Re: Cherenkov radiation [ incl. blue flash and criticality ]

["J. J. Rozental" <joseroze@netvision.net.il>]

Dear Jaro,

In my message it was mentioned a reference about the Cherenkov effect
detected during the Radiological Accident in Goiania. Research was carried
out by the Radiation Emergency Assistance Center in Oak Ridge and I would
like to ask to Dr. Robert Ricks or any colleague  from the REAC/TS to
comment the research that was made by the REAC/TS .
Now, about your comment that the tritium exit signs or radium watch dials
isn't Cherenkov radiation, I do agree, however isn't blue color too, as the
Goiania Accident.

Jose Julio Rozental
joseroze@netvision.net.il
Israel



----- Original Message -----
From: "Franta, Jaroslav" <frantaj@aecl.ca>
To: "Multiple recipients of list" <radsafe@romulus.ehs.uiuc.edu>
Sent: Monday, November 13, 2000 7:20 PM
Subject: RE: Cherenkov radiation [ incl. blue flash and criticality ]


> J.J. Rozental wrote :
>
> On 3 September 1987, a shielded, strongly radioactive caesium-137 source
> (50.9 TBq, or 1375 Ci, at the time) was removed from its protective
housing
> in a teletherapy machine in an abandoned clinic in Goiania, Brazil, and
> subsequently ruptured. The radioactive source was in the form of cesium
> chloride salt, which is highly soluble and readily dispersible.
>
> After the source capsule was ruptured, the remnants of the source were
sold
> for scrap to a junkyard owner. He noticed that the source material glowed
> blue in the dark, and over a period of days friends and relatives come and
> saw the phenomenon, fascinated. Fragments of the source the sizes of rice
> grains were distributed to several families attracted by the
> glow-in-the-dark radioactive caesium chloride salt ...Thus began one of
the
> most serious radiological accidents ever to have occurred.
>
> In USA, this Charenkov effect was studied by the REAC/TS Director Robert
> Ricks.
> <><><><><><><><><><><><>
>
> COMMENT / QUESTION :
>
> Perhaps another Radsafer can confirm this, but I very much doubt that the
> glow seen with this cesium source was Cerenkov radiation - just as the
glow
> of tritium exit signs or radium watch dials isn't Cerenkov radiation
either.
> The obvious observable difference is that the Cerenkov radiation is
emitted
> in the surrounding (transparent) medium (such as water), whereas the
> aforementioned fluorescing objects emit the light directly.
> I'm no expert, but I believe this has to do with the chemistry of the
> material -- the pure metal, be it cobalt-60 or cesium137 or a spent fuel
> rod, does NOT glow, nor does it cause Cerenkov radiation to be emitted if
> its in dry air (for example, in the recent Co-60 incident in Thailand
there
> were never any reports of the sources glowing.... in this case an
> unfortunate lack of a feature that might have acted as warning sign to
some
> ! ). But - as already stated by Doug Minnema - we have all seen bright
> Cerenkov light emitted in pools storing Co-60 sources at food irradiation
> facilities and the like....
>
> As for taking photographs of a blue flash (or, no doubt, its absence) from
a
> criticality in air, I think the key here is an OUTDOOR experiment
> photographed or filmed from a great distance with a telephoto lens -- as I
> mentioned before, the old Jackass Flats desert tests of nuke rocket
engines,
> or outdoor tests of Pu & HEU critical assemblies (for indoor photography
its
> possible to use periscope-type arrangements with adequate shielding for
the
> camera....)
>
> Regarding Arnold Dion's posting saying that,
>
> "More to the point, a rerun of the Daghlian accident was performed on
> October 2, 1945 by Aebersold, Frisch and Slotin. They were not able to
> see a blue glow in a darkened room in which 6 X 10E15 fissions occurred
> and the intensity of prompt gammas increased within "several seconds."
>
> ....presumably the three who performed the rerun experiment were well away
> and/or shielded from the ionizing radiation, so that the Cerenkov blue
flash
> could not form inside their eyes & so they didn't see anything - proving
the
> point ( did they use the
> periscope-type arrangement suggested above ? ).
>
> Thank you.
>
> Jaro
> frantaj@aecl.ca


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