CHE 141 1st edition Lecture 38Current LectureNuclear Transmutation: Neutron Bombardment- Nuclear transmutation may also be achieved via neutron bombardment- There is no electrostatic repulsion between neutrons and nuclei to overcome - Neutron capture the addition of a neutron to a nuclide resulting in an increase in isotope number by 1 while retaining the same atomic number- Activation making a radioactive isotope by neutron capture Transuranic Elements- Transuranic elements, elements with atomic number Z>92 greater than the atomic number of uranium- Transuranic elements are not typically found naturally and can only be artificially synthesizedMagic Number- Magic number-nuclides that have 2, 8, 20, 28, 50, 82, or 126 nucleons have a higher than average nuclear binding energy per nucleon and thus are more stable against nuclear decay- Nucleons also have a tendency to pair together thus stable nuclides with even numbers of nucleons are more abundantEffects of Radiation on Life- Nuclear reactions produce ionizing radiation in the from of an alpha particle, beta particle, and gamma ray- X-rays and short-wavelength (therefore high-energy) ultraviolet rays are also forms of ionizing radiationThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- The ionization of atoms and molecules in living tissue can lead to radiation sickness, cancer, birthdefects, and death- Marie Curie and Irene Joliot-Curie died prematurely from radiation-related illnesses- Medical definition of ionizing radiation photons and particles that have sufficient energy to removed an electron from water: H20(l) 1216 kJ mol^-1H20+(aq) + e-- H20+ reacts with another water molecule to form a hydronium ion and a hydroxyl free radical: H20+(aq) + H20(l) H30+(aq) + OH(aq)- Free radical an odd-electron molecule with an unpaired electron in its Lewis structure- Free radicals such as OH react rapidly with biomolecules and can destroy cells.- Human body is composed largely of water- Water molecules are the most abundant ionizable target in an organism exposed to nuclear radiation- Effects of radiation can be divided into three different types:- Acute radiation damage- Increased cancer risk- Genetic defects- Acute radiation damage exposure to large amounts of radiation in a short period of time- Increased cancer risk arises from lower doses of radiation over extended periods of time- Genetic defects may also arise from exposure to radiation- Absorbed dose is the quantity of ionizing radiation absorbed by a unit mass of living tissue- The SI unit of absorbed radiation dose is the grey (Gy)- 1 Gy is 1 joule of radiation energy per kilogram of body mass, 1 J kg^-1 (or 1 J/kg)- Alternative units- 1 rad (radiation absorbed dose) = 0.01 Gy- 1 rad = 0.01 J kg^-1- Grays (or rads) express dosage but do not indicate the amount of tissue damage caused by that dosage- Relative biological effectiveness (RBE) is a factor which accounts for the differences in physical damage caused by ionizing radiation- Effective dose is a measure of the amount of tissue damage caused by ionizing radiation- The SI unit of effective dose is the Sievert (Sv). Effective dose (Sv) = absorbed dose (Gy) x RBE- RBE is unitless so both Gy and Sv are in J kg^-1Radioactivity and Medicine- Radioactivity can be very useful in medicine- Radionuclides are used both in the detection and treatment of diseases- Diagnostic Radiology use of radioactive “tracers” to generate image of organ or tissue (e.g. PET scans)- Therapeutic Radiology use of ionizing radiation to kill cancerous tissue/tumors. Radiation source can be internal or externalMedicine: Diagnosis- We can track the movement and accumulation of radionuclides in the body to assess circulation and organ function- A tiny quantity of radioactive isotope (tracer) is used together with a much larger amount of a stable isotope (carrier)- Radioactive tracers help in the diagnosis of disease- Positron-emission tomography (PET) is used to monitor cell activity in organs such as the brain- Uses short-lived neutron poor (positron emission) nuclide tracers such as 11C, 15), and 18F in a glucose carrier- The rate at which glucose is metabolized in various regions of the brain is monitored by detecting gamma rays produced by positron-electron annihilationsMedicine: Radiotherapy- Ionizing radiation kills cells and causes most damage to cells that grow and divide rapidly- Cancer cells reproduce much faster than normal cells, so radiation is effective at killing them- Radiotherapy uses a source of radiation to kill tumors- External radiation sources such as a beam of gamma rays can be used to treat surgically inaccessible tumors- Unfortunately gamma radiation destroys healthy cells also, thus patients receiving radiation therapy frequently suffer symptoms of radiation sickness- The gamma ray beam is moved in a circular path around the tumor, maximizing the exposure of the tumor while minimizing the exposure of the surrounding healthy tissue- Radiologists must control the dose a patient receives very carefully- Administering the radiation internally can minimize exposure of healthy tissue- Radiation source can be enclosed in a platinum capsule and surgically implanted in a cancerous tumor- Platinum capsule is chemically inert and acts a filter, absorbing alpha and beta particles and allowing gamma rays to pass into the tumor- Chemical properties of a nuclide can be used to direct it to a tumor site (much like with
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