The flash first, then the fireball, exactly as in any nuclear explosion, just small-scale.
READ FIRST our general article on how “depleted” uranium weapons (like these shells and missiles) work explaining how nuclear criticity is reached. One great case : Baghdad 2003, the US war.
Some pretend “depleted” uranium weapons were first developed by Israel. They were developed by the USA much earlier, during the Manhattan project. See this article for first occurences. But, at least in 1940-45, depleted uranium was not added to the nano-nukes.
BLU warheads (still used) are well known for these flashes. A multiplicity of such flashes can be seen at the dropping of a CBU bomb, it can be also seen in each video of a BLU-82 “Daisy Cutter” drop or of many bombs during the Vietnam War (see video inbetween 01:00 and 01:15 and also later). This is not a missile powered weapon, dropped slowly for anti-personal effect, the nuclear energy is not focused in a single direction to destroy a tank and hence the flash is more visible. See also this Russian copy of the BLU-82 : a flash can also be seen in the smoke plume at the very beginning of the video. Same for the newer MOAB, the flash is obvious if you slow down to the maximum the Youtube video at 0:20. This works also with missiles on the instant of the blast (undelayed), see for instance here for the Brimstone. Below for a US bunker buster the flash is bright and powerful :
Video available here, with more flashs during carpet bombing, see esp. at 3:28 the MOAB flash.
(That’s a bunker buster so most of the energy is directed inside the ground and the flash is less visible relative to the power of the bomb)
Very clear at the exact impact of an Israeli Military Industries bunker buster :
As you can see the flash comes always before the fireball, at the very beginning of the explosion, exactly as in any nuclear test even though it’s much much less powerful. Israeli raid on Gaza 2014 (video) :
Another example with a thermobaric bomb : one can see very easily the production of light in the bottom left corner.
See also the video of a German Panzerfaust DM32 “Bunkerfaust” for very clear flashes of light (from 01:59). Same story : small amounts of U235 compressed with powerful explosives.
The workings of this Russian “thermite” bomb (Syria 2016) are identical :
Here is something trickier, pictured at the beginning of the article (in a particularly blatant case): the flash in the SECONDARY blast a few seconds after impact of a “depleted” uranium shell during the First Gulf War is also clear proof of a criticality event (first link : soldier report, second link : National Geographic documentary on the Gulf War, third link : video of a flash recorded after the impact) : two criticity events in fact, one at impact to drill a hole into the bunker or the tank and the second one a few seconds later thanks to delayed neutrons. In France these antitank shells are known sometimes as “obus-flash”. A testimony told me about these weapons that “the warhead drills a hole in the tank, and a few seconds later the flash melts down the tank“.
Here is a great example (the pictures at the beginning) : this video of the plume of “plasma” after a Saudi bomb smoked a bunker in Yemen. There is a first explosion at 0:16 at the impact of a very fast missile. Then at 0:21 there is an explosion INSIDE the plume, which spreads lots of sparkles and creates a blinding light all around the city (so people need to duck for cover). At 0:23 when the camera comes up again one can still see the light of the flash, that is STILL totally blinding since there is no reason (like a wall spreading around the material) for the nuclear reaction to be interrupted.
Such an almost blinding flash of light can be created only by a nuclear detonation. Have you ever seen a car explosion generating a flash of light ?… The use of small amounts of highly enriched uranium + a neutron source (beryllium / heavy water + sodium 24 / thallium 208 / polonium 210 – or a uranium – (palladium) – deuterium – tritium mix) in “depleted” uranium shells and missiles generates fast neutrons (from (a, n) or (gamma,n) reactions or a low energy nuclear reaction in the case of the tritium mix, see again links just above). These neutrons are slowed down because they have to cross the beryllium tamper. The fission of 235U from slowed down neutrons generates at the impact a first fission shot (criticality event). The uranium 235 is concentrated on the tip of the missile or in the center of the cone of the shaped charge (so that the entire uranium mass is 0.2% or 0.72% of 235U but the core is 95% 235U). For the Brimstone missile, the BLU bombs, the MOAB this happens directly at the first blast, because there is fission, but then the matter is spread around (because there is no receptacle like a tank…) so it cannot react again.
In the case of tanks and of the Saudi missile the delay comes from the delayed neutrons from the first criticality event. Even 1% of fission neutrons from a criticality event (that is the percent of neutrons that are delayed) means a HUGE amount of neutrons. Furthermore let’s underline that in average delayed neutrons are much slower than prompt neutrons, in average 405 keV instead of 2 MeV, which means they will need much less moderation for starting up fission. The mix has oxydated, helping also slowing down these neutrons. The delayed neutrons will come progressively (with an average delay in a nuclear reactor is about 10 seconds according to Charpak, Journé and Garwin in their book De Tchernobyl en tchernobyls but many will come before that and there are several waves with different half lives but some waves will produce neutrons that are slower than others) and this delay matches pretty well the observated timeframe between impact and explosion + flash.
In the tank, the magma is full of neutrons from the fissions, the (a,n) and (n,2n) and the cavity it has dug into the bottom of the tank allows for compaction of the magma. The tank is an almost closed “cave” (there’s just the hole of the shell on a side), the bodies of the crew have burned, thus there is vapor in the tank (the human body is mostly made out of water), neutrons spraying out of the molten uranium onto the top of the “cave” and reflected into the core are slowed down by the vapor. The U235 from the tip is obviously now in the state of a gas, partly mixed with vapor, the atoms of the U235 gas move VERY fast, improving sharply the probability of a collision with a neutron. The tank behaves exactly as a nuclear reactor with a positive void coefficient and the core explodes. The flashs are clearly a proof of the arrival of the delayed neutrons. The amounts of energy released cannot of course be compared to a kiloton-range nuclear bomb, yet this is a nuclear explosion.
Same for the much bigger Yemen bomb : the only sensible explanation for that second explosion is exactly the same as above, the U235 of the tip of the weapon, oxidized, is vaporised into the air by the first explosion and is into the plume, together with the hydrogen that is used in the fuel of the missile and may be used as a cryogenic coolant for a highly radioactive neutron source in the warhead (it may have also been present in big quantities in the ammunition warehouse that was targeted, as fuel for rockets for instance). Furthermore U235 in the plume is HIGHLY AGITATED because it’s so hot, and this increases the probability of a neutron crossing the path of an U235 atom. Hydrogen is also an excellent neutron moderator. What is the ONLY hypothesis for a delayed explosion, at 0:21, that creates so much BLINDING LIGHT and that actually happens inside a PLUME is CLEARLY and DEFINITIVELY a phase of supercriticity of the oxidised U235 inside the plume, above the ground, thanks to an excess of delayed neutrons from the first impact. End. But this wouldn’t have happened without a first supercriticity shot, demonstrating hence clearly the fact that flashes at impact, even though less powerful (when they are not totally underground, hiding the flash), are also the testimony of an uncontrolled chain reaction of fission.
Please download the ebook but the main point is simply that depleted uranium is not needed at all for armour piercing. It should be easy to understand to anybody having good basic knowledge of what nuclear energy means !