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Principle of radiation. Suppat ittimakin , md. Radiation. What is the radiation? Production of radiation effect of radiation Radiation protection. radiation. emission or transmission of energy in the form of wave or particle through space or through a material medium
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Principle of radiation Suppat ittimakin, md.
Radiation • What is the radiation? • Production of radiation • effect of radiation • Radiation protection
radiation • emission or transmission of energy in the form of wave or particle through space or through a material medium • Light, heat and sound are also types of radiation • Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particle • Ionizing radiation carries more than 10 ev enough to ionize atoms and molecule and break chemical bonds
X-ray • A form of electromagnetic radiation • Discovered by Wilhelm Conrad Röntgen
Production of x-ray • Bremsstrahlung • This is radiation given off by the electrons as they are scattered by the strong electric field near the high-Z(proton number) nuclei • Continuous spectrum • Intensity of the x-ray increases linearly with decreasing frequency, from zero at the energy of the incident electrons, the voltage on the x-ray tube
Production of x-ray • When a fast moving electron collides with a K-shell electron, the electron in the K-shell is ejected (provided the energy of incident electron is greater than the binding energy of K-shell electron) leaving behind a 'hole' • This hole is filled by an outer shell electron (from the L-shell, M-shell etc) with an emission of a single X-ray photon, called characteristic radiation, with an energy level equivalent to the energy level difference between the outer and inner shell electron involved in the transition.
Production of x-ray • So the resulting output of a tube consists of a continuous bremsstrahlung spectrum falling off to zero at the tube voltage, plus several spikes at the characteristic lines
X-ray tube cathode anode
Collimator • Two collimators: One collimator is placed between the sample and the analyzing crystal and one is placed between the analyzing crystal and the detector • made of lenses or curved mirrors • narrow the beam of x-ray to a certain area
Analyzing crystal • Crystals consist of a periodic arrangement of atoms or molecules • When parallel x-rays (x-ray photons) strike a pair of parallel lattice planes, every atom within the planes acts as a scattering center and emits a secondary wave
Detector • two main types of detectors are used wavelength dispersive XRF spectrometers: the gas proportional counter and the scintillation counter • Change into images
Effect of the radiation to cells • act directly on the cellular component molecules or indirectly on water molecules • resulting in breakage of chemical bonds or oxidation • Breaking of the DNA • misrepairsof the dna induction of mutations, chromosome aberrations, or cell death
RSNA 2013: Understanding the Importance of Dose Evaluation and Reporting
Radiation safety ALARA As Low As Reasonably Achievable
ALARA • a radiation safety principle for minimizing radiation doses and releases of radioactive materials by employing all reasonable methods • every radiation dose of any magnitude can produce some level of detrimental effects which may be manifested as an increased risk of genetic mutations and cancer
ALARA 1) Awareness of potential radiation hazards, exposure levels and safety controls in their work areas2) Awareness of operating and emergency procedures 3) Awareness of practices that do not seem to follow the ALARA philosophy 4) Compliance with wearing personnel dosimetry and ensuring it’s return to the RSD at the proper exchange frequency
Radiation exposure Factors • Time: The less time you spend exposed to radiation the lower your dose • Distance: Like most other physical phenomena, radiation decreases with distance in accordance with the inverse square law • Shielding:Every shielding material has a "halving thickness." the thickness required to reduce the radiation intensity by half So if the halving thickness of a material is 1 inch, then a 1 inch thick sheet will cut the radiation to 50%. Two inches will cut the radiation to 25%, 3 inches to 12.5%, and so forth.
Radiation exposure Factors (cont) • Traditionally lead is used for shielding because it has a very low halving thickness (0.4 inches)
Radiation with pregnancy • Licensees are required to attempt to prevent pregnant workers from exceeding ~ 55 millirem during any one month. • The desire is to avoid a large dose to the fetus during the 8th to the 15th weeks of the pregnancy as this is the period during which it is most sensitive to potential radiation-induced effects • Thus, it is incumbent upon the pregnant employee to strongly consider officially notifying the Radiation Safety Division as soon as she is aware of her pregnancy.
references • Radiation safety manual; stanford university (revise march 2010) • Brenner DJ, Hall EJ. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007;357:2277–2284 • Radiology ACo. Appropriateness criteria, 2004–2001. American College of Radiology Web site • RSNA 2013: Understanding the Importance of Dose Evaluation and Reporting
