[0PingWithJesus]

One line in the piece says "Observing the direct effects of radiation, although possible, requires extraordinary circumstances.". While this is mostly true, you can actually observe radiation directly, with your own eyeballs, without any extraordinary methods. Basically all you need is a radioactive source, scintillator and a very dark room. That's how scintillation counting was done back in the day. This sort of device is called a Spinthariscope, you can find examples of them on youtube and what you see is a lot like the map in the OP. So I'd say the author did a good job.

[4gotunameagain]

The author probably counts these as indirect effects, as it is the collision of the α particles with zinc sulfide, and not a direct effect of radiation like Cherenkov.

[RugnirViking]

isnt cherenkov also caused by interaction with water molecules?

edit: the article goes into a little more detail and talks about how its due to the different speeds of light in water and vaccuum, and I don't know enough about semantics or physics to say what this means about my original question :)

[0PingWithJesus]

It's kinda a complicated question. Cherenkov radiation can be produced in any medium that has index of refraction greater than 1, that's what allows the charged particle radiation to go faster than the light it produces, which ultimate is what causes the Cherenkov light. The process is not reliant on the specific molecular/chemical/whatever properties of the medium, only dependent on the index of refraction. But, the index of refraction in turn comes from polarizabilty and magnetic susceptibility of the medium. Those factors depend on both what atoms & molecules exist in the medium, but also the structure of those molecules. For example, ice and water have the some chemical composition, but slightly different indices of refraction.

[SiempreViernes]

Well, for the purposes of observing the Cherenkov light it is fairly important the material is transparent at blue wavelengths :)

[0PingWithJesus]

To be a bit nit-picky, Cherenkov light typically has a wide spectrum. For water it spans the entire optical range, peaking around 350nm and dying off at longer wavelengths. So you could, for example, put dye in water such that it absorbed more blue light, but you'd still be able to observe some red light from the Cherenkov radiation escaping. But the signal would be much fainter.

Although, one further caveat, changing a materials absorption spectrum will also change it's refractive index as a function of wavelength, which will in turn effect how much Cherenkov light is emitted at each wavelength. So the situation is more complicated still.

[diracs_stache]

Agreed the classical electrodynamic approach lets us derive this relationship in terms of electric fields (Ampere-Maxwell and Gauss given a suitable gauge), a change in permittivity /varepsilon lets us change the region of this effect