Why does ionizing radiation hamper radio communication? After having finished the second episode of the HBO Chernobyl series, wherein a helicopter flying too close to the core loses radio communication with the ground and is unreachable, I started thinking about why radio signals would be hampered.
If one were to be in the very direct vicinity (<10m) of the Chernobyl nuclear reactor meltdown, exposed to very high levels of ionizing radiation, what exactly would cause radio communication break down?
The first thing that came to mind was that the ionization of materials would perhaps increase the radio equipment's conductivity, causing potentially damaging surges of current (rendering the electronics either broken or unusable), but if one were to have so-called "radiation-hard" devices (both emitter and receiver), are there be any other potential ways in which intense ionizing radiation might disrupt a radio communication channel, rendering it garbled/unintelligible?
 A: Ionizing radiation strips electrons from atoms, thus creating a plasma. A plasma consists of mobile charged electrons and ions, and acts as a conductor. Electromagnetic radiation is strongly reflected and attenuated by interacting mostly with electrons accelerated by the electric field; ions are much heavier, so are accelerated less.
Electrons oscillate at the EM frequency, and there is a characteristic frequency, below which EM signals cannot propagate. This plasma frequency depends on the electron density, and is approximately given by
$$f_p = 9 \sqrt{n_e}$$
where $f_p$ is in Hz, and $n_e$ in $m^{-3}$.
For example, at an electron density of $10^{12} m^{-3}$, typical of the ionosphere, $f_p = 9$ MHz. Note that molecule density in the lower atmosphere is about $10^{25} m^{-3}$, so it only requires a relatively small ionization fraction to block communications. In addition, even at frequencies above $f_p$, communications signals can be distorted by dispersion, since the plasma acts like a frequency dependent dielectric. 
