title: Depth-dose curves for 90Sr and natural and depleted uranium in Mylar.
abstract: Strontium and uranium are common sources used to calibrate personal dosimeters and survey meters for beta radiation. Since the absorbed dose rate of low-penetrating beta radiation decreases significantly with increased depth in tissue or dosimeters, it is necessary to describe the dose rate accurately as a function of depth. Complete depth dose information from zero to 1000 mg/cm2 is currently unavailable for strontium and uranium. This paper describes the generation of accurate depth-dose curves in Mylar for 90Sr and slabs of natural and depleted uranium from 0 to 1000 mg/cm2, utilizing an extrapolation chamber. The absorbed dose rate produced by natural uranium was found to decrease from 235 mrad/hr at a depth of 7 mg/cm2 to 43 mrad/hr at 300 mg/cm2 to 4.8 mrad/hr at 1000 mg/cm2. The dose rate produced by depleted uranium was found to decrease from 205 mrad/hr at 7 mg/cm2 to 34 mrad/hr at 300 mg/cm2 to 2.3 mrad/hr at 1000 mg/cm2. A 1-mCi extended area 90Sr source (encapsulated in 50 mg/cm2 AG) was found to produce an absorbed dose rate of 16,997 mrad/hr at 57 mg/cm2, 5000 mrad/hr at 300 mg/cm2, and 27.1 mrad/hr at 1050 mg/cm2. Doses to deep organs have been determined historically at depths ranging from 300 to 1000 mg/cm2. The results of this study show that 90Sr and uranium produce significant absorbed dose rates at a depth of 300 mg/cm2. Thus, if doses for deep depths are determined at 300 mg/cm2 for mixed beta-gamma exposures, the dose will be overestimated due to the presence of the beta component. The depth-dose curves generated in this study can be used by dosimeter processors to normalize the response of their dosimeters to the shallow (7 mg/cm2) and deep (1000 mg/cm2) depths defined by the U.S. Nuclear Regulatory Commission.
mesh_terms: D002138:Calibration; D004583:Electrons; D010795:Phthalic Acids; D011092:Polyethylene Glycols; D011093:Polyethylene Terephthalates; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000295:instrumentation; D013326:Strontium Radioisotopes; D014501:Uranium
chemical_list: D010795:Phthalic Acids; D011093:Polyethylene Terephthalates; D013326:Strontium Radioisotopes; C025539:Lavsan; D011092:Polyethylene Glycols; D014501:Uranium