SIGINT planes vs. radioisotope mapping
Tim May
timcmay at got.net
Fri Jun 6 10:23:08 PDT 2003
On Friday, June 6, 2003, at 08:26 AM, Thomas Shaddack wrote:
> On Wed, 4 Jun 2003, Trei, Peter wrote:
>
>> It appears that they can't tell the medical isotopes from others....
>
> They have no chance to distinguish isotope type with just a plain
> Geiger.
> For an identification, they would need a gamma spectrometer, which is a
> toy that AFAIK is not yet portable and cheap enough for mass
> deployment.
>
>
I certainly never implied in any way that a simple G-M tube would be
useful for this. Implicit in my radioistope mapping comment was that a
gamma ray spectrometer would be used.
As for portability, the one I used in my lab in 1979-82 was not
terribly heavy. The heaviest part was the LN dewar, which was large and
floor-standing. A large dewar is certainly not needed.
The rest of the assembly, even 20 years ago, was mostly portable: the
germanium detector head, some preamps and pulse-height analyzers, and a
multichannel analyzer. Most of this stuff is now done on laptops, the
MCA and analysis software part. Without researching this on the Net, I
would thus conjecture the entire gamma ray spectrometer could fit in a
small carry-on case, using a small dewar.
Certainly for the cost of operating a light plane, such a spectrometer
would be a minor cost by comparison.
And note that this is just what can be easily bought on the open
market...N.E.S.T. (Nuclear Emergency Search Team) and similar LEO
people almost certainly have more miniaturized detector setups.
I expect most of the N.E.S.T. detectors are also gamma ray
spectrometers, probably now so portable they fit unobtrusively into
briefcases for use in crowded areas. As we discussed a few months ago
(and I think I discussed this in _particular_ with Thomas!), the S/N
advantages of using a spectrometer are enormous. Thousand-to-one
improvements in general S/N are easily achievable. Even more if the MCA
software is looking for pairs or triples or n-tuples of gamma peaks and
inferring likely radioisotopes.
(I used this approach in 1981 to solve a major problem in IBM computers
which were using Intel chips...and I don't mean the alpha particle soft
error problem. This was a different problem, involving a beta source
trapped in some of the packages. For this I used a pair of large sodium
iodide crystals (which my well-equipped lab just happened to have in a
storage cabinet, fortunately for us) and looked for a specific decay
mode that resulted in a pair of gammas sent out in opposite directions.
By using coincidence logic over microsecond intervals, enormous
improvements in S/N could be achieved. Basically, background radiation
vanished and only the specific beta decay mode we were looking for
appeared.)
--Tim May
--Tim May
"Extremism in the pursuit of liberty is no vice."--Barry Goldwater
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