12THREE WAVE PARAMETERS ARE NEEDED TO DESCRIBE ELECTROMAGNETIC RADIATION: VELOCITY, WAVELENGTH, AND FREQUENCY
13Frequency and Wavelength The sine wave model of electromagnetic energy describes variations in the electric and magnetic fields as the photon travels with velocity c. The important properties of this model are frequency, represented by f, and wavelength, represented by the Greek letter lambda (λ).
23PROPERTIES OF X-RAYS HIGHLY PENETRATING, INVISIBLE RAYS ELECTRICALLY NEUTRALPOLYENERGETICLIBERATE MINUTE AMOUNTS OF HEAT ON PASSING THROUGH MATTERTRAVEL ORDINARILY IN STRAIGHT LINESTRAVEL WITH THE SPEED OF LIGHT IN VACUUMIONIZE GASES INDIRECTLYCAUSE FLUORESCENSE OF CERTAIN CRYSTALSCANNOT BE FOCUSED BY LENSAFFECT PHOTOGRAPHIC FILMPRODUCE CHEMICAL AND BIOLOGICAL CHANGESPRODUCE SECONDARY AND SCATTER RADIATION
24RADIATION ATTENUATION IS THE REDUCTION IN INTENSITY RESULTING FROM SCATTERING AND ABSORPTION
25STRUCTURES THAT ABSORB X-RAYS ARE CALLED RADIOPAQUE ????
26STRUCTURES THAT ATTENUATE X-RAYS ARE CALLED RADIOLUCENT ??
27Where:I1=Intensity 1 at D1I2Intensity 2 at D2D1Distance 1 from sourceD2Distance 2 from sourceIn physics, an inverse-square law is any physical law stating that a specified physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity.
28The intensity of ELECTROMAGNETIC RADIATION from a point source (energy per unit of area perpendicular to the source) is inversely proportional to the square of the distance from the source; so an object (of the same size) twice as far away, receives only one-quarter the energy (in the same time period).
29The picture above demonstrates the typical x-ray tube used to produce a point source of x-rays. Then as radiation exits the tube it diverges to cover an increasingly larger area as the distance from the source increases. Notice that area "A" is smaller and the radiation is more concentrated than in an equal area "A1" which is some distance from "A." Each square A1 is the same size as "A" but only 1/4 the number of photons occupies it because of the divergence of the radiation with increasing distance.
32In spite of the advances in radiation protection, such as collimators, cones, and positive beam limiting devices, distance is still the best tool for radiation protection and remains the most common method of protecting personnel, visitors, and adjacent patients from ionizing radiation use. But few persons in the health care environment understand why distance effectively protects them and therefore continuously question, “At what distance am I considered safe? The answer lies in understanding the relationship of ones distance from a source to exposure intensity. The type(s) of radiation one is exposed to as well as its energy content are also factors that affect personal dose. A safe distance can be accurately estimated from the vector of radiation exposure and its initial intensity using the inverse square law. The radiographer should note that this law applies only to a point source of radiation such as the primary beam. Additionally, the inverse square law applies only to electromagnetic radiation (x-rays and gamma rays), and does not apply to particulate ionizing radiation, or scatter radiation which is the major type of occupational radiation exposure personnel should encounter.
35Virtual Lab LinkDemonstrates the inverse square law of light with a lightbulb and detector. The lightbulb's intensity and the detector's distance can be adjusted to see how they affect the reading. There are two bulbs and detectors to allow side-by-side comparisons