Radionuclides give off unique spectral signatures. I-131 looks different from Tc-99m (another common medical isotope) which looks different from cobalt-60 (an industrial isotope) which looks different from uranium.
Spectral signatures are the most obvious way which one would hope to differentiate nuclides. This is relatively easy in the laboratory environment. However, with all of the material between the source (imagine it inside a cargo container) and the detector (somewhere outside), the original emitted spectrum is significantly washed out. In other words, the sharp peaks are no longer sharp, and may not even be distinguishable peaks at all.
Even if we could distinguish uranium and its decay chain daughters, those nuclides are common sources of background radiation. Thus, we still have problems with false positives.
The timely detection of special nuclear materials is a challenging problem. The US is pouring a lot of money into research towards this end, but we are far from having a workable solution. The detector technology must continue to improve (CZT is a step in this direction). But in the end, algorithms and methods will likely play an indispensable role. So while the suggestion of putting a detector in every phone is entirely impractical with today's technology, it may hint at a potential solution to the problem.
I believe the linked article is referring to the 4S design http://en.wikipedia.org/wiki/Toshiba_4S, at least the picture is the same one I've seen in 4S presentations. This is the same reactor which the residents of Galena, Alaska are pursuing.
Following the external links in the wikipedia article, you can find that this reactor is still fueled by uranium, although it is in a metal alloy form. That's in contrast with the typical ceramics (uranium dioxide) which is used in most light water reactors in the world. We do have experience with metallic fuels, but not nearly as much as with UO_2.
One other unique aspect of this reactor: it uses liquid sodium for cooling. Most light water reactors use water, not surprisingly, as their moderator and coolant. People have experimented with liquid sodium as a coolant in the past, and are continuing to research advanced "Generation IV" reactors which could use liquid sodium. I believe the main challenges in doing something like this is not the nuclear design (figuring out how many neutrons are needed) but mitigating practical issues such as corrosion.
About the lithium, the article says that it is used for control purposes. In other words, the lithium is absorbing neutrons, while the fuel is producing them.
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Radionuclides give off unique spectral signatures. I-131 looks different from Tc-99m (another common medical isotope) which looks different from cobalt-60 (an industrial isotope) which looks different from uranium.
Spectral signatures are the most obvious way which one would hope to differentiate nuclides. This is relatively easy in the laboratory environment. However, with all of the material between the source (imagine it inside a cargo container) and the detector (somewhere outside), the original emitted spectrum is significantly washed out. In other words, the sharp peaks are no longer sharp, and may not even be distinguishable peaks at all.
Even if we could distinguish uranium and its decay chain daughters, those nuclides are common sources of background radiation. Thus, we still have problems with false positives.
The timely detection of special nuclear materials is a challenging problem. The US is pouring a lot of money into research towards this end, but we are far from having a workable solution. The detector technology must continue to improve (CZT is a step in this direction). But in the end, algorithms and methods will likely play an indispensable role. So while the suggestion of putting a detector in every phone is entirely impractical with today's technology, it may hint at a potential solution to the problem.
Following the external links in the wikipedia article, you can find that this reactor is still fueled by uranium, although it is in a metal alloy form. That's in contrast with the typical ceramics (uranium dioxide) which is used in most light water reactors in the world. We do have experience with metallic fuels, but not nearly as much as with UO_2.
One other unique aspect of this reactor: it uses liquid sodium for cooling. Most light water reactors use water, not surprisingly, as their moderator and coolant. People have experimented with liquid sodium as a coolant in the past, and are continuing to research advanced "Generation IV" reactors which could use liquid sodium. I believe the main challenges in doing something like this is not the nuclear design (figuring out how many neutrons are needed) but mitigating practical issues such as corrosion.
About the lithium, the article says that it is used for control purposes. In other words, the lithium is absorbing neutrons, while the fuel is producing them.