When Henri Becquerel placed uranium salts on a photographic plate and then developed the plate, he found a foggy image. The image was caused by rays that.

When Henri Becquerel placed uranium salts on a photographic plate and then developed the plate, he found a foggy image. The image was caused by rays that had not been observed before. For his discovery of radioactivity, Becquerel shared the 1903 Nobel Prize for Physics with Marie and Pierre Curie.

Nuclear Decay What happens during nuclear decay? During nuclear decay, atoms of one element can change into atoms of a different element altogether.

Nuclear Decay Radioactivity is the process in which an unstable atomic nucleus emits charged particles and energy. Any atom containing an unstable nucleus is called a radioactive isotope, or radioisotope for short. Radioisotopes of uranium—primarily uranium-238—were the source of radioactivity in Becquerel’s experiment.

Nuclear Decay About 26,000 years ago, more than 100 mammoths died at a sinkhole in Hot Springs, South Dakota. Scientists found the age of the remains by measuring amounts of the radioisotope carbon-14 in the mammoth bones.

Nuclear Decay Unlike stable isotopes such as carbon-12 or oxygen-16, radioisotopes spontaneously change into other isotopes over time. Nuclear decay occurs when the composition of a radioisotope changes. Uranium-238 decays into thorium-234, which is also a radioisotope.

Types of Nuclear Radiation
What are three types of nuclear radiation? Common types of nuclear radiation include alpha particles, beta particles, and gamma rays.

Scientists can detect a radioactive substance by measuring the nuclear radiation it gives off. Nuclear radiation is charged particles and energy that are emitted from the nuclei of radioisotopes.

Alpha Decay An alpha particle is a positively charged particle made up of two protons and two neutrons—the same as a helium nucleus. When a uranium-238 sample decays, it emits alpha particles. An alpha particle has a 2+ charge. An alpha particle has a mass of 4 amu. The symbol for an alpha particle, 4He, shows its mass and charge. 2

Alpha decay, nuclear decay that releases alpha particles, is an example of a nuclear reaction. In alpha decay, the product isotope has two fewer protons and two fewer neutrons than the reactant isotope.

The nuclear equation for the alpha decay of uranium-238 is shown below. The mass number on the left (238) equals the sum of the mass numbers on the right ( ). The atomic number on the left (92) equals the sum of the atomic numbers on the right (90 + 2). The equation is balanced.

Beta Decay When thorium-234 decays, it releases negatively charged radiation called beta particles. A beta particle is an electron emitted by an unstable nucleus. The symbol for a beta particle is 0e. -1

During beta decay, a neutron decomposes into a proton and an electron. The proton stays trapped in the nucleus, while the electron is released. A beta particle is assigned an atomic number of –1. A beta particle is assigned a mass number of 0.

In beta decay, the product isotope has one proton more and one neutron fewer than the reactant isotope. The mass numbers of the isotopes are equal because the emitted beta particle has essentially no mass. The balanced equation for beta decay of thorium-234 is shown below.

Gamma Decay A gamma ray is a penetrating ray of energy emitted by an unstable nucleus. Gamma radiation has no mass and no charge. Like X-rays and visible light, gamma rays are energy waves that travel through space at the speed of light.

During gamma decay, the atomic number and mass number of the atom remain the same. The energy of the nucleus decreases. Gamma decay often accompanies alpha or beta decay. Thorium-234 emits both beta particles and gamma rays (abbreviated as ) as it decays.

The penetrating power of nuclear radiation varies with the type.

Balancing Nuclear Equations Write a balanced nuclear equation for the alpha decay of polonium-210.

Balancing Equations Read and Understand What information are you given? Use the periodic table to obtain the atomic number of polonium.

Balancing Equations Read and Understand What information are you given? Reactant isotope = polonium-210 Radiation emitted = He (alpha particle) Use the periodic table to obtain the atomic number of polonium. Reactant isotope = Po

Balancing Equations Plan and Solve
What unknowns are you trying to calculate? What equation contains the given information?

What unknowns are you trying to calculate? Atomic number of product isotope, Z = ? Mass number of product isotope, A = ? Chemical symbol of product isotope, X = ? What equation contains the given information?

Write and solve equations for atomic mass and atomic number. According to the periodic table, the element with an atomic number of 82 is lead, Pb. So, X is Pb. The balanced nuclear equation is shown below.

Write and solve equations for atomic mass and atomic number. 210 = A = Z + 2 210 – 4 = A – 2 = Z 206 = A = Z According to the periodic table, the element with an atomic number of 82 is lead, Pb. So, X is Pb. The balanced nuclear equation is shown below.

Balancing Equations Look Back and Check Is your answer reasonable?

Balancing Equations Look Back and Check Is your answer reasonable?
The mass number on the left equals the sum of the mass numbers on the right. The atomic number on the left equals the sum of the atomic numbers on the right. The equation is balanced.

Describing Ionic Compounds
1. Write a balanced nuclear equation for the alpha decay of thorium-232.

1. Write a balanced nuclear equation for the alpha decay of thorium-232. Answer:

2. Write a balanced nuclear equation for the beta decay of carbon-14.

2. Write a balanced nuclear equation for the beta decay of carbon-14. Answer:

3. Determine the product of alpha decay for americium-241.

3. Determine the product of alpha decay for americium-241. Answer:

4. Determine the product of beta decay for strontium-90.

4. Determine the product of beta decay for strontium-90. Answer:

Effects of Nuclear Radiation
How does nuclear radiation affect atoms? Nuclear radiation can ionize atoms.

Background radiation is nuclear radiation that occurs naturally in the environment. Radioisotopes in air, water, rocks, plants, and animals all contribute to background radiation. Cosmic rays are streams of charged particles (mainly protons and alpha particles) from outer space. Background radiation levels are generally low enough to be safe.

Most rocks contain at least trace amounts of radioactive elements. The mineral autunite is an important source of uranium.

When nuclear radiation exceeds background levels, it can damage the cells and tissues of your body. Alpha particles can cause skin damage similar to a burn. Beta particles can damage tissues in the body more than alpha particles. Gamma rays can penetrate deeply into the human body, potentially exposing all organs to ionization damage.

Ionizing radiation can break chemical bonds in proteins and DNA molecules. Alpha particles are not a serious health hazard unless an alpha-emitting substance is inhaled or eaten. Radon gas is a potentially dangerous natural source of alpha particles because it can be inhaled. Prolonged exposure to radon-222 can lead to lung cancer.

Radon gas is produced underground as the uranium in rocks and soil decays. Radon gas dissolved in water is released through agitation. Insulation, modern windows, and modern building materials keep radon from escaping. Radon naturally diffuses up through the ground. Radon enters through pinholes and cracks in the foundation. Radon is produced by the nuclear decay of uranium found in rocks and soil.

Detecting Nuclear Radiation
What devices can detect nuclear radiation? Devices that are used to detect nuclear radiation include Geiger counters and film badges.

A Geiger counter uses a gas-filled tube to measure ionizing radiation. When nuclear radiation enters the tube, it ionizes the atoms of the gas. The ions produce an electric current, which can be measured. The greater the amount of nuclear radiation, the greater the electric current produced in the tube is.

Wearing protective clothing, a firefighter uses a Geiger counter to test the ground for radioactivity.

Many people who work with or near radioactive materials wear film badges to monitor their exposure to nuclear radiation. The badge contains a piece of photographic film. The film is developed and replaced periodically. The exposure on the film indicates the amount of radiation exposure for the person wearing the badge.

What happens when an atomic nucleus decays?
Assessment Questions What happens when an atomic nucleus decays? The atom loses an electron and gains energy. Some of the protons in the nucleus are converted to neutrons. A nucleus breaks into two parts of approximately equal mass. An unstable nucleus emits charged particles and energy.

What happens when an atomic nucleus decays?
Assessment Questions What happens when an atomic nucleus decays? The atom loses an electron and gains energy. Some of the protons in the nucleus are converted to neutrons. A nucleus breaks into two parts of approximately equal mass. An unstable nucleus emits charged particles and energy. ANS: D

During alpha decay, the nucleus emits an alpha particle, or
Assessment Questions During alpha decay, the nucleus emits an alpha particle, or proton. neutron. deuterium nucleus. helium nucleus.

During alpha decay, the nucleus emits an alpha particle, or
Assessment Questions During alpha decay, the nucleus emits an alpha particle, or proton. neutron. deuterium nucleus. helium nucleus. ANS: D

Assessment Questions Which isotope balances the nuclear equation for the alpha decay of thorium-232?

Assessment Questions Which isotope balances the nuclear equation for the alpha decay of thorium-232? ANS: C

Nuclear radiation can damage cells in the body by
Assessment Questions Nuclear radiation can damage cells in the body by ionizing atoms in molecules in the cell. making holes in the cell wall. making isotopes in the cell radioactive. causing water to vaporize and rupture the cell.

Nuclear radiation can damage cells in the body by
Assessment Questions Nuclear radiation can damage cells in the body by ionizing atoms in molecules in the cell. making holes in the cell wall. making isotopes in the cell radioactive. causing water to vaporize and rupture the cell. ANS: A

Assessment Questions A Geiger counter measures radiation by detecting ions formed when charged particles pass through a tube filled with gas. True False

Assessment Questions A Geiger counter measures radiation by detecting ions formed when charged particles pass through a tube filled with gas. True False ANS: T

These stone tools from the archaeological site in Cactus Hill, Virginia, are at least 15,000 years old. Scientists estimated the age of the site based on rates of nuclear decay.

Half-life How do nuclear decay rates differ from chemical reaction rates? Unlike chemical reaction rates, which vary with the conditions of a reaction, nuclear decay rates are constant.

Half-life A half-life is the time required for one half of a sample of a radioisotope to decay. After one half-life, half of the atoms in a radioactive sample have decayed, while the other half remains unchanged. After two half-lives, half of the remaining radioisotope decays. After three half-lives, the remaining fraction is one eighth.

Half-life The half-life for the beta decay of iodine-131 is 8.07 days.

Half-life Every radioisotope decays at a specific rate. Half-lives can vary from fractions of a second to billions of years.

Half-life Iridium-182 undergoes beta decay to form osmium-182. The half-life of iridium-182 is 15 minutes. After 45 minutes, how much iridium-182 will remain of an original 1-gram sample? Calculate how many half-lives will elapse during the total time of decay.

Half-life After three half-lives, the amount of iridium-182 has been reduced by half three times. After 45 minutes, gram of iridium-182 remains. 0.875 gram of the sample has decayed into osmium-182.

Radioactive Dating How do scientists determine the age of an object that contains carbon-14? In radiocarbon dating, the age of an object is determined by comparing the object’s carbon-14 levels with carbon-14 levels in the atmosphere.

Radioactive Dating The artifacts from Cactus Hill were dated by measuring levels of carbon-14, which has a half-life of 5730 years. Carbon-14 is formed in the upper atmosphere when neutrons produced by cosmic rays collide with nitrogen-14 atoms. Carbon-14 undergoes beta decay to form nitrogen-14.

Radioactive Dating Plants absorbing carbon dioxide during photosynthesis maintain the same ratio of carbon-14 to carbon-12 as in the atmosphere. Animals have the same ratio of carbon isotopes as the plants they eat. When a plant or animal dies, it can no longer absorb carbon. After death, the organism’s carbon-14 levels decrease as the radioactive carbon decays.

Radioactive Dating If the ratio of carbon-14 to carbon-12 in a fossil is half the atmospheric ratio, the organism lived about 5730 years ago. Because atmospheric carbon-14 levels can change over time, the calculated age of the fossil is not totally accurate. To get a more accurate radiocarbon date, scientists compare the carbon-14 levels in a sample to carbon-14 levels in objects of known age.

Radioactive Dating Radiocarbon dating can be used to date any carbon-containing object less than 50,000 years old. Objects older than 50,000 years contain too little carbon-14 to be measurable, so scientists measure the amounts of radioisotopes with longer half-lives than carbon-14.

Radioactive Dating Radiocarbon dating helps archaeologists learn more about ancient civilizations. This Egyptian mummy case, containing the remains of a cat, is 1900 years old.

Assessment Questions Cesium-137 has a half-life of 30 years. You find a sample with 3 g of cesium-137. How much cesium-137 existed in the sample 90 years ago? 9 g 27 g 24 g 18 g

Assessment Questions Cesium-137 has a half-life of 30 years. You find a sample with 3 g of cesium-137. How much cesium-137 existed in the sample 90 years ago? 9 g 27 g 24 g 18 g ANS: C

What factors influence nuclear decay rates?
Assessment Questions What factors influence nuclear decay rates? pressure temperature concentration number of neutrons in nucleus

What factors influence nuclear decay rates?
Assessment Questions What factors influence nuclear decay rates? pressure temperature concentration number of neutrons in nucleus ANS: D

Assessment Questions What radioisotope is most commonly used to determine the age of archaeological artifacts made of wood? lithium-7 carbon-14 potassium-40 uranium-235

Assessment Questions What radioisotope is most commonly used to determine the age of archaeological artifacts made of wood? lithium-7 carbon-14 potassium-40 uranium-235 ANS: B

This painting of an alchemist’s laboratory was made around 1570
This painting of an alchemist’s laboratory was made around For centuries, these early scientists, known as alchemists, tried to use chemical reactions to make gold. The alchemists failed in their attempts to turn lead into gold.

Nuclear Reactions in the Laboratory
How do artificial transmutations occur? Transmutation is the conversion of atoms of one element to atoms of another. Scientists can perform artificial transmutations by bombarding atomic nuclei with high-energy particles such as protons, neutrons, or alpha particles.

Transmutation involves a nuclear change, not a chemical change. Nuclear decay is an example of a transmutation that occurs naturally. Transmutations can also be artificial.

In 1919, Ernest Rutherford performed the first artificial transmutation by exposing nitrogen gas to alpha particles. Some of the alpha particles were absorbed by the nitrogen nuclei. Each newly formed nucleus then ejected a proton, leaving behind the isotope oxygen-17.

Transuranium Elements
How are transuranium elements produced? Elements with atomic numbers greater than 92 (uranium) are called transuranium elements. Scientists can synthesize a transuranium element by the artificial transmutation of a lighter element.

All transuranium elements are radioactive, and they are generally not found in nature. Neptunium was the first transuranium element synthesized. In 1940, scientists at the University of California, Berkeley, bombarded uranium-238 with neutrons, producing uranium-239. The uranium-239 underwent beta decay to form neptunium-239.

Most transuranium elements have only been produced for research, but some are synthesized for industrial use. Americium-241 is a transuranium element used in smoke detectors. The decay of plutonium-238 is used to generate electrical energy in some space probes.

In 1977, NASA launched Voyager 1 and Voyager 2 spacecraft to explore the outer solar system. They are powered by the alpha decay of plutonium-238.

Particle Accelerators
Some transmutations require particles that are moving at extremely high speeds. Particle accelerators cause charged particles to move very close to the speed of light. The fast-moving particles collide with atomic nuclei. Scientists have produced more than 3000 different isotopes.

Scientists also conduct collision experiments in order to study nuclear structure. More than 200 different subatomic particles have been detected. A quark is a subatomic particle theorized to be among the basic units of matter. According to the current model of the atom, protons and neutrons are made up of quarks.

This particle detector records subatomic particles produced in the Tevatron, the most powerful particle accelerator in the world. The Tevatron is located at Fermilab in Batavia, Illinois.

Which of the following is a type of atom transmutation?
Assessment Questions Which of the following is a type of atom transmutation? alpha decay gamma decay chemical reaction ionization

Which of the following is a type of atom transmutation?
Assessment Questions Which of the following is a type of atom transmutation? alpha decay gamma decay chemical reaction ionization ANS: A

Assessment Questions To study the structure of the atomic nucleus, scientists use particle accelerators to combine small nuclei into larger nuclei. cause chemical reactions to occur rapidly. cause collisions of particles moving near the speed of light. magnify nuclei so they can be studied on a computer monitor.

Assessment Questions To study the structure of the atomic nucleus, scientists use particle accelerators to combine small nuclei into larger nuclei. cause chemical reactions to occur rapidly. cause collisions of particles moving near the speed of light. magnify nuclei so they can be studied on a computer monitor. ANS: C

Assessment Questions Scientists make transuranium elements by the artificial transmutation of lighter elements. True False

Assessment Questions Scientists make transuranium elements by the artificial transmutation of lighter elements. True False ANS: T

Transmutations involve more than just the conversion of one element into another—they also involve the conversion of mass into energy. Nuclear energy released by nuclear reactions is used as an alterative source of energy.

Nuclear Forces Under what conditions does the strong nuclear force overcome electric forces in the nucleus?

Nuclear Forces The strong nuclear force is the attractive force that binds protons and neutrons together in the nucleus. Over very short distances, the strong nuclear force is much greater than the electric forces among protons.

Nuclear Forces The protons in the nucleus are all positively charged, so they tend to repel one another. The strong nuclear force binds protons and neutrons together in the nucleus. The strong nuclear force does not depend on charge. It acts among protons, among neutrons, and among protons and neutrons.

Nuclear Forces At the distance of a proton width, the strong nuclear force is more than 100 times greater than the electric force that repels protons. The strong nuclear force quickly weakens as protons and neutrons get farther apart.

Nuclear Forces Strong nuclear forces and electric forces act upon particles in the nucleus. Strong Nuclear Forces Neutron Neutron Proton Proton Electric Forces Neutron Neutron Proton Proton

Nuclear Forces The Effect of Size on Nuclear Forces The greater the number of protons in a nucleus, the greater is the electric force that repels those protons. The more protons and neutrons in a nucleus, the more possibilities there are for strong nuclear force attractions. Because the strong nuclear force only acts over short ranges, the possibility of many attractions is never realized in a large nucleus.

The larger number of electric forces makes the nucleus less stable.
Nuclear Forces The strong nuclear forces easily overcome the electric force between the protons. The larger number of electric forces makes the nucleus less stable. Nuclear Forces Acting on a Proton of a Small Nucleus Nuclear Forces Acting on a Proton of a Large Nucleus

Nuclear Forces Unstable Nuclei A nucleus becomes unstable, or radioactive, when the strong nuclear force can no longer overcome the repulsive electric forces among protons. While the strong nuclear force does not increase with the size of the nucleus, the electric forces do. All nuclei with more than 83 protons are radioactive.

Fission What property of fission makes it so useful? Fission is the splitting of an atomic nucleus into two smaller parts. In nuclear fission, tremendous amounts of energy can be produced from very small amounts of mass.

Fission In 1938, Otto Hahn and Fritz Strassman bombarded uranium-235 with high-energy neutrons to produce more massive elements. Their experiments instead produced isotopes of a smaller element, barium. Lise Meitner and Otto Frisch determined that uranium-235 nuclei had been broken into smaller fragments.

Fission Meitner predicted that fission releases energy. The nuclear energy released by the fission of 1 kilogram of uranium-235 is equivalent to the chemical energy produced by burning more than 17,000 kilograms of coal.

Fission The fission of uranium-235 yields smaller nuclei, neutrons, and energy. Neutron

Fission The fission of uranium-235 yields smaller nuclei, neutrons, and energy. Neutron Energy

Fission Converting Mass Into Energy When the fission of uranium-235 is carried out, about 0.1 percent of the mass of the reactants is lost during the reaction. This “lost” mass is converted into energy. In 1905, Albert Einstein had introduced the mass-energy equation.

Fission E represents energy, m represents mass, and c represents the speed of light (3.0 × 108 m/s). The conversion of a small amount of mass releases an enormous amount of energy. According to the law of conservation of mass and energy, the total amount of mass and energy remains constant.

Fission Triggering a Chain Reaction A uranium-235 nucleus decays into two smaller nuclei and releases two or three neutrons. If one of the neutrons is absorbed by another uranium-235 nucleus, another fission can result. In a chain reaction, neutrons released during the splitting of an initial nucleus trigger a series of nuclear fissions.

Fission The fission of one nucleus can trigger a chain reaction.

Fission In an uncontrolled chain reaction, all of the released neutrons are free to cause other fissions. The result is a fast, intense release of energy. Nuclear weapons are designed to produce uncontrolled chain reactions.

Fission In a controlled chain reaction, some of the neutrons are absorbed by other materials resulting in only one new fission for each splitting of an atom. The heat from controlled chain reactions can be used to generate electrical energy.

Fission In order to sustain a chain reaction, each nucleus that is split must produce, on average, one neutron that causes the fission of another nucleus. This condition corresponds to a specific mass of fissionable material. A critical mass is the smallest possible mass of a fissionable material that can sustain a chain reaction.

Fission Nuclear Energy from Fission Nuclear power plants generate about 20 percent of the electricity in the United States. In a nuclear power plant, controlled fission of uranium-235 occurs in a vessel called a fission reactor. Nuclear power plants do not emit air pollutants.

Nuclear power plants do have safety and environmental issues.
Fission Nuclear power plants do have safety and environmental issues. Workers in nuclear power plants need to wear protective clothing to reduce their exposure to nuclear radiation. Nuclear power produces radioactive isotopes with half-lives of hundreds or thousands of years.

Fission Unfortunately, a product of controlled chain reactions is radioactive waste. A crane lowers drums of radioactive waste into a landfill in Hanford, Washington.

Fusion Fusion is a process in which the nuclei of two atoms combine to form a larger nucleus. As in fission, during fusion a small fraction of the reactant mass is converted into energy.

Fusion The sun and other stars are powered by the fusion of hydrogen into helium. Inside the sun, an estimated 600 million tons of hydrogen undergo fusion each second. Fusion requires extremely high temperatures. Inside the sun, matter exists as plasma, a state of matter in which atoms have been stripped of their electrons.

Fusion Scientists envision fusion reactors fueled by two hydrogen isotopes, deuterium (hydrogen-2) and tritium (hydrogen-3). The fusion of deuterium and tritium produces helium, neutrons, and energy. Two main problems in designing a fusion reactor are achieving the high temperatures required and containing the plasma.

Fusion The Tokamak Fusion Test Reactor at the Princeton Plasma Physics Laboratory was one of the very few fusion reactors that have been built.

Why do nuclei become less stable as the atomic number increases?
Assessment Questions Why do nuclei become less stable as the atomic number increases? The strong nuclear forces become too strong and expel particles. The strong nuclear forces become weaker and cannot overcome electrical forces. The electrical forces become stronger and overcome strong nuclear forces. The electron cloud becomes too large and increases pressure on the nucleus.

Why do nuclei become less stable as the atomic number increases?
Assessment Questions Why do nuclei become less stable as the atomic number increases? The strong nuclear forces become too strong and expel particles. The strong nuclear forces become weaker and cannot overcome electrical forces. The electrical forces become stronger and overcome strong nuclear forces. The electron cloud becomes too large and increases pressure on the nucleus. ANS: C

Which of the following statements about nuclear fission is false?
Assessment Questions Which of the following statements about nuclear fission is false? Fission is the splitting of a nucleus into two smaller parts. Fission produces tremendous amounts of energy from a small mass. Mass is conserved during nuclear fission. Fission does not always yield the same products.

Which of the following statements about nuclear fission is false?
Assessment Questions Which of the following statements about nuclear fission is false? Fission is the splitting of a nucleus into two smaller parts. Fission produces tremendous amounts of energy from a small mass. Mass is conserved during nuclear fission. Fission does not always yield the same products. ANS: C

Assessment Questions How is nuclear energy converted to electrical energy in a nuclear power plant? Nuclear fusion releases electrons that then flow through wires. Fission reactions in the core of the reactor release charged particles that form the current. A fission reaction produces energy as heat, which converts water to steam that drives a turbine connected to a generator. Neutrons from the nuclear fission process drive a turbine that is connected to a generator.

Assessment Questions How is nuclear energy converted to electrical energy in a nuclear power plant? Nuclear fusion releases electrons that then flow through wires. Fission reactions in the core of the reactor release charged particles that form the current. A fission reaction produces energy as heat, which converts water to steam that drives a turbine connected to a generator. Neutrons from the nuclear fission process drive a turbine that is connected to a generator. ANS: C

Assessment Questions Why has nuclear fusion not been used to produce power on Earth. Fusion only occurs in high temperature plasmas, which cannot yet be controlled. Nuclear fusion requires deuterium, which is not available on Earth. Fusion does not produce enough energy to justify its use. Scientists do not yet know how to start a fusion reaction.

Assessment Questions Why has nuclear fusion not been used to produce power on Earth. Fusion only occurs in high temperature plasmas, which cannot yet be controlled. Nuclear fusion requires deuterium, which is not available on Earth. Fusion does not produce enough energy to justify its use. Scientists do not yet know how to start a fusion reaction. ANS: A

When Henri Becquerel placed uranium salts on a photographic plate and then developed the plate, he found a foggy image. The image was caused by rays that.

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When Henri Becquerel placed uranium salts on a photographic plate and then developed the plate, he found a foggy image. The image was caused by rays that.

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Presentation on theme: "When Henri Becquerel placed uranium salts on a photographic plate and then developed the plate, he found a foggy image. The image was caused by rays that."— Presentation transcript:

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