Overview
Very frequently gemstones can take any of a number of colors, depending on a variety of factors. The factors that turn topaz blue (for example) are very rare in nature, but can be replicated if the topaz is exposed to radiation in a nuclear reactor or an electron accelerator. The problem is that these can cause the topaz to do more than turn blue – sometimes it also makes them radioactive. For this reason, regulators require that jewelry companies that use blue topaz should survey the gems before they’re shipped to stores for sale to characterize the amount of radioactivity in the stones and make sure they are safe to sell and ship. On top of that, their home state had additional requirements for them to receive and store potentially radioactive gems until they could be tested. That’s where I came in – helping the company navigate the regulatory requirements and develop a stand-alone radiation safety program.
The main problem(s)
Bombarding gemstones with neutrons (in a nuclear reactor) or with high-energy electrons (in an electron accelerator) can cause them to become radioactive. Before these gems can be sold to anyone who lacks a radioactive materials license (a jewelry store, for example, or a boyfriend to give as a gift) they need to be checked to confirm that they don’t contain enough radioactivity to require regulation.
The primary guidance document relevant to this sort of license was a regulatory guide called NUREG 1556 volume 8 (Program-Specific Guidance about Exempt Distribution Licenses) along with the ever-fascinating (I’m being serious here!) NUREG 5883 (Health Risk Assessment of Irradiated Topaz) – this one’s a little dated, but still has some useful information. These references, of course, are not the main problem – but they bring it up. Specifically, they call for a fairly fool-proof methodology for making sure that not a single irradiated gemstone with excessive amounts of radioactivity is released for unrestricted use. The problem is that this methodology calls for checking every single gemstone for a long enough time to show it’s non-radioactive, likely requiring fairly sophisticated and expensive equipment. To follow the preferred protocol would require a trained full-time radiochemist and a radiochem lab – both of which are expensive – to confirm the absence of radioactivity that nobody realistically expects to be present. I tried to introduce a simpler methodology that would be easier and less expensive to implement – one that wouldn’t require opening every single box and digging through it to find every single piece of jewelry with blue topaz in it.
The solution
What I wanted to do was to find a way to check enough gems to constitute a good statistical sample and to count them long enough to identify the presence of radioactivity in excess of the exemption limits – and all using commercially available equipment. Statistics not being one of my strong points, this took a while for me to work through. Once I figured out how many gems would constitute a good statistical sample and how long they should be counted to have a 95% chance of detecting elevated radioactivity levels I worked out a fairly simple sampling and counting procedure and developed a spreadsheet to do the calculations.
There were some other references I explored along the way. For example, some IAEA documents confirmed that bombardment with electrons with less than about 7 MeV of energy were unable to eject a neutron from most atomic nuclei, meaning that gems irradiated with lower energies were highly unlikely to become radioactive. I was also able to confirm that gems that had been irradiated inside a nuclear reactor would need to be stored until they decayed to exempt nuclide concentrations before the reactor facility would be permitted to ship them – thus, reactor-irradiated gems only needed to be spot-checked. This sort of analysis greatly reduced the number of gems that might be a concern.
Additional snags along the way
Very little of this was consistent with the methodology that NUREG 1556 vol 8 or NUREG 5883 called for and the NRC folks reviewing the license application were concerned that the novel procedures were too likely to miss the occasional “hot” gemstone. They also had questions about some of the statistical analysis I’d done, and some concerns about activation of some less-common elements. Part of the problem (I came to believe) was that the NUREGs, while guidance documents, provided a de facto standard that, if followed precisely, guaranteed that no regulations would be violated; by straying from the NUREGs they needed to assure themselves that I was able to develop something of comparable quality in a short period of time, working on my own. It took the better part of a year to work through these concerns, but they finally granted a license after many rounds of back-and-forth.
And the final resolution!
The final version of the documents (including a lengthy Technical Basis Document outlining all of the reasoning and calculations, looked a lot like my first submission; after so many comments and replies, emails, and months this surprised (but gratified) me.