Nuclear Chemistry PDF

# Nuclear Chemistry ## Radiation Technology Radiation technologists work in hospitals or imaging centers where nuclear medicine is used to diagnose and treat a variety of medical conditions. ## 5.1 Natural Radioactivity Unstable nuclei spontaneously emit small particles of energy called radiati...

# Nuclear Chemistry ## Radiation Technology Radiation technologists work in hospitals or imaging centers where nuclear medicine is used to diagnose and treat a variety of medical conditions. ## 5.1 Natural Radioactivity Unstable nuclei spontaneously emit small particles of energy called radiation to become more stable. **Learning Goal:** Describe alpha, beta, positron, and gamma radiation. ## Radioisotopes A radioisotope: - has an unstable nucleus and emits radiation - can be one or more isotopes of an element - includes the mass number in its name Carbon-14, a radioactive isotope of carbon that is used for archeological dating, has a mass number of 14 and an atomic number of 6. - Mass number (protons and neutrons) - Atomic number (protons) - Symbol of element C-14 5730 yrs = ½ life ## Types of Radiation Emitted Radioisotopes emit radiation such as: - **alpha (α) particles**, identical to a helium nucleus $^4_2He$ - **beta (β) particles**, high-energy electrons $^0_{-1}e$ - **positrons (β⁺)** $^0_{+1}e$ (Antimatter) - **pure energy** called **gamma (γ) rays** $^0_0γ$ ## Alpha Particles An alpha (α) particle: - is identical to a helium nucleus - has 2 protons and 2 neutrons - has a mass number of 4 - has a charge of 2+ - has a low energy compared to other radiation particles Alpha particle $^4_2He$ or α 2-4 cm from source ## Beta Particles A beta (β) particle: - is a high-energy electron - has a mass number of 0 and a charge of 1- - forms in an unstable nucleus when a neutron changes into a proton and an electron Beta particle $^0_{-1}e$ or β ## Positrons A positron (β⁺): - has a mass number of 0 and a charge of 1+ - forms in an unstable nucleus when a proton changes into a neutron and a position Positrone $^0_{+1}e$ or β+ ## Gamma Rays A gamma ray: - is high-energy radiation - has a mass number of 0 and a charge of 0 - is a form of energy emitted from an unstable nucleus to give a more stable, lower-energy nucleus Gamma ray $^0_0γ$ or γ ## Some Forms of Radiation | Type of Radiation | Symbol | Mass Number | Charge | |---|---|---|---| | Alpha Particle | $^4_2He$ α | 4 | 2+ | | Beta Particle | $^0_{-1}e$ β | 0 | 1- | | Positron | $^0_{+1}e$ β⁺ | 0 | 1+ | | Gamma Ray | $^0_0γ$ γ | 0 | 0 | | Proton | $^1_1H$ p | 1 | 1+ | | Neutron | $^1_0n$ n | 1 | 0 | ## Biological Effects of Radiation Ionizing radiation strikes molecules in its path. - It damages the cells most sensitive to radiation: rapidly dividing cells in bone marrow, skin, and reproductive organs, and cancer cells. - Cancer cells are highly sensitive to radiation; large doses of radiation are used to destroy them. - The normal tissue around cancer cells divides at a slower rate and suffers less damage from radiation. - Radiation may cause malignant tumors, leukemia, anemia, and genetic mutations. ## Radiation Protection Radiation protection requires: - paper and clothing for alpha particles - a lab coat or gloves for beta particles - a lead shield or thick concrete wall for gamma rays - limiting the amount of time spent near a radioactive source - increasing the distance from the source ## Nuclear Reactions Nuclear equations use atomic symbols to show the changes in nuclear reactions. **Learning Goal:** Write a balanced nuclear equation for radioactive decay, showing mass numbers and atomic numbers. $ ^{238}_{92}U$ → $ ^{234}_{90}Th$ + $^4_2He$ ## Radioactive Decay A process called radioactive decay: - an unstable nucleus spontaneously breaks down by emitting radiation - is described by writing a nuclear equation Radioactive nucleus → new nucleus + radiation (α, β,β⁺, γ) ## Nuclear Equations **Core Chemistry Skill: Writing Nuclear Equations** In a balanced nuclear equation: - the sum of the mass numbers on each side of the equation must be the same - the sum of the atomic numbers on each side of the equation must be the same Mass number sum: 251 = 251 $ ^{251}_{98}Cf$ → $ ^{247}_{96}Cm$ + $^4_2He$ Atomic number sum: 98 = 98 ## Alpha Decay $^4_2He$ When a radioactive nucleus emits an alpha particle, a new nucleus forms with a mass number that is decreased by 4 and an atomic number that is decreased by 2. ## Writing an Equation for Alpha Decay **Example:** Write the balanced nuclear equation for the alpha decay of Americium-241, used in smoke detectors. $ ^{241}_{95}Am$ → ___ + $^4_2He$ **Step 1** Write the incomplete nuclear equation. $ ^{241}_{95}Am$ → ___ + $^4_2He$ **Step 2** Determine the missing mass number. 241 = ? + 4 241 - 4 = ? 241-4 = 237 (mass number of new nucleus) **Step 3** Determine the missing atomic number. 95 = ? + 2 95 - 2 = ? 95 - 2 = 93 (atomic number of new nucleus) **Step 4** Determine the symbol of the new nucleus. On the periodic table, the element that has atomic number 93 is neptunium, Np. The atomic symbol for this isotope of Np is written $ ^{237}_{93}Np$. **Step 5** Complete the nuclear equation. $ ^{241}_{95}Am$ → $ ^{237}_{93}Np$ + $^4_2He$ ## Beta Decay A beta particle is an electron emitted from the nucleus when a neutron in the nucleus breaks down to form a proton and a beta particle, increasing the atomic number by 1. ## Writing an Equation for Beta Decay **Example:** Write the balanced nuclear equation for the beta decay of yttrium-90, used in cancer treatment and as a colloidal injection into large joints to relieve the pain caused by arthritis. $ ^{90}_{39}Y$ → $ ^{90}_{40}Zr$ + $^0_{-1}e$ **Step 1** Write the incomplete nuclear equation. $ ^{90}_{39}Y$ → ___ + $^0_{-1}e$ **Step 2** Determine the missing mass number. 90 = ? + 0 90 - 0 = ? 90-0 = 90 (mass number of new nucleus) **Step 3** Determine the missing atomic number. 39 = ? - 1 39 + 1 = ? 39+1 = 40 (atomic number of new nucleus) **Step 4** Determine the symbol of the new nucleus. On the periodic table, the element that has atomic number 40 is zirconium (Zr). The atomic symbol for this isotope of Zr is written $ ^{90}_{40}Zr$. **Step 5** Complete the nuclear equation. $ ^{90}_{39}Y$ → $ ^{90}_{40}Zr$ + $^0_{-1}e$ ## Positron Emission $^0_{+1}e$ In positron emission: - a proton is converted to a neutron and a positron - the mass number of the new nucleus is the same, but the atomic number decreases by 1 ## Gamma Emission $^0_0γ$ In gamma emission: - energy is emitted from an unstable nucleus, indicated by the symbol m following the mass number - the mass number and the atomic number of the new nucleus are the same $ ^{99m}_{43}Tc$ → $ ^{99}_{43}Tc$ + $^0_0γ$ ## Summary of Radiation Types | Radiation Source | Radiation | New Nucleus | |---|---|---| | Alpha emitter | $^4_2He$ | New element <br> Mass number - 4 <br> Atomic number - 2 | | Beta emitter | $^0_{-1}e$ | New element <br> Mass number same <br> Atomic number + 1 | | Positron emitter | $^0_{+1}e$ | New element <br> Mass number same <br> Atomic number - 1| | Gamma emitter | $^0_0γ$ | Stable nucleus of the same element <br> Mass number same <br> Atomic number same | ## 5.3 Radiation Measurement **Learning Goal**: Describe the detection and measurement of radiation. ## Geiger Counter A Geiger counter is a common instrument that: - detects beta and gamma radiation - uses ions produced by radiation to create an electrical current ## Units for Measuring Radiation Units for measuring radiation activity include the following: - **curie (Ci)**—the number of disintegrations that occurs in 1 s for 1 g of radium, equal to 3.7 × 10¹º disintegrations/s - **becquerel (Bq)**—the SI unit of radiation activity, which is 1 disintegration/s - **rad (radiation absorbed dose)**—measures the amount of radiation absorbed by a gram of material such as body tissues. - **rem (radiation equivalent in humans)—**measures biological effects of different kinds of radiation. ## Measuring Radiation Damage The rem (radiation equivalent in humans) measures: - **alpha particles,** which do not penetrate the skin; however, if they enter the body, extensive damage may occur in tissues - **high-energy radiation**, which causes more damage than alpha particles and includes beta particles, high-energy protons, and neutrons that travel into tissue - **gamma rays**, which are damaging because they travel a long way through body tissue ## Dosimeters Measure Radiation Exposure People who work in radiation laboratories wear dosimeters attached to their clothing. Dosimeters detect the amount of radiation exposure from the following: - X-rays - Gamma rays - Beta particles ## Radiation Exposure The average person in the United States is exposed to 3.6 mSv of radiation annually. Exposure to radiation occurs every day from naturally occurring radioisotopes in: - buildings where we live and work - food and water - the air we breathe Sources of naturally occurring isotopes include the following: - potassium-40 in potassium-containing foods - cosmic radiation from the Sun Medical sources of radiation include X-rays and mammograms. | Source | Dose (mSv) | |---|---| | **Natural** | | Ground | 0.2 | | Air, water, food | 0.3 | | Cosmic rays | 0.4 | | Wood, concrete, brick | 0.5 | | **Medical** | | Chest X-ray | 0.2 | | Dental X-ray | 0.2 | | Mammogram | 0.4 | | Hip X-ray | 0.6 | | Lumbar spine X-ray | 0.7 | | Upper gastrointestinal tract X-ray | 2 | | **Other** | | Nuclear power plants | 0.001 | | Television | 0.2 | | Air travel | 0.1 | | Radon | 2* | *Varies widely ## Radiation Sickness Exposure to radiation: - of less than 0.25 Sv usually cannot be detected. - whole body exposure of 1 Sv produces a temporary decrease in the number of white cells. - of greater than 1 Sv may induce radiation sickness, causing nausea, vomiting, fatigue, and reduced white-cell counts. Exposure to radiation of 5 Sv is expected to cause death in 50% of the people receiving that dose. Often the measurement for an equivalent dose will be in millirems (mrem) - 1 rem = 1000 mrem - The SI unit is the sievert (Sv). - 1 Sv = 100 rem | Measurement | Common Unit | SI Unit | Relationship | |---|---|---|---| | Activity | curie (Ci) | becquerel (Bq) | 1 Ci = 3.7 × 10¹⁰ disintegrations/s | | Absorbed Dose | Rad | gray (Gy) | 1 Gy = 100 rad | | Biological Damage | rem | sievert (Sv) | 1 Sv = 100 rem | ## Lethal Doses of Radiation The larger the dose of radiation received at one time, the greater the effect on the body. Exposure to radiation of 5 Sv is expected to cause death in 50% of the people receiving the dose. This amount or radiation to the whole body is called the **lethal dose** for one-half the population, or **LD₅₀**. | Life From | LD₅₀ (Sv) | | ---|---| | Insect | 1000 | | Bacterium | 500 | | Rat | 8 | | Human | 5 | | Dog | 3 | ## Half-Life of a Radioisotope The **half-life** of a radioisotope is the time for the radiation level (activity) to decrease (decay) to one-half of its original value. ## Half-Lives of Radioisotopes | Element | Radioisotope | Half-Life | Type of Radiation | |---|---|---|---| |*Naturally Occurring Radioisotopes*| | Carbon-14 | $ ^{14}_{6}C$ | 5730 yr | Beta | | Potassium-40 | $ ^{40}_{19}K$ | 1.3 × 10⁹ yr | Beta, gamma | | Radium-226 | $ ^{226}_{88}Ra$ | 1600 yr | Alpha | | Strontium-90 | $ ^{90}_{38}Sr$ | 38.1 yr | Alpha| | Uranium-238 | $ ^{238}_{92}U$ | 4.5 × 10⁹ yr | Alpha | |*Some Medical Radioisotopes*| | Carbon-11 | $ ^{11}_{6}C$ | 20 min | Positron | | Chromium-51 | $ ^{51}_{24}Cr$ | 28 days | Gamma | | Iodine-131 | $ ^{131}_{53}I$ | 8.0 days | Gamma | | Oxygen-15 | $ ^{15}_{8}O$ | 2.0 min | Positron | | Iron-59 | $ ^{59}_{26}Fe$ | 44 days | Beta, gamma | | Radon-222 | $ ^{222}_{86}Rn$ | 3.8 days | Alpha | | Technetium-99m | $ ^{99m}_{43}Tc$ | 6.0 h | Beta, gamma | ## 5.5 Medical Applications Using Radioactivity Different radioisotopes are used to diagnose and treat a number of diseases. | Isotope | Half-Life | Radiation | Medical Application | |---|---|---|---| | Au-198 | 2.7 days | Beta | Liver imaging; treatment of abdominal carcinoma| | Ce-141 | 32.5 days | Beta | Gastrointestinal tract diagnosis; measuring blood flow to the heart. | | Cs-131, Pb-103, prostate | | | | | | | | Isotope | Half-Life | Radiation | Medical Application | | --- | --- | --- | --- | | Ir-192 | 74 days | Gamma | Treatment of breast and prostate cancer | | P-32 | 14.3 days | Beta | Treatment of leukemia, excess red blood cells, and pancreatic cancer | | Pd-103 | 17 days | Gamma | Prostate brachytherapy | | Sm-153 | 46 h | Beta | Treatment of bone cancer | | Sr-85 | 65 days | Gamma | Detection of bone lesions; brain scans | | Tc-99m | 6.0 h | Gamma | Imaging of skeleton and heart muscle, brain, liver, heart, lungs, bone, spleen, kidney, and thyroid; most widely used radioisotope in nuclear medicine | | Xe-133 | 5.2 days | Beta | Pulmonary function diagnosis | | Y-90 | 2.7 days | Beta | Treatment of liver cancer |