Big detector tubes are absolutely the way to go to detect neutrons. Richard had the right idea!
The picuture in the Images Section show the 2 foot tall 6 inch in diameter moderater tube for a 22" by 1" active area neutron tube. I had been trying to get a BF3 tube to detect but I am limited in my voltage of my Ludlums to 2,500 volts. This particular tube is multiple atmospheres and requires voltage as high as 5,600 volts (which I do not have). Somewhat discouraged I deceided to buy a brand new He3 tube of the same dimension. I had been hesitant becasue the output signal is 3 to 4 times smaller than the BF3 tube. None the less, I put the tube into the moderator and started to bring the voltage up slowly as I adjusted the threshold settings. At 1,700 volts magic happened. I fiddled with the threshold and did a coulple of fusor runs on two different days. After crunching the numbers and running lower and lower fusor voltages. At 10 KV and 10ma, I measured 4,000 neutrons/sec detected 18 inches from my fusor. This gave 24 extra counts a minute on the Ludlum 2200.
Run, don't walk and go buy a bid He3 Detector!
Frank S.
P.S. You don't need NIMs and Preamps and you may be able to used a portable scaler counter if it has an adjustable discriminator and threshold adjustment. I now have the tube detecting using my hand held Ludlum 2241-2. Nothing against NIMs but portable has its advantages.
Run, don't walk and go buy a big He3 Detector!
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Frank Sanns
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Run, don't walk and go buy a big He3 Detector!
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Richard Hull
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Re: Run, don't walk and go buy a big He3 Detector!
Wow! If you bought that baby brand new it must have cost a gang o' bucks, unless you got it as an NOS item.
I am glad you are enjoying the gratifying results of the He3 detector. You can now detect marginal neutron levels
Richard Hull
I am glad you are enjoying the gratifying results of the He3 detector. You can now detect marginal neutron levels
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: Run, don't walk and go buy a big He3 Detector!
Bit big for the job, but a microwave oven transformer with the normal doubler will give you the 5000 volts - if you hook it up with a variac, it should make a set up for 0 - to about 6000v - usual precautions with High Current/High Voltage. A ripple filter on the O/P will clean the DC.
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AllenWallace
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Re: Run, don't walk and go buy a big He3 Detector!
Frank,
What is your background rate? Also, what is your elevation?
My 22" He3 tube has a background rate of about 30 cpm, and I'm at 4700 feet.
Allen Wallace
What is your background rate? Also, what is your elevation?
My 22" He3 tube has a background rate of about 30 cpm, and I'm at 4700 feet.
Allen Wallace
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Frank Sanns
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Re: Run, don't walk and go buy a big He3 Detector!
Richard,
He3 is never cheap. As you know just the gas in these big tubes alone are in the hundreds of dollars. Even NOS is not cheap but they are a great value!
John,
Thanks for the idea but I don't think I am going to be needing it. The tube looks to be bad. Used one of Carl Willis's supplies and ran the voltage way up. Still no count so the BF3 must have leaked out.
Allen,
I live at 1150 feet. My background counts are between 6 and 9 counts per minute. Thirty sounds high to me. Since the tube is new I would not suspect it but rather the leads or the threshold setting. See Carl Willis's and Richard's post on setting up the tube.
With the quiet tube, I can detect a source against the moderater that is emitting 10-12 neutrons/second isotropically. Only took a couple of back to back counts for 3 minutes with and without the source to confirm it. This may sound astonishing but it was confirmed during a recent visit here by Carl Willis. These tubes are great!
Frank S.
He3 is never cheap. As you know just the gas in these big tubes alone are in the hundreds of dollars. Even NOS is not cheap but they are a great value!
John,
Thanks for the idea but I don't think I am going to be needing it. The tube looks to be bad. Used one of Carl Willis's supplies and ran the voltage way up. Still no count so the BF3 must have leaked out.
Allen,
I live at 1150 feet. My background counts are between 6 and 9 counts per minute. Thirty sounds high to me. Since the tube is new I would not suspect it but rather the leads or the threshold setting. See Carl Willis's and Richard's post on setting up the tube.
With the quiet tube, I can detect a source against the moderater that is emitting 10-12 neutrons/second isotropically. Only took a couple of back to back counts for 3 minutes with and without the source to confirm it. This may sound astonishing but it was confirmed during a recent visit here by Carl Willis. These tubes are great!
Frank S.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Richard Hull
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Re: Run, don't walk and go buy a big He3 Detector!
My normal neutron background with the 22" He3 in the lab varies from 10/min to 18/min with the most common being 12-15/minute.
The only draw back to the He3 tube is that it is still electronic in nature and the output signal is low. This leaves it open for problems in nightmare pulsed energy and high RFI background situations. This is why the bubble detector backup is so important.
I understand there exists, but have only moderately experienced, a thermal background issue with BF3 tubes. The obvious result is a higher background at higher ambient temps and a reduced count at frigid temps. The span can amount to up to 40% background differential between about 20 deg F and 100 deg F. I checked my records here and I have seen a differential of about 20% using this system hot to cold. I, unfortunately, can't separate variable background days (cosmic) from a temeprature variation based on data in hand.
The ultimate test would be to conduct a heating and cooling test on the same day where the background might remain more of less constant compared to the artificially cycled temp range.
As an aside, The more we actively involve ourselves in neutron metrology and the more we talk and hammer out issues, we become increasingly immune to the old saw that our metrology is amateurish or flawed. At least 3 or 4 of us are armed with neutron metrology in hand that far exceeds many other researchers in CF and have practical experience approaching that used in some fusion labs!
Most improtantly, we are leary of being fooled by our instrumentation and don't take forgranted that it speaks truthfully at every turn. This is probably the greatest lesson to be learned and absorbed in neutron metrology.
The very size of this forum, being the largest by far here, shows the great concern and respect this entire fusion site has for the issue of replication and verification based on genuine sceintific measurement that will stand up.
Richard Hull
The only draw back to the He3 tube is that it is still electronic in nature and the output signal is low. This leaves it open for problems in nightmare pulsed energy and high RFI background situations. This is why the bubble detector backup is so important.
I understand there exists, but have only moderately experienced, a thermal background issue with BF3 tubes. The obvious result is a higher background at higher ambient temps and a reduced count at frigid temps. The span can amount to up to 40% background differential between about 20 deg F and 100 deg F. I checked my records here and I have seen a differential of about 20% using this system hot to cold. I, unfortunately, can't separate variable background days (cosmic) from a temeprature variation based on data in hand.
The ultimate test would be to conduct a heating and cooling test on the same day where the background might remain more of less constant compared to the artificially cycled temp range.
As an aside, The more we actively involve ourselves in neutron metrology and the more we talk and hammer out issues, we become increasingly immune to the old saw that our metrology is amateurish or flawed. At least 3 or 4 of us are armed with neutron metrology in hand that far exceeds many other researchers in CF and have practical experience approaching that used in some fusion labs!
Most improtantly, we are leary of being fooled by our instrumentation and don't take forgranted that it speaks truthfully at every turn. This is probably the greatest lesson to be learned and absorbed in neutron metrology.
The very size of this forum, being the largest by far here, shows the great concern and respect this entire fusion site has for the issue of replication and verification based on genuine sceintific measurement that will stand up.
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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AllenWallace
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Re: Run, don't walk and go buy a big He3 Detector!
>Thirty [counts per minute] sounds high to me.
Not really. A google search shows that the background neutron flux increases with elevation:
Sea Level = 1X
2000 ft = 2X
4500 ft = 3X
40K ft = 100X
Robert Hull indicates he is getting about 15 CPM background near sea level.
My detector background rate is 30 CPM@4700 ft, but if I normalize to sea level, it's only about 10 CPM.
Your background rate of about 10 cpm @1000 ft (forgive my rounding) normalizes to about 7 CPM.
My tube has an state-of-the-art intregrated power supply/amplifier and it's discriminator voltage was set by the factory, so I'm pretty confident in it.
I suspect that your rate is a little bit low and from your earlier description, perhaps you need more voltage.
Not really. A google search shows that the background neutron flux increases with elevation:
Sea Level = 1X
2000 ft = 2X
4500 ft = 3X
40K ft = 100X
Robert Hull indicates he is getting about 15 CPM background near sea level.
My detector background rate is 30 CPM@4700 ft, but if I normalize to sea level, it's only about 10 CPM.
Your background rate of about 10 cpm @1000 ft (forgive my rounding) normalizes to about 7 CPM.
My tube has an state-of-the-art intregrated power supply/amplifier and it's discriminator voltage was set by the factory, so I'm pretty confident in it.
I suspect that your rate is a little bit low and from your earlier description, perhaps you need more voltage.