EDIT: Someone linked to the Wikipedia article for uranium tiles, which says that the majority of the radiation comes from the decay products and is beta radiation[1]. Beta radiation has a weighing factor of 1, which makes your calculation pretty much correct!
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EDIT 2: Looking more closely it appears that the dosimeter in the video is switched to µSv/h, so it's reading 0.1 mSv/h anyway and the whole discussion below can be skipped if you're not interested in the difference between Gy and Sv.
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If I remember my lectures correctly (Wikipedia did help me here), the conversion is 1 Roentgen ~ 00.1 Gray (Gy), which is a slightly different unit from Sievert (Sv).
1 Gy is 1 J/kg of absorbed energy, however the biological effects change depending on the type of radiation. Sv is Gy adjusted by a weighing factor. It's 1 for gamma rays, where 1 Gy = 1 Sv, but for alpha particles it's 20 [0].
Uranium-238 emits alpha particles, which get stopped by a few cm of air or even dead skin. So the effective dose you are receiving from the decay of U-238 is probably closer to 0 mSv/h.
Or, if you eat it and it's inside you, 2 mSv/h, at which point you should probably be quite worried.
The decay products of U-238 however are beta emitters, which changes the calculation again. The beta particles can penetrate the skin, but the weighing factor for beta radiation is 1, so it can reach you but is also less dangerous.
So what's the actual final value? I honestly don't know, radiation can be complicated, and I just wanted to share the difference between Gy and Sv!
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EDIT 2: Looking more closely it appears that the dosimeter in the video is switched to µSv/h, so it's reading 0.1 mSv/h anyway and the whole discussion below can be skipped if you're not interested in the difference between Gy and Sv.
==========
If I remember my lectures correctly (Wikipedia did help me here), the conversion is 1 Roentgen ~ 00.1 Gray (Gy), which is a slightly different unit from Sievert (Sv).
1 Gy is 1 J/kg of absorbed energy, however the biological effects change depending on the type of radiation. Sv is Gy adjusted by a weighing factor. It's 1 for gamma rays, where 1 Gy = 1 Sv, but for alpha particles it's 20 [0].
Uranium-238 emits alpha particles, which get stopped by a few cm of air or even dead skin. So the effective dose you are receiving from the decay of U-238 is probably closer to 0 mSv/h.
Or, if you eat it and it's inside you, 2 mSv/h, at which point you should probably be quite worried.
The decay products of U-238 however are beta emitters, which changes the calculation again. The beta particles can penetrate the skin, but the weighing factor for beta radiation is 1, so it can reach you but is also less dangerous. So what's the actual final value? I honestly don't know, radiation can be complicated, and I just wanted to share the difference between Gy and Sv!
[0]: https://en.wikipedia.org/wiki/Sievert [1]: https://en.wikipedia.org/wiki/Uranium_tile