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Nuclear Chemistry Chemical reaction: electrons are transferred or shared between atoms Nuclear Reaction: nucleus of an atom changes Isotope: atoms of an element with same number of protons but different number of neutrons, e.g.126 C, 136 C : isotopes are of same element Nuclide: Atoms of an element with a specific number of protons and neutrons Used to describe atomic forms of different elements, e.g. 126C, 168O Stable nuclide: (nucleus) does not easily undergo change Unstable nuclide: (nucleus) spontaneously undergo change Radioactivity: radiation (high energy) spontaneously emitted from unstable nucleus Radioactive Nuclide: one that will spontaneously emit radioactivity Alpha (, 42He) Beta (, 0-1e) Gamma(00) Characteristi Helium Nucleus electron High Energy ray cs Travel dist. in 2-4 cm 200-300 cm 500 m air Tissue Dept 0.05 mm 4-5 mm >50 cm Shielding Paper, clothing Heavy clothing, Lead, thick concrete gloves Use in Not very useful as it Used to treat Used in diagnosis and treatment Medicine does not penetrate malignancy, e.g. P- of malignancy, e.g. I-131 use to tissues 32 used to treat detect iodine uptake by thyroid leukemia I-131 also used to treat hyperthyroidism- Technecium-99 used to detect brain tumors, hemorraging or blood clots Source of Radiation Exposure: Fig 11.12 Constantly exposed to low levels of radiation Low levels of exposure: Chromosome damage, if not repairednew abnormal cells produced Rapidly dividing cells e.g. bone marrow, lymph nodes, embryonic tissues are most sensitive One of first sign of over exposure is drop in red blood cell count Radioactive Decay Parent nuclei Daughter Nuclei + Radiation Balancing equation: (1) sum of subscripts on both sides equal (2)sum of superscripts on both sides equal 211 83 Bi 4 2 + 207 Tl 81 Balance the following equations: 238 U 92 4 2 + Th 238 Be 92 0 -1 + B 238 U 92 4 2 + Th 226 Ra 88 4 2 + 0 + Rn 0 Half-life (t1/2) : time for ½ of a given quantity of radioactive substance to decay Radionuclides used in diagnostic medicine have short half-lives; why? Is the half-life dependent on external conditions such as temperature or pressure? Nitrogen –13 has a half-life of 10 minutes. If a sample has an activity of 40 Ci and the procedure requires 30 minutes, what is the remaining activity of the radioisotope? Time elapsed 0 min 10 min 20 min 30 min Number of t1/2 0 1 23 Remaining 40Ci 20Ci 10Ci 5Ci activity Iron-59, used in the determination of bone-marrow function, has a half-life of 46 days. If the laboratory receives a sample of 8.0 g of iron-59, how many grams are still active after 184 days? The half-life of iodine-131 is 8.0 days. How much of a 0.32 g of I-131 will remain after a period of 24 days? Nuclear Fusion: two nuclei combine to form a larger one Process by which the sun generates its energy 3 1 H + 2 H 1 135 He 53 + 1 n 0 Nuclear Fission: large nucleus splits to form two smaller ones and release large amounts of energy and free neutrons 238 U + 92 1 n 0 135 53 I + 97 Y + 4 10n 39 Controlled nuclear fusion: used in nuclear plants H.W. Radioactive Isotopes A radioactive isotope •has an unstable nucleus. •emits radiation to become more stable. •can be one or more of the isotopes of an element Nuclear Radiation Nuclear radiation •is the radiation emitted by an unstable atom. •takes the form of alpha particles, neutrons, beta particles, positrons, or gamma rays. Types of Radiation Alpha () particle is two protons and two neutrons 0 Beta () particle is a high-energy electron e -1 Positron (+) is a positive electron 0e +1 Gamma ray is high-energy released from a nucleus Radiation Protection Shielding for Radiation Protection Chapter 9 Nuclear Radiation Alpha Decay When a radioactive nucleus emits an alpha particle, a new nucleus forms that has •a mass number that is 4 less than that of the initial nucleus. •an atomic number that is decreased by 2. Balancing Nuclear Equations Guide to Balancing a Nuclear Equation Equation for Alpha Decay Write an equation for the alpha decay of 222Rn. STEP 1 Write the incomplete equation 222 Rn ?s + 4He 86 2 STEP 2 Determine the mass number 222 – 4 = 218 STEP 3 Determine the atomic number 86 – 2 = 84 STEP 4 Determine the symbol of element 84 = Po STEP 5 Complete the equation 222 218 Rn Po + 4He 86 84 2 Beta Decay A beta particle •is an electron emitted from the nucleus. •forms when a neutron in the nucleus breaks down. 1 0 n e + 1H 0 -1 1 Writing An Equation for a Beta Emitter Example Solution 60 60 Co Ni + 0e 27 28 1 beta particle Positron Emission Gamma Radiation Summary of Types of Radiation Summary of Types of Radiation Summary of Changes in Mass and Atomic Numbers Producing Radioactive Isotopes Radioactive isotopes are produced •when a stable nucleus is converted to a radioactive nucleus by bombarding it with a small particle. •in a process called transmutation. Example Solution mass numbers 60 = 60 59 1 56 4 Co + n Mn + He 27 0 25 2 27 = 27 atomic numbers Chapter 9 Nuclear Radiation 9.3 Radiation Measurement 9.4 Half-Life of a Radioisotope 9.5 Medical Applications Using Radioactivity Radiation Measurement A Geiger counter •detects beta and gamma radiation. •uses ions produced by radiation to create an electrical current. Radiation Units Units of radiation include •Curie - measures activity as the number of atoms that decay in one second. •rad (radiation absorbed dose) - measures the radiation absorbed by the tissues of the body. •rem (radiation equivalent) - measures the biological damage caused by different types of radiation. Units of Radiation Measurement Exposure to Radiation Exposure to radiation occurs from •naturally occurring radioisotopes. •medical and dental procedures. •air travel, radon, and smoking cigarettes. Half-Life The half-life of a radioisotope is the time for the radiation level to decrease (decay) to one-half of the original value. Decay Curve A decay curve shows the decay of radioactive atoms and the remaining radioactive sample. Half-Lives of Some Radioisotopes Radioisotopes •that are naturally occurring tend to have long half-lives. •used in nuclear medicine have short half-lives. Half-Lives of Some Radioisotopes Radioisotope Half-life 14 C 5730 yr 40 K 1.3 x 109 yr 226 Ra 1600 yr 238 U 4.5 x 109 yr 51 Cr 28 days 131 I 8 days 59 Fe 46 days 99m Tc 6.0 hr Half-Life Calculations In one half-life, 40 mg of a radioisotope decays to 20 mg. After two half-lives, 10 mg of radioisotope remain. 40 mg x 1 x 1 = 10 mg 2 2 Example The half life of 123I is 13 hr. How much of a 64 mg sample of 123I is left after 26 hours? 1) 32 mg 2) 16 mg 3) 8 mg Solution 2) 16 mg STEP 1 Given 64 g; 26 hr; 13 hr/half-life STEP 2 Plan 26 hours Number of half-lives STEP 3 Equalities 1 half-life = 13 hr STEP 4 Set Up Problem Number of half-lives = 26 hr x 1 half-life = 2 half-lives 13 hr 64 mg 32 mg 16 mg Solution Medical Applications Radioisotopes with short half-lives are used in nuclear medicine because •they have the same chemistry in the body as the nonradioactive atoms. •in the organs of the body, they give off radiation that exposes a photographic plate (scan) giving an image of an organ. Some Radioisotopes Used in Nuclear Medicine Example Which of the following radioisotopes are most likely to be used in nuclear medicine? 40 1) K half-life 1.3 x 109 years 42 2) K half-life 12 hours 131 3) I half-life 8 days Solution Which of the following radioisotopes are most likely to be used in nuclear medicine? Radioisotopes with short half-lives are used in nuclear medicine. 42 2) K half-life 12 hours 131 3) I half-life 8 days Chapter 9 Nuclear Radiation 9.6 Nuclear Fission and Fusion Nuclear Fission Nuclear Fission When a neutron bombards 235U, • an unstable nucleus of 236U undergoes fission (splits). • smaller nuclei are produced such as Kr-91 and Ba-142. • neutrons are released to bombard more 235U. Energy 1 235 236 91 142 1 n + U “ U” Kr + Ba + 3 n + 0 92 92 36 56 0 When a neutron bombards 235U, •an unstable nucleus of 236U undergoes fission (splits). •smaller nuclei are produced such as Kr-91 and Ba-142. •neutrons are released to bombard more 235U. 1 235 n + U “236U” 91 Kr + 142Ba + 3 1n + 0 92 92 36 56 0 Nuclear Fission Diagram 1 n + 235U “236U” 91 Kr + 142Ba + 3 1n + energy 0 92 92 36 56 0 Example Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction. 1 235 137 n + U Te + ?X + 2 1n + energy 0 92 52 ? 0 Solution 1 235 137 n + U Te + 97Zr + 2 1n + energy 0 92 52 40 0 Chain Reaction A chain reaction occurs •when a critical mass of uranium undergoes fission. •releasing a large amount of heat and energy that produces an atomic explosion. Nuclear Power Plants In nuclear power plants, •fission is used to produce energy. •control rods in the reactor absorb neutrons to slow and control the chain reactions of fission. Nuclear Fusion Fusion •occurs at extremely high temperatures (100 000 000°C). •combines small nuclei into larger nuclei. •releases large amounts of energy. •occurs continuously in the sun and stars. Example Indicate if each of the following describes 1) nuclear fission or 2) nuclear fusion. ___ A. a nucleus splits. ___ B. large amounts of energy are released. ___ C. small nuclei form larger nuclei. ___ D. hydrogen nuclei react. ___ E. several neutrons are released. Solution Indicate if each of the following is 1) nuclear fission or 2) nuclear fusion. 1 A. a nucleus splits. 1, 2 B. large amounts of energy are released. 2 C. small nuclei form larger nuclei. 2 D. hydrogen nuclei react. 1 E. several neutrons are released.
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