[ RadSafe ] Detecting DU at a distance via beta particle emission.

Robert J. Gunter rjgunter at chpconsultants.com
Tue Jan 8 15:52:02 CST 2008

Other factors would be the geometry of the source.  A projectile, or
fragment would be much different than a slab of DU.  You are probably not
looking for bricks, but maybe so.  In addition, if you are looking for them
with a detector (in other words they are not visible right there in front of
you), they may be covered with dirt or debris, or oxidized which would
attenuate the betas.  A simple solution to find what you can see is to
assume a point source and do a solid angle calculation assuming 4pi
emanations and what would "hit" your detector.  Figure in your efficiency
(by the time it travels through air, the E will be diminished), and compare
this to your background to see if you can distinguish it.

Another way is to put your probe on a string and get it closer to the ground
(maybe with some "feet"), thereby saving your knees....

Good luck.


Robert J. Gunter, CHP
CHP Consultants
rjgunter at chpconsultants.com
Tel:  +(865) 387-0028
Fax:  +(865) 483-7189

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf
Of Geo>K0FF
Sent: Monday, January 07, 2008 1:07 PM
To: radsafe at radlab.nl
Subject: [ RadSafe ] Detecting DU at a distance via beta particle emission.

Detecting DU at a distance via beta particle emission.

DU (Depleted Uranium) is uranium with the majority of the U-235 removed,
leaving behind U-238 and U-234. 
I prefer to think of DU as refined U-238. The metal has many industrial and
scientific uses, mainly because of its high density, being 1.7 times as
dense as lead. A few common uses would be counterweights and radiation
shielding. DU is used in projectiles because of its unique density,
pyrophoricity and "self-sharpening" characteristics.

The only progeny present that can be detected at a distance would be
Pa-234m, a beta emitter. 
With a maximum energy of  2.28 MeV, the betas would travel approximately
20-25 feet in air, using the rule of thumb of 10-12 feet per MeV.
A sensor would have to be appreciably closer than the maximum distance to
detect the beta particles.

Because of self-shielding, DU metal's surface beta rate is in ratio of the
surface size, not the thickness or 
volume of the sample. In other words a thin sheet would have the same beta
surface emission rate as a thick sheet.
Indeed, DU Slabs are used in the lab to calibrate probes. 

The best "calculations" are done in the lab with a DU slab and a detector!
Using a 2 pound cylinder of DU metal and 
a pancake probe, about 6 feet is as far as you can get and still obtain
usable (statistically significant) readings. Any closer and the readings 
ramp up quickly. With a 100 Cm^2 alpha-beta scintillator on a Thermo ELECTRA
alpha-beta meter, the range is extended to about 10 to 12 feet. 

George Dowell
GEOelectronics at netscape.com
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