Answer to Question #1633 Submitted to "Ask the Experts"

Q

A follow-up from one of my previous questions about uranium glazes in older ceramics: what would be your best guess as to the dose in rem that a person would receive if they still used one of these ceramics as dinnerware and what would an antique collector's dose be from a ceramic, say sitting on the table in the kitchen? What type of activity do these old ceramic pieces with uranium glaze have; are we talking nanocuries or millicuries?

A

The following information comes from NUREG-1717 "Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials" (2001). There is little available information about the total uranium activity found in the dinnerware that employed uranium-containing glaze. The levels used in the glaze are known, but the amount of glaze per plate, cup, or whatever, is not well known. One estimate put the figure at 4.5 grams of uranium in one plate. Obviously, the larger the plate and the greater the amount of glaze, the higher the activity. This one estimate of 4.5 grams of uranium translates into approximately 1.5 microcuries of uranium, that is, 1.5 microcuries of ²³⁸U (alpha emitter), 1.5 microcuries of ²³⁴Th (beta emitter), and 1.5 microcuries of ^234mPa (beta emitter). If the glaze employed natural uranium, there would also be 1.5 microcuries of the alpha emitter ²³⁴U. If the glaze employed depleted uranium, relatively little ²³⁴U would be present. The gamma emissions from these nuclides are relatively low. As such, the largest exposure would be the beta dose to the hands. One estimate placed this at 0.5 to 20 mrad/h on contact. Handling the plates for 1.5 hours per day was estimated to result in 2 to 10 rem per year to the hands. Another estimate was that someone seated before a typical place setting would receive 3 mrad/h to the hands and approximately 0.3 mrad/h to the torso. NUREG-1717 did its own calculations and came up with an effective dose equivalent of 50 mrem per year to the maximally exposed user of such dinnerware—typical users would have substantially lower doses. Keep in mind that the NUREG number is an effective dose equivalent rather than a dose to the hands. For a homeowner who did not use the dinnerware, but simply had it on display, NUREG-1717 estimated the effective dose equivalent to be 0.06 mrem per year. Paul Frame, CHP, PhD