Thanks AdrianP

The links take you to one of the most concise and lucid articles I have read. It's easily understood, even by the braindead likes of myself. Does anyone else have info about actual radon levels in mines? :thumbup:

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The snag is that in Cornwall/Devon, a lot of the crosscourses have U in them and mines vary from being tepid to gas mark 6. The stale air point is very valid indeed. A local mine we go in that has thin air at the end got me curious. I saw a plan of it and the low oxygen end had high radon. 42WL.

Several mines which are pretty much walk-ins for any local kids with torches are hot and several of them cause a mica tubed geiger counter to go off the scale. For me, this end of things provokes great interest.

There are some very very interesting mines around here which either "wrong" atmosphere or very high levels of radiation. It would be good to monitor the risk and make the right decisions regarding PPE.

One of our good walk ins has a radioactive crosscourse and by my calculations, gives you 16 hours to get to 20mSv.

Interesting that the above paper mentions 50mSv, which is the american radiation workers maximum dose. I think our rad workers are allowed 10mSv and miners 20.

I had problems, which is why I wanted to find out how you make sense of a geiger counter output which is in Bq.

In people's maths, Bq seems to mutate into Bq/M^3 which I can't see a counter being able to measure. Obviously you need one which deals with volume as well........

Since a mine's radon derived atmosphere is going to be a constant composition and only the conc that varies, I would have thought it would be possible to correlate a geiger output with a rough estimate of mSv.

At some point I'd like to have a look in S Terras, it is possible with the right precautions, I'd also like to have a look around United Mines (no oxygen) as you would have been one of the very very few people in there. A lot of the local mines have had a few people in them. Again, these are often using rumours/dizzyness to ascertain whether they should continue. I want to use data from instruments.

There is an article about Radon in Old Gunnislake Mine, where some local uni spods (I expect) went into OGM with a geiger counter and shat themselves, so they did the Bq>>>>Actual Dose (Gy ?) calculation. Sadly, you can only buy it online or look in your uni library.

Anyway, nice article indeed. Cheers

With regards to cornwall and devon in particular, things can become interesting even on surface.

A few years ago I was involved in building a new school between Camborne & Redruth, Part L of the building regs enow effectively mean that buildings have to be sealed up like a baked bean can, as a result if radon can get in, things get quite hot very quick.

After completion of the school all of the classrooms were monitored for 6 months, the results in one clasroom came up with a background level of over 12,000 Bq/m3. The intervention level is 150 (I believe)

There is an article about Radon in Old Gunnislake Mine, where some local uni spods (I expect) went into OGM with a geiger counter and shat themselves, so they did the Bq>>>>Actual Dose (Gy ?) calculation. Sadly, you can only buy it online or look in your uni library.

Anyway, nice article indeed. Cheers

You could probably get a copy from the BL with the full ref.

Title: Radon in a disused mine in Cornwall, UK
Author(s): Gavin K. Gillmore, Gillian Pearce, Antony R. Denman

Journal: Environmental Management and Health

Year: 2001
Volume: 12
Issue: 5
Page: 500 - 509

DOI: 10.1108/EUM0000000006038

Publisher: MCB UP Ltd

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I remember reading a paper by Gilliain Pearce back in the early nineties quoting levels (in Beqs) in Tolgarrick mine, which adjoins Sth Terras. Readings in excess of 50 MBq!!! I had the data here for years, but havn't seen it for a long time. She also produced a video tape of her and some friend taking readings in there with a geiger counter. Looked like one of those old Amex jobs from the early 70s with dodgey Germanium transistor amplifiers. When they got old the battery voltage vs output parameters varied wildly.
By the way, I've heard the Bequerel refered to as the Buggerall, and there seems to be a confusing array of measurement units with Sieverts, Curies, Bequerels, Rems and a few others I can't seem to recall right now, and how do these equate to a Working Level? Confused!! 😢 :blink:

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You should be confused! I did a physics degree many years ago and I am confused too.

But I have been looking at radon detectors and the position is not as good as I had hoped. A lot of detectors sold to the public are only really useful for gamma, and maybe just about beta, and will not detect alpha. There are good alpha detectors, for domestic use, explicitly for Radon, but they seem to be the integrating type which eventually, after many days, give you an average reading. We need something more immediate!

I am still looking. If I can find a source of inexpensive silicon detectors, I am fairly confident of being able to design some cheap electronics to make it work, but I don't think that geiger tubes are sufficiently robust. A mica window tube will work, of course.

I will make further enquiries.

Alan

You need a mica tube and that's that, they are expensive and fragile though.

I like Bq's. That's like the temperature in there, your geiger counter is like a thermometer.

mSv is how quick you are actually cooking and Gy's are how well you are actually cooked.

Once you know the rough conversion, the output of your plebian meter is what is required.

That's what I would like to know

Stuey,

I am looking into something like this http://www.canberra.com/pdf/Products/Detectors_pdf/C36115-PIPS-SS.pdf , if they can be obtained at reasonable cost.

Seems that it will be a lot more rugged than a GM tube, and also very good for alphas.

If I have understood correctly (not done much reading yet), the device can discriminate between particles of different energy, so it ought to be possible to distinguish between Radon gas, and other alpha emitters which may be found in similar places, including some of the daughter products.

I doubt that the electronics necessary to support one of these will be terribly expensive, but the detector itself may be. But I will find out soon. One of my colleagues who is not at work today knows a bit more about this subject, and knows of some possible manufacturers.

It seems to me that if a complete, packaged unit with rechargeable battery could be made for £100, it would likely be viable. But that depends on getting a suitable sensor (theer are other manufacturers) for about £50.

Alan

Stuey,

I am looking into something like this http://www.canberra.com/pdf/Products/Detectors_pdf/C36115-PIPS-SS.pdf , if they can be obtained at reasonable cost.

Seems that it will be a lot more rugged than a GM tube, and also very good for alphas.

If I have understood correctly (not done much reading yet), the device can discriminate between particles of different energy, so it ought to be possible to distinguish between Radon gas, and other alpha emitters which may be found in similar places, including some of the daughter products.

I doubt that the electronics necessary to support one of these will be terribly expensive, but the detector itself may be. But I will find out soon. One of my colleagues who is not at work today knows a bit more about this subject, and knows of some possible manufacturers.

It seems to me that if a complete, packaged unit with rechargeable battery could be made for £100, it would likely be viable. But that depends on getting a suitable sensor (theer are other manufacturers) for about £50.

Alan

Looks like a cheapish component, but as you say, will command a premium.

You can bet your bottom dollar that somewhere in china this stuff is available at 1/10 of the cost. I don't really think that these detectors should be that pricey really, they are merely along the lines of a pocket calculator. Apart from the sensor price, both sorts of detector are highly crappy really. You aren't dealing with the old brass/mahogany handmade days of Griffin and George.

These days it is less about a specialist company needing to charge a premium for a low demand specialist component, more like someone making a fortune out of the Chinese. I say "beat them at their own game". When I get exceptionally bored, I will see what I can find.

I once saw a cheap detector -Gawd knows what it was meant to detect - based around an audio output transistor as the detector. This was a common silicon power transistor namely the 2N3055. A metal cased device with the top hacked off to expose the 'bare' chip inside. Thinking back on it now, it sounds like one of those crappy Practical Wireless circuits that you spend quids and quids building to find it doesn't work and weeks later finding several apologies for wrong component values having been quoted. 😮 a cheap, working alternative would be most welcome!

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Stuey and Roy,

Yes it should be cheap. I understand it to be simply a very large area diode. A big, old-fashioned power transistor would likely work too.

It just occurred to me that modern dynamic RAM, as used in PCs etc, is cheap, and has a truly massive problem with alpha particles unless it is covered with a layer of a compound which does not emit alphas. As we know, you don't need much thickness to stop them. The normal epoxy used for the outer package does contain traces of alpha emitters, which would cause an excessive number of single-bit errors. That is giving me ideas.

I do work with people who can procure bare semiconductor die, fit them to substrates, and package them suitably. I bet they could do a nice thin mica window. If the quantity was right, the price might be too. I will ask next time I see them, in a week or so.

Oh, and thinking about it, the CCD or diode array in a digital camera should also detect alphas quite well. If someone wants to risk their SLR underground, they could take the lens off, to allow alphas in, and take a suitable exposure of darkness. The background will be noisy on a long exposure, but I expect any alphas to leave very bright spots. I have an old Ricoh which is broken, all that is wrong is that is wrong is that the motorised lens covers stick, and neither open nor close fully. I could sacrifice that to a good cause, provided I can find a way of fooling it into taking pictures with no lens fitted, having first found how to remove the lens.

But I saw an inexpensive "solid state beta" detector in about 1972, which was also very good for alphas. I am still trying to track down the source of these.

Funnily enough, my employer, on another site, makes neutron detectors, but as we don't expect much fission in the mines, I doubt that these would be useful. They are not cheap, or small, or robust.

Google shows lots of scientific papers about solid state alpha detectors, but we want a simple semiconductor at a simple semiconductor price, not a lab prototype.

A silicon photocell, for making electricity from sunlight, is basically a large area diode, but I don't know if its characteristics would be suitable. If I had a decent alpha source, I could test one, but it is not too easy to obtain legal alpha sources in the UK. Yet you can legally get things containing a small amount of Polonium in the US. Maybe I need to purchase a specimen of pitchblende.

This link http://books.google.co.uk/books?id=BXpF3n-OjvEC&pg=PA150&lpg=PA150&dq=geiger+counter&source=web&ots=-DTziKhw9W&sig=OnOMBLbO3PugAAdPvr44ItoWhfE&hl=en&sa=X&oi=book_result&resnum=10&ct=result#PPR15,M1  might be interesting.

Alan