Transcript Slide 1
RADIATION TERMS AND UNITS DOSE The energy imparted to matter by ionizing radiation per unit mass of irradiated material. The unit of absorbed dose is the rad. DOSE EQUIVALENT: The quantity used by regulatory agencies related to risk of biological damage to radiation workers from ionizing radiation. This quantity generally pertains to external exposure. It is the product of the absorbed dose in tissue and all other necessary factors at the location of interest. The unit of dose equivalent is the rem. 1000 mrem = one rem BACKGROUND RADIATION: Natural and Man-Made Sources Average Annual Dose from Background Radiation= 300 mrem/year RADIATION PROTECTION GUIDES (RPG’s): Occupational Exposure Limits Whole Body Exposure Limit for Radiation Workers: Individual Organ Limit for Radiation Workers: 5 rem/year 50 rem/year Declared Pregnant Radiation Worker: 0.5 rem/term of pregnancy NRC: Regulatory Guide 8.13 - Instruction Concerning Prenatal Radiation Exposure Unrestricted Area Limits For the General Public (non-users): 2 mrem/hour 100 mrem/year Radiation Protection Guides are not easily applied to the use of analytical x-ray equipment. Personal radiation monitoring badges are small and could easily miss detecting the very narrow radiation beam produced by the equipment. The University of Connecticut places area monitoring badges on cabinettype, and other inherently safe, analytical x-ray equipment to detect any change in the area exposure rates. X-ray equipment users who utilize units other than the cabinet units may be issued a personal monitoring badge. If the University of Connecticut’s Radiation Safety Officer provides dosimetry to a worker, it shall be worn by the operator during x-ray equipment use and stored in an appropriate location in the laboratory when not in use. s ow s is easonably chievable The University of Connecticut is committed to keeping exposures to radiation ALARA (As Low As is Reasonably Achievable). This means that every reasonable effort shall be made to maintain radiation exposures as far below the dose limits as practical, taking into account the state of the technology, the economics of the improvements in relation to the benefits, and other socioeconomic considerations. Each worker shall keep radiation exposures to themselves and others ALARA UConn ALARA Goals: Ten percent of RPG’s Whole body: 0.5 rem/year or 500 mrem/year Individual Organs: 5 rem/year TYPICAL ANALYTICAL X-RAY BEAM RADIATION INTENSITY Location Dose Rate Primary Beam at X-ray Tube Port Several Thousand rads/second Primary X-ray Beam at End of 10cm Collimator Several Thousand rads/minute Scattered Radiation <1millirad/hour – Several Hundred millirad/hour (depending on distance from sample) ANALYTICAL X-RAY BEAM HAZARDS The principal hazard from analytical x-ray equipment is a localized skin burn from direct exposure to the primary x-ray beam caused by insertion of the fingers into the primary beam. A localized radiation burn could occur within 1-2 seconds of contact with the primary beam. Symptoms of a localized radiation burn could take up to several weeks to manifest, depending on the dose. Extreme cases include amputation of fingers. Leakage of the primary beam through voids or the tube housing has the potential to result in an exposure exceeding regulatory limits. Scattered radiation or secondary photons from samples or other irradiated material can also cause exposures. Diffracted x-rays or x-rays from rectifiers in the high voltage supply can be easily shielded. RADIATION BURNS FROM HIGH INTENSITY X-RAY BEAMS Type of Tissue Damage Dose Required (rads) Perceptible Reddening of Skin (Erythema) 300 Dry Desquamation of Skin 1000 Wet Desquamation and Blistering 1500 Ulceration and Necrosis of Skin or Flesh 3000 Source: ANSI/HPS N43.2-2001 X-RAY BURN PHOTOGRAPHS Image copyrighted by Radiology Centennial, Inc. X-rays burns can produce acute radiodermatitis. Photo obtained from http://www.cdc.gov/niosh RADIATION PROTECTION-EXTERNAL SOURCES Time: Minimize time near radiation source Distance: inverse square law Radiation levels decrease by the Shielding: Thin sheet of lead RADIATION LEVELS The local components of an analytical x-ray system shall be located and arranged and shall include sufficient shielding or access control to preclude an overexposure. No radiation levels should exist around the local component area which could result in an individual in close proximity receiving a dose in excess of the limits specified in applicable University of Connecticut, state, and/or federal regulations. For systems utilizing x-ray tubes, these levels shall be met at any specified tube rating. A local component is defined as part of an analytical x-ray system, and includes areas that are struck by x-rays during operation. Examples of such components include radiation source housings, port and shutter assemblies, collimators, sample holders, cameras, detectors, and shielding, but do not include power supplies, transformers, amplifiers, readout devices, and control panels. Thickness of Lead (mm) Required for a Primary Beam Barrier Located 5 cm from Focal Spot HIGH VOLTAGE (kVp) ANODE CURRENT (mA) 50 kVp 70 kVp 100 kVp 20 1.5 5.6 7.7 1.6 5.8 7.9 1.6 5.9 ---- 1.7 ---- ---- 40 80 160 Source: ANSI/HPS N43.2-2001 RADIATION SURVEYS The Radiation Safety staff shall perform radiation surveys of all analytical x-ray systems sufficient to demonstrate compliance: a. a. Upon installation of the equipment, and at least once every 12 months thereafter. Annual radiation measurements shall not be required if the Radiation Safety staff can demonstrate compliance with applicable state and/or federal regulations; b. Following any change in the initial arrangement, number, or type of local components in the system; c. Following any maintenance requiring the disassembly or removal of a local component in the system; d. During the performance of maintenance or alignment procedures if the procedures require the presence of a primary x-ray beam when any local component in the system is disassembled or removed; e. Any time a visual inspection of the local components in the system reveals an abnormal condition; and f. Whenever a personnel monitoring device shows a significant increase over the previous monitoring period or the readings are approaching the limits specified in applicable University of Connecticut, state, and/or federal regulations. Radiation Safety staff shall be notified immediately when the designated laboratory supervisor of analytical x-ray equipment becomes aware of any of the above conditions. The equipment shall not be utilized until Radiation Safety demonstrates compliance with University regulations.