[EE] Radon Gas Detection, How to engineer my own?

[Jason White]

Hello everyone,

Recently I learned my neighbor has high levels of Radon in their basement
(they installed a mitigation system). Naturally, I was curious as to the
level in my own basement and purchased an electronic radon meter [1] from
the local hardware store [2]. Testing shows that my basement has a
concentration of roughly 20pC/L. (I am currently working on reducing the
level)

One inconvenient aspect of the electronic meter it does not provide an
instantaneous reading. It takes 48 hours to obtain the first reading. And
all subsequent readings are provided by the meter as a long term average.
That got my thinking: can I build my own Radon (alpha particle) meter?

As I understand it a electronic Radon sensor is essentially a large spark
gap. A potential is applied across the gap and when Radon gas decays it
emits alpha particles which causes the air in the gap to ionize - causing a
momentary spark across the gap. With this type of sensor I would assume the
level of radon gas is proportional to the number of sparks across the gap
per second.

I would like to learn: what it would take to design my own radon gas meter?
(For fun, not commercially) Any advice or links to resources (formulas,
charts) would be greatly appreciated.

I have not torn apart/reverse engineered my meter yet because I do not want
to alter the calibration. The documentation states that the sensor voltage
in my meter is 250 volts (DC?). I would assume higher voltages and larger
spark gap areas would yield higher sensitivity. I would have to wonder if
dust and other contaminants would be an issue for this type of detector?

[1] SafetySiren Pro Series 3 Radon Gas Detector, Claims initial accuracy of
20% or +/-1pC/L (whichever is greater).
[2] Home Depot

[Jean-Paul Louis]

Hi Jason,
Did you look at Geiger counter? There are many designs available online.
You could modify the firmware to provide integration if the count over
time, and whatever else info you want.

Just a thought,
Jean-Paul
N1JPL

On Sun, Sep 30, 2018, 11:41 AM Jason White <

Post by Jason White
Hello everyone,
Recently I learned my neighbor has high levels of Radon in their basement
(they installed a mitigation system). Naturally, I was curious as to the
level in my own basement and purchased an electronic radon meter [1] from
the local hardware store [2]. Testing shows that my basement has a
concentration of roughly 20pC/L. (I am currently working on reducing the
level)
One inconvenient aspect of the electronic meter it does not provide an
instantaneous reading. It takes 48 hours to obtain the first reading. And
all subsequent readings are provided by the meter as a long term average.
That got my thinking: can I build my own Radon (alpha particle) meter?
As I understand it a electronic Radon sensor is essentially a large spark
gap. A potential is applied across the gap and when Radon gas decays it
emits alpha particles which causes the air in the gap to ionize - causing a
momentary spark across the gap. With this type of sensor I would assume the
level of radon gas is proportional to the number of sparks across the gap
per second.
I would like to learn: what it would take to design my own radon gas meter?
(For fun, not commercially) Any advice or links to resources (formulas,
charts) would be greatly appreciated.
I have not torn apart/reverse engineered my meter yet because I do not want
to alter the calibration. The documentation states that the sensor voltage
in my meter is 250 volts (DC?). I would assume higher voltages and larger
spark gap areas would yield higher sensitivity. I would have to wonder if
dust and other contaminants would be an issue for this type of detector?
[1] SafetySiren Pro Series 3 Radon Gas Detector, Claims initial accuracy of
20% or +/-1pC/L (whichever is greater).
[2] Home Depot
--
Jason White
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[Jason White]

Hello Jean-Pau,

For some reason I recall reading that the window material(s) commonly used
in Geiger counters was not transparent to alpha particles? Perhaps I will
need to do some research.

-Jason White

[Wouter van Ooijen]

Post by Jason White
I would like to learn: what it would take to design my own radon gas meter?
(For fun, not commercially) Any advice or links to resources (formulas,
charts) would be greatly appreciated.

The setup you describe doesn't measure radon perse, but alpha particles.
As far as harm to you that doesn't matter much.

The detector you describe is a Geiger-Muller tube. The main challenge
(apart from filling the tube with a specific gass at a low pressure) for
detecting alpha particles is that nearly everything (including a sheet
of paper, to give you an idea) will block alpha particles. A very thin
sheet of mica seems to be the preferred window material. Summary: don't
try to build your own alpha-detecting GM tube, buy one.

The rest of the circuit isn't that special and examples can be found on
the web.

You probably won't gain much in 'instanteneous readout': the amount of
(detected) alpha particles is very low, so averaging over some period is
required to get a measurement with some accuracy.

[Chris Smolinski]

Coincidentally, I sell geiger counters. So the following may not be unbiased :)

You can detect radon by proxy by picking up the decay of it's daughter products. It's non trivial to convert geiger counter readings into radon levels (pCi/liter) and while my detectors can be used to detect radon, they don't measure actual radon levels, and I don't sell them as products to do such. If your goal is to get accurate radon levels, you should buy a product designed to do that.

But you can observe changes in radon levels fairly easily by observing the change in the geiger counter output (counts per minute) as it is relatively linear. From experimentation, it varies with the weather; high and low pressure systems can affect the flow of radon gas from the ground into your house (typically the basement). You can even use a fan and piece of filter cloth to trap the radon daughter products in front of the geiger tube, essentially amplifying the signal. (I sell such a contraption)

A "pancake" style geiger tube has a large area mica window, and is substantially more sensitive to the alpha and beta rays from the radon products vs a small diameter end window tube, it's a function of the tube window surface area. Of course you can increase your averaging time period to reduce statistical noise, the rule that doubling the averaging period reduces the noise by the square root of two applies.

"Typical" background radiation levels vary with the sensitivity of the geiger counter which is a function of the tube type and size. In engineering units, 10-20 uR/hr is a good ballpark figure. Higher if you live at high altitudes or in areas with high background radiation levels . This is 10-20 CPM with a small end window tube and maybe 45-90 CPM with a large pancake tube. Mostly what you are detecting here is cosmic rays (hence the altitude variation), the pancake detector is not significantly more sensitive for them.

Chris Smolinski
Black Cat Systems
Westminster, MD USA
http://www.blackcatsystems.com

Post by Wouter van Ooijen

Post by Jason White
I would like to learn: what it would take to design my own radon gas meter?
(For fun, not commercially) Any advice or links to resources (formulas,
charts) would be greatly appreciated.

The setup you describe doesn't measure radon perse, but alpha particles.
As far as harm to you that doesn't matter much.
The detector you describe is a Geiger-Muller tube. The main challenge
(apart from filling the tube with a specific gass at a low pressure) for
detecting alpha particles is that nearly everything (including a sheet
of paper, to give you an idea) will block alpha particles. A very thin
sheet of mica seems to be the preferred window material. Summary: don't
try to build your own alpha-detecting GM tube, buy one.
The rest of the circuit isn't that special and examples can be found on
the web.
You probably won't gain much in 'instanteneous readout': the amount of
(detected) alpha particles is very low, so averaging over some period is
required to get a measurement with some accuracy.
--
Wouter "Objects? No Thanks!" van Ooijen
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Sean Breheny]

This is the kind of question which made the piclist such a great place to
be - too bad there aren't many of these questions nowadays.

Chris did a really good job answering this. I just wanted to add, for
perspective, the literal meaning of 1 pC/L. 1 Curie is defined as the
activity (decay events per second) of 1 gram of pure Radium 226, which is
about 37 billion events per second.

A picocurie is 1 trillionth of this, or 0.037 events per second. So 1 pC/L
is only 0.037 events per second per liter. This should help you to see why
some significant amount of averaging is needed to get a good measurement at
such low concentrations of radioactive material.

I have a vintage CDV-700 6B geiger counter with an aftermarket modern
pancake probe (like Chris mentions). In a series of tests I did about 2
years ago, my geiger counter read a background reading in my apartment of
47 counts per minute with no cover on the probe and 42 counts per minute
with a plastic cover, each averaged over about an hour. I think most of
this difference is from the reduced flow of Radon to the face of the probe.

I think your only hope of obtaining a faster reading update rate is to use
a fan to draw large volumes of air into your sensor. The only way that
this will help you, though, is if you either compress the air and have a
sensor inside the compressed air volume OR have a filter which you collect
solid Radon decay product particles on.

Sean


On Sun, Sep 30, 2018 at 3:30 PM Chris Smolinski <

Post by Chris Smolinski
Coincidentally, I sell geiger counters. So the following may not be unbiased :)
You can detect radon by proxy by picking up the decay of it's daughter
products. It's non trivial to convert geiger counter readings into radon
levels (pCi/liter) and while my detectors can be used to detect radon, they
don't measure actual radon levels, and I don't sell them as products to do
such. If your goal is to get accurate radon levels, you should buy a
product designed to do that.
But you can observe changes in radon levels fairly easily by observing the
change in the geiger counter output (counts per minute) as it is relatively
linear. From experimentation, it varies with the weather; high and low
pressure systems can affect the flow of radon gas from the ground into your
house (typically the basement). You can even use a fan and piece of filter
cloth to trap the radon daughter products in front of the geiger tube,
essentially amplifying the signal. (I sell such a contraption)
A "pancake" style geiger tube has a large area mica window, and is
substantially more sensitive to the alpha and beta rays from the radon
products vs a small diameter end window tube, it's a function of the tube
window surface area. Of course you can increase your averaging time period
to reduce statistical noise, the rule that doubling the averaging period
reduces the noise by the square root of two applies.
"Typical" background radiation levels vary with the sensitivity of the
geiger counter which is a function of the tube type and size. In
engineering units, 10-20 uR/hr is a good ballpark figure. Higher if you
live at high altitudes or in areas with high background radiation levels .
This is 10-20 CPM with a small end window tube and maybe 45-90 CPM with a
large pancake tube. Mostly what you are detecting here is cosmic rays
(hence the altitude variation), the pancake detector is not significantly
more sensitive for them.
Chris Smolinski
Black Cat Systems
Westminster, MD USA
http://www.blackcatsystems.com

Post by Wouter van Ooijen

Post by Jason White
I would like to learn: what it would take to design my own radon gas

meter?

Post by Wouter van Ooijen

Post by Jason White
(For fun, not commercially) Any advice or links to resources (formulas,
charts) would be greatly appreciated.

The setup you describe doesn't measure radon perse, but alpha particles.
As far as harm to you that doesn't matter much.
The detector you describe is a Geiger-Muller tube. The main challenge
(apart from filling the tube with a specific gass at a low pressure) for
detecting alpha particles is that nearly everything (including a sheet
of paper, to give you an idea) will block alpha particles. A very thin
sheet of mica seems to be the preferred window material. Summary: don't
try to build your own alpha-detecting GM tube, buy one.
The rest of the circuit isn't that special and examples can be found on
the web.
You probably won't gain much in 'instanteneous readout': the amount of
(detected) alpha particles is very low, so averaging over some period is
required to get a measurement with some accuracy.
--
Wouter "Objects? No Thanks!" van Ooijen
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

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[Sean Breheny]

I just thought of another thing to think about - there are three kinds of
radiation detectors, considered by function:

1) Single-event non-proportional detectors
2) Single-event proportional detectors
3) Continuous rate detectors

Category 1 is mostly Geiger-Mueller tubes. Category 2 includes
scintillation detectors (material which emits light in response to
ionization, coupled to a sensitive photodetector like a photomultiplier
tube or avalanche photodiode) as well as gas-proportional tubes. Category
3 is mostly ionization chambers.

In this context, single event detection means that there is a good
probability (>10%) of seeing each individual decay event whose emissions
intersect the detector. Actual probability will depend on type of radiation
(alpha, beta, gamma, neutron, muon, etc.) and energy level of the
particles. Proportional means that information about the energy level of
each event is preserved in the detector output (usually by a varying
amplitude of output pulse). Continuous rate means that the detector doesn't
output pulses but rather a current which is proportional to the radiation
level - but this also assumes that the radiation level is high enough for
the continuous current to be more than just a few electrons per second)

The same basic detector CAN operate in all three modes/categories by
varying the voltage applied and the pressure of the gas inside. An
ionization chamber measures the leakage current through an air gap with a
moderately high applied voltage (maybe 250V). More radiation means more
ions generated which means more leakage - but each ionization event makes
only a few electrons so you can't detect individual events. However, this
also means that the detector cannot be overwhelmed by even very high
radiation levels. Going to a slightly higher voltage (about 600V usually)
and lower gas pressure, some gas-multiplication effects can happen. This is
where each ionization event causes a localized avalanche. There is a
multiplication factor but it isn't so high that the entire tube is ionized
during each event. Therefore, within certain resolution limits, energy
information is preserved. Going even higher (900 to 1000V) and using
special mixtures of gasses makes a GM tube. The secret to a GM tube is that
each ionization event not only causes an avalanche but there is UV light
emitted from the avalanche. This UV light then causes the gas in areas
surrounding the actual ionization event to ionize and break down into an
avalanche. This then in turn produces additional UV light until the entire
tube breaks down and conducts at once. This produces a massive
magnification factor, making single events easily detectable, BUT you also
need a quenching mechanism (in a GM tube this is part of the gas mixture
which causes ion recombination to overcome the avalanche effect after a
brief time - roughly 10s of microseconds) otherwise the tube would remain
broken-down indefinitely after just one event. This means that a GM tube
can be easily saturated and read almost no counts at all in response to
very high radiation fields. It also means that information about the energy
of the radiation per event is lost.

Sean


On Sun, Sep 30, 2018 at 3:30 PM Chris Smolinski <

Post by Chris Smolinski
Coincidentally, I sell geiger counters. So the following may not be unbiased :)
You can detect radon by proxy by picking up the decay of it's daughter
products. It's non trivial to convert geiger counter readings into radon
levels (pCi/liter) and while my detectors can be used to detect radon, they
don't measure actual radon levels, and I don't sell them as products to do
such. If your goal is to get accurate radon levels, you should buy a
product designed to do that.
But you can observe changes in radon levels fairly easily by observing the
change in the geiger counter output (counts per minute) as it is relatively
linear. From experimentation, it varies with the weather; high and low
pressure systems can affect the flow of radon gas from the ground into your
house (typically the basement). You can even use a fan and piece of filter
cloth to trap the radon daughter products in front of the geiger tube,
essentially amplifying the signal. (I sell such a contraption)
A "pancake" style geiger tube has a large area mica window, and is
substantially more sensitive to the alpha and beta rays from the radon
products vs a small diameter end window tube, it's a function of the tube
window surface area. Of course you can increase your averaging time period
to reduce statistical noise, the rule that doubling the averaging period
reduces the noise by the square root of two applies.
"Typical" background radiation levels vary with the sensitivity of the
geiger counter which is a function of the tube type and size. In
engineering units, 10-20 uR/hr is a good ballpark figure. Higher if you
live at high altitudes or in areas with high background radiation levels .
This is 10-20 CPM with a small end window tube and maybe 45-90 CPM with a
large pancake tube. Mostly what you are detecting here is cosmic rays
(hence the altitude variation), the pancake detector is not significantly
more sensitive for them.
Chris Smolinski
Black Cat Systems
Westminster, MD USA
http://www.blackcatsystems.com

Post by Wouter van Ooijen

Post by Jason White
I would like to learn: what it would take to design my own radon gas

meter?

Post by Wouter van Ooijen

Post by Jason White
(For fun, not commercially) Any advice or links to resources (formulas,
charts) would be greatly appreciated.

The setup you describe doesn't measure radon perse, but alpha particles.
As far as harm to you that doesn't matter much.
The detector you describe is a Geiger-Muller tube. The main challenge
(apart from filling the tube with a specific gass at a low pressure) for
detecting alpha particles is that nearly everything (including a sheet
of paper, to give you an idea) will block alpha particles. A very thin
sheet of mica seems to be the preferred window material. Summary: don't
try to build your own alpha-detecting GM tube, buy one.
The rest of the circuit isn't that special and examples can be found on
the web.
You probably won't gain much in 'instanteneous readout': the amount of
(detected) alpha particles is very low, so averaging over some period is
required to get a measurement with some accuracy.
--
Wouter "Objects? No Thanks!" van Ooijen
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

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[Jason White]

Thank you Wouter, Chris, and especially Sean.

From what I have read a basic ionization chamber like the one

described by Sean Breheny and linked to [1] by Brooke Clark is exactly
what I am looking for. A metal tube with center electrode and forced
air via fan sounds easy to construct. Once set up periodic readings of
leakage current (possibly through amplifier) via multi-meter would
provide me with the information I am looking for [2]. Although I am
somewhat unclear as to how operation of an ionization chamber with a
filter (to trap solid radon by products) would work.

[1] http://www.techlib.com/science/ionchamber.htm
[2] although dust, humidity, and temperature will likely cause quite
some variation

I just thought of another thing to think about - there are three kinds of
1) Single-event non-proportional detectors
2) Single-event proportional detectors
3) Continuous rate detectors
Category 1 is mostly Geiger-Mueller tubes. Category 2 includes
scintillation detectors (material which emits light in response to
ionization, coupled to a sensitive photodetector like a photomultiplier
tube or avalanche photodiode) as well as gas-proportional tubes. Category
3 is mostly ionization chambers.
In this context, single event detection means that there is a good
probability (>10%) of seeing each individual decay event whose emissions
intersect the detector. Actual probability will depend on type of radiation
(alpha, beta, gamma, neutron, muon, etc.) and energy level of the
particles. Proportional means that information about the energy level of
each event is preserved in the detector output (usually by a varying
amplitude of output pulse). Continuous rate means that the detector doesn't
output pulses but rather a current which is proportional to the radiation
level - but this also assumes that the radiation level is high enough for
the continuous current to be more than just a few electrons per second)
The same basic detector CAN operate in all three modes/categories by
varying the voltage applied and the pressure of the gas inside. An
ionization chamber measures the leakage current through an air gap with a
moderately high applied voltage (maybe 250V). More radiation means more
ions generated which means more leakage - but each ionization event makes
only a few electrons so you can't detect individual events. However, this
also means that the detector cannot be overwhelmed by even very high
radiation levels. Going to a slightly higher voltage (about 600V usually)
and lower gas pressure, some gas-multiplication effects can happen. This is
where each ionization event causes a localized avalanche. There is a
multiplication factor but it isn't so high that the entire tube is ionized
during each event. Therefore, within certain resolution limits, energy
information is preserved. Going even higher (900 to 1000V) and using
special mixtures of gasses makes a GM tube. The secret to a GM tube is that
each ionization event not only causes an avalanche but there is UV light
emitted from the avalanche. This UV light then causes the gas in areas
surrounding the actual ionization event to ionize and break down into an
avalanche. This then in turn produces additional UV light until the entire
tube breaks down and conducts at once. This produces a massive
magnification factor, making single events easily detectable, BUT you also
need a quenching mechanism (in a GM tube this is part of the gas mixture
which causes ion recombination to overcome the avalanche effect after a
brief time - roughly 10s of microseconds) otherwise the tube would remain
broken-down indefinitely after just one event. This means that a GM tube
can be easily saturated and read almost no counts at all in response to
very high radiation fields. It also means that information about the energy
of the radiation per event is lost.
Sean
On Sun, Sep 30, 2018 at 3:30 PM Chris Smolinski <

Post by Chris Smolinski
Coincidentally, I sell geiger counters. So the following may not be unbiased :)
You can detect radon by proxy by picking up the decay of it's daughter
products. It's non trivial to convert geiger counter readings into radon
levels (pCi/liter) and while my detectors can be used to detect radon, they
don't measure actual radon levels, and I don't sell them as products to do
such. If your goal is to get accurate radon levels, you should buy a
product designed to do that.
But you can observe changes in radon levels fairly easily by observing the
change in the geiger counter output (counts per minute) as it is relatively
linear. From experimentation, it varies with the weather; high and low
pressure systems can affect the flow of radon gas from the ground into your
house (typically the basement). You can even use a fan and piece of filter
cloth to trap the radon daughter products in front of the geiger tube,
essentially amplifying the signal. (I sell such a contraption)
A "pancake" style geiger tube has a large area mica window, and is
substantially more sensitive to the alpha and beta rays from the radon
products vs a small diameter end window tube, it's a function of the tube
window surface area. Of course you can increase your averaging time period
to reduce statistical noise, the rule that doubling the averaging period
reduces the noise by the square root of two applies.
"Typical" background radiation levels vary with the sensitivity of the
geiger counter which is a function of the tube type and size. In
engineering units, 10-20 uR/hr is a good ballpark figure. Higher if you
live at high altitudes or in areas with high background radiation levels .
This is 10-20 CPM with a small end window tube and maybe 45-90 CPM with a
large pancake tube. Mostly what you are detecting here is cosmic rays
(hence the altitude variation), the pancake detector is not significantly
more sensitive for them.
Chris Smolinski
Black Cat Systems
Westminster, MD USA
http://www.blackcatsystems.com

Post by Wouter van Ooijen

Post by Jason White
I would like to learn: what it would take to design my own radon gas

meter?

Post by Wouter van Ooijen

Post by Jason White
(For fun, not commercially) Any advice or links to resources (formulas,
charts) would be greatly appreciated.

The setup you describe doesn't measure radon perse, but alpha particles.
As far as harm to you that doesn't matter much.
The detector you describe is a Geiger-Muller tube. The main challenge
(apart from filling the tube with a specific gass at a low pressure) for
detecting alpha particles is that nearly everything (including a sheet
of paper, to give you an idea) will block alpha particles. A very thin
sheet of mica seems to be the preferred window material. Summary: don't
try to build your own alpha-detecting GM tube, buy one.
The rest of the circuit isn't that special and examples can be found on
the web.
You probably won't gain much in 'instanteneous readout': the amount of
(detected) alpha particles is very low, so averaging over some period is
required to get a measurement with some accuracy.
--
Wouter "Objects? No Thanks!" van Ooijen
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

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