[ RadSafe ] Best technique to detect contamination of DUinhugearea

Fri Mar 12 10:52:53 CST 2010

Hi Gary:

Measurement of the lower energy photopeaks for the 186 KeV gamma may be
difficult because of the high noise (Compton scattering) in that part of the
spectra.  Also, another of the radium progeny, Pb-214, emits gamma peaks at
242 keV (7.43 %), 295 keV (19.3 %) and 352 keV (37.6 %) not to mention that
the cosmic background is always present.  Given that the isotopic abundance
of U-235 is already low (0.7%) compared to U-238 naturally, and depleted U
still has perhaps 0.3% U-235, will there be enough time & signal to easily
detect the difference with the high background at the lower energies?  I
don't know the answer to this, and would really like to have an answer.  

Also remember that U and progeny is not the only critter out there: There is
also significant K-40 and some Th-232 progeny in the natural background
which will also be quite variable.

With my 3X3 inch NaI(Tl) crystal with 1024 channel MCA, it's a little hard
to optimize for the 609 KeV Bi-214 photopeak and get good resolution at low
energies.  At least, that is my experience (remember that I am a mere
geologist!) with my own equipment.

Perhaps someone from one of the labs can step-up and figure this out. Falah
has the same problem that I do to try to use a towed array in an area of 300
km^2.

Dan ii

--
Dan W McCarn, Geologist
2867 A Fuego Sagrado
Santa Fe, NM 87505
+1-505-310-3922 (Mobile – New Mexico)
HotGreenChile at gmail.com (Private email)

-----Original Message-----
From: Forsee, Gary [mailto:Gary.Forsee at illinois.gov] 
Sent: Friday, March 12, 2010 08:58
To: Dan W McCarn
Subject: RE: [ RadSafe ] Best technique to detect contamination of
DUinhugearea

Morning Dan,

I'm always leary about posting on radsafe due to my recent (two or three
years) entry into this industry and, consequent, lack of experience.
However, I enjoy gleaning information from the list and, every so often, try
to toss out a thought or two.  

I thought I would pose a question to you on the detection of DU over (and in
the presence of) natural uranium and see what you thought.  I'm quite fond
of ludlum's model 2221, a single channel analyzer / count rate instrument.
By setting a 'window' for a specific energy range, one can effectively scan
for isotopes of interest while eliminating extraneous counts.  For the
purpose you stated below, why couldn't someone run two 2221's - one windowed
for U235 (186 keV) and one for U238 (1001 keV).  Data dump both (live) to a
spreadsheet or database that analyzes the proportion of counts from each
instrument.  The ratio (once corrected for detector efficiency in the
respective energy regions) should approximate the isotopic abundance of U235
to U238 in natural uranium.  When this ratio is heavily distorted by count
rates in 1001 region, any manner of user notification could be implemented.
More simply, just a time and GPS stamp would be logged with that data
collection which indicates the presence of DU (or at least an abundance of
U238 in a concentration not consistent with natural uranium).

I am currently gearing up to use a similar approach for determining ambient
radium 226. I would greatly appreciate your insight to this approach and
it's viability.

Thanks Dan,

Gary Forsee
Div. of Nuclear Safety
Illinois

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Dan W McCarn
Sent: Friday, March 12, 2010 3:24 AM
To: 'Brennan, Mike (DOH)'; radsafe at health.phys.iit.edu
Subject: Re: [ RadSafe ] Best technique to detect contamination of
DUinhugearea

Hi Falah:

Before you go too far on this survey, it is absolutely important to
understand the natural / geogene background to evaluate the mechanisms of
uranium reconcentration.  For instance, evaporative pumping in a desert
environment sometimes forms radioactive caliches, also called hardpan,
pedogenic calcretes, and sometimes silcretes. Also, other geological
features such as phosphatic sediments will host significant uranium. Typical
pedogenic silcretes (thinking about the Ogallala Fm in the USA High Plains)
has 75-150 ppm uranium.  Pedogenic calcretes may have 50-100 ppm. 
Phosphatic rocks frequently have 100-125 ppm U. (100 ppm == 0.01% U). 

I suspect that the geogene background may swamp the anthropogenic DU except
in the target zones.

Agricultural soils may also accumulate uranium in the soil profile from the
high evapotranspiration of irrigation waters bearing uranium and other
minerals. Other factors to consider are the historical use of phosphate
fertilizers which contain significant amounts of uranium.

The vadose zone (unsaturated soils) frequently allows oxidized uranium to
percolate downward fairly rapidly.  One soil transect that I reviewed in
Kazakhstan examined the vertical migration of uranium / radium bearing
waters from uranium exploration boreholes with flowing artesian waters. The
one feature that I found quite interesting was that the uranium was fairly
uniform throughout the entire vertical 2 m or so of the measured section.
In other words, it was quite mobile.  The radium tended to remain in the
upper soil zone, probably adsorbed onto clays.

The ability of a soil to retain minerals through time is called the leaching
coefficient. I discuss this in:

McCarn, Dan W. (2004): Scoping Calculations: Natural and anthropogenic
multi-pathway risks associated with naturally occurring uranium
mineralization in aquifers; IAEA-TECDOC-1396, pp.289-315.

http://www-pub.iaea.org/MTCD/publications/PDF/te_1396_web.pdf

The decay of Pa-234 results in a gamma at 1001 KeV energy, since the DU is
in secular equilibrium with Th-234 and Pa-234 after a few months.  The decay
of radium to progeny results in a good gamma emitter with the beta decay of
Bi-214 with several gamma photopeaks. These include the 609 KeV (46.1%),
1120 KeV (15.1%) and a 1765 KeV (15.4%) photopeaks.  Depending on the radium
concentration, the 1120 KeV gamma may mask the 1001 KeV gamma with a NaI(Tl)
detector / spectrometer, making it difficult to determine the U-238 (Pa-234)
concentrations without a longer counting time. But that only addresses the
U-238 and not whether the measured U-238 is DU... 

If there is a mechanism of caliche formation, the uranium concentrated in it
will most likely be "recent" in a geological time-scale sense. This means
that the time for in-growth has not been sufficient for the natural uranium
to reach secular equilibrium (1-2 million years) with Ra-226 and Bi-214. If
you can accurately distinguish the Bi-214 from the Pa-234 photopeaks, this
may only indicate the relative age of the caliche.

In my project area in the San Luis Valley, I estimated that the total U
remobilization was on the order of 75 Tonnes per year for the last 100 years
dissolved in 1.275 X 10^9 M^3 water / year.  This is due to the
concentration of uranium into regional redox-controlled roll-fronts over a 5
km X 60 km zone (300 km^2) in the underlying rock, and the interception of
that zone by numerous irrigation wells. I suspect that most of the uranium
(as is the case in Kazakhstan) is rapidly remobilized downward through the
vadose zone and then into the unconfined aquifer.

I would be very interested in how you solve the problem of measurement - to
be able to discriminate the natural uranium background from the DU "on the
fly".  I have a similar problem: to distinguish the mineralized uranium
phases in the soil from the remobilized uranium from the irrigation water
and fertilizers. 

My best!

Dan ii

--
Dan W McCarn, Geologist
2867 A Fuego Sagrado
Santa Fe, NM 87505
+1-505-310-3922 (Mobile - New Mexico)
HotGreenChile at gmail.com (Private email)

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Brennan, Mike
(DOH)
Sent: Thursday, March 11, 2010 17:51
To: radsafe at health.phys.iit.edu
Subject: Re: [ RadSafe ] Best technique to detect contamination of DU
inhugearea

Hi, Falah.

A couple of questions, and some early thoughts:

1) What is the purpose of the survey?  Is it to find concentrations, such as
burnt-out vehicles, or sent projectiles, or is it to characterize lower
level contamination?

2) What level of resolution are you looking for?  An airborne remotely
piloted vehicle would be a good choice if can meet your needs.  It might be
a good first step as a general survey, even if it doesn't give you high
quality data, as it should be able to identify places that deserve a closer
look.

3) What is the non-rad hazard level?  Unexploded ordinance and land mines
could drive an option that otherwise might be sub-optimal.  For example, it
might be cheaper to tow a trailer mounted system with a helicopter than with
a truck, if there is a high risk of land mines (it only takes a couple of
your rad techs getting blown to pieces to really mess up your budget).

4) Even with a ground vehicle in a safe area, it might be worthwhile to look
into RPVs.  Once you take the people out of the vehicle you free up a lot of
payload for other things.  This field advances almost daily, so you might be
the first to put together a system to do the things you want.

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Falah Abu-Jarad
Sent: Thursday, March 11, 2010 4:11 PM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] Best technique to detect contamination of DU in
hugearea

Dear ALL
Your advice is greatly appreciated:
There is potential to perform survey for possible DU contamination in huge
area 10 km x 30 km as a result of gulf war. The area is desert-sandy and not
uniform.

What is the best technique to perform that survey?

Is FIDLER with GPS and data timing is the best?
What is the range of the price for individual and array system with trailer?
Recommended manufacturer and it contact!
Best regards

Dr. Falah Abu-Jarad
abujarad2 at yahoo.com

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