[ RadSafe ] Portal monitors to detect SNM

[John Jacobus]

Won't it be easier to look for the neutron emissions,
or are the emission rates too low?  How difficult is
it to detect muons?

--- A  Karam <paksbi at rit.edu> wrote:
> 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
> 
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+++++++++++++++++++
"Embarrassed, obscure and feeble sentences are generally, if not always, the result of embarrassed, obscure and feeble thought."
Hugh Blair, 1783

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com

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