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Structure of the Atom Nucleus Neutrons + + + Protons Electrons (Electron Clouds)
Radioactivity DefinitionAny spontaneous change in the state of the nucleus accompanied by the release of energy. Major Types alpha ( ) particle emission (decay) beta ( ) particle emission ( -), positron emission ( +) and orbital electron capture (ec) gamma ( ) decay including internal conversion
Ionizing Radiation Definition - Any type of radiation possessing enough energy to eject an electron from an atom, thus producing an ion.Major Types of Ionizing Radiation Alpha, Beta, Gamma Alpha Particle Large Mass (nuclei) – Helium + + Atom with a +2 charge Beta Particle Small Mass - Electron (subatomic particle) Gamma Photon No Mass (Electromagnetic and X-Rays Radiation)
Decay has a discrete energy that can be measured andrelated to the parent. The neutron to proton ratio is tolow ! + 4He Nucleus + Ejected from Nucleus + + + + + +2 + + This is radioactive!! Most of the energy associated with (monoenergetic) 238U 4He + 234Th
Decay Either too many neutrons or too many protons neutrino Change a neutron into a proton take away - charge + - + Electron (negatron) + + + + + + anti-neutrino Change a proton + into a neutron + take away + charge (positron)3 products share energy – therefore beta has a continuous range of energies
Electron Capture X-rayChange proton into neutron X-ray
Decay• Emission of a photon from the nucleus• Most often occurs after or emission when nucleus is left in an excited state• Given off with discrete energies• Can measure photon energy and possibly identify parent + + Gamma Photon + + + + + + + or +2 - neutrino
Radiation Dosimetry Units Exposure, X: amount of charge produced anywhere in air by thecomplete stoppage of all electrons liberated by photons in an incremental volume of air per unit mass of air in that volume.Standard International (SI) unit: Coulomb/kilogram (C/kg)Traditional unit: roentgen ( R ) 1 R = 2.58x10-4 C/kgExposure definition applies only to photons of energy less than or equal to 3 MeV interacting in air.
Radiation Dosimetry Units Absorbed dose: RADis the energy deposited by any type of ionizing radiation in a volume element of mass. SI unit: gray (Gy) Traditional unit: rad 1Gy = 100 radAbsorbed dose definition applies to all forms of ionizing radiation in any material.
Relative Biological Effectiveness and Quality Factor Relative Biological Effectiveness (RBE) ( Biological effect of radiation Y at dose X Biological effect of 250 kVp x-rays at dose X ) Both produce the same biological effect. Quality factor (Q) radiation Q photon, 1 proton, neutron 10 alpha 20
Relative Biological Effectiveness Ln (S) Shoulder of curve indicates cell repair at low doses No shoulder - no cell repair EffectSame Biological Effect Dn DDifferent Dose from 2 types of radiation Dose
Radiation Dosimetry Units Dose Equivalent Dose equivalent: allows the description of the biologicaleffect of an absorbed dose of a particular type of radiation or mixed radiations for the Human Body. Dose Equivalent (DE) in Rem = Dose in Rads x Q SI unit: sievert (Sv) traditional unit: rem 1 Sv = 100 rem millirem For photons: 1 R 1 rad = 1 rem
External Radiation Exposure Definition: Exposure of the body from radiation originating outside of the body Level of Hazard and Control Depend Upon:1. Type of Radiation (Alpha, Beta Gamma)2. Energy of the Radiation (Low or high energy)3. Dose Rate (Low or high dose rate)
Reducing External Radiation Exposure•Time: reduce time spent in radiation area•Distance: stay as far away from the radiation source as possible•Shielding:interpose appropriate materials between the source andthe body
Radioactive WasteWe will discuss - Low Level Radioactive Waste High Level Radioactive Waste Mining Tailings
Radioactive WasteLow Level Radioactive waste consists of microcurie, millicurie and at times curie activity waste.(A Curie is a unit of nuclear transformations. 1 Curie is 3.7 x1010 transformations per second)
Radioactive Waste Low level radioactive liquids are either: – Incinerated – Deep well injected (not as frequent anymore) – Solidified – Sewer Disposed (Regulations allow curie levels of some isotopes to be sewer disposed of if dilution is large enough)
Radioactive Waste Radioactive animal carcasses are either incinerated or buried onsite.
Radioactive Waste Small sealed sources are “Stabilized” in concrete and buried. Stabilized concrete is concrete that is certified to resist wear for a certain time period.
Radioactive Waste Low level contaminated solid wastes are buried. GSU has it’s solid waste “Supercompacted” at 30,000 psi to reduce the volume to be buried
Radioactive WasteMost low level wastes come from Governmentand Utilities. These consist of contaminatedsolids from nuclear reactor usage and weaponconstruction.
Radioactive Waste Colleges, research and medical applications account for less than 25% of the low level Radioactive wastes created
Radioactive Waste Class A low-level radioactive waste is the least hazardous, containing mostly short-lived radionuclides that will be reduced in radioactivity (decay) in a relatively short time. It contains only small amounts of radionuclides that take a relatively short time to decay. Class A waste will be disposed of in concrete canisters that will maintain their shape and strength for hundreds of years.
Radioactive Waste Class B low-level radioactive waste is more hazardous than Class A waste. Most of it comes from nuclear reactors. It must be in a stable form for disposal and will also be disposed of in concrete canisters. Stabilization can be accomplished by solidifying liquid waste, compacting solid waste, or placing the low-level radioactive waste in a container that will be stable for many years. Class B low- level radioactive waste makes up only a small percent of the waste volume generated; but along with Class C waste, it contains the largest portion of the total radioactivity.
Radioactive Waste Class C low-level radioactive waste is the most hazardous and must be handled accordingly. It also must be disposed of in a stable form.
Radioactive Waste The compact system was set up by NRC to have all states share in the responsibility of disposal of radioactive waste and to limit waste transport distance. Georgia is in the Southeast compact. Until 1992, all states within the SE compact (excluding Florida) would host a LLRW landfill on a 20-25 year revolving timetable.
Radioactive Waste Kentucky was the first (Maxie Flats), then South Carolina (Barnwell). In 1995, North Carolina was to open a site but the citizens protested and sued. The State legislature refused. North Carolina was then “kicked out” of the S.E. compact and left with no place to dispose of waste. Other States followed N.C.’s lead and refused This lead to the collapse of the traditional compact system and the
Radioactive WasteIn the past, many Universities andcompanies were allowed to bury theirradioactive wastes onsite. Some wereallowed to deep well inject liquidradioactive waste.
Radioactive Waste N.I.M.B.Y.NotInMyBackYard The true politics of Hazardous Waste
Radioactive WasteDid North Carolina, by not opening up a waste site, better protect it’s citizens?
Radioactive Waste High-Level Radioactive Waste is: the irradiated fuel from the cores of nuclear reactors, the liquid and sludge wastes that are left over after irradiated fuel has been reprocessed (a procedure used to extract uranium and plutonium), the solid that would result from efforts to solidify that liquid and sludge from reprocessing.
Radioactive WasteBecause there is currently no high level radioactive waste disposal facility, HLRW is held On-Site in water pools
Radioactive WasteOnce these Pools are full, Waste is transferred to casks which are also held on-site