Geology Photo of the Week #14 – Dec 2-8

This week’s photo, which is posted mid-week instead of at the beginning is one that I only took this Monday. I was away all day at the Royal Military College SLOWPOKE-2 reactor doing some neutron activation of cesium and calcium. We were making minute quantities of Cs-134 and Ca-41 for research purposes on the accelerator mass spectrometer. This photo is one that I was able to take while we were running the reactor. I am planning on doing a post on the SLOWPOKE reactor in the near future…sometime this month, but I thought I’d show this picture as a start.

The photo is of Cherenkov radiation in the cooling water  around the reactor. Cherenkov radiation is caused by a charged particle such as an electron or a gamma photon enters the water at a speed greater than the speed of light in water. This results in a the wavelength of the particle lengthening when it enters the water and causes the water molecules to polarize (gain opposite charges) and revert rapidly back to neutral (normal charges). This change in charge in the water molecules releases the blue glow.

Cherenkov radiation at the RMC SLOWPOKE-2 reactor. (Photo: Matt Herod)



Matt Herod is a Ph.D Candidate in the Department of Earth Sciences at the University of Ottawa in Ontario, Canada. His research focuses on the geochemistry of iodine and the radioactive isotope iodine-129. His work involves characterizing the cycle and sources of 129I in the Canadian Arctic and applying this to long term radioactive waste disposal and the effect of Fukushima fallout. His project includes field work and lab work at the André E. Lalonde 3MV AMS Laboratory. Matt blogs about any topic in geology that interests him, and attempts to make these topics understandable to everyone. Tweets as @GeoHerod.


  1. Nice picture, and nice post, but photons aren’t charged, and don’t cause Cherenkov radiation.

    I’m a nuclear physicist, and give quite a lot of outreach talks about its uses, so I enjoy following your blog to learn about nuclear applications in geology.

    • Hi Paul, Thanks for your comment! My mistake. I am not sure I understand where I went wrong? The gamma photons entering the water are not charged but induce a charge change in the water, correct? This charge change results in a blue photon (also uncharged) right?

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