Re: Field Detection of Pu

[chapmanja@ornl.gov (Jeff Chapman)]

Bates,

I don't know enough of the specifics to provide you with the best answer,
so I'll keep my reply broad.  The question is one of sensitivity desired,
ease of use, and how the measurement impedes the desired throughput.
Options to consider:

1.  Use of 5"x5" NaI detector to monitor the presence and activity of the DU.
2.  Depending on the intensity of the higher energy gamma-rays---1Mev and
possibly a 2.6 MeV from Tl208 (?)---the compton continuum may be too large
to make use of NaI to set regions of interest in the Pu region.  There are
techniques to deal with this however and you might consider this.  The NaI
of course is cheap, robust, and sensitive---I'd attempt to use it as much
as feasible.
3.  If the NaI doesn't offer the resolution you need and you've expended
alternatives for dealing with the sea of compton events, go to a high-res
germanium.  You may want to use high-res Ge for determining U-enrichment
using one of several possible spectral deconvolution codes (caveat emptor).
4.  Pu will produce neutrons, so possible suggestion is to build large-area
neutron detectors packs (polyethylene moderated, Cd-wrapped He-3 tubes).
Off hand, I don't know the sensitivity you desire, but Pu240 produces 1000
n/s/g.  U-produced neutrons are negligible in this case.
5.  Finally, hand-help HP instruments may come in very handy for making a
go-nogo decision, but this would have to be evaluated.  For example,the
available photon flux from Pu is much greater than for U, given equivalent
mass.  Once a thin layer of contaminated materails can be isolated, perhaps
a phoswhich-type detector will be fruitful.

Once the waste is drummed, there are a number of NDA systems available for
making an accurate determination using active neutron interrogation,
passive neutron coincidence counting, and transmission-corrected gamma-ray
scanning.

Jeff Chapman
Applied Radiation Measurements Group
ORNL


>------------------------------
>
>Date: Thu, 23 Apr 1998 07:21:55 -0600
>From: Bates.Estabrooks@rfets.gov (Bates Estabrooks)
>To: radsafe@romulus.ehs.uiuc.edu
>Subject: Field Detection of Pu
>Message-ID: <199804231359.AA01265@rfgate.rfets.gov>
>
>          RADSAFERs:
>          
>          Maybe some of you all could offer a suggestion.
>          
>          Rocky Flats will, in a few weeks, begin excavating a 
>          1950s-vintage trench in which drums of depleted uranium chips 
>          and turnings (mixed with cutting coolants)  were buried.
>          
>          As each intact drum (highly unlikely), or its carcass with 
>          contents (very likely), is excavated, we would like to know 
>          rather promptly whether we have any "surprises" such as Pu or 
>          highly-enriched uranium.  We know that large quantities of DU 
>          are buried there, but since the facility also worked with Pu 
>          and HEU, there is a small chance of these things being found 
>          also.
>          
>          Therefore, can anyone recommend a quick screen using field 
>          instruments that we might be able to perform on each backhoe 
>          bucket of stuff to indicate whether either of these fissile 
>          substances (pu or HEU) are present in significant quantities?
>          
>          We have a fairly broad range of portables including the SAIC 
>          AP-2.
>          
>          Thanks for your help.
>          
>          Bates Estabrooks
>          bates.estabrooks@rfets.gov
>          303-966-3769