[ RadSafe ] RE: Portal monitors to detect SNM

[Dimiter Popoff]

 The new muon based technique sounds promising, what I miss so far
is the time it takes to scan a container. If it is fast enough,
this may well be the way to go.

 I have said it before, those mickey-mouse NaI based devices are
completely useless (especially since they cost as much as a HPGe
based system could cost).
 Although the gamma spectrum is weak and low energy dominated thus easy to
shield neutron activation of the materials nearby will produce
gamma which can be detected reasonably fast (given the high resolution).

Dimiter

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Dimiter Popoff               Transgalactic Instruments

http://www.tgi-sci.com                 ++359/2/9923340
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> Subject: RE: [ RadSafe ] Portal monitors to detect SNM
> Date: Wed, 13 Apr 2005 09:31:54 -0400
> From: "A  Karam" <paksbi at rit.edu>
> To: <radsafe at radlab.nl>
> 
> Detectors looking strictly at radiation can be foiled by shielding.  
> When surveying the nuclear weapons on my submarine (unshielded), I could 
> measure both gamma and neutron radiation at low levels, and in close 
> proximity (perhaps 10 cm away).  Using a large NaI detector, I could 
> read elevated count rates from a few meters away.  However, the gamma 
> radiation emitted by nuclear weapons is fairly easy to shield and I 
> would consider it an unreliable way to detect them.  Similarly, the 
> neutrons emitted are fairly easily shielded and I would also consider 
> that an unreliable detection method.  We have to assume that terrorists 
> will be intelligent enough to install a few cm of lead and a few tens of 
> cm of borated plastic around a nuclear weapon to reduce the chance of 
> detection.  Similarly, we must assume that a terrorist importing RDD 
> materials would use sufficient shielding to make detection very 
> difficult.  As a case in point, the blood bank irradiator at my former 
> employer's facility contained over 5000 Ci of Cs-17, yet was so 
> well-shielded that a dosimeter placed directly on it consistently 
> recorded no exposure each quarter.  We must remember, too, that a few 
> tons of shielding in a cargo container is not going to alarm anyone - we 
> expect cargo containers to be heavy.
>
> The most promising technology I have seen is the Los Alamos system using 
> cosmic ray muons.  Muons are very penetrating and their scattering angle 
> depends on the atomic number of the material through which they are 
> passing.  By carefully analyzing the scattering angles of muons passing 
> through a container, LANL researchers were able to reliably detect 
> high-atomic number materials, and even to obtain images (in one case, a 
> C-clamp; in another case, lead bars cut to form the letters LANL).  The 
> muon flux and their detection efficiency was such that they performed 
> this with a 1-minute integration time.  They wrote their results up in 
> Nature a few years ago, and a recent press release noted that this work 
> is continuing and being expanded.  This promises to be the best way to 
> "look" inside of containers for specific elements of interest.
>
> Andy
> 
> ________________________________
> 
> From: radsafe-bounces at radlab.nl on behalf of Rick Orthen
> Sent: Wed 4/13/2005 9:07
> To: 'Matt Wald'; radsafe at radlab.nl
> Subject: RE: [ RadSafe ] Portal monitors to detect SNM
> 
> 
> 
> Matt--Your excellent question has fell on deaf ears.  It appears that 
> this
> list is now populated by less than a half-dozen people who are obsessed 
> with
> anything other than radiation protection or health physics.  If you have
> questions about wind farms, teratogenic sperm, mythology and such, hang
> around.
> 
> As far as the cargo portals, unfortunately you'll have to look elsewhere 
> for
> an informed response.  Perhaps the manufacturer, SAIC-Exploranium?  And 
> I
> would doubt (for obvious security reasons) you'll find anyone willing to
> disclose the technical limitations of the portals.
> 
> Rick Orthen
>