The recent post in images forum regarding background count has me interested in the general background counts around the group here.
If you have a geiger counter why not post your average background count. I would suggest that you take both and indoor and out door count.
We should specify a few things to make the tests understood better. (A mica windowed counter might well indicate a higher background count than a thin metal cased geiger tube like the lionel tubes found in the civil defense counters.)
I'll start the ball rolling.
Counter details:
Simple counter setup based on NIM bin arrangement.
Detector: 2" pancake, LND 3711 type mica windowed tube.
Tube voltage 875 volts
Outdoor count average of three days 29.4 cpm
Indoor in lab 128.6 cpm
I have a number of minerals and sources in the lab and it is a bit higher background than outdoors. The Radon level in the lab is actually well within spec. 3.8pCi/Liter. I have a radon analyzer system and find that the lab is only slightly elevated above my upstairs lab area 2.9pCi/Liter. The lab high count is due to Gamma only, I figure.
Richard Hull
Background counts
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Richard Hull
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Background counts
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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ChrisSmolinski
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Re: Background counts
Richard,
Have you tried placing a shield over the mica window to block alpha/beta, for a guesstimate of the gamma component?
Also... I've been curious for a while about coming up with a crude calibration, or maybe relationship is a better word, between GM readings and radon levels, experimentally. My thought was to place some uranium ore in a sealed bucket, then run a pipe to a second chamber containing the detector. (maybe downhill, hoping the higher density of the radon will cause it to flow to the second chamber?) By controlling the flow of radon, you might be able to vary the concentration (pCi/L) in the detector chamber. One of the charcoal filters that you send out to a lab could be placed in there as well. Perform the test for varying CPM levels, sending the charcoal filter out for each test for analysis, and maybe determine the relationship? It might get expensive at the $20 a pop or so they charge for radon testing. And would only be valid for that one detector... One difficulty is the detector is picking up more of the radon decay products (Pb214, Bi214, etc) than the radon itself.
Thoughts?
Richard Hull wrote:
> Outdoor count average of three days 29.4 cpm
> Indoor in lab 128.6 cpm
>
> I have a number of minerals and sources in the lab and it is a bit higher background than outdoors. The Radon level in the lab is actually well within spec. 3.8pCi/Liter. I have a radon analyzer system and find that the lab is only slightly elevated above my upstairs lab area 2.9pCi/Liter. The lab high count is due to Gamma only, I figure.
>
> Richard Hull
Have you tried placing a shield over the mica window to block alpha/beta, for a guesstimate of the gamma component?
Also... I've been curious for a while about coming up with a crude calibration, or maybe relationship is a better word, between GM readings and radon levels, experimentally. My thought was to place some uranium ore in a sealed bucket, then run a pipe to a second chamber containing the detector. (maybe downhill, hoping the higher density of the radon will cause it to flow to the second chamber?) By controlling the flow of radon, you might be able to vary the concentration (pCi/L) in the detector chamber. One of the charcoal filters that you send out to a lab could be placed in there as well. Perform the test for varying CPM levels, sending the charcoal filter out for each test for analysis, and maybe determine the relationship? It might get expensive at the $20 a pop or so they charge for radon testing. And would only be valid for that one detector... One difficulty is the detector is picking up more of the radon decay products (Pb214, Bi214, etc) than the radon itself.
Thoughts?
Richard Hull wrote:
> Outdoor count average of three days 29.4 cpm
> Indoor in lab 128.6 cpm
>
> I have a number of minerals and sources in the lab and it is a bit higher background than outdoors. The Radon level in the lab is actually well within spec. 3.8pCi/Liter. I have a radon analyzer system and find that the lab is only slightly elevated above my upstairs lab area 2.9pCi/Liter. The lab high count is due to Gamma only, I figure.
>
> Richard Hull
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Richard Hull
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Re: Background counts
There is no real difference with a 1mm aluminum cover on the pancake. All the elevated count is gamma. All possible sources are located outside the range of the alpha or beta particles.
Richard Hull
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jon Rosenstiel
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Re: Background counts
Here's what I got.... (From southern California)
Counter details:
Ludlum 2200 counter/ratemeter
Detector: Eberline HP-260 2" pancake mica windowed tube.
Tube voltage: 900
Outdoor: 47.8 cpm
Indoor, in lab: 47.8 cpm
Indoor, in lab, on the concrete floor: 80.4 cpm.
The detector to floor, (concrete), distance was the same for both the indoor and outdoor counts.
I slipped a sheet of paper between the detector and the concrete, there was no change in the count rate. I then slipped a sheet of 0.016 Al between the detector and the concrete, the count rate dropped to 66.8 cpm. Guess the concrete is emitting beta & gamma, but no alpha. (Man, gotta’ get my hands on a gamma spectrometer!)
My radioactives are stored in a 12' x 12' out building, the count rate in that building was 80 cpm.
Jon Rosenstiel
Counter details:
Ludlum 2200 counter/ratemeter
Detector: Eberline HP-260 2" pancake mica windowed tube.
Tube voltage: 900
Outdoor: 47.8 cpm
Indoor, in lab: 47.8 cpm
Indoor, in lab, on the concrete floor: 80.4 cpm.
The detector to floor, (concrete), distance was the same for both the indoor and outdoor counts.
I slipped a sheet of paper between the detector and the concrete, there was no change in the count rate. I then slipped a sheet of 0.016 Al between the detector and the concrete, the count rate dropped to 66.8 cpm. Guess the concrete is emitting beta & gamma, but no alpha. (Man, gotta’ get my hands on a gamma spectrometer!)
My radioactives are stored in a 12' x 12' out building, the count rate in that building was 80 cpm.
Jon Rosenstiel
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AllenWallace
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Re: Background counts
When reporting the background rates, please also specify your elevation above sea level. I live at 4700 feet and I know that the I expect to see more cosmic rays than someone near sea level.
Also, please report the error tolerance of your measurements.
To do this, simply calculate the standard deviation (take the square root of the total count) and divide by the duration of the measurement.
For example, R. Hull reported a mean rate of 29.4 count/min over a period of 3 days. We can infer that he counted a total of about 127,000 counts. The square root is 356 or .082 counts per minute. It would be more accurate to say the he reported a mean rate of 29.4 +/- .082 cpm. Since Richard took such a long measurement, his 0.2% error is so small that it is hardly worth reporting.
However, since I don’t have easy access an accumulating GM counter at the moment, and I know others may be in the same situation, just take a reading of a shorter duration and report your error tolerance.
I just measured my simple homemade GM detector clicking away at 24 counts in 2 minutes. The standard deviation (square root) is 4.89, so I’ll report that the background rate in my living room is 12 +/- 2.4 cpm or 12 cpm with a 20% error.
Another way of saying this is that I have a 68% confidence that my true background rate is between 9.6 and 14.4 cpm. If I use two standard deviations, I can say that I have a 95% confidence that my true background rate is between 7.1 and 16.9 cpm.
That's *much* more sloppy than Richard's measurement, but It took me only 2 minutes compared to Richard's 3 days.
Allen Wallace
Also, please report the error tolerance of your measurements.
To do this, simply calculate the standard deviation (take the square root of the total count) and divide by the duration of the measurement.
For example, R. Hull reported a mean rate of 29.4 count/min over a period of 3 days. We can infer that he counted a total of about 127,000 counts. The square root is 356 or .082 counts per minute. It would be more accurate to say the he reported a mean rate of 29.4 +/- .082 cpm. Since Richard took such a long measurement, his 0.2% error is so small that it is hardly worth reporting.
However, since I don’t have easy access an accumulating GM counter at the moment, and I know others may be in the same situation, just take a reading of a shorter duration and report your error tolerance.
I just measured my simple homemade GM detector clicking away at 24 counts in 2 minutes. The standard deviation (square root) is 4.89, so I’ll report that the background rate in my living room is 12 +/- 2.4 cpm or 12 cpm with a 20% error.
Another way of saying this is that I have a 68% confidence that my true background rate is between 9.6 and 14.4 cpm. If I use two standard deviations, I can say that I have a 95% confidence that my true background rate is between 7.1 and 16.9 cpm.
That's *much* more sloppy than Richard's measurement, but It took me only 2 minutes compared to Richard's 3 days.
Allen Wallace
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Richard Hull
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Re: Background counts
My neighborhood's elevation: ~305 feet above sea level.
I usually take long readings for reporting purposes so that the std dev is a non-issue. Even an hour count will push the std dev into relative insignificance. Note* Rainy days can throw a monkey wrench into the works as radon will evolve from the soil and send readings often interestingly and significantly higher.
Richard Hull
I usually take long readings for reporting purposes so that the std dev is a non-issue. Even an hour count will push the std dev into relative insignificance. Note* Rainy days can throw a monkey wrench into the works as radon will evolve from the soil and send readings often interestingly and significantly higher.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jon Rosenstiel
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- Joined: Thu Jun 28, 2001 1:30 am
- Real name: Jon Rosenstiel
- Location: Southern California
Re: Background counts
Allen,
My elevation is 190ft. The count times were 5 hours, (300 minutes), giving a standard deviation of +/- 0.4 cpm.
Jon Rosenstiel
My elevation is 190ft. The count times were 5 hours, (300 minutes), giving a standard deviation of +/- 0.4 cpm.
Jon Rosenstiel
Re: Background counts
Had to go run some data... and find out the elevation of the lab....
Using a Monitor4 radiation detector with LND xxx (possibly the 712) G-M tube, got two quite similar readings as follows
23 hr consecutive run and a 5 hr run on different days,
avg background = 13.2 cpm
Bldg is a new standard tilt up concrete structure.
We're in Cypress CA, listed as 118 ft elevation.
Haven't yet done one at home lab, which is at higher elevation.
Dave Cooper
Using a Monitor4 radiation detector with LND xxx (possibly the 712) G-M tube, got two quite similar readings as follows
23 hr consecutive run and a 5 hr run on different days,
avg background = 13.2 cpm
Bldg is a new standard tilt up concrete structure.
We're in Cypress CA, listed as 118 ft elevation.
Haven't yet done one at home lab, which is at higher elevation.
Dave Cooper
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ChrisSmolinski
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Re: Background counts
I'm not sure that it is simple to estimate the error tolerance of background readings, because they are constantly changing. I see a 2:1 variation over the course of 24 hours in the long term trend (taking 5 minute averages and plotting them out). We're talking real long term variations, not statistical noise.
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Richard Hull
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Re: Background counts
Thanks for you input numbers Dave.
Chris is correct, and, as I have mentioned before, there are diurnal variations, solar cycle variations,etc. The most variable of the variables is the "leach rate" for ground locked radon gas which is seasonal and really related to local rainfall, directly.
In my area I have seen 50% variations at the same spot 1" above weather exposed soil in three hour long timed runs.
Still, we like to assign an average value ( quantitatively impossible for the area).
Real low std dev.'s borne of long collection times are great, but they are for that moment or run only and have little meaning outside of that narrow temporal window.
Richard Hull
Chris is correct, and, as I have mentioned before, there are diurnal variations, solar cycle variations,etc. The most variable of the variables is the "leach rate" for ground locked radon gas which is seasonal and really related to local rainfall, directly.
In my area I have seen 50% variations at the same spot 1" above weather exposed soil in three hour long timed runs.
Still, we like to assign an average value ( quantitatively impossible for the area).
Real low std dev.'s borne of long collection times are great, but they are for that moment or run only and have little meaning outside of that narrow temporal window.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Re: Background counts
my battery powered geiger runs at 890 volts
with a LND 712 geiger tube
Humm my indoor count is 28.6 cpm
outdoor count is 24.5 cpm over three day
I live in a concrete slab single level house with radioactives in the back room
My elevation is still to be determined...but it can not be that high in the lowlands of Mississippi.
Keep on Fusing!
Larry Leins
Fusor Tech
with a LND 712 geiger tube
Humm my indoor count is 28.6 cpm
outdoor count is 24.5 cpm over three day
I live in a concrete slab single level house with radioactives in the back room
My elevation is still to be determined...but it can not be that high in the lowlands of Mississippi.
Keep on Fusing!
Larry Leins
Fusor Tech
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Jon Rosenstiel
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Re: Background counts
Larry,
How do you get away with operating the 712 at 890V? The LND spec sheet gives the operating range as 450V to 650V.
Did you check the count rate with your detector directly on the floor? My background count rate is over 30 cpm higher when I place my detector on the concrete. (Pancake detector).
Jon Rosenstiel
How do you get away with operating the 712 at 890V? The LND spec sheet gives the operating range as 450V to 650V.
Did you check the count rate with your detector directly on the floor? My background count rate is over 30 cpm higher when I place my detector on the concrete. (Pancake detector).
Jon Rosenstiel
Re: Background counts
Hi Jon:
The tube is a 7127 LND and yes the voltage is high but the amperage is very small. The concrete in my Mississippi house is a lot quieter than my baracks floor in Colorado or my old house in Arkansas. I had to read the back of the tube the number had worn on top from handling. I thought it was a subminy of the 714 series it has the thin window and all.
Oh well!
Keep on Fusing!
Larry Leins
Fusor Tech
The tube is a 7127 LND and yes the voltage is high but the amperage is very small. The concrete in my Mississippi house is a lot quieter than my baracks floor in Colorado or my old house in Arkansas. I had to read the back of the tube the number had worn on top from handling. I thought it was a subminy of the 714 series it has the thin window and all.
Oh well!
Keep on Fusing!
Larry Leins
Fusor Tech
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ChrisSmolinski
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Re: Background counts
The 7127 is also rated for 500 volts. You're able to
operate it at 900V?
operate it at 900V?
Re: Background counts
Hi Chris:
I read it off the tube itself.
The kit I had must have had a cookie cutter aproach to it.
A nine volt battery runs it.
It uses a 555 oscillator to drive a very small trani.
I paid a grand total of 34 dollars for it in kit form.
I've had it since 1983....not a problem with voltage being too high....you could touch it.
It seems to work pretty good....I had it put against a calibrated unit ....it seemed to be in working order.
Keep on Fusing!
Larry Leins
Fusor Tech
I read it off the tube itself.
The kit I had must have had a cookie cutter aproach to it.
A nine volt battery runs it.
It uses a 555 oscillator to drive a very small trani.
I paid a grand total of 34 dollars for it in kit form.
I've had it since 1983....not a problem with voltage being too high....you could touch it.
It seems to work pretty good....I had it put against a calibrated unit ....it seemed to be in working order.
Keep on Fusing!
Larry Leins
Fusor Tech