The Nucleus, Radioactivity, and Nuclear Medicine Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 9 The Nucleus, Radioactivity, and Nuclear Medicine Denniston Topping Caret 5th Edition

9.1 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

9.1 Natural Radioactivity Nuclear Symbols mass number number of protons and neutrons 9.1 Natural Radioactivity atomic symbol atomic number number of protons

Writing Nuclear Symbols This defines an isotope of boron In nuclear chemistry, often called a nuclide This is not the only isotope of boron boron-10 also exists How many protons and neutrons does boron-10 have? 5 protons, 5 neutrons 9.1 Natural Radioactivity

Three Isotopes of Carbon Each nucleus contains the same number of protons Only the number of neutrons is different With different numbers of neutrons the mass of each isotope is different 9.1 Natural Radioactivity

9.1 Natural Radioactivity Unstable Isotopes Some isotopes are stable The unstable isotopes are the ones that produce radioactivity To write nuclear equations we need to be able to write the symbols for the isotopes and the following: alpha particles beta particles gamma rays 9.1 Natural Radioactivity

9.1 Natural Radioactivity Alpha Particles Alpha particle (a) - 2 protons, 2 neutrons Same as He nucleus (He2+) Slow moving, and stopped by small barriers Symbolized in the following ways: 9.1 Natural Radioactivity

9.1 Natural Radioactivity Beta Particles 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 Symbolized in the following ways: 9.1 Natural Radioactivity

9.1 Natural Radioactivity Gamma Rays Gamma rays (g) - pure energy (electromagnetic radiation) Highly energetic The most penetrating form of radiation Symbol is simply… 9.1 Natural Radioactivity g

Properties of Alpha, Beta, and Gamma Radiation 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 9.1 Natural Radioactivity

9.2 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

9.2 Writing a Balanced Nuclear Equations Alpha Decay 238 = 234 + 4 9.2 Writing a Balanced Nuclear Equations mass number 92 = 90 + 2 atomic number

9.2 Writing a Balanced Nuclear Equations Beta Decay Upon decomposition, nitrogen-16 produces oxygen-16 and a beta particle In beta decay, one neutron in nitrogen-16 is converted to a proton and the electron, the beta particle is released 9.2 Writing a Balanced Nuclear Equations

9.2 Writing a 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 Usually gamma rays are emitted along with alpha or beta particles 9.2 Writing a Balanced Nuclear Equations

Predicting Products of Nuclear Decay To predict the product, simply remember that the mass number and atomic number are conserved What is the identity of X? 9.2 Writing a Balanced Nuclear Equations 239 Np 93

9.3 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

9.3 Properties of Radioisotopes Stable 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 9.3 Properties of Radioisotopes

9.3 Properties of Radioisotopes Half-Life 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 9.3 Properties of Radioisotopes

Half-Lives of Selected Radioisotopes 9.3 Properties of Radioisotopes

Decay Curve for the Medically Useful Radioisotope Tc-99m 9.3 Properties of Radioisotopes

Predicting the Extent of Radioactive Decay 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 radioactive decay is the only path for removal of the isotope from the body? Calculate n, the number of half-lives elapsed using the half-life as the conversion factor n = 2.0 days x 1 half-life / 0.5 days = 4 half lives Calculate the amount remaining 10.0 ng 5.0 ng 2.5 ng 1.3 ng 0.63 ng 1st half-life 2nd half-life 3rd half-life 4th half-life 0.63 ng remain after 4 half-lives 9.3 Properties of Radioisotopes

9.4 Nuclear Power Energy Production E = mc2 Equation by Albert Einstein shows the connection between energy (E) and mass (m) c is the speed of light The equation shows that a very large amount of kinetic energy can be formed from a small amount of matter Release this kinetic energy to convert liquid water into steam The steam drives an electrical generator producing electricity

Nuclear Fission 9.4 Nuclear Power Fission (splitting) - occurs when a heavy nuclear particle is split into smaller nuclei by a smaller nuclear particle 9.4 Nuclear Power Accompanied by a large amount of energy Is self-perpetuating Can be used to generate steam

Fission of Uranium-235 9.4 Nuclear Power Chain reaction - the reaction sustains itself by producing more neutrons 9.4 Nuclear Power

Representation of the “Energy Zones” of a Nuclear Reactor 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 9.4 Nuclear Power

Nuclear Fusion 9.4 Nuclear Power 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: No commercially successful plant exists in U.S. 9.4 Nuclear Power

Breeder Reactors 9.4 Nuclear Power 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 9.4 Nuclear Power

9.5 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

Radiocarbon Dating 9.5 Radiocarbon Dating 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: 9.5 Radiocarbon Dating The half-life of carbon-14 is 5730 years This information is used to calculate the age

9.6 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

9.6 Medical Applications of Radioactivity 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 9.6 Medical Applications of Radioactivity

9.6 Medical Applications of Radioactivity 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 9.6 Medical Applications of Radioactivity

9.6 Medical Applications of Radioactivity Tracer Studies 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 9.6 Medical Applications of Radioactivity

Making Isotopes for Medical Applications 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 9.6 Medical Applications of Radioactivity

Examples of Artificial Radioactivity Tracer in the liver Used in the diagnosis of Hodgkin’s disease 9.6 Medical Applications of Radioactivity

Preparation of Technetium-99m 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 9.6 Medical Applications of Radioactivity

9.7 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

9.7 Biological Effects of Radiation Radiation Exposure and Safety Shielding Alpha and beta particles need a low level of shielding: lab coat and gloves Lead, concrete or both are required for gamma rays Distance from the Radioactive Source Doubling the distance from the source decreases the intensity by a factor of 4 9.7 Biological Effects of Radiation

Radiation Exposure and Safety 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 9.7 Biological Effects of Radiation

9.8 Measurement of Radiation 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

9.8 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 9.8 Measurement of Radiation

9.8 Measurement of Radiation The Geiger Counter Detects ionizing radiation Has largely been replaced by more sophisticated devices 9.8 Measurement of Radiation

9.8 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 9.8 Measurement of Radiation

Units of Radiation Measurement The Curie The amount of radioactive material that produces 3.7 x 1010 atomic disintegrations per second Independent of the nature of the radiation 9.8 Measurement of Radiation

9.8 Measurement of Radiation Units of Radiation Measurement 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 9.8 Measurement of Radiation

Units of Radiation Measurement Rad - 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 9.8 Measurement of Radiation

Units of Radiation Measurement 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 9.8 Measurement of Radiation