Secondary radiation and the dentist

Abstract

Secondary radiation is produced when­ ever a body of matter is exposed to roentgen-ray radiation. Most of the secondary radiation present in a dental office origi­ nates at the face of the patient; however, the air, the dental equipment and any­ thing else lying in the path of the use­ ful beam of roentgen rays will also emit secondary radiation. Secondary radia­ tion scatters in all directions from its place of origin while the x-ray machine is operating, and ceases when the expo­ sure is terminated. For purposes of clarity, the following definitions of symbols are included: 1. The unit of quantity of roentgenray radiation is the “roentgen,” desig­ nated by the symbol “r.” 2. The unit of electrical pressure ap­ plied to an x-ray tube is the “peak kilo­ volt” designated by the symbol “kvp.” 3. The unit of quantity of electrical current passing through an x-ray tube is the “milliampere,” designated by the symbol, “ma.” 4. The unit of daily usage of an x-ray , • , “ma. sec.” . . machine is the -----:--------. This unit is day the product of the number of milliamperes of current flowing through an x-ray tube and the number of seconds that the machine is operated per day. The National Committee on Radiation Protection1'3 has issued recently revised recommendations relative to permissible radiation exposures of persons who are occupationally exposed to radiation. The net effect of these recommendations is to reduce the average basic maximum exposure limit from 0.3 to 0.1 r per week. In light of present knowledge, the exposure of one who is exposed occupa­ tionally to roentgen-ray radiation at the rate of 0.100 r per week, is not expected to cause detectable bodily injury at any time during his lifetime. If a dentist always avoids the path of the useful roentgen-ray beam and if the manufacturer of his x-ray machine has built the head of the machine prop­ erly so as to keep leakage radiation below the recommended limits for diagnostic x-ray machines,4 then the only major source of radiation that presents any ap­ preciable hazard to the dentist is the secondary radiation that scatters from the patient’s head. The recommended limits4 for diagnostic x-ray machines are as follows: