Gavin Stairs on sun 5 jan 03
Yes, Sam, sizable lumps of depleted AND natural uranium are to be found in
aircraft, hospital radiology clinics and other places. However, they
should be encapsulated in a tough epoxy or other coating, avoiding human
contact with small particles. Massive uranium like this exhibits a
property called self shielding, meaning that the radiation from most of the
mass is never seen, as it is trapped inside the lump by the heavy
surrounding metal. So what you are exposed to is the radiation from a thin
layer at the surface. The layer is a couple of millimeters thick. On the
other hand, the radiation from the material in a glaze coat is not
materially diminished by self shielding, as it is dispersed in a relatively
light matrix of glass. So the dose you get from a plate may be only a bit
less than what you get from that lump of pure uranium. Also, the epoxy
coating will trap the alpha radiation, which is the most damaging to human
tissues.
And do take note of Edouard's most recent post about the availability of
uranium leachate at the surface of dinnerware glazed with uranium. Note
also that depleted uranium is merely natural uranium with SOME of its U235
removed. There is still quite a lot of U235 in it, and the radiation dose
from depleted uranium is merely reduced, not eliminated. U238 also emits
radiation, but at a lesser rate.
You should also be aware that if you work around uranium habitually, you
should be designated a radiation worker, which means you have to be
monitored for radiation exposure, and the permissible dose is higher,
presumably in compensation for the careful monitoring. Also, in facilities
which machine uranium, or otherwise process it in powder or unencapsulated
forms, there are regulations to confine the powder to a "hot" zone, and
workers within that zone must wear protective equipment and follow other
precautions.
Even with all of this, I have seen people handling uranium dust hazards
with alarming nonchalance. There is one saving grace with the stuff: it is
so dense that even fine dust falls rapidly to the ground. So the
inhalation hazard is that much diminished. But please do not adopt the
attitude that this stuff is innocuous. It is not. It won't kill you dead
on the spot, but cumulative exposure can lead to future illness or death.
One last thing: uranium is actually quite a common element. So our
exposure to uranium dust by other means is not negligible. One large
source of airborne uranium is coal fired power plants. In fact, the danger
to the public from radiation exposure on a day to day basis is much higher
from burning coal than from uranium powered nuclear plants, according to
some estimates. That doesn't take into account the risk of large scale
catastrophe, or the long term problem of waste storage, but it does show
that we should not be simplistic in our evaluations.
All the best to you, Gavin
At 07:52 PM 04/01/2003 -0800, you wrote:
>Re depleated uraniun. FYI - In case you don't know,
>depleted uranium is used in most commercial airplanes
>to balance the flaps and control surfaces - and so on.
>Reason - it is is very heavy as related to size. This
>material is a 'controlled material' but in some cases
>just sits around while the flight control
>surfaces/parts are being overhauled - while the
>aircraft is in overhaul. A lot of mechanics are in
>close touch with this material ,but after 42 years in
>the commercial aircraft industry, I have never seen
>one "glow in the dark"---yet. Sam in Daly City
>
>
>\--- Catherine White wrote:
> > Uranium in the '60s:
> >
> > Rhodesia, 1965 (Zimbabwe 1978). Prime Minister Ian
> > Smith proclaimed the
> > country's independence. Britain retaliated with a
> > trade embargo. That was
> > the end of readily available uranium, at least for
> > me. I had a small
> > quantity that I may never have used given that I
> > don't glow in the dark.
> > ;-)
> >
> > Catherine in Yuma, AZ
> > Two ancient electric kilns. Both outside.
> > It never rains here at the Mexican
> > border.
> > One partner, one kid, one dog, two
> > cats. All inside.
> >
> >
>=====================================================
> > > 1) Accidental contamination from uranium compounds
> > through contact with
> > > ceramic dinnerware, by Ralph W. Sheets, Clifton C.
> > Thompson
> > Edouard Bastarache
> >
> >
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