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module 7
| Question | Answer |
|---|---|
| Radiation exposure can be minimized by following three principles. | 1)Time 2)Distance 3)Shielding i.e cardinal principles |
| EDE (Effective dose equivalence)limiting system | A system that provides a method for assessing radiation exposure and associated risk of biologic damage to radiation workers and the general public. |
| Occupational exposure | Radiation exposures occurring in the workplace and in the course of an individual's employment. |
| EDE (Effective dose equivalence) limits | The upper boundary dose of ionizing radiation that will result in a negligible risk of bodily injury or genetic damage to the recipient. |
| Whole-body annual total EDE | 50 millisiervets (5000mrem) |
| EDE limit during pregnancy for occupational safety | 5 millisieverts (500mrem) monthly dose should not exceed 0.5millisieverts (50mrem) |
| First dose limit established | 1902, at that time it was 500mSv (50,000mrem)per week or 2500rem per year. |
| Primary radiation | Radiation from the useful beam. Most intense, most hazardous and the hardest to protect from. |
| Secondary radiation | Includes both leakage radiation from the x-ray tubing and scatter radiation. |
| Primary protective barrier | Any wall toward which the primary beam may be directed. It is designed to prevent primary radiation from reaching personnel or other people on the other side of the barrier. |
| Secondary protective barrier | Designed to protect areas from secondary radiation. |
| Primary protective barriers are made out of what? | Concrete, concrete block, or brick. As a general rule 4inch of concrete is equal to 1/16 of an inch of lead sheeting. Minimum height of a primary barrier is 7 feet above the floor of the x-ray room when the x-ray tube is 5 to 7 feet from the wall. |
| General rule of thumb for scatter radiation | the intensity of scatter radiation 1 meter from the patient is 0.1% of the intensity of the useful beam directed at the patient. |
| Leakage radiation rule | Leakage radiation measured at a distance of 1 m (3.3 feet) from the x-ray source must not exceed 100 milliroentgens per hour (2.58 x 10-5 C/kg/hr) when the tube is operated continuously at its highest current for its full potential. |
| What are secondary protective barriers made out of? | Constructed of lead sheets 1/32 of an inch thick, gypsum board, lead glass, or lead acrylic. Walls that are considered secondary protective barriers may be constructed with four layers of 5/8-inch gypsum board. |
| Workload | The radiation-output weighted time when an x-ray generator is actually delivering radiation; specified either in units of mA seconds per week or mA minutes per week. |
| When designing thickness of protection barriers they must consider four factors. | Distance, occupancy, workload and use. |
| Inverse square law | Law stating that the intensity of radiation is inversely proportional to the square of the distance from the radiation source. |
| Relationship between radiation intensity and distance follows the inverse square law | the intensity of the radiation is inversely proportional to the square of the distance from the radiation source. |
| Occupancy factor | A factor used to modify the shielding requirements for a particular barrier by accounting for the percentage of time that the space beyond the barrier is occupied. |
| Use factor | The proportional amount of time during which the x-ray beam is energized or directed toward a particular barrier; also called the beam-direction factor. |
| Lead apron has how much lead protection in it? | lead equivalent thickness from 0.25 to 1 mm. The most widely used apron has a 0.5-mm thickness. |
| Protective drape | A protective barrier used in fluoroscopy; consists of a sliding panel with a minimum of 0.25-mm lead equivalent. Helps with scatter radiation. |
| Bucky slot cover | A protective shield that covers the Bucky slot opening in the side of the x-ray table during a fluoroscopic examination when the Bucky tray is moved to the foot end of the table. |
| Cumulative timer | A radiation protection device used during fluoroscopy that either sounds an alarm or interrupts the x-ray beam after the fluoroscope has been activated for 5 minutes to ensure that the operator is aware of the ON time of the beam. |
| To what type of radiation exposure does the effective dose equivalent (EDE) system apply? | Occupational exposure and exposure of the general public |
| In the design of protective structural shielding, what type of radiation is most hazardous and most difficult to protect against? | Primary Radiation |
| What is the best location for the control panel exposure switch? | Either stationary on the control panel or on a short cord so that it can be used only from within the control booth |
| Why are secondary barriers always given a use factor of 1? | Scatter radiation and leakage radiation are always present when the tube is energized |
| What is the effective dose equivalent for occupants of controlled areas? | Less than 1000 microsieverts (100 mR)/week |
| What are U.S. government standards for dose limits based on? | National Council on Radiation Protection and Measurement (NCRP) recommendations |
| What is the recommended cumulative whole-body EDE limit? | Age in years multiplied by 10 mSv (1000 mrem) |
| What are primary protective barriers? | Those at which the primary beam is directed |
| What is the most common protective barrier material used in primary barriers? | Lead sheets bonded to wood or sheet rock |
| During a mobile radiographic examination, if the factors of distance and shielding are equal, where should the radiologic technologist stand in relation to the primary beam scattering object line? | At a 90-degree angle |
| The cumulative timer is used in fluoroscopy to ensure the radiologic technologist is aware of which of the following? | The total beam on time |
| Quality control of the radiographic equipment is primarily the responsibility of which of the following? | The medical physicist |
| DAP | (Dose area product) is a quantity that reflects not only the dose but also the volume of tissue irridated. |
| Controlled area | An area that is occupied primarily by radiology personnel and patients. Based on the recommended occupational dose limit. |
| Uncontrolled area | Can be occupied by anyone; therefore, the maximum exposure rate allowed is based on the recommended dose limit for the public of 100mrem/yr (1mSv/yr) |
| Resolving time | The minimum time between ionization's that can be detected. |
| Photocathode | A device that emits electrons when illuminated. |
| Photoemission | A process where electrons are emitted from the photocathode. |
| Collector (for scintillation) | Absorbs the electron pulse from the last dynode and conducts it to the preamplifier. |
| Preamplifier (for scintillation) | Provides an initial state of pulse amplification. It is attached to the base of the PM tube, a structure that provides support for the glass envelope and internal structures. |
| The overall result of scintillation detection is.. | That a single photon interaction produces a burst of light; this, in turn, produces photoelectron emission, which then is amplified to produce a relatively large electron pulse. |
| What is TLD | Thermoluminescence Dosimetry. It is the emission of light by a thermally stimulated crystal following irradiation. |
| Types of scintillation phosphors | Many different types of liquids, gases, and solids can respond to ionizing radiation by scintillation. |
| What is the atomic number of lithium fluoride (LiF)? | 8.2 |
| Limit of leakage | Must be no more than 100mR per hour at a distance of 1m from the housing. |
| What are the four types of highly accurate devices that are used for measuring radiation? | Gas-filled detectors (ionization chamber, proportional counter and the Geiger-Muller counter), scintillation detector; used in nuclear medicine, TLD and OSL; used especially for occupational radiation. |
| ICRP | International Commission on Radiological Protection. has recommended a whole-body dose limit of 20 mSv (2000 mrem), and this limit is currently under consideration in the United States. |
| Four pounds per square foot is equal to what? | A sheet of lead 1/16 of an inch thick. |
| Three steps of quality control are the following: | acceptance testing of the equipment upon installation, routine performance evaluation of all equipment, and correction of any problems. |
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volcomgrl12