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

["Franta, Jaroslav" <frantaj@aecl.ca>]

 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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