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The question is derived from an experiment... "Red" tungsten TIG welding electrodes consists 2% of thorium-232. They are slightly radioactive... I have such electrodes, so I checked their radioactivity by an NR-750 Geiger counter (indeed they are radioactive).

I interpreted that particles, which are detected, are electrons from beta decay. But if I put electrodes behind a few mm steel shield, I still detect some events. Why? Does it mean that X-rays are also emitted? But why?

According to Thorium series, only alpha particles and beta particles are emitted.

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  • $\begingroup$ Is there a control? What is the result of removing the welding electrodes, but keeping the steel shield (there could be contaminants in the steel)? What about the background radiation (with enough events to be statistically meaningful)? $\endgroup$ Apr 24, 2022 at 9:07
  • $\begingroup$ Metal shield doesn't radiate itself in this experiment. Radiation is function of electrodes. $\endgroup$
    – Andrew123
    Apr 24, 2022 at 22:44

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Tl-208, in the decay series, is a strong gamma-ray emitter. That's probably what you're seeing.

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  • $\begingroup$ But it is not listed a gamma ray, but as beta (β− decay)(?). $\endgroup$ Apr 24, 2022 at 8:59
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    $\begingroup$ @Peter Beta decay disturbs the balance of the nuclear shell structure, so it often leaves the daughter nucleus in an excited state, and it soon loses that extra energy via gamma emission(s). Alpha decay generally has a more symmetrical effect on the shell structure, but some alpha decays are followed by gamma emission. $\endgroup$
    – PM 2Ring
    Apr 24, 2022 at 10:45

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