Ionizing Radiation 2

Information about Ionizing Radiation 2

Published on January 4, 2008

Author: Heather

Source: authorstream.com

Content

Ionizing Radiation Fundamentals of Industrial Hygiene by Plog & Quinlan:  Ionizing Radiation Fundamentals of Industrial Hygiene by Plog & Quinlan Toxicology Chapter 10 Sept. 22, 2004 Connie Gaskill Wilhelm Roentgen X-ray 1895 Health & Safety Professional:  Health & Safety Professional General knowledge of: the nature of radiation the detection of radiation Permissible Exposure Limits (PELs) biological effects of radiation monitoring techniques, procedures and control measures pp.257 Facility Personnel:  Facility Personnel Need to be properly advised of radiation hazards and safe procedures pp. 257 Types of Ionizing Radiation:  Types of Ionizing Radiation Alpha-Particles Beta-Particles Neutrons X-Radiation Gamma-Radiation Light- form of radiation we can see Infrared-form of radiation we can feel as heat Radio and TV wave-forms of radiation we can neither see nor feel pp,261 Alpha-Particles α:  Alpha-Particles α Originates in the nuclei of radioactive atoms during disintegration 2 protons and 2 neutrons (mass #of 4) structurally the same as the nucleus of a helium atom α-particle emission changes an atom to one having an atomic number lowered by 2 and an atomic mass lowered by 4 Upon slowing down, combine with electrons from the material they are passing, and thus become helium atoms. pp.261 Alpha-Particles α:  Alpha-Particles α Positive charge of 2 units Interact electrically with human tissues and other matter Range in energy to over 7 MeV. Travel only a short distance: 4 in. (10cm) in air Stopped by the dead, outer layer of the skin, a film of water, a sheet of paper, or other paper thin material pp.261 Alpha-Particles α:  Alpha-Particles α Produced by elements with high atomic numbers Internal radiation hazard Chemically similar to calcium in their action within the body Damages tissue by emitting alpha-particles as they disintegrate Other alpha-particles concentrate in body organs such as the kidney, liver, lungs, and spleen pp.261 Alpha Decay:  Alpha Decay Beta-Particles β:  Beta-Particles β Electrically charged particles ejected from the nuclei of radioactive atoms during disintegration Generally have a negative electrical charge of 1 unit and the same mass as electron Negative beta-particle emission causes the disintegrating atom to change into an element of a higher atomic number pp.262 Beta-Particles β:  Beta-Particles β Internal radiation hazards when taken into the body Maximum range in wood is about 1.5 in (4cm) Can penetrate the human body to a depth of 0.1-0.5 in (0.2-1.3cm) Skin burns from extremely high doses of beta-radiation (requires only about 70keV of energy for a beta-particle to penetrate the outer layer of skin pp.262 Beta-Particles β:  Beta-Particles β Nucleotide specific Broad distribution of energies ranging from near zero up to the maximum value specific for the particular radionuclide. Maximum range for one may be 6 inches (15cm) Maximum range for another may be 60 feet (18m) The higher energy beta-particles penetrate farther, transfer more energy, and cause more damage pp.262 Beta-Particles β:  Beta-Particles β Emitted from a wide range of light and heavy radioactive elements Some have a velocity approaching the velocity of light Relatively more hazardous externally than alpha-particles because their penetration power is greater Shielding by aluminum (light metal), plexiglasTm, walls of a room pp.262 Beta Decay:  Beta Decay Neutrons (1930):  Neutrons (1930) No electrical charge exists within the nuclei of all atoms except those of the lightest isotope of hydrogen Released on disintegration of certain radioactive materials (fissionable isotopes) Short and long ranges dependent on: method by which a particular neutron was produced material through which they pass interactions with atoms from the material from which they pass type of collisions that occur pp.263 Neutrons:  Neutrons Average depth of penetration in human tissue is about 0.25 in (0.6cm) to several inches In the human body, most of the captures that occur take place in hydrogen or nitrogen atoms With the nucleus in an excited state, the atom returns to the ground state by releasing a proton, gamma-ray, beta-particles, or alpha-particles these secondary emissions produce the damage in tissue pp.263 Neutrons:  Neutrons Exposure occurs around reactors, accelerators, and sources designed to produce neutrons the task of determining the neutron dose is difficult The amount of harm caused by a dose is dependent not only on the number of neutrons absorbed but also on their energy distribution pp.263 X-Radiation:  X-Radiation Produced in the orbiting electron portion of the atom or from free electrons Machine produced, outside of the nucleus The voltage across the electrodes of the vacuum tube determines the energy of the electrons which determines the wavelength and penetrating quality of the resulting x-rays The energy of an x-ray is inversely proportional to its wavelength; the more energy- the shorter the wavelength pp.263 X-Radiation:  X-Radiation Hard, short wavelengths penetrate several centimeters of steel Soft, long wavelengths are less penetrating Both of these expressed in half-value layer (the thickness of material necessary to reduce the incident radiation by one-half pp.263 Gamma-Radiation:  Gamma-Radiation Produced in the nucleus emitted spontaneously from radioactive materials Identical to X-radiation except for its source being the nucleus of an atom Energy specific to radionucleotide Wide range of wavelengths or energies External exposure problem due to deep penetration half value shielding for 1.0MeV gamma radiation is slightly more than 0.5in (1.3cm) of steel pp.263 Gamma Emission:  Gamma Emission Radioactive Decay Calculations:  Radioactive Decay Calculations pp.264 Biological Effects of Radiation:  Biological Effects of Radiation Human body can tolerate a certain amount of exposure from natural sources (background radiation) average annual background dose is around 300mR/y External radiation presents differently than internal radiation once inside, the radionuclides are absorbed, metabolized, and distributed throughout the tissues and organs according to the chemical properties pp.264 Biological Effects of Radiation:  Biological Effects of Radiation Effects of irradiation are studied looking for effects on the living cells changes in biochemical reactions evidence of production of disease changes in life or normal growth patterns pp.264 Types of Injuries:  Types of Injuries Somatic injuries to individuals Genetic injuries passed on to future generations Degree of injury Total dose rate at which the dose is received kind of radiation body part receiving it pp.265 Types of Injuries:  Types of Injuries Skin redness, dermatitis, hair loss, eye inflammation, cancer and blood diseases Bone damage, cataracts, skin, lung, and other cancers, shorter life span Human reproductive systems (transmitted to succeeding generations) pp.265 Relating Dosage to Damage:  Relating Dosage to Damage The maximum permissible levels denote the maximum radiation dose that can be tolerated with little chance of later development of adverse effects The BEIR V report from the National Academy of Sciences gives information on biological effects of ionizing radiation pp.266 Standards and Guides:  Standards and Guides NCRP-National Council on Radiation Protection and Measurements Maximum permissible levels of external and internal radiation Nuclear Regulatory Commission establishes “Permissible Doses, Levels, and Concentrations” in 10 CFR 20. ICRP-International Commission on Radiological Protection and Measurements 2000 Threshold Limit Value® Acceptable practice is to keep the exposure as low as reasonably achievable (ALARA) 18 and under limited to educational and training purposes and should be less than 0.1 rem per year pp. 267 Monitoring Instruments:  Monitoring Instruments Variety of detectors and readout devices None is universally applicable Selection of most appropriate detector or detectors for each radiation measurement Measurement of radiation fields in the vicinity of a radiation source Measurement of surface contamination Airborne radioactivity pp. 268 Film Badges:  Film Badges Worn on outer clothing Gamma-, x-ray, and high energy beta-radiation Small piece of photographic film with silver atoms wrapped in an opaque cover and supported with a metal backing. Pinned to clothing or worn as a ring Amount of darkening compared to a control film pp.268 Film Badges:  Film Badges Thermoluminescence Detectors:  Thermoluminescence Detectors TLDs widespread use gamma-, x-ray, and beta-radiation worn as body badges or finger rings small chips of lithium fluoride Stored energy released on readout-readings cannot be repeated. Includes 2 or more chips in a dosimeter pp. 268 Thermoluminescence Detectors:  Thermoluminescence Detectors Pocket Dosimeters:  Pocket Dosimeters Direct-reading portable unit shaped like a pen with a pocket clip. Use to measure x-ray, and gamma-radiation may respond to beta-radiation contains a quartz fiber, a scale, a lens to observe the movement of the fiber across the scale, and an ionization chamber Allows the determine the radiation dose while working rather than waiting until after periodic processing pp. 269 Pocket Dosimeters:  Pocket Dosimeters Electronic Alarm Dosimeters:  Electronic Alarm Dosimeters Monitors x-ray, and gamma-radiation usually Geiger-Mueller tubes with an automatic audible alarm if significant exposure rates are encountered or at a preset total integrated exposure digital readouts compact lightweight similar to a pager pp. 269 Electronic Alarm Dosimeters:  Electronic Alarm Dosimeters Ionization Chambers:  Ionization Chambers Measure the ionization in a small volume of air. 2 plates or electrodes with an electrical potential between them placed in a container filled with air Measures ionization directly and is energy independent. Can measure gamma-, x-ray, beta-, and if a thin enough window, alpha-radiation pp. 269 Ionization Chambers:  Ionization Chambers Geiger-Mueller Counters:  Geiger-Mueller Counters Used for beta-, gamma-, and x-radiation survey measurements capable of detecting very small amounts of radiation especially sensitive to vet-radiation Uses an ionization chamber filled with a special gas and has a greater voltage supplied between its electrodes. Does not give a uniform response for different radiation energy levels Accurate only or the type of radiation for which it is calibrated pp. 269 Geiger-Mueller Counters:  Geiger-Mueller Counters Other Monitoring Instruments:  Other Monitoring Instruments Scintillator designed to measure light flashes created by the interaction of ionizing radiation and scintillator materials useful for sensitive measurements of alpha- and beta-gamma-radiation pp. 270 Liquid scintillation counter :  Liquid scintillation counter Calibration:  Calibration Calibration of radiation meters is a laboratory procedure carried out by qualified experts Possible and permissible to calibrate meters by comparing a radiation-measuring instrument with a standard radiation source of known output Up to date manuals Familiarity with regulations pp. 270 Basic Safety Factors:  Basic Safety Factors External radiation exposure hazards Basic protection measure associated with: time distance shielding pp. 271 Time:  Time Direct relationship between exposure dose and duration of exposure, reducing the exposure time by one-half reduces the dose received by one-half. Knowledge of dose rate and the aximum dose acceptable exposure time can be calculated. Dose received spread over several employees Minimum necessary exposure should be planned for a work task pp. 271 Distance:  Distance INVERSE SQUARE LAW external penetration radiation exposure with change in distance from source doubling the distance from the source decreases the exposure to 1/4 of the original amount From 2 - 20 m, exposure decreased to (2/20)2 or 1% of the original amount pp.271 Safe Distance:  Safe Distance Distance non-operating workers must maintain from the radiation source in order to receive no more exposure than that specified in the NCRP Radiation Protection Guides, even if personnel were to remain at that distance continually. Ropes/barricades used for nonoperating workers or bystanders. Magenta on Yellow-standard radiation symbol pp272 Sheilding:  Sheilding Neutrons-stopped most effectively by light nuclei (Hydrogen atoms most effective). Water, materials rich in hydrogen content and carbon atoms make good shields Gamma-emitters-cladding, heavy walls and covers on containers, cells with thick, high density-concrete walls Gamma radiation-deep layer of water Cobalt-60 emit more than one gamma each with different energies pp. 272 Control Programs:  Control Programs Safe working procedures, detect and measure radiation, make surveys, concern with decontamination and disposal, laboratory and other special services, and record keeping. Erection of barriers and warning signs, attendants at restricted localities, closing off of the area Establish safe exposure times Decontamination before leaving work pp. 274 Sources of Radiation:  Sources of Radiation Consider the amount and kind of radiation sources used in a contemplated operation Classify the lab or work area required for radioactive materials of differing toxicity Radionuclides often used: radiation measurements discloses useful information. Pp.275 Sealed Sources:  Sealed Sources Keeping external exposures under control alarms interlocks strict control access thorough monitoring keeping track of presence and condition Operate the source so that other persons are not accidentally irradiated pp. 276 Radiation-Producing Machines:  Radiation-Producing Machines Portable/Non-portable X-ray machines Accelerators pp. 276 Radioisotopes:  Radioisotopes Wide range of hazards depending on quantities and types as well as kinds of operations being performed. IAEA- International Atomic Energy Agency’s publication, Safe Handling of Radionuclides (capable of spontaneously emitting radiation. Explains the hazard classification for unsealed radioactive sources. Pp. 276 Radioactive Metals:  Radioactive Metals Normal uranium or an alloy safely handled without personal protection for a few hours/week SMART? Safe Handling Practices, gloves, metal cladding or a paint-type surface coating, respiratory protection OTHERS? Must be handled remote control, ventilated enclosure, exhaust filters pp. 322 Criticality:  Criticality Fissioning, or breaking apart of nuclei with emission of neutrons at a rate faster than neutrons are absorbed or lost from the system Instantaneous bust of neutrons with high level gamma-radiation Uranium-235 Plutonium-239 Fatalities Severe radiation exposure-even at considerable distances pp.277 Plutonium:  Plutonium Highly hazardous alpha-emitter MUST be handled under rigidly controlled conditions Glove boxes (dry boxes) carefully designed and expensive Maintained at a negative pressure May necessitate an inert atmosphere such as argon or nitrogen to avoid fires. Pyrophoric under certain conditions Plutonium-239 is fissionable-critical with sufficient amounts present Filtered by 2 or more HEPA filters in series Alarms pp. 278 Operational Factors:  Operational Factors Area involved Number of employees exposed and where Chemical/Physical states of the radioactive material and the nature of its use Possible incident occurrence and possible locations Other hazards involved Nature of possible exposure: Controlled/Accidental Inherent danger of the material from internal/external effect on humans Probability of detection Current conditions Possible effects on operations pp. 278 Employee Exposure Potential:  Employee Exposure Potential No more difficult to prevent than more common types of industrial accidents Important that the appropriate monitoring instruments be available and properly maintained and calibrated pp. 279 External Hazards:  External Hazards Determined by continuos monitoring, dosimeters, or previous measurements limiting the rate of exposure limiting the length of exposure time High exposure levels- rotate personnel to prevent above guide level exposure NCRP Report No. 116 Limitation of Exposure to Ionizing Radiation Once in a lifetime allowances for handling an extremely serious situations. pp. 279 Internal Hazards:  Internal Hazards Inhalation is the most frequent route of entry of radioactive material into the body. Routine/Constant air sampling Hand and foot monitoring Broken skin less common route of entry into the body Can be more serious than entry through the lungs Recognize potential hazardous conditions Tertiated water vapor rapidly absorbed through unbroken skin pp.279 Pp.279 Sources of Information:  Sources of Information Fundamentals of Industrial Hygiene 5th Edition Barbara A. Plog Patricia J. Quinlan

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