[article transferred from its original place on depleteduranium.org for more clarity in organisation]
The Yekaterinburg Fireball happened most probably at a much lower altitude than previously expected, say 15-20 km, on 14 November 2014, just before the CSTO (Collective Security Treaty Org., the Russian NATO) conference on air-missile defence. These altitudes for explosions are typical of missile interception which would really take place at the last instants before impact of the ICBM. Furthermore the Gazelle missiles can sprint at 20 km/s and this is probably too short and too close to the ground to be detected by thermal imagery of missile reactors (used to watch for ICBM take off).
A nuclear EMP has 3 phases, E1 from gamma interaction with the atmosphere and E3 are the more significant but E3 was significantly reduced by the solar flare which was extremely intense in October – November 2014. E1 is not significant below 20 km (see the two Metatech reports E1 see p. 23, E3 see p. 15) and at the same altitude the double flash of light starts to be moderated by the lack of oxygen and fades into an ambiguous simple flash. The airburst is also limited for the same reason. This is even more significant since the power of the warhead was certainly limited to approx. 15 kilotons to reduce collateral effects. The warhead was certainly a neutron bomb : they are used by Gazelle missiles to pre-emptively fission part of the plutonium of the incoming ICBM and defuse it. Neutron bombs do not create as much fission products as a normal bomb because the usual depleted uranium shell (fissioned by high energy neutrons, a technology used to improve the yield of a bomb) is absent in neutron bombs. Furthermore, the closest country (Kazakhstan) to have an “independent” monitoring system for nuclear explosions is also a member of the CSTO.
Thanks to Megan Eskey for the help.