Answer to Question #4526 Submitted to "Ask the Experts"

Q

Our facility has two liquid scintillation analyzers (LSA) and a gamma counter, both devices have standards (¹⁴C and ³H 20 ml vials for the LSA) and a ¹²⁵I plastic rod for the gamma counter. All have activity less than 0.5 µCi. Are these considered sealed sources and should I be leak testing them? Also, our GM (Geiger Müller) detectors have plastic check sources attached (¹³⁷Cs <0.1 µCi). Are these also to be leak tested?

A

I will state up front that I would not expect any of the sources you have described to be subject to mandatory leak testing, but I am including some information below that may be helpful in explaining and expanding on this answer. The definition of a sealed source varies somewhat depending on who is providing the definition and what the intent is relative to handling/use of the source. For example, the U.S. Nuclear Regulatory Commission (NRC) in 10CFR30.4 states "Sealed source means any by product material that is encased in a capsule designed to prevent leakage or escape of the byproduct material." The U.S. Department of Energy (DOE) in regulation 10CFR835.2 defines a sealed source with the following words: "Sealed radioactive source means a radioactive source manufactured, obtained, or retained for the purpose of utilizing the emitted radiation. The sealed radioactive source consists of a known or estimated quantity of radioactive material contained within a sealed capsule, sealed between layer(s) of non-radioactive material, or firmly fixed to a non-radioactive surface by electroplating or other means intended to prevent leakage or escape of the radioactive material. Sealed radioactive sources do not include reactor fuel elements, nuclear explosive devices, and radioisotope thermoelectric generators."



In general, not all sealed sources, regardless of what definition might be used, are subject, by law, to regular leak tests. Usually, exemption of a sealed source from leak testing is granted on the basis of the half-life of the radionuclide and/or the quantity of radioactivity. For example, the NRC in 10CFR35.67f specifies independent conditions under which sealed sources are exempt from leak testing. One of these conditions is if the half-life of the radionuclide involved is less than 30 days; another condition is if, for a beta-gamma emitting radionuclide, the activity is less than 3.7 x 10⁶ Bq (100 µCi) or, for an alpha emitter, less than 3.7 x 10⁵ Bq (10 µCi). The DOE uses the term "accountable sealed radioactive source" to describe a sealed source that is subject to various controls, including routine inventorying and leak testing; see the above DOE web site for the definition of accountable sealed source, and see 10CFR835.1202 for discussion of DOE requirements for such accountable sources. The quantity of activity that makes a sealed source accountable varies among radionuclides; the respective quantities are given in Appendix E of 10CFR835.



In the broad definition of sealed source used by the NRC your sources might all be considered sealed sources, although the LSA vials are a bit fuzzy unless they are permanently sealed. If you are operating as a medical licensee under 10CFR35, all the sources would be exempt from leak-testing. Indeed, the source activities you have described are all referred to as exempt quantities in NRC jargon, meaning that a specific license is not required to possess them because of the small amounts of activity involved. This is discussed in 10CFR30.18. By inference, such sources would not expectedly be subject to mandatory leak testing. If your facility operates under a specific license or broad scope license issued by the NRC or by an NRC agreement state, you should check that license to see whether it specifies conditions for leak testing of sealed sources.



Anecdotally, a number of years ago, when I was RSO (radiation safety officer) at a university, we had dozens of low-activity check sources, many of them of the plastic encapsulation type buttons and rods. We did include them in a program of leak testing and, over a period of perhaps 20 years, we identified about a half dozen that did leak and which we withdrew from use. This is only to point out that such sources may degrade with time and, especially if a rather large number of such sources are in use, a program of leak testing may be beneficial. In a situation where few sources are involved and a leak testing program involving other sources is not already ongoing, establishment of a program is probably not worthwhile.



George Chabot, PhD, CHP