The Nucleus, Radioactivity, and Nuclear Medicine Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 10 The Nucleus, Radioactivity, and Nuclear Medicine Denniston Topping Caret 4th Edition

10.1 Natural Radioactivity Radioactivity – process by which atoms emit energetic particles or rays. Radiation – the particles or rays emitted. comes from the nucleus Nuclear symbols – what we use to designate the nucleus. Atomic symbol Atomic number Mass number

10.1 Natural Radioactivity mass number number of protons and neutrons atomic symbol 10.1 Natural Radioactivity atomic number number of protons This symbol is the same as writing boron-11.

10.1 Natural Radioactivity Remember for section 2.2, this defines an isotope of boron. In nuclear chemistry this is often called a nuclide. This is not the only isotope (nuclide) of boron. boron-10 also exists How many protons and neutrons does boron-10 have? 5 protons, 5 neutrons 10.1 Natural Radioactivity

10.1 Natural Radioactivity Some isotopes are stable The unstable isotopes are the ones that produce radioactivity. To write nuclear equations (section 10.2) we need to be able to write the symbols for the isotopes and the following: alpha particle beta particles gamma rays 10.1 Natural Radioactivity

10.1 Natural Radioactivity Alpha Particles 1 Alpha particle (a) – 2 protons, 2 neutrons. Same as He nucleus (He2+) Slow moving, and stopped by small barriers. Symbolized in the following ways: 10.1 Natural Radioactivity

10.1 Natural Radioactivity Bata Particles 1 Beta particles (b) – fast-moving electron. Emitted from the nucleus as a neutron is converted to a proton. Higher speed particles, more penetrating than alpha particles. The symbol is… 10.1 Natural Radioactivity

10.1 Natural Radioactivity Gamma Rays 1 Gamma Rays (g) – pure energy (electromagnetic radiation.) Highly energetic, the most penetrating form of radiation. Symbol is simply… 10.1 Natural Radioactivity g

10.1 Natural Radioactivity Properties of Alpha, Beta, and Gamma Radiation 1 Ionizing radiation – produces a trail of ions throughout the material that it penetrates. The penetrating power of the radiation determines the ionizing damage that can be caused. Alpha particle < beta particle < gamma rays. 10.1 Natural Radioactivity

10.2 Writing a Balanced Nuclear Equation Nuclear equation - used to represent nuclear change. In a nuclear equation, you do not balance the elements, instead... the total mass on each side of the reaction arrow must be identical the sum of the atomic numbers on each side of the reaction arrow must be identical

10.2 Writing Balanced Nuclear Equations Alpha Decay 238 = 234 + 4 10.2 Writing Balanced Nuclear Equations mass number 92 = 90 + 2 atomic number

10.2 Writing Balanced Nuclear Equations Beta Decay 10.2 Writing Balanced Nuclear Equations

10.2 Writing Balanced Nuclear Equations Gamma Production Gamma radiation occurs to increase the stability of an isotope. The energetically unstable isotope is called a metastable isotope. The atomic mass and number do not change. 10.2 Writing Balanced Nuclear Equations Usually gamma rays are emitted along with alpha or beta particles.

10.2 Writing Balanced Nuclear Equations Predicting Products of Nuclear Decay To predict the product, simply remember that the mass number and atomic number is conserved. 10.2 Writing Balanced Nuclear Equations What is the identity of X? 239 Np 93

10.3 Properties of Radioisotopes Nuclear Structure and Stability Binding Energy - the energy that holds the protons, neutrons, and other particles together in the nucleus. Binding energy is very large. When isotopes decay (forming more stable isotopes,) binding energy is released.

10.3 Properties of Radioisotopes Important factors for stable isotopes. Ratio of neutrons to protons. Nuclei with large number of protons (84 or more) tend to be unstable. The “magic numbers” of 2, 8, 20, 50, 82, or 126 help determine stability. These numbers of protons or neutrons are stable. Even numbers of protons or neutrons are generally more stable than those with odd numbers. All isotopes (except 1H) with more protons than neutrons are unstable. 10.3 Properties of Radioisotopes

10.3 Properties of Radioisotopes Half-Life 3 Half-life (t1/2) - the time required for one-half of a given quantity of a substance to undergo change. Each radioactive isotope has its own half-life Ranges from a fraction of a second to a billion years. The shorter the half-life, the more unstable the isotope. 10.3 Properties of Radioisotopes

10.3 Properties of Radioisotopes

10.3 Properties of Radioisotopes Half-Life Calculation A patient receives 10.0 ng of a radioisotope with a half-life of 12 hours. How much will remain in the body after 2.0 days, assuming that radioactive decay is the only path for removal of the isotope form the body. 10.3 Properties of Radioisotopes

10.4 Nuclear Power 4 Energy Production E = mc2 Equation by Albert Einstein shows the connection between energy (E) and the mass (m) c is the speed of light The equation shows that a very large amount of energy can be formed from a small amount of matter.

10.4 Nuclear Power Nuclear Fission Fission (splitting) occurs when a heavy nuclear particle is split into smaller nuclei by a smaller nuclear particle. 10.4 Nuclear Power Accompanied by a large amount of energy. Is self perpetuating. Can be used to generate steam.

10.4 Nuclear Power Chain reaction - the reaction sustains itself by producing more neutrons

A nuclear power plant uses a fissionable material as fuel. Energy released by the fission heats water produces steam drives a generator or turbine converts heat to electrical energy 10.4 Nuclear Power

10.4 Nuclear Power Nuclear Fusion Fusion (to join together) - combination of two small nuclei to form a larger nucleus. Large amounts of energy is released. Best example is the sun. An Example: 10.4 Nuclear Power No commercially successful plant exists in U.S.

10.4 Nuclear Power Breeder Reactors Breeder reactor - fission reactor that manufactures its own fuel. Uranium-238 (non fissionable) is converted to plutonium-239 (fissionable). Plutonium-239 undergoes fission to produce energy. 10.4 Nuclear Power

5 10.5 Radiocarbon Dating Radiocarbon dating - the estimation of the age of objects through measurement of isotopic ratios of carbon. Ratio of carbon-14 and carbon-12 Basis for dating: Carbon-14 (a radioactive isotope) is constantly being produced by neutrons from the sun.

Living systems are continually taking in carbon. The ratio of carbon-14 to carbon-12 stays constant during its lifetime. Once the living system dies, it quits taking in the carbon-14. The amount of carbon-14 decreases according to the reaction: 10.5 Radiocarbon Dating The half-life of carbon-14 is 5730 years. This information is used to calculate the age.

10.6 Medical Applications of Radioactivity Modern medical care uses the following: Radiation in the treatment of cancer. Nuclear medicine - the use of radioisotopes in the diagnosis of medical conditions.

10.6 Medical Applications Cancer Therapy Using Radiation Based on the fact that high-energy gamma rays cause damage to biological molecules. Tumor cells are more susceptible than normal cells. Example: cobalt-60 Gamma radiation can cure cancer but can also cause cancer. 7 10.6 Medical Applications

10.6 Medical Applications Nuclear Medicine The use of isotopes in diagnosis. Tracers - small amounts of radioactive substances used as probes to study internal organs. Nuclear imaging - medical techniques involving tracers. Example: Iodine concentrates in the thyroid gland. Using radioactive 131I and 125I will allow the study of how the thyroid gland is taking in iodine. 10.6 Medical Applications

Isotopes with short half-lives are preferred for tracer studies. Why? They give a more concentrated burst. They are removed more quickly from the body. Examples of imaging procedures: Bone disease and injury using technetium-99m Cardiovascular disease using thallium-201 Pulmonary disease using xenon-133 10.6 Medical Applications

10.6 Medical Applications Making Isotopes for Medical Applications 8 Artificial radioactivity - a normally stable, nonradioactive nucleus is made radioactive. Made in two ways: In core of a nuclear reactor In particle accelerators - small nuclear particles are accelerated to speeds approaching the speed of light and slammed into another nucleus. 9 10.6 Medical Applications

10.6 Medical Applications Examples of artificial radioactivity: Tracer in the liver 10.6 Medical Applications Used in the diagnosis of Hodgkin’s disease.

Some isotopes used in nuclear medicine have such a short half-life that they need to be generated on site. 99mTc has a half-life of only 6 hours. 10.6 Medical Applications

10.7 Biological Effects of Radiation Radiation Exposure and Safety The Magnitude of the Half-Life Isotopes with short half-lives have one major disadvantage and one major advantage. Disadvantage: larger amount of radioactivity per unit time. Advantage: if accident occurs, reaches background radiation levels more rapidly

10.7 Biological Effects Shielding Alpha and beta particles need low level of shielding (lab coat and gloves.) Lead, concrete or both required for gamma rays. Distance from the Radioactive Source Doubling the distance from the source decreases the intensity by a factor of 4. 10.7 Biological Effects

10.7 Biological Effects Time of Exposure Effects are cumulative Types of Radiation Emitted Alpha and beta emitters are generally less hazardous then gamma emitters. Waste Disposal disposal sites are considered temporary. 10.7 Biological Effects

10.8 Measurement of Radiation 11 Nuclear Imaging Isotope is administered. Isotope begins to concentrate in the organ. Photographs (nuclear images) are taken at periodic intervals. Emission of radioactive isotope creates the image.

10.8 Detection and Measurement of Radiation Computer Imaging Computers and television are coupled Gives a continuous and instantaneous record of the voyage of the isotope throughout the body. Gives increased sensitivity CT scanner is an example 10.8 Detection and Measurement of Radiation

10.8 Detection and Measurement of Radiation The Geiger Counter Detects ionizing radiation 10.8 Detection and Measurement of Radiation Has largely been replaced by more sophisticated devises.

10.8 Detection and Measurement of Radiation Film Badges A piece of photographic film that is sensitive to energies corresponding to radioactive emissions. The darker the film, when developed, the longer the worker has been exposed. 10.8 Detection and Measurement of Radiation

10.8 Detection and Measurement of Radiation Units of Radiation Measurement 12 The Curie The amount of radioactive material that produces 3.7 x 1010 atomic disintegrations per second. Independent of the nature of the radiation 10.8 Detection and Measurement of Radiation

10.8 Detection and Measurement of Radiation The Roentgen The amount of radiation needed to produce 2 x 109 ion pairs when passing through one cm3 of air at 0oC. Used for very high energy ionizing radiation only. 10.8 Detection and Measurement of Radiation

10.8 Detection and Measurement of Radiation Radiation absorbed dosage. The dosage of radiation able to transfer 2.4 x 10-3 cal of energy to one kg of matter. This takes into account the nature of the absorbing material. 10.8 Detection and Measurement of Radiation

10.8 Detection and Measurement of Radiation The Rem Roentgen Equivalent for Man Obtained by multiplication of the rad by a factor called the relative biological effect (RBE) RBE = 10 for alpha particles RBE = 1 for beta particles Lethal dose (LD50) - the acute dosage of radiation that would be fatal for 50% of the exposed population. LD50 = 500 rems. 10.8 Detection and Measurement of Radiation

The End Chapter 10