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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Just after a cursor search of facts, it appears with a normal scintillator plastic detector, gamma exclusion is the real problem.
link to previous thread: bismuth ?
Is lead (or any high mass shielding) the only way to selectively exclude false (non-neutron) flashes? If I put 1 cm of scintillating plastic, surrounded by 5 cm of lead I could exclude 90% of the gamma, and insignificant neutron quantity. But a 10cm diameter lead ball doesn't sound light in mass. In fact if I drop it from 300 feet up, I bet it could kill.
Is there any clever way to deal with this? Or are neutron detectors just kinda at this disadvantage in general?
EDIT: 5.8kg =12.7lbs, crap on a stick
NOTE TO SELF: look up lithium iodide in the morning.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
ZnS:Ag is a common neutron scintillator material that has very low gamma sensitivity. You generally wouldn't even need to worry about gamma shielding. The construction is often referred to as a Hornyak button. Bicron makes some of these neutron detectors.
In general though, he3 tubes are preferred for neutron detection. When biased properly you can easily discriminate non-neutron counts out simply because they have a much lower amplitude.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
dude_500 wrote ...
ZnS:Ag is a common neutron scintillator material that has very low gamma sensitivity. You generally wouldn't even need to worry about gamma shielding. The construction is often referred to as a Hornyak button. Bicron makes some of these neutron detectors.
In general though, he3 tubes are preferred for neutron detection. When biased properly you can easily discriminate non-neutron counts out simply because they have a much lower amplitude.
never heard this let me research this further! this is why i post here on 4hv.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Possibly, there is a NASA paper from the late 1980's concerning superconductors being used as a radiation shield. It seems that the secret is to deflect the gammas and X-rays rather than absorb them, same sort of idea as a metamaterial I guess.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
What sort of nuclear industrial accident from small spill or leak to actual meltdown would need neutron detection to manage it?
The pocket dosimeters used throughout the nuclear industry worldwide detect gammas and energetic betas only.
My advice: don't waste your time on this neutron red herring.
Use a common miniature GM dosimetry tube like ZP1313, or if you want to go solid state, use a PIN photodiode like BPX65, which has been used in some miniature dosimeter designs since the 1980s.
The miniature GM tube has the advantage of low cost and simple circuitry which you can expect to work well right away. It also offers excellent immunity to destruction by intense ionizing radiation, where a PIN photodiode might suffer irreversible changes.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Proud Mary wrote ...
What sort of nuclear industrial accident from small spill or leak to actual meltdown would need neutron detection to manage it?
The pocket dosimeters used throughout the nuclear industry worldwide detect gammas and energetic betas only.
My advice: don't waste your time on this neutron red herring.
Use a common miniature GM dosimetry tube like ZP1313, or if you want to go solid state, use a PIN photodiode like BPX65, which has been used in some miniature dosimeter designs since the 1980s.
The miniature GM tube has the advantage of low cost and simple circuitry which you can expect to work well right away. It also offers excellent immunity to destruction by intense ionizing radiation, where a PIN photodiode might suffer irreversible changes.
So i was presuming in reactor related accidents the presence or absence of Neutron emission can be indicitive of how bad a reactor "event" is. Is it a mere 3 mile island or the next Chernobyl...
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
The problem here is that core damage will generate a similar number of neutrons as a melt-down, so without further information is just tells you things are bad or not. Directed beams of gammas IMHO are a more accurate way to tell, as this suggests a full melt-down is imminent or in progress.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
If it was my problem, I would choose a PIN diode gamma ray spectrometer. The PIN diode array, its charge amplifiers, and telemetry modulator drivers would weigh very little. The Multichannel Analyzer (MCA) at the ground station would, with suitable software, directly identify the radionuclides responsible.
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Neutron scintillation detector.
