AW: Question on Properties of Aluminum at Research Reactor

["Franz Schoenhofer" <franz.schoenhofer@CHELLO.AT>]

-----Ursprüngliche Nachricht-----

Von: owner-radsafe@list.vanderbilt.edu

[mailto:owner-radsafe@list.vanderbilt.edu]Im Auftrag von Paul E.

Benneche

Gesendet: Dienstag, 22. April 2003 19:05

An: radsafe@list.vanderbilt.edu

Cc: Paul Benneche

Betreff: Question on Properties of Aluminum at Research Reactor



high pressure water or lye.  However, some time after cleaning the

radionuclides reappear on the surface of the aluminum (detectable at the

surface with a thin window, large area, gas flow proportional counter, but

not readily removable).  We hypothesize that if there is uranium, thorium

or some other radionuclide within the aluminum that the cleaning that we

are doing may be selectively removing shortlived radioactive daughter

products from the surface that are then returning by building in over time

from their parent isotope.  Note, this gate frame was far enough distant

from the reactor that there was no possibility of neutron activation of

the material.



When examined by a long count on a germanium detector the following

radionuclides were observed above background levels in the gate frame

material:



Pb-212, Pb-214, Bi-214, Co-60 and Eu-152



The lead and bismuth may be from naturally occurring uranium / thorium

that may be in the aluminum and the cobalt and europium are activation

products that may have been "absorbed" out of the water.



------------------------------------------------



I would support your explanation on the Co and Eu having been adsorbed from

the water. For the radon daughters, which accumulate after cleaning the most

simple explanation would be, that it is simply plate out of daughter

products from radon-isotopes in the air. Since you obviously use a very

sensitive contamination detector and a long count on a Ge-detector you might

detect the plate-out radionuclides. You should have a measurement of radon

concentration in ambient air and then try to figure out, whether this

concentration could explain the concentration of the radionuclides adsorbed.



Aluminium usually contains small amounts of thorium. We had many years ago

the problem with out low-level-Ge-detector, because the end-cap was made by

aluminium and showed a lot of "thorium" lines. After replacing it by a

extra-pure copper end cap we had no problems any more. I do not believe that

the thorium impurity would be the reason of your problem. Is it really a

problem for disposing of the aluminium?



Hope this helps!



Franz



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