New Hand-Held Detector Determines Radiation Type

Red Leader writes: "This article covers a new portable radiation detector. A serious problem with conventional Geiger counters is that they don't indicate the type of radiation they're picking up. Thus, fissile material can be disguised as medical stuffs. This device uses a 'low-power cryogenic cooling mechanism originally designed for the aerospace industry' to cool a germainum detector rather than a really big thick-walled steel tank of liquid nitrogen."

Question...

[andfarm]

How does it tell different end uses of radioactive material apart? Uranium is uranium, no matter whether it's for medical or terroristic (?) uses.

Re:Question...

[akiaki007]

Medical personalle will not be carrying Uranium on a plane.

Re:Question...

[JabberWokky]

Yes, but radioactives are shipped via plane, and passanger airliners often carry cargo as well.

But that's not the point here - this is for scanning packages in bulk at customs, etc. Basically this allows anybody to seperate out non-medical controlled radioactives from medical controlled radioactives.

--
evan

Re:Question...

[Hal-9001]

Since there are no unique medical uses for uranium, that shouldn't be a problem.

Re:Question...

[sphealey]

Since there are no unique medical uses for uranium, that shouldn't be a problem.

Uranium has been, and I believe sometimes still is, used as a coloring agent for tooth fillings. It adds the tinge of yellow needed to make white fillings look natural and also adds strength to the ceramic filling.

Now, the amount involved is a few micrograms so I doubt that it is of concern anyway. But it is a legitimate medical use.

sPh

Re:Question...

[calidoscope]

As other psoters have mentioned, Uranium does not have medical uses.

The advantage of the GeLi detectors is very good energy resolution for gamma rays, but they do need to be cooled. The breakthrough is using a portable cooling source so you don't need to drag an LN2 dewar around.

"Uranium is uranium" is a big misunderstanding on your part - U-238 and U-235 have very different properties (and distinct gamma spectra). It would be extremely helpful to know if a Uranium sample was depleted, natural or highly enriched.

Re:Question...

[mmontour]

As other psoters have mentioned, Uranium does not have medical uses.

However, Plutonium-238 was (is?) used as a power source in some pacemakers [wisc.edu]. It's not the bomb isotope, so I guess this detector will be able to tell the difference.

Re:Question...

[esonik]

They didn't specifically say that they use a GeLi detector (they could also use high purity Ge).

One should mention that GeLi detectors need to be cooled all the time, even when not in operation, otherwise the Li distribution in the Ge crystal would be destroyed and the detector useless. This is not the case for high purity Ge detectors.

Germanium? Odd choice.

[glenmark]

Could have used mercuric iodide detectors. Then they would have only needed to use a simple Peltier cooler. Been used for a decade and a half in portable x-ray fluorescence spectrometers [thermo.com] manufactured by my previous employer. (I performed R&D work with on these detectors.)

Re:Germanium? Odd choice.

[CowbertPrime]

afaik, fluorescence spectrometers measure photons delivered by excitation-decay of electrons in the sample material. Thus, you emit from the device some photons - these photons hit the sample surface, in your case probably structural materials - the materials absorb the photon, and re-emit photons at a stokes-shifted wavelength. I don't think HgI2 detector materials can be adapted to be used for measurements described in the paper, especially if it only detects a narrow spectral range (x-ray and gamma rays are orders of magnitude apart). I could be wrong though, since all of my experience comes from IR/UV fluorescence micro/spectro-scopy.

-p.c. lai
undergraduate
molecular & cell biology
univ. of connecticut

Re:Germanium? Odd choice.

[glenmark]

You are correct that XRF spectrometers require a source of excitation photons. The mercuric iodide devices which I referenced use a variety of radioactive isotopes as their sources, including Am-241, which is a gamma source. The spectral range for mercuric iodide detectors is similar to that of germanium detectors (at least from what I remember of my work in this field almost a decade ago), although the resolution is not quite as good as that yielded by liquid nitrogen-cooled germanium (one of the things I was working on improving, in addition to extending the detector's usable lifetime). However, the spectral range and resolution of mercuric iodide should be suitable for this particular application. The existing XRF equipment could easily be modified for this purpose. Exclude the excitation sources, and calibrate the software to recognize the appropriate peaks.