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

[Dan W McCarn]

Hi -

Although secular equilibrium between U-238 and Th-234 (24.10 ± 0.03 d HL) &
Pa-234 (1.159 ± 0.016 m HL) is reached in about 200 days, secular
equilibrium with U-234 would require on the order of 1 million years to
achieve (based on Bateman, 1910).  Following enrichment, some U-235 and
U-234 is present in DU, but a potential problem occurs in the enriched
uranium product.

Secular disequilibrium in the environment is a result of two processes: 1)
natural decay; and 2) geochemical speciation and differential aqueous
mobilization / mineralization of various species in the decay chain.

Because of the secular disequilibrium between U-238 and U-234 as well as
disequilibrium in the "bottom-half" of the decay chain, measurement of
chemical U is not so straightforward based on total gamma, unless one uses
the 1001 KeV photopeak from the Pa-234m decay.  From my "read" of the
nuclear data, Pa-234m has a 1.159 ± 0.016 m half-life and emits a 1001.025 ±
0.022 KeV gamma with a probability of 0.832 ± 0.010 based on IAEA-CRP-XG
data.  It also has a 766.358 ± 0.020 KeV gamma with a probability of 0.318 ±
0.005. 

http://www-nds.iaea.org/sgnucdat/a3.htm

I would like to refer to IAEA-TECDOC-1396 to the Cogema paper "Downstream
constraints on product specification and ISL mining methods", G. Capus,
COGEMA, Velizy, Cedex, France, pp.213-220.

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

The U-234 creates a radiological issue when the source of Natural U is
enriched in U-234 by geochemical processes (Physicists beware! Yes, there is
a difference!) Because of the alpha recoil during U-238 decay, formation of
Th-234 and Pa-234, the U-234 has been dislodged from the uraninite or
coffinite mineral lattice and is much more prone to leaching!  Thus the
U-234 in the mined product can be significantly higher than equilibrium
conditions would allow.

The enrichment of U-234 when the U-234/total U ratio is high leads to a
product which has some undesirable radiological properties based on the ASTM
C996 standard.

This problems tends to be in ISL (in situ Leach) mineable sandstone deposits
and not in other types of deposits such as the Proterozoic
Unconformity-Related types mined in Canada and Australia.

To quote George Campus:

Abstract. As uranium is more and more considered as a commodity, miners are
producing natural uranium “as it comes out of the ground”, forgetting
sometimes that its isotopic composition can vary. Focusing on the 234U
content of commercial concentrates coming from mining operations, it is
reported that some batches are presenting difficulties. For these batches,
ASTM C996 Standard specification requirements are not always met. It seems
that this is only the case for certain uranium batches recovered through
solution mining. Out of specification batches reaching the market now are
more likely to cause problems than in the past. The main reason is that
downstream from the front-end of the fuel cycle, the average U235 assay
tends to increase significantly with the fuel burnup. And the economic ratio
between uranium and SWUs prices is leading towards high tails assay. As ISL
is increasing its output, it is important to understand the phenomenon at
its roots and analyze the consequences of the problem. This paper is aimed
at recalling the major facts explaining the U234 content variations and
their potential consequences. To conclude, possible mitigation measures are
discussed.

Dan ii

Dan W. McCarn, Geologist; 3118 Pebble Lake Drive; Sugar Land, TX 77479; USA
Cell: +1-505-710-3600; Home: +1-281-903-7667; Fax: +1-713-241-1012; 
Office: +1-713-241-5726; Austria:  +43-676-725-6622
HotGreenChile at gmail.com


-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf
Of Geo>K0FF
Sent: Monday, January 07, 2008 2:56 PM
To: Edmond Baratta; radsafe at radlab.nl
Subject: Re: [ RadSafe ] Detecting DU at a distance via beta particle
emission.

">I have a simple question:  If U-235 is removed in the separation from 
U-238,
> why isn't U-234 removed at the same time???
>
> Ed Baratta"

Not all the U-235 is removed, only down to 0.2-0.3%. Sometimes only down to 
0.4% from 0.711 %. ANY reduction
from the natural ratio of U-238/U-235 qualifies the end product to be called

DU. Probably not all the U-234 is removed either, but the U-234 comes back 
(decay daughter), the U-235 never does . Someone else will have to comment 
on the U-234 levels initially left in DU metal, if any, I don't know.

Every atom of Pa-234m that decays, turns into U-234. Because of the great 
disparity between the two half-lives, 1.2 minutes vs. 240,000 years, the 
contribution of U-234 to the radiation from DU is minimal.

Bottom line, if you have U-238, you will son have Th-234, Pa-234m and U-234.

These used to be called Uranium I, Uranium  X1, Uranium X2 and Uranium 
II.(Glasstone)

Yes there are X-ray produced by the beta particles due Bremsstrahlung that 
can be detected using low energy gamma scintillator probes. That is another 
subject and I would like to hear from someone who has used this method in 
practice.
Alpha spectroscopy is the main method for detecting small amounts of DU, but

that is not at a distance, therefore yet another (and interesting) subject.


Same deal with Radium. Assuming a 100% efficient refinement, all the lower 
daughters will again reach equilibrium in a period of time.
It is inevitable in a decay chain where the parent has a long half-life 
compared to the daughters.

DU will never reach equilibrium in human time scale because U-238 has a long

half-life yes, but the daughter U0234 and Th-230 also have long half lives, 
so the refinement will only result in partial equilibrium.

My interest in DU is only scientific, not political. I am not anti-radiation

in any way.

George Dowell
GEOelectronics at netscape.com