β/γ radiation in caves and mines

CJ

Member
Yesterday I decided to have a play with my radiation detector in a Peak District cave/mine as I was curious to compare the background levels of radiation compared to the surface. First of all, it's worth pointing out that this device does NOT use a Geiger-Müller tube, it's a scintillation counter..
For anyone who doesn't know; scintillation counters are far superior when it comes to radiation sensitivity and detecting lower levels of radiation. The other advantage is that they're much tougher and doesn't rely on a fragile glass tube. All in all, they're pretty cool bits of tech... However, they're only really good for detecting X-ray/gamma and beta radiation. This means that I'm only detecting the beta and gamma radiation associated with the decay of radon daughters. I have not done a literature review, so I'm sure there's already an abundance of studies into the comparative background radiation found underground, but reading them is less fun.

Above Ground.PNG

^^
As you can see, above the shaft I'm getting an average count per min of 36, and an average reading of 0.06µSv per hour.

Below Ground.JPG

^^
Below ground I'm getting an average CPM of 99 and twice the average µSv/h

In summary: for every hour spent underground, I was exposed to around 0.12µSv/h!! DOUBLE what I would be exposed to above ground.
To put this into perspective, that's the same as A CHEST X-RAY! Just kidding... It's actually the same as 1x 150g banana per hour (albeit cumulative).
Those numbers do add up over time, especially when each digging session can easily be 6-8h+
But I'd wager that the exposure to alpha particles are more "concerning" (comparatively speaking)?

For more info on radiation dosing and comparisons: Radiation Exposure Chart
 

Boy Engineer

Active member
Do take the time to do a literature review, as you’ll then see why alpha particles (or rather, the dose/damage they contribute) are of particular interest and concern in a poorly ventilated underground environment. It may not be as much fun as playing with a meter, but you’ll get a better idea of your risk.
 
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Boy Engineer

Active member
Just to add, ventilation rates aren’t necessarily a panacea.
Sorry to add confusion. Ventilation will reduce levels, but it depends where the air has been, enroute to the location of interest. In a previous life I was involved in room and pillar mining and the ventilation circuits were long and a considerable area of exposed rock was traversed. Even with a positive gale blowing, residence times were sufficient for high equilibrium. In those situations filtration is necessary.
 

CJ

Member
Do take the time to do a literature review, as you’ll then see why alpha particles (or rather, the dose/damage they contribute) are of particular interest and concern in a poorly ventilated underground environment. It may not be as much fun as playing with a meter, but you’ll get a better idea of your risk.
I was referring to a literature review of specifically the beta/gamma radiation underground (since the alpha particle surveys are fairly well reported for the main peak district caves and UK caves alike). As it's usually only ever the alpha particles that are discussed, and for good reason as you allude to, coupled with the fact that the other particles are such a small % of the total decay energy - I wanted to focus on them instead.
 

Cantclimbtom

Well-known member
Will be interesting to see your follow up in 6 months as I've heard (but don't know the accuracy) that summer versus winter has a significant difference
 

CJ

Member
Will be interesting to see your follow up in 6 months as I've heard (but don't know the accuracy) that summer versus winter has a significant difference
Based on the rate of progress being made at the dig site, I'd say it's quite likely that I'll be there in 6 months anyway 😅 On a similar note, it was interesting to see that the dig was still draughting well despite the temperature being +/- the same inside and outside.
 

Pete K

Well-known member
Thought it worth me dropping this link in here for the BCA's radon page in case anyone is not aware of it:
Radon Underground, although a weighty read, is something cavers in Derbyshire and other high radon areas would really benefit from reading. It's a bit tilted towards led caving, but has useful info to education recreational cavers too.
 
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PeteHall

Moderator
Thought it worth me dropping this link in here for the BCA's radon page in case anyone is not aware of it:
Radon Underground, although a weighty read, is something cavers in Derbyshire and other high radon areas would really benefit from reading. It's a bit tilted towards led caving, but has useful info to education recreational cavers too.

Thanks for sharing the link, here are the important bits (as far as I'm concerned anyway) for anyone who can't be bothered to read it
It is possible to compute the approximate increased risk of lung cancer from exposure to radon resulting from a single caving trip. [This] gives an increased risk of lung cancer from one trip of about 1 in 200,000.
By comparison,
There has been an average of 1.3 deaths per year over the last 35 years. This gives an estimated risk of death for a recreational caver from an accident in a cave during one caving trip of about 1 in 38,000.

So if I'm reading that right, you're 5 times more likely to die caving than you are to die from lung cancer caused by Radon exposure while caving (and you're pretty unlikely to die caving anyway).

Meanwhile, you are 25 times more likely to get lung cancer if you smoke (at all levels of Radon exposure).

In short, Radon is the last of your worries as a caver, so no point worrying about it (y)
 

Bob Mehew

Well-known member
From a radiological harm view point alpha particles are twenty times as significant as beta or gamma rays. Simply put, this is because a alpha particle is a helium 4 nucleus without any electrons. So when it ploughs into a cell, it deposits all of its energy in that cell. Where as a beta particle is a fast moving electron so passes through a number of cells before it gives up all of its energy. A gamma (and X) ray is a very high energy light photon and behaves similarly to a beta particle in term so interacting with cells. In extremely crude terms, think of the difference between a bus and a car ploughing into a person. Hence the focus on alpha particles. But do note that for each alpha particle emitted, there will also be a gamma ray. The decay of Uranium 238 which gives rise to radon 222 is also emitting beta particles and gamma rays. Those atoms decaying near the rock surface will emit gamma rays which will pass into the cave and that is what is being measured by CJ.

CJ - You may wish to try putting your detector inside an aluminium can. That will shield the detector from the beta particles but make little difference to the level of gamma rays. I would be interested to hear if it makes a difference to the count.

One point to note is that the uranium is not necessarily at a uniform concentration in the rock or cave. So in certain caves you may find different levels of radiation at different places. Note it is not just parts of the limestone but also the sediment banks which may have higher radiation levels. (Eroded Northampton sandstone is a case in point.)

I don't have the time spare for a week or so to provide a comparison of radiation impact between radon which for convenience is usually measured in Bq per metre cubed and gamma rays which are usually measured in micro sieverts. That calculation is a bit complicated (in truth very complex having not done it for some years).

I have on my list of to dos to rewrite that bit of Radon Underground on risk. But like everything else, it got overtaken by more pressing events. You only need read the first chapter to get an introduction to the geological and radiological aspects. Chapter 2 of Rob Hyland's thesis is well written and gets into more detail on radon, download it from http://eprints.hud.ac.uk/id/eprint/4839/1/DX193594.pdf .

The comment "I have not done a literature review, so I'm sure there's already an abundance of studies into the comparative background radiation found underground, but reading them is less fun.". I am not sure there is much published on measuring beta gamma levels underground - because the radon impact is more significant. But I have to admit I have not done a literature review. I wonder if there might be a seam of radium down one of those caves.
 

mikem

Well-known member
So if I'm reading that right, you're 5 times more likely to die caving than you are to die from lung cancer caused by Radon exposure while caving (and you're pretty unlikely to die caving anyway).

Meanwhile, you are 25 times more likely to get lung cancer if you smoke (at all levels of Radon exposure).

In short, Radon is the last of your worries as a caver, so no point worrying about it (y)
Actually radon varies between areas & even certain caves, so can easily be ten times that risk for a particular trip (or even higher), which would bump it into double the likelihood of an accident (admittedly some cavers are safer than others, so even that ratio isn't fixed...). Of course it'll never be as high a percentage as smoking, but still something to be aware of, & diggers may be particularly at risk, as they are visiting the same bit of passage regularly for extended periods (plus taking more dust into their lungs)
 
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mikem

Well-known member
Based on the rate of progress being made at the dig site, I'd say it's quite likely that I'll be there in 6 months anyway 😅 On a similar note, it was interesting to see that the dig was still draughting well despite the temperature being +/- the same inside and outside.
Small spaces will be more affected by temperature difference, whilst LARGE passages will take longer for pressure to equalise...
 

CJ

Member
Small spaces will be more affected by temperature difference, whilst LARGE passages will take longer for pressure to equalise...
So you're saying I'm not on track to find the Hamps/Manifold master cave? Heart-breaking stuff
 

pwhole

Well-known member
Actually radon varies between areas & even certain caves, so can easily be ten times that risk for a particular trip (or even higher), which would bump it into double the likelihood of an accident (admittedly some cavers are safer than others, so even that ratio isn't fixed...). Of course it'll never be as high a percentage as smoking, but still something to be aware of, & diggers may be particularly at risk, as they are visiting the same bit of passage regularly for extended periods (plus taking more dust into their lungs)
The anecdotal story (and I haven't seen the numbers personally) is that one trip into Giants Hole in Castleton in summer equates to someone's annual recommended radon dose - in winter it's pretty 'normal'. I do smoke, so tend to stay away, though I do also try to mitigate any damage as best I can! All the showcaves there have massive ventilation systems installed, either bringing fresh air in or taking cave air out, as the risk to guides is considerable over long periods.

And having now seen some of the very funky mineralisation where I assume CJ is testing, I suspect it would be worth further investigation ;)
 
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mikem

Well-known member
So you're saying I'm not on track to find the Hamps/Manifold master cave? Heart-breaking stuff
Was it draughting in or out, had the exterior pressure risen or dropped? (Actually I was suggesting the opposite...)
 

CJ

Member
Was it draughting in or out, had the exterior pressure risen or dropped? (Actually I was suggesting the opposite...)
Oh I see what you mean now, clearly the coffee hadn't kicked in when I read your message ;) Draughting out, and the exterior pressure has risen compared to previous tests. It was noticeably less than over the winter months but you can easily feel it at constrictions.
 

pwhole

Well-known member
I'm no geologist, but I do wonder what other components may affect higher levels of radon in certain areas. There's no shale at CJ's site, but the shale around Castleton is uraniferous, and the Odin Fault, on the edge of the shale/limestone boundary (at surface) is likely to be very, very deep - which could also then explain the abundance of exotic minerals found there, and the intense colouring of Blue John within the boulder bed immediately above and adjacent to the fault on Treak Cliff - uraniferous collophane has also been found. I heard a rumour that investigations were done in the 1950s around the slopes of Mam Tor to see whether it may have been worthwhile mining there (it wasn't), but that may be anecdotal. Similarly the elaterite (bitumen) outflow at Windy Knoll, which is always recharging, may be related. Trevor Ford's articles on the mineralogy and geochemical prospecting of the area in the 1976 PDMHS 'Special Edition' Bulletin on Odin Mine are well worth a read.

I don't know much about the geology in the south of the district, but presumably the basement of igneous rock is still present beneath the limestone?
 

Bob Mehew

Well-known member
The anecdotal story (and I haven't seen the numbers personally) is that one trip into Giants Hole in Castleton in summer equates to someone's annual recommended radon dose - in winter it's pretty 'normal'.
Not anecdotal.

"One hour in Giant's Hole in summer would be sufficient to exceed the recommended maximum annual 'additional' dose of radiation for a member of the public and during the ten caving trips made to collect the data for June and July 1988, Middleton received almost 500 WLM (> 36 mSv) of exposure. This represents over 70 per cent of the maximum permitted annual dose for a classified radiation worker..." quote from Cave Science Vol 18 No 2 August 1991 p 67 to 70 .
 
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