New Type of Imager Could Help Spot Smuggled Nuclear Materials (sciencemag.org) 21
sciencehabit shares a report from Science Magazine: Much as a smoke detector gives only a vague idea of where a fire is, current methods to detect smuggled nuclear materials are slow and imprecise. But a new technique that images nuclear materials based on the neutrons and gamma rays they shed can locate these dangers in record time, scientists report. The new technique -- neutron-gamma emission tomography (NGET) detection -- relies on detectors that emit light when struck by either a neutron or a gamma ray and measure the time of arrival with nanosecond precision. Suppose two detectors sit face to face, separated by 1 meter or so, and that a nucleus decays and emits a neutron that hits one detector and a gamma ray that hits the other. The difference in the arrival times, when accounting for the detailed physics of the nuclear decay process, defines a fuzzy, somewhat spherical shell in space in which the nucleus could have been. Timing many neutron-gamma ray pairs with several detectors produces a set of probability shells that should intersect at a point -- the location of the source. The ability to pinpoint a source may offer a "paradigm shift" in nuclear safeguards, the researchers say. NGET detectors might also be shrunk to fit on a drone. That offers "a really fascinating possibility" of quickly mapping radiological contamination at disaster sites like Fukushima or Chernobyl, they say. The findings appear in the journal Science Advances.
New? (Score:2)
They use a different kind of detection tube but it's nothing original.
I proposed something very much like this to my bos (Score:2)
I worked in pet imaging; I proposed a system to localize and locate the meltedparts at Fukushima, but I was told " we only do medical tomography."
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Is that pet or PET? Because we have quite enough cute cat pics already, thank you.
False (Score:4, Interesting)
If the UN atomic agency built highly sensitive neutrino detectors and placed them around the world they could detect the location of every single nuclear weapon or enrichment of nuclear material.
Negatives:
1. The cost for global coverage is probably around $150 billion at minimum. And that is assuming they are land based rather than on satellites (which would have to be hundreds of tons.)
2. The location of every nuclear weapon and nuclear enriching process will be known.
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If the UN atomic agency built highly sensitive neutrino detectors and placed them around the world they could detect the location of every single nuclear weapon or enrichment of nuclear material.
Negatives: 1. The cost for global coverage is probably around $150 billion at minimum. And that is assuming they are land based rather than on satellites (which would have to be hundreds of tons.) 2. The location of every nuclear weapon and nuclear enriching process will be known.
You are very confused on this subject.
Nuclear weapons do produce neutrinos - when they explode. The actual mechanism are beta decays of fission products, which is very intense in the seconds after the explosion. Fission reactors can be detected with neutrino emissions for the same reason, fission product decay, and the Earth emits geo-neutrinos from natural beta decay.
The alpha emitters that make up fissile masses do not emit any neutrinos at all, neither do isotope enrichment processes.
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The products of alpha decay undergo beta decay don't they? For example U-235 to Thorium 231 which beta decays.
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Here is a quote from an article in PRL: https://journals.aps.org/prl/a... [aps.org] "In addition to monitoring the reactor during operation, observing antineutrino emissions from long-lived fission products could also allow monitoring the reactor when it is shut down, provided very low detector backgrounds can be achieved. Antineutrino monitoring could also be used to distinguish different levels of fuel enrichment."
It won't work in the real world! (Score:4, Insightful)
I've worked on a variety of radiation detection systems, including lab work on correlated n-gamma detections of spontaneous fissions.
Perhaps the technology has evolved hugely since the work I was involved in, but our data conclusively showed that it is very easy to shield against (or at least frustrate) n-gamma detections. Just wrap your fissionable material in a neutron moderator (such as polyethylene) and a neutron absorber (which can be added to the polyethylene), and the neutrons will be scattered and absorbed, with the few that escape having a wide spectrum and fuzzy time signatures.
Then, for your portal to have any hope of success, it must also directly detect such shielding. Which is much tougher to do.
Without the neutron detections to provide a time correlation reference, the gammas from spontaneous fission are lost in the background. You simply won't reliably see them unless your detector is centimeters away, not the multiple meter distance of portals.
Our approach was to intentionally stimulate fissions by using a low-power neutron beam (from a small amount of Californium 252 placed in the roadway, with the neutron flux energy-shaped, collimated and directed upward), then look for increased fission gammas, which are much more difficult to hide or disguise when you have enough of them. Additionally, our approach would complement existing portals, all of which already use gamma or X-Ray sources in their normal operation.
Things get even more fun when you use an array of extremely sensitive gamma scintillators, such as LaBr (Lanthanum Bromide), where the gamma energy and direction can be resolved with very high precision, to the point where we could identify the precise isotope mix present in the fissionable material with a reduced number of gamma detections.
The key is to have our neutron flux be orders of magnitude higher than that expected from spontaneous fissions, yet low enough to not pose any kind of hazard to the surrounding area (hence having the neutron beam directed upwards). This flux would allow us to penetrate neutron shielding to a level adequate to still generate enough gammas for our sensitive detectors.
As a side benefit, our system would also detect the ingredients for "dirty bombs", including isotope identification, localization and activity estimation.
Anyone wanting to surreptitiously transport fissionable material will not be a total idiot, and will likely be at least as smart as cocaine smugglers who use airplanes, submarines and tunnels, where their goal is simply to bypass the inspection portals.
For such folks, a bit of shielding will be a no-brainer.
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hazard to anyone driving over it, and to any aircraft for hundreds of meters upwards
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My reading of the article was that the primary goal was not to locate deliberately hidden material (although they might have aspirations to that in the future) but to pinpoint scattered or lost material. Their example being cleanup after Fukushima - using their detector to more quickly find concentrations of escaped material to clean up.
From your experience with detection systems, do you think that a real-world environment (town with buildings, or trees in to country) would also effectively frustrate any d
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I had a similar thought about shielding. I also thought about false positives. There's a lot of things that are quite legal that emit neutrons and gamma. Certain kinds of granite as an example. Just rock in general will contain some uranium and thorium naturally. Sand from certain places are rich in thorium. What of hiding some nuclear material with medical equipment? There is such a thing as "nuclear medicine". There's clock face lit from tritium and other materials, especially in older items. I r
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There was a big freak-out in one of the ports (Houston? Can't remember now.) when radiation detectors were first being tried at the ports. The clay in cat litter would set them off in sufficient quantities, and a shipment from somewhere like Pakistan was delayed for a while. (Why anyone would ship cat litter from overseas is another question entirely.)
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I've worked on a variety of radiation detection systems, including lab work on correlated n-gamma detections of spontaneous fissions.
Perhaps the technology has evolved hugely since the work I was involved in, but our data conclusively showed that it is very easy to shield against (or at least frustrate) n-gamma detections. Just wrap your fissionable material in a neutron moderator (such as polyethylene) and a neutron absorber (which can be added to the polyethylene), and the neutrons will be scattered and absorbed, with the few that escape having a wide spectrum and fuzzy time signatures.
You are right that the localization in space aspect is easily defeated since it depends on the neutrons not being scattered. Anything containing a lot of hydrogen - plastic, paraffin wax, water - will scatter all neutrons at least once within a few inches of material. And it will be of little use with highly enriched uranium which emits very few neutrons at all.
But detecting plutonium is much easier - if you can detect any neutrons at all above the cosmic ray background you have a good reason to believe nu
Small enough to wear around the neck (Score:2)
And maybe light enough for this three-eyed deer we found wandering around the woods in Chernobyl
I see (Score:2)
"The difference in the arrival times, when accounting for the detailed physics of the nuclear decay process, defines a fuzzy, somewhat spherical shell in space in which the nucleus could have been."
So you build a multi-million dollar detector to see if the suspect with the nuclear material has it in his shoes or in his shirt-pocket when you are a meter away.
Great, so no time wasted checking the other pockets.
Subject (Score:1)
VERY useful because . . . . (Score:2)
It seems likely to me that nukes have already been smuggled into many countries via shipping containers, only a small fraction of which are ever inspected.
Detecting huge amounts of radiation has been a solved problem for a century, but detecting the much smaller amounts that would remain after being carefully shielded was not.
The better we get at detecting radiation from afar, in very small quantities, the better our chances of finding and eliminating these weapons.
Large states still have ICBMs, subs, and o