitted by radioisotopes is called ionizing radiation.

It is not possible for humans to see, hear, smell, or feel ionizing radiation. • People must rely on detection devices to alert them to the presence of radiation and to monitor its level. • These devices work because of the effects of the radiation when it strikes atoms or molecules in the detector.

Radiation can expose a photographic plate. • When the plate is developed, its darkened areas show where the plate has been exposed to radiation. • X-rays allow doctors to see inside the body without having to cut into the body. Color was added to highlight parts of the image.

Radiation emitted in a smoke detector ionizes the nitrogen and oxygen in the air, and a current flows. When smoke particles attach to the ions, the ions lose their charge. What happens next?

Once the ions in the air inside the smoke detector lose their charge, the current decreases. An electronic circuit detects the drop in current, which causes an alarm to sound.

Geiger counters, scintillation counters, and film badges are commonly used to detect radiation.

Geiger Counter A Geiger counter uses a gas-filled metal tube to detect radiation. • When ionizing radiation penetrates a thin window at the end of the tube, the gas inside the tube becomes ionized. • Each time a Geiger tube is exposed to radiation, current flows. • The bursts of current drive electronic counters or cause audible clicks from a built-in speaker.

Geiger Counter Geiger counters can detect alpha, beta, and gamma radiation. • Astronomers use Geiger counters to detect cosmic rays from outer space. • Geologists use Geiger counters to search for radioactive minerals. • This person is using a Geiger counter to check for radiation in contaminated dirt at a spill site.

Scintillation Counter A scintillation counter uses a phosphor- coated surface to detect radiation. • When ionizing radiation strikes the surface, the phosphor produces bright flashes of light, or scintillations. • The number of flashes and energies are detected electronically.

Scintillation Counter Scintillation counters are more sensitive than Geiger counters. • They can detect some radiation that would not be detected by a Geiger counter. • Scintillation counters are used to track the path of radioisotopes through the body. • They are also used to monitor the possible transport of radioactive materials across national borders and through airports.

Film Badge This is a diagram of a typical film badge. • The badge contains layers of photographic film covered with black light-proof paper. • To reach the film, radiation must pass through a filter, which absorbs some radiation, or a transparent area through which radiation can pass easily.

Film Badge People who work with or near ionizing radiation must wear a film badge to monitor their exposure while they are at work. • At specific intervals, the film is removed and developed. • The strength and type of radiation exposure are determined by comparing the darkness of the film in all the exposed areas.

Using Radiation What are some practical uses of radioisotopes? • Although radiation can be harmful, it can be used safely and has many important applications. Radioisotopes are used to analyze matter, study plant growth, diagnose medical problems, and treat diseases.

Analyzing Matter Scientists use radiation to detect trace amounts of elements in samples. • This process is called neutron activation analysis.

Analyzing Matter • A sample is bombarded with neutrons from a radioactive source. • Some atoms in the sample become radioactive. • The half-life and type of radiation emitted can be detected and analyzed by a computer. – Because this data is unique for each isotope, scientists can determine what radioisotopes were produced and infer what elements were in the original sample.

Analyzing Matter • Museums use this process to detect art forgeries. • Crime laboratories use it to analyze gunpowder residue.

Using Tracers Radioisotopes called tracers are used in agriculture to test the effects of herbicides, pesticides, and fertilizers on plants. • A tracer is introduced into the substance being tested. • Next, plants are treated with the tagged substance. • Devices that detect radioactivity are used to locate the substance in the plants.

Using Tracers The tracer may also be monitored in animals that consume the plants, as well as in water and soil.

Diagnosing Medical Problems Radioisotopes can be used to detect disorders of the thyroid gland, which is located in the throat. • To diagnose thyroid disease, the patient is given a drink containing a small amount of the radioisotope iodine-131. • After about two hours, the amount of iodide uptake is measured by scanning the patient’s throat with a radiation detector.

Diagnosing Medical Problems • The radioisotope technetium-99m is used to detect brain tumors and liver disorders. • Phosphorus-32 is used to detect skin cancer.

Treating Diseases Radiation is one method used in the treatment of some cancers. • Cancer is a disease in which abnormal cells in the body are produced at a rate far beyond the rate for normal cells. • The mass of cancer cells that result from this runaway growth is called a tumor.

Treating Diseases Fast-growing cancer cells are more susceptible to damage by high-energy radiation such as gamma rays than are healthy cells. • Radiation can be used to kill the cancer cells in a tumor.

Treating Diseases Some normal cells are also killed, however, and cancer cells at the center of the tumor may be resistant to the radiation. • The benefits of the treatment and the risks to the patient must be carefully evaluated before radiation treatment begins. • Cobalt-60 and cesium-137 are typical radiation sources for cancer therapy.

Treating Diseases Salts of radioisotopes can also be sealed in gold tubes and directly inserted in tumors. • This method of treatment is called seeding. • The salts emit beta and gamma rays that kill the surrounding cancer cells. • Because the radioisotope is in a sealed container, it is prevented from traveling to other parts of the body.

Treating Diseases Prescribed drugs containing radioisotopes of gold, iodine, or phosphorus are sometimes used in radiation therapy. • A dose of iodine-131 larger than that used to detect thyroid diseases can be given to a patient to treat the disease. • The iodine that collects in the gland emits beta particles and gamma rays, which provide therapy.

Describe the benefits and risks of radiation therapy for cancer.

Radiation therapy can kill cancer cells at a higher rate than healthy cells, so it can be used to destroy fast-growing tumors. However, it also damages healthy cells, and cells in the center of the tumor may not be reached by the radiation.

Geiger counters, scintillation counters, and film badges are commonly used to detect radiation.

Radioisotopes are used to analyze the composition of matter, study plant growth, diagnose medical problems, and treat diseases.

ionizing radiation: radiation with enough energy to knock electrons off some atoms of a bombarded substance to produce ions

Electrons and the Structure of Atoms

• The ability to detect particles emitted when nuclei decay helps scientists study processes that take place in living organisms. • This ability also allows scientists to determine the age of fossils and other objects.