Polonium spark plugs spectrum (no polonium left there of course)

[Svilen]

I got recently five Firestone Polonium spark plugs from the 50-ties, unused and with the original packing, nice for collecting. Since they were giving ~5 imp/s higher activity than the background in the castle (~15/s) I recorded the spectrum, even when no polonium-210 is expected inside after maybe more than 180 half lives have passed (if they put some there at all, since it was more or less just a marketing gimmick, but well I guess they did). Just for information, Po-210 is an alpha emitter that decays directly to stable Pb-206, but about one in 100 000 alpha emissions will cause an excitation in the nucleus which results in the emission of a gamma ray with a maximum energy of 803 keV.

The weak activity I have is hard to measure with my detector, but looks like there are some radium decay chain traces, most likely from the porcelain insulators. Other opinions?

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[MartinM]

How about induced radioactivity caused by alpha particles?

[Svilen]

Not from this amount of Polonium, not after all this time and definitely not Radium as a result.