"Breeze block"

[Chris Hogg]

Yup. But if you'd read upthread, you'd see they've already been covered. It's the uranium and thorium in the coal ash that gets people's knickers in a twist.

[The Natural Philosopher]

technically you are correct.

[The Natural Philosopher]

And quite a lot of transitional elements like radium/polonium etc etc

[Jethro_uk]

Which leads into an interesting question I encountered recently ...

Lets suppose that 100,000 years ago a civilisation of h. Sapiens emerged and attained the *exact* same level of technological advancement as we enjoy today.

Then something caused them to lose it all.

What - if any - traces of them could we sensibly expect to survive for us to find now.

Or, if you don't like the premise, more straightforwardly, is there

*anything* modern man could do that could leave a 100,000 year legacy ????

What would our nuclear test sites (and waste) look like in 100,000 years time ???? Given that they aren't that confident we can contain it at Sellafield for 100 years ??????

[The Natural Philosopher]

Greens prtobably

Tons and tons.

Mainly of concrete. Brued under the strata.

Also there wouldn't be any uranium or thorium left.

Tons and tons. Mainly of concrete

Like nothing special.

What does Hiroshima look like 73 years after being bommbed by an A-bomb?

(it was never 'cleaned up')

[Tim Streater]

Coal contains one part per million uranium.

Actually of course everything is "slightly" radioactive, but some things more so. Like granite, too, so don't go to Dartmoor or you'll glow.

[Tim Streater]

Bananas because of the potassium.

[Tim Streater]

Read up about the Oklo natural reactor, and how the uranium there came to be concentrated. Seems that uranium can be dissolved in oxygenated water. Oklo was at the junction of two rivers, one with oxygenated water, the other not. The former could carry the uranium downstream, but at the junction it would precipitate out, thus concentrating it.

Possibly that same happened somehow with coal deposits.

Interestingly the Oklo reactor of 2 billyun years ago couldn't happen today, as the proportion of U235 to U238 was around 3% then, only 0.7% today.

Also of interest is that the waste products of the reactor have not migrated significantly over the period of time since, so people worrying about Sellafield are wetting themselves unnecessarily.

[Tim Streater]

Come come come. Of course it's a normal environmental circumstance. What else would it be?

[The Natural Philosopher]

Actually thet depnds on waqht you mean by 'things' Vast quantities of pure elements are not radioactive at all.

But any mixture is likely to contain some that are.

Human beings are fairly radioactive, for example.

[The Natural Philosopher]

What is more natural than an atmoic bomb? I know, a fusion bomb! Also known as a supernova, that created at least half the earth's elements.

Harnesssing natural radioactivity is no different to harnessing wind or solar power, also created by a far more dangerous reactor with no shielding that - unlike earth bound reactors - does pose a serious health hazard.

[harry]

The Japan bombs did not explode at ground level. Most of the radioactivity was dispersed in the atmosphere.

[John Rumm]

I think its just the fact that the combustion process in effect concentrates the trace elements of radioactive elements weight for weight. So start with a million tons of coal, and it will have small quantity of uranium and thorium naturally present in it. Burn it, and the quantity of uranium and thorium will stay roughly the same (presumably a small amount escapes to the atmosphere), but its now concentrated into a much smaller volume of ash. Making the ash appear more radioactive that the coal originally did.

(Thorium contamination is a general problem with many things you dig out of the ground. It particularly affects rare earth element mining. Until recently when people have started to consider it might actually become a useful fuel, its had negative cost - i.e. you had to pay to get someone to take it off your hands)

[Jimmy Wilkinson Knife]

Carrots? Since they make you see in the dark....

[Chris Hogg]

Yes, I realise that, but if you assume, quite reasonably IMO, that coal is a mix of coalified organic matter derived from tree ferns etc that were around in the Carboniferous period (approximately 300 to 350 million years ago), and inorganic material such as sand, silt and clay deposited at the same time (and which would make up the bulk of the ash after the coal was burnt), which of those two components contains more uranium and thorium than the equivalent materials today? I don't see why the sand, silt and clay in coal should be significantly different from the stuff used to make bricks today, nor do I see why the coalified tree ferns should contain it either. Is modern wood ash, e.g. from wood-burners, significantly radioactive? I doubt it.

So my question remains: where has the uranium and thorium in coal, come from? I doubt there will be an answer, unless some lab somewhere has ground up some coal samples _very_ fine and done a density separation, or more probably a flotation, to separate the organic component from the inorganic, and measured the radioactivity in each.

[Jimmy Wilkinson Knife]

I find it's always a good idea to ignore all alarmists. We don't have global warming, we just had two feet of snow. We don't have a shortage of bees, I can see 20 in my front garden right now.

[Chris Hogg]

Try this for a start, and dispel a very tiny portion of your massive ignorance

[Tim Streater]

I suggested a possible answer.

[Tim Streater]

Ah, I must have imagined being in bed for a week with very bad sunburn when aged 19, because I foolishly spent the whole day on the beach.

[Chris Hogg]

Oklo, IIRC. While I realise that uranium and thorium might be transported by groundwater, that doesn't really explain why they should be incorporated into deposits that eventually became coal, especially as coal deposits are widely distributed across the world.

OK so in the Carboniferous, the land masses were very differently distributed to what they are today*, but I still find that explanation unlikely. It would require a rather unique set of circumstances to apply to may large areas of Everglade-type swamp, and why don't other non-coal deposits of similar age also contain raised levels of U and Th. Or perhaps they do.