Morbius
Dearly Missed
I'm a little puzzled by this. One also gets a characteristic blue glow using glass. Why should that be?

It has to do with what excited states of the medium are. It's NOT the high speed particle that is
radiating - it is the medium. The medium is being excited by the high speed particle and de-exciting
by emitting a photon. What is special about Cherenkov radiation is that all the photons from a given
high energy particle can interfere constructively. You get the constructive interference only because
the particle is faster than the photons in the medium.

But what color the glow is is due to the electron energy levels being excited in the transparent medium.

Just as in my example with "neon tubes" - neon glows red, krypton glows green, xenon glows blue,
mercury vapor glows blue.....

Dr. Gregory Greenman
Physicist

mgb_phys
Homework Helper
So do you ever see other colors in cerenkov or is that the particle energies needed to achieve the speed are high enough that they produce high energy uv-blue excitation states ?
Could they also give x-rays, if they excited a k electron?

Morbius
Dearly Missed
So do you ever see other colors in cerenkov or is that the particle energies needed to achieve the speed are high enough that they produce high energy uv-blue excitation states ?
Could they also give x-rays, if they excited a k electron?
mgb_phys,

Sure - you can get Cherenkov X-rays if you excite energy levels high enough:

http://www.iop.org/EJ/article/1063-...quest-id=e43a04b0-bfc6-44b1-8141-3c249bea2d09

http://www.iop.org/EJ/article/1063-...quest-id=e43a04b0-bfc6-44b1-8141-3c249bea2d09

http://www.spiegel.de/international/0,1518,367260,00.html

In fact, the shorter wavelengths are more prevalent:

Unlike fluorescence or emission spectra that have characteristic spectral peaks, Čerenkov radiation is continuous. Around the visible spectrum, the relative intensity of one frequency is approximately proportional to the frequency. That is, higher frequencies (shorter wavelengths) are more intense in Čerenkov radiation. This is why visible Čerenkov radiation is observed to be brilliant blue. In fact, most Čerenkov radiation is in the ultraviolet spectrum - it is only with sufficiently accelerated charges that it even becomes visible; the sensitivity of the human eye peaks at green, and is very low in the violet portion of the spectrum.

There is a cut-off frequency for which the equation above cannot be satisfied. Since the refractive index is a function of frequency (and hence wavelength), the intensity doesn't continue increasing at ever shorter wavelengths even for ultra-relativistic particles (where v/c approaches 1). At X-ray frequencies, the refractive index becomes less than unity (note that in media the phase velocity may exceed c without violating relativity) and hence no X-ray emission (or shorter wavelength emissions such as gamma rays) would be observed. However, X-rays can be generated at special energies corresponding to core electronic transitions in a material, as the index of refraction is often greater than 1 at these energies.

Dr. Gregory Greenman
Physicist

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Don't remember the isotope, but it was some type of radioactive vitamin (B3 maybe).
B12 (cobalamin) has a cobalt atom, and both Cobalt-57 (100% ε, 271.74 d) and Cobalt-60 (100% β-, 1925.28 d) are used in radiology, so maybe it was an isotopically labeled B12, cobalamin-57Co or cobalamin-60Co?

http://en.wikipedia.org/wiki/Vitamin_B12