Some calculations show that any glow in air from these radioactive elements is *NOT* due to Cerenkov radiation.

The energy of a particle is m*c^{2}*gamma, where gamma = 1.0/sqrt(1.0 - (v/c)^{2}).

(m is the article rest-mass, c is the speed of light, v is the velocity of the particle. See any book on relativistic mechanics for these formulas.)

This energy includes both the 'kinetic energy' of the particle, as well as its 'rest energy', which is given by m*c^{2}.

Tables that list the energy of emitted radiation don't count the rest energy, so it then works out that:

E_{radiation, from tables} = m*c^{2}*(gamma - 1)

For the case of air, with n=1.003, the speed required for Cerenkov radiation is c * (1/1.003), which works out to gamma - 1 = 11.94.

Alphas have a mass of around 3700 MeV/c^{2}, so to reach the required speed they would need to have a kinetic energy of around 44 GeV. No alpha emission is anywhere near this energetic, 8 MeV is a very energetic alpha. So, alphas won't generate Cerenkov radiation.

Betas are a little closer. The electron mass is 0.511 MeV/c^{2}, so to emit Cerenkov radiation they would need a kinetic energy of 6.1 MeV. This is still too high, for example Cs-137 betas are (maximum) 0.514 MeV, less than 10% of the required energy.

If you put your beta emitter in water (n=1.333), then you *can* get Cerenkov radiation. Then, you just need gamma - 1 = 0.51, and for the electron you just need a kinetic energy of 0.26 MeV. The Cs-137 betas are energetic enough to manage this.

Conclusion: If you see glowing in the air around a radioactive lump, the glow is not from Cerenkov radiation.