Thanks for the reply, Smirky.
I’ve got most of the chemistry and general issues under control, and am trying to find out if these specific gauges are known to have high levels.
Since the original post, I’ve contacted the person that I got it from and received a reply that he’d sold out of them. Apparently U.S. Customs bought a bunch of them to test their radiation detection gear. So that sounds like these Blinkers might have a reputation for higher detectable emissions than the average gauge.
The only way I’ll know for sure, is to buy another one and test it as a comparison, or to track down someone who has done the same.

Cheers, Willie.