1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 10 Lecture Outline Prepared by Andrea D. Leonard University of Louisiana at Lafayette

10.1Introduction A. Isotopes C mass number (A) atomic number (Z) the number of protons + the number of neutrons mass number (A) number of protons number of neutrons 6 12 – 6 = 6 atomic number (Z)=the number of protons =

10.1Introduction A. Isotopes 3 Isotopes are atoms of the same element having a different number of neutrons.

10.1Introduction A. Isotopes 4 Of the known isotopes of all elements, 264 are stable and 300 are naturally occurring but unstable. A radioactive isotope, called a radioisotope, is unstable and spontaneously emits energy to form a more stable nucleus. Radioactivity is the nuclear radiation emitted by a radioactive isotope. An even larger number of radioactive isotopes, called artificial isotopes, have been produced in the laboratory.

10.1Introduction B. Types of Radiation 5 An alpha (α) particle is a high-energy particle that contains 2 protons and 2 neutrons. alpha particle:  or 4 2 He It has a +2 charge and a mass number of 4. Types of radiation: alpha particles, beta particles, positrons, and gamma radiation.

10.1Introduction B. Types of Radiation Alpha particles are the heaviest of the radioactive particles, so they can’t penetrate materials very far. Alpha particles can be stopped by a piece of paper or your skin. Lab coats and gloves are sufficient protection from alpha particles. Some uses: smoke detectors, antistatic devices Some sources: Radon-222, Uranium-238, Thorium

10.1Introduction B. Types of Radiation 7 A beta (β) particle is a high-energy electron. beta particle: β or 0 −1 e It has a −1 charge and a negligible mass compared to a proton. A β particle is formed when a neutron (n) is converted to a proton (p) and an electron (e). 1 0 n 1 1 p neutronproton + 0 −1 e  particle

β particles are much lighter than alpha particles, and can penetrate human tissue. Heavy lab coats and gloves must be worn when working with substances that emit them. β particles are widely used in radiation therapy Some isotopes – Carbon-14, Phosphorus-32, Iodine Introduction B. Types of Radiation

9 A positron is called an antiparticle of a β particle. Their charges are opposite, but their masses are the same (i.e., effectively zero). A positron has a +1 charge and is called a “positive electron.” positron: β + or 0 +1 e A positron is formed when a proton is converted to a neutron. 1 0 n 1 1 p neutronproton e positron

Substances that emit positrons are used Positron Emission Tomography (PET) Some isotopes – Carbon-11, Fluorine Introduction B. Types of Radiation

11 Gamma rays are high-energy radiation released from a radioactive nucleus. gamma ray:  They are a form of energy, so they have no mass and no charge.

10.1Introduction B. Types of Radiation Gamma rays are sometimes emitted by themselves More often, gamma rays accompany alpha or beta particles Gamma rays are useful in medical imaging and in cancer treatment A thick lead shield is needed to stop gamma rays. Some isotopes: Cobalt-60, Technetium-99m 12

10.1Introduction B. Types of Radiation 13

10.1Introduction C. The Effects of Radioactivity 14 Radioactivity cannot be detected by the senses, yet it can have a powerful effect. Nuclear radiation will damage or kill rapidly dividing cells such as bone marrow, skin, and the reproductive and intestinal systems. Cancer cells divide rapidly as well, making radiation an effective treatment for cancer. Food is irradiated, exposed to gamma radiation, to kill any living organism in the food. Afterwards, the food is not radioactive, and has a considerably longer shelf life.

10.2Nuclear Reactions 15 Radioactive decay is the process by which an unstable radioactive nucleus emits radiation. A nuclear equation can be written for this process: original nucleus new nucleus + radiation emitted The following must be equal on both sides of a nuclear equation : The sum of the mass numbers (A) The sum of the atomic numbers (Z)

10.2Nuclear Reactions A. Alpha Emission 16 Alpha emission (alpha decay) is the decay of a nucleus by emitting an  particle.

10.2Nuclear Reactions A. Alpha Emission 17 HOW TO Balance an Equation for a Nuclear Reaction Example Write a balanced nuclear equation showing how americium-241 decays to form an  particle. Step [1] Write an incomplete equation with the original nucleus on the left and the particle emitted on the right Am 4 2 He +?+?

10.2Nuclear Reactions A. Alpha Emission 18 HOW TO Balance an Equation for a Nuclear Reaction Step [2] Calculate the mass number and atomic number of the newly formed nucleus on the right Am 4 2 He + mass number 241 − 4 = 237 atomic number 95 − 2 = Step [3] Use the atomic number to identify the new nucleus and complete the equation. Np

10.2Nuclear Reactions B. Beta Emission 19 Beta emission is the decay of a nucleus by emitting a β  particle; 1 neutron is lost and 1 proton is gained.

10.2Nuclear Reactions C. Positron Emission 20 Positron emission is the decay of a nucleus by emitting a positron, β + ; 1 proton is lost and 1 neutron is gained.

10.2Nuclear Reactions D. Gamma Emission 21 Gamma emission is the decay of a nucleus by emitting  radiation. The  rays are a form of energy only. Their emission causes no change in the atomic number or the mass number. 99m 43 Tc Tc  Technetium-99m is a metastable isotope; it decays by gamma emission to the more stable (but still radioactive) technetium-99.

10.2Nuclear Reactions D. Gamma Emission 22 Commonly,  emission accompanies  or β emission.

10.3Half-Life A. General Features 23 The half-life (t 1/2 ) of a radioactive isotope is the time it takes for one-half of the sample to decay. The half-life of a radioactive isotope is a property of a given isotope and is independent of the amount of sample, temperature, and pressure.

10.3Half-Life A. General Features 24

10.3Half-Life A. General Features 25 HOW TO Use a Half-Life to Determine the Amount of Radioisotope Present Example If the half-life of iodine-131 is 8.0 days, how much of a 100. mg sample remains after 32 days? Step [1] Determine how many half-lives occur in the given amount of time. 32 days 1 half-life 8.0 days x=4.0 half-lives

10.3Half-Life A. General Features 26 HOW TO Use a Half-Life to Determine the Amount of Radioisotope Present Step [2] For each half-life, multiply the initial mass by one-half to obtain the final mass mg initial mass x 1212 x 1212 x 1212 x 1212 The mass is halved four times. = 6.25 mg final mass

10.3Half-Life B. Archaeological Dating 27 Radiocarbon dating uses the half-life of carbon-14 to determine the age of carbon-containing materials. The ratio of radioactive carbon-14 to stable carbon-12 is a constant value in a living organism. Once the organism dies, the carbon-14 decays without being replenished. By comparing the ratio of C-14 to C-12 in an artifact to the same ratio present in organisms today, the age of the artifact can be determined. The half-life of C-14 is 5,730 years.

10.4Detecting and Measuring Radioactivity 28 The amount of radioactivity in a sample is measured by the number of nuclei that decay per unit time— disintegrations per second. Common units include: 1 Curie (Ci) = 3.7 x disintegrations/second 1 Curie (Ci) = 1,000 millicuries (mCi) 1 Curie (Ci) = 1,000,000 microcuries (  Ci) 1 becquerel (Bq) = 1 disintegration/second Thus, 1 Ci = 3.7 x Bq.

10.4Detecting and Measuring Radioactivity 29 Several units are used to measure the amount of radiation absorbed by an organism. The rad—radiation absorbed dose—is the amount of radiation absorbed by one gram of a substance. The rem—radiation equivalent for man—is the amount of radiation that also factors in its energy and potential to damage tissue. 1 rem of any type of radiation produces the same amount of tissue damage.

10.4Detecting and Measuring Radioactivity 30 The average radiation dose per year for a person is about 0.27 rem. Generally, no detectable biological effects are noticed for a radiation dose less than 25 rem. A single dose of 25–100 rem causes a temporary decrease in white blood cell count. A dose of more than 100 rem causes radiation sickness—nausea, vomiting, fatigue, etc. The LD 50 —the lethal dose that kills 50% of a population—is 500 rem in humans, while 600 rem is fatal for an entire population.

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10.5Focus on Health and Medicine A. Radioisotopes Used in Diagnosis 32 Radioisotopes can be injected or ingested to determine if an organ is functioning properly or to detect the presence of a tumor. Technetium-99m is used to evaluate the gall bladder and bile ducts and to detect internal bleeding. Thallium-201 is used in stress tests to diagnose coronary artery disease. Using a scan, normal organs are clearly visible, while malfunctioning or obstructed organs are not.

10.5Focus on Health and Medicine A. Radioisotopes Used in Diagnosis 33

10.5Focus on Health and Medicine B. Radioisotopes Used in Treatment 34

10.5Focus on Health and Medicine C. Positron Emission Tomography 35 Positron emission tomography (PET) scans use radioisotopes which emit positrons which enable scanning of an organ. PET scans can detect tumors, coronary artery disease, Alzheimer’s disease, and track the progress of cancer. A PET scan is a noninvasive method of monitoring cancer treatment.

10.5Focus on Health and Medicine C. Positron Emission Tomography 36

10.6Nuclear Fission and Nuclear Fusion A. Nuclear Fission 37 Nuclear fission is the splitting apart of a heavy nucleus into lighter nuclei and neutrons. It can begin when a neutron bombards a uranium-235 nucleus: U n Kr Ba n 3 The bombarded U-235 nucleus splits apart into krypton-91, barium-142, and three high-energy neutrons, while releasing a great deal of energy.

38 The released neutrons can then bombard other uranium nuclei, creating a chain reaction. Critical mass: The minimum amount of U-235 needed to sustain a chain reaction. 10.6Nuclear Fission and Nuclear Fusion A. Nuclear Fission Nuclear fission is the splitting apart of a heavy nucleus into lighter nuclei and neutrons. It can begin when a neutron bombards a uranium-235 nucleus: U n Kr Ba n 3

10.6Nuclear Fission and Nuclear Fusion A. Nuclear Fission 39 A nuclear power plant uses the large amount of energy released in fission. This energy is used to boil water and create steam, which turns a turbine and generates electricity. The dangers of generating nuclear power are possible radiation leaks and the disposal of nuclear waste. Radiation leaks can be minimized by containment facilities within the power plant itself. Nuclear waste is currently buried, but it is unclear whether this is the best method.

10.6Nuclear Fission and Nuclear Fusion B. Nuclear Fission 40 Nuclear fusion is the joining together of two light nuclei to form a larger nucleus. 2 1 H H 4 2 He 1 0 n + A neutron and a large amount of energy are also produced. Fusion is not currently useable as an energy source because it can only occur at extremely high temperatures and pressures. Hydrogen-2 (deuterium) and hydrogen-3 (tritium) undergo fusion to create a helium nucleus: