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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?

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    $\begingroup$ Independent of the accuracy of the tv series, did you think of the effect of the ionizing radiation? Basically the helicopter would be in an envelope of ionized atmosphere, and absorption/reflection of the radio waves from/to the helicopter would be hampered. Like we can communicate long distance around thanks to the ionosphere, or contact is lost during atmospheric reentry, depending on the plasma frequency. $\endgroup$
    – Alchimista
    Jun 19, 2019 at 13:56
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    $\begingroup$ @Alchimista I think this is the answer,radio communication depends on the ionosphere, and if an ion sphere is generated around the accident communication is lost $\endgroup$
    – anna v
    Jun 19, 2019 at 14:17
  • $\begingroup$ @Anna I agree but I am not able to judge about the actual case. Perhaps a direct influence/damage to the electronics might be possible. Always assuming realism. ... Perhaps O will change it to an A if nobody does it better. $\endgroup$
    – Alchimista
    Jun 19, 2019 at 14:24
  • $\begingroup$ I am asking about the case that damage to the electronics is barred (radiation-hard electronics). In that case, how exactly does the ionizing radiation interrupt the radio signals? $\endgroup$ Jun 19, 2019 at 14:38
  • $\begingroup$ @annav, Re, "radio communication depends on the ionosphere." some forms of radio communication--most notably, so-called "shortwave" communication, using frequencies between 3Mhz and 30Mhz, is possible over long distances at night because the signals reflect off of gradients in the ionosphere. Long-distance shortwave communication never was completely reliable, and it is little-used in this age of satellites and fiber optic cables. Most modern radio communication is strictly line-of-sight, using frequencies that are mostly unaffected by space weather. $\endgroup$ Jun 19, 2019 at 16:05

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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.

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