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Answer to Question #1347 Submitted to "Ask the Experts"Category: Policy, Guidelines, and Regulations The following question was answered by an expert in the appropriate field: Q
I am working with a titration that employs the use of a 0.1M
concentration of thorium nitrate. I recognize that this material is
radioactive and am in need of precautions to take while working with
the powder and then the solution that will be used in the analysis.
A
Thorium nitrate is radioactive and, as a refined compound of 232Th,
technically "source material" under the U.S. Nuclear Regulatory
Commission's (or equivalent Agreement State) rules and regulations. Per
10 CFR 40, small quantities (that is, less than 15 pounds) may be
transferred and utilized for research under a "general license." Thus,
no "specific license" with respective to additional radiation
protection conditions is required for use. However, that does not
relieve one from the radiation protection criteria in 10 CFR 20. These
regulations relate to internal and external dose limits for workers and
the public. All the NRC's regulations can be found online.
As far as precautions, if possible you should consult a health physicist, as thorium nitrate is quite soluble and the airborne concentration limits quite low. Depending on the age of the material, it may have in-growth of its short-lived decay products. There are nine alpha, beta/gamma emitting decay products, but the first radionuclide 228Ra (with a 5.75 year half-life) determines the state of equilibrium. It takes about 25 to 30 years for all the decay products to reach full equilibrium, once removed through chemical purification. A small quantity of thorium would not present a significant external radiation exposure hazard. These materials should be easily detected with a Geiger counter and exposure estimates made from such readings. Nonetheless, working with powders to produce a 0.1 M solution might cause an airborne/inhalation/internal exposure/dose concern. I'd recommend working in a good fume hood with at least 100 linear feet per minute open-face velocity. Surveys of the hood with wet filter smear should be made after to ensure no residual surface contamination is present. You should check on disposal of the solutions, as your institution may have low-level radioactive waste acceptance criteria and/or sewering restrictions. David J. Allard, CHP
Answer posted on 5 November 2001. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.
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