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 2.GQ Geiger Muller Counter
 Is my wall radioactive?

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Damien68 Posted - 09/04/2019 : 11:12:58
Since I started my meter, I have a very stable operation.
He was sensitive to his position, I think I found why.

In any case, when my detector is out far from everything, I have 22 CPM (average)
Inside the house, on my desk it is 27CPM
And close to the wall of my house he goes to 32CPM (on the inside or outside side of the wall.

my wall is build with hollow breeze + plastered brick + plaster

Also as I am in Bretagne in France, I am in high risk radon zone.

But radon emits alpha particles, in principle it is not detected by GMC-500, but could it be partially?

Below is a recording that I made,
Can someone help me understand what it could be, if it can be radon?
The levels are not very violent either, but could be different if I did the same thing with a GMC-600.
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9   L A T E S T    R E P L I E S    (Newest First)
Damien68 Posted - 09/06/2019 : 07:22:54
I did some fast qualitative tests,
I use a 'U' bent sheet of 15/10 millimeter of steel as shielding. it may be a little too thick, I'll try to find a 1mm

Now I have the following results are done on fast periods of 1h each (is short but is just to have qualitative informations)

in my garden without shield: 22CPM
in my garden with shield: 22 CPM, apparently the shield is neutral

on my wall without GMC500 rear cover: 33CPM
on my wall with a steel shield: 29CPM

if we remove the floor level on these two last measure it gives

on my wall without shield: +11 CPM
on my wall with 1.5mm steel shield: +7 CPM

the numbers are not very accurate but it suggests that we mostly have couples of (Beta + GAMA)

But you're right Ullix, in any case, there is no matter to worry, these are very very low levels, that's why it takes a long time to integrate, so it's reassuring.
But it's always amazing to discover things we've never seen (and that we will never really see) even though we already knew it existed, we can almost touch them :)

ullix Posted - 09/06/2019 : 01:11:37
I don't see any reason to suspect Radon as a source of radiation in your home, let alone a significant one. And even if it were even detectable - the radiation that you have measured is very low!

If you want to further characterize the type of radiation, I suggest this:

The radiation from our environment is predominantly beta (K40, U, Th, etc). The plastic case of a counter is already absorbing a good chunk of the betas. So, take off the backplate to have tube exposed, and then with this naked tube go close to the wall, tiles, stoneware, etc. and register counts over a sufficiently long time. Poisson verification recommended!

Actually, you might want to leave a space of a few mm. This will allow you to insert some shielding material to absorb all betas and only let the gammas pass almost unchanged. The difference between the counts with/without shielding will then provide an estimate for the betas and gammas.

The shielding could be glass (3mm), aluminum (3mm), copper (2mm), steel (1mm). But since those materials may result in the creation of Bremsstrahlung, confounding your results, you might also experiment with sandwiched material (plastic + metal).

More details on all those consideration in my Potty Training ( )

Damien68 Posted - 09/05/2019 : 09:58:49
It's true, Ullix could be right, I have the same detections but a little weaker on the internal walls with thin brick and plaster, and my office is well ventilated, I have an outside door that stays open all day (in summer).
In short, I don't worry too much, I would see at ocasuion if I can make a radon balance or buy a detector.
EmfDev Posted - 09/05/2019 : 09:40:26
If you're worried that it's radon, maybe put some ventilation?
Maybe your friends have some radon/alpha detector maybe try to verify with their units.
There could also be that the wall contains some slightly radioactive materials and actually not radon just as ullix said. If it is indeed because of radon, then it shouldn't be only present near the wall but throughout the house.
Damien68 Posted - 09/05/2019 : 02:01:17
Hi Ullix, thank you for your comments, which are interesting, the materials can also be the main cause.
"far from everything" is relative, ie enough to see the level drop and the influence of the house disappear in the noise, even if it remains of course natural radioactivity and instrument Background.
ullix Posted - 09/05/2019 : 01:25:43
I would argue that you never are "far from everything", because on the one side you will have the whole earth, and on the other other half the universe. Both contribute to the count rates measured, which we call the background.

It is also not surprising that wall material, and tiles in particular, contribute to the background. This may be due to an enhanced concentration of Potassium ( see my Potty Training article) or due to contributions of heavy metals, including some of the Uranium & friends intentional (colors) or un-intentional mixtures.

Just be aware of what your background is at any spot. It should be rather constant. If not, make sure the tube is not acting up before you blame anyone for missile explosions ;-)

By the way, GQ is specifying their counters with the M4011 tube as having an
"Instrument Background: < 0,2 pulses/s" (see any of their manuals)
i.e. the counter / tube assembly may contribute up to 12CPM! Nothing one can do about it.
Damien68 Posted - 09/05/2019 : 01:04:58
Hi EmfDev,

I confirm my levels, they are stable and repeatable.
Over the nights and the days I have small temperature changes that I do not see disturbing my measurements but the changes are straightforward and systematic when I approach my wall and they stay with right stability.

At the same time, I found what I did not understand:
Looking to the chain of disintegration of Uranium 238, of which radon gas (Rn222) is a part:

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We see that in the short term, the 'radon 222' Gas (Rn222) in his disintegration sequence emits 3 alpha particles and 2 beta particles to arrive at 'Lead 210'(Pb210).
Then after, with a half-life of 22 years, it emit 2 Beta and 1 alpha to arrive at 'Lead 206'(Pb206) stable and not radioactive.

Because of my wall is build with hollow breeze and the radon gas and its derivatives are confined inside,
My GMC-500 must see Beta particles emited during Pb214->Bi214 and Bi214->Po214 desintegration,
and peraps because my house have more 40 years old, the 2 beta particles emited during Pb210->Bi210 and Bi210->Po210 desintegration.

All these elements are highly coherent
I have all trusts in this (measurement, instrument and interpretation).
The levels are correct, it is part of the natural radioactivity.
If in a flea market, I find an old pot of lead paint, I would take it to shield my wall;)
but sure, I do not need thorium lamp mantle or other to test my devices.

Damien68 Posted - 09/04/2019 : 13:09:38
The temperature is about the same about 24 C
I made measurements against the wall at the same temperature as far from everything.

Likewise the interior against the wall and on my desk is same temperature and the measurement is diferent.

I also see the Ullix post and do some experimentation, but I do not find significatives variations of the measurement depending on the temperature, I just test around 20 and 30 C.

But I will redo more measurements with my wall.

EmfDev Posted - 09/04/2019 : 12:31:43
Ullix has tested the tube few days ago and thinks that the tube can be affected by temperature. How is temperature different from outside? Just to make sure it's not a part of why the increase in CPM near the wall.

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