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Nuclear panic

Dear Reader,

It has come to my attention that in Austria a series of schools were evacuated following the discovery of a “hot rock”, a person named Thomas Neff found a rock with a GM (geiger) counter which was emitting what he regarded as a lot of radiation. It has been reported that this rock was a lump of uranium.

Now I am trying to find out what is happening, Thomas Neff does seem rather hard to find, I have found that a person with this name works at MIT. I have also noticed that another person with this name exists in Germany. It appears that the name Thomas Neff may be a very common name, which can result in confusion.

If any of my readers can put me in touch with the right Thomas Neff, I would be glad to discuss with him the facts of this case.

Now I thought the estimate of 210 mSv per year was rather high, now we should consider how much radium-226 is required to deliver this dose. I have chosen this radionuclide as it is the daughter of uranium which will deliver (with its daughters) the vast majority of the gamma dose from uranium ores.

210 mSv per year is 5.75 microSv per day. Which will work out as 24 microSv per hour.

As one curie of radium-226 and its daughters will deliver 0.79 rads per hour at one meter, this will be 7.9 mGy per hour. Now we can calculate that to get a dose rate of 24 microGy per hour will require 329 times less radioactivity at a distance of 1 meter.

As the half life of uranium-238 is 4.468×109 years, then 3.04 mg of radium will exist in 8830 grams of uranium.

This is because after a long time the rate of decay of the radium (half life of 1620 years) will be equal to the rate of the decay of the uranium. For every Bq (disintegration per second) of uranium-238 there will be 1 Bq of radium-226.

I think that such a lump of uranium ore is rather difficult to obtain. Also the self adsorption of radiation by the ore will greatly reduce the dose per hour near to it. I think that this is a rather unlikely rock.

Now if we consider the idea of a rock which is kept at a distance of 20 cm in a band and that the 210 mSv dose per year is a hand dose then 25 times less uranium ore is needed. This will still be 353.2 grams of uranium. This is a lot of uranium, it is a bit more like a paperweight than a stone which I expect to be displayed in a school.

I am trying to get hold of the people who did the radiometric measurements on the uranium stone, right now it looks like it would be difficult to get this radiation level from natural uranium. If I get more information I will give you an update. Bye for now.

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