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

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

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

Device for the image production

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

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 misrepairs of the dna induction of mutations, chromosome aberrations, or cell death

Tolerance dose for each organ

Radiation safety

RSNA 2013: Understanding the Importance of Dose Evaluation and Reporting

As Low As Reasonably Achievable 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 areas 2) 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)

Shielding???

Personal shielding

Structure shielding

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

Thank you for your attention