When Spock looks at the readout, it says "unknown form of radiation."
Kind of like smelling something you've never smelled before. "Detection" and "identification" are two different things.
Of course, "radiation" usually means electromagnetic radiation in strict usage, so really nothing could be "unknown" if its wavelength can be established. Unusual, yes.
In practice, the word "radiation" is often stretched to include things like alpha and beta particles, and other things that are actually bits of matter being thrown off of something. Anything considered "unknown" would probably have to fall into that category.
Heck, Spock should take it up with the vendors.