* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 1
Survey
Document related concepts
Radioactive decay wikipedia , lookup
Nuclear fission wikipedia , lookup
Nuclear binding energy wikipedia , lookup
Isotopic labeling wikipedia , lookup
Nuclear fission product wikipedia , lookup
Fallout shelter wikipedia , lookup
Nuclear and radiation accidents and incidents wikipedia , lookup
Valley of stability wikipedia , lookup
Ionizing radiation wikipedia , lookup
Background radiation wikipedia , lookup
Nuclear transmutation wikipedia , lookup
Transcript
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 11 5 B atomic symbol atomic number number of protons 9.1 Natural Radioactivity Writing Nuclear Symbols 11 5 B • 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 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 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: 4 2 He 2 4 2 He α 4 2 α 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: 0 1 e 0 -1 β β 9.1 Natural Radioactivity Gamma Rays • Gamma rays (g) - pure energy (electromagnetic radiation) • Highly energetic • The most penetrating form of radiation • Symbol is simply… g 9.1 Natural Radioactivity 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 9.2 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 92 U 238 = Th He 234 90 234 4 2 + 4 mass number 92 = 90 + atomic number 2 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 nitrogen16 is converted to a proton and the electron, the beta particle is released 16 7 N O e 16 8 0 -1 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 Tc 99m 43 Tc g 99 43 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 239 92 UX e 0 -1 • What is the identity of X? 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 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 9.4 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 9.4 Nuclear Power Nuclear Fission • Fission (splitting) - occurs when a heavy nuclear particle is split into smaller nuclei by a smaller nuclear particle 1 0 n 235 92 U 236 92 U 92 36 Kr Ba 3 n energy 141 56 1 0 •Accompanied by a large amount of energy •Is self-perpetuating •Can be used to generate steam 9.4 Nuclear Power Fission of Uranium-235 • 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 • 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: 2 H 3 H 4 He 1n energy 1 1 2 0 • No commercially successful plant exists in U.S. 9.4 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 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 14 7 N n C H 1 0 14 6 1 1 9.5 Radiocarbon Dating 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 14 14 0 to the reaction: C N e 6 7 -1 • 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 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 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 197 79 Au n 1 0 198 79 Au • Tracer in the liver • Used in the diagnosis of Hodgkin’s disease 66 30 Zn p 1 1 67 31 Ga 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 99 42 Mo Tc e 99m 43 0 -1 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 9.8 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 The Geiger Counter • Detects ionizing radiation • Has largely been replaced by more sophisticated devices 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 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