So, my mom is a former Maxwell employee who now does her own defense contracting, and makes this same type of part.
As I understand it, when there is a nuclear event, it generates x-rays followed by the EMP. The goal is to have warheads in flight to be able to continue to their target, so the strategy is to employ an NED. When an event is detected, the warhead shuts down its electronics for the duration of the EMP, and then powers back up.
With her NED, she uses an ASIC for detection. I might get some details wrong, but the ASIC has a physical array in it, and the x-rays flip bits in the array. When enough bits get flipped, one can infer a nuclear event. Because it is an ASIC it is really small, which has important advantages for space-born avionics.
my sister and mother where in WMD, my father was in Oil industry. My only sane options where either compete with them by going to High Speed Trading in African originated goods markets or give up and become a Hippie, I mostly took the later option and live 400km from them.
Sorry for the late response to this. I have had mixed feelings for a while - it gives a good living to the family, but on the other had we all want to work towards the betterment of the world.
For my mom, at first she was very gung ho about it - arsenal of democracy and the importance of having a strong nation. Now she is having second thoughts, and is looking to follow her passion which is something in the education space.
EMP generally refers to the radio-frequency flash. This device is for the ionizing radiation flash -- gamma rays, x-rays, and neutrons -- that can be extremely damaging to devices that are powered on. For example, the ionizing radiation can cause power transistors to turn on unconditionally, which can fire rockets, burn out power converters, and so forth.
I've worked for a French military chopper (Tiger, NH-90) company, and they do the same, they short-circuit everything (even the batteries) so that the induced current doesn't grill semiconductors but flows freely through copper.
They do that for a very short time, so the cinetic energy in the moving rotor keeps the helicopter airborne.
When an event is detected, the warhead shuts down its electronics for the duration of the EMP, and then powers back up.
I doubt this, since the EMP is moving at the speed of light, whereas the delay times inherent in most circuitry and the time required to power down most circuitry would be at least an order of magnitude (most likely more) larger.
Why does the rate of propagation matter? I presume that during the course of the explosion there are several sequential phases. If phase x emits some non-EMP but detectable signal, say an X-Ray burst and phase y emits the EMP, both of which propagate at the same rate, then you have time(y) - time(x) to respond to detecting x before the EMP from y reaches you.
Explosions, like all other macro scale phenomena are not instantaneous, they just appear so until an appropriately small time step is applied.