Cherenkov radiation

[Avatar28]

I know it's caused when something exceeds the speed of light in a given material. But what causes it and what is it, exactly? Also, how long can it last? I've visited the old nuclear reactor at Oak Ridge and our tour went around the top of the old reactor pool. Anyways, looking down into the pool it still seemed like you could see a faint bluish/purplish/whitish glow.

[Nicolas]

Anyways, looking down into the pool it still seemed like you could see a faint bluish/purplish/whitish glow.

light?

I know the reactor pools of the active nuclear power plant I used to live next to had a blue colour even when not being "on". When the reactors are on, it is the Cherenkov radiation that gives a blue glow, which continues for some time after the reactor is shut down. But this is only a rather short amount of time.

The reactor pools still looks blue after a long time. I think you don't have to look at radiation to find the explanation, but at one or more of the following explanations:

-underwater lights
-wall colour
-water colour (maybe some additives added, which happen to be blue?)

As seen from photos there is a clear difference between the blue "glow" of the active reactor, and the blue water when it is not active.

[George]

There are numerous google sites which explain it nicely.

Here is one... Cherenkov effect (http://www.iridis.com/glivar/Cherenkov_effect)

I had to give an engineering speech on a topic of my choice. When I visited the campus reactor and saw the blue glow, I made a colorful speech about it.

It is amazing that it is the water which is radiating the light. I never thought water would make a good light source. :o 8)

[Avatar28]

That's why I was wondering. The reactor had long been decommissioned. I didn't know if it could be caused by residual radioactivity causing it. They indicated that it was still radioactive down there or that the water was or some such. You'll have to forgive me, it's been quite a few years, but I distinctly remember the glow. It WAS very faint. Not nearly as bright as some of the pictures I saw online. Very ghostly and if there had been more than the rather dim lighting we had in there at the time, I don't think it would have been visible.

[Nicolas]

So the water looks blue even when shut down due to resiual radiation?

[swansont]

It's from the electrons emitted in beta decays, so as long as there is residual radiation of sufficient energy (most, if not all, unstable fission fragments are beta-decayers) there will be the potential for Cerenkov radiation.

[Eta C]

You'll have to forgive me, it's been quite a few years, but I distinctly remember the glow. It WAS very faint. Not nearly as bright as some of the pictures I saw online. Very ghostly and if there had been more than the rather dim lighting we had in there at the time, I don't think it would have been visible.

Remember that the photos could have had long exposures that would exaggerate the brightness of the Cerenkov radiation. As others have pointed out, the reactor doesn't have to be in operation to produce the light (although the intensity is higher when it is operating). Electrons from the various radionuclides produced by uranium fission are sufficient.