I think most of the radiation in that sample is alpha. The gamma peak they measured the 2nd-highest count for is the 59 keV from Am-241. The invisible monster they can't detect is the 5,486 keV alpha generated by that same isotope. That's the main hazard there—should someone remove the sample from the glass vial and somehow get significant exposure to dust. (Otherwise, the glass is more than sufficient shielding).
I think most of the radiation in that sample is alpha. The gamma peak they measured the 2nd-highest count for is the 59 keV from Am-241. The invisible monster they can't detect is the 5,486 keV alpha generated by that same isotope. That's the main hazard there—should someone remove the sample from the glass vial and somehow get significant exposure to dust. (Otherwise, the glass is more than sufficient shielding).