classic example of bad neutron metrology

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Richard Hull
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classic example of bad neutron metrology

Post by Richard Hull » Sun Feb 11, 2018 8:34 pm

As an electronics experimenter, among other things, I take a subscription to "Nuts and Volts" magazine. They typically have a regular article on "near space" balloon launches focusing on the various electronics packages. This is getting to be the new ham radio for those who used to like contacting Australia and get the QSL cards. Today you just take your $10.00/month cell phone and call "down-under" in seconds, clear as a bell, no QRM.

Anyhow, the latest issue sports a near space launch during the recent eclipse. Part of that launch included an electronic Geiger counter and a BTI bubble detector. The author, in a photo, noted the 40 bubbles on its return from near space, (above 90,000 feet) and says that it detected 40 neutrons! I strained to see the binning data on the BTI in the photo, but alas, could not see it. The author must have figured that was just "tech stuff" on the label. Oh well, so much for another example of why regular folks can't be trusted to take neutron measurements. Shades of cold fusion electro-chemists having a whack at it.

Another fact is no mention that this detector only detected fast neutrons for the most part or that at that altitude energetic matter particles come in at billions of electron volts, which just might trigger a bubble or two. The BTI detectors are "binned" using fast neutrons at ground level. All bets are off if you ditch 18 miles of atmosphere that clobber the bulk of deadly space radiation before it reaches sea level.

With these launches, pressure and temperature at altitude can affect things, too. If a mica windowed GM detector was used, its little window would not be stressed but relaxed a bit...OK...., but what effect would the cold and low pressure have on a BTI binning, even if the author had bothered to do the total dose conversion back to some sort of averaged neutron count.

The upshot is that good neutron counting is tough and why we are so tough on would-be applicants to the neutron club. This reminder is important to all who would think neutron counting is a snap just because you have a neutron counter.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Steven Sesselmann
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Re: classic example of bad neutron metrology

Post by Steven Sesselmann » Sun Feb 11, 2018 10:36 pm


Apart from the questionable metrology, I would be concerned about how the bubble detector behaves at low atmospheric pressure/temperature. The idea of using a bubble detector is fine, but it would have to be enclosed inside a chamber at constant 1 ATM pressure and temperature.

Steven - Gamma Spectrometry Systems - Various papers and patents on RG

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