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I have never seen an explanation of the physics behind it, a polished metal finish is more reflective of heat radiation than a white finish, polished metal is a nightmare in thermography, which I was involved in long ago. It is a really cool way of saying "this is a nuclear bomber" though.It would appear that the silver finish was adequate for nuclear bombs based on the fact that the Enola Gay, Bockscar, and their escorts didn't seem to suffer (far as I know) any damage from the blast other than the jolt from the shockwave.
Later, it seems they went to white: If it's not classified, I'm guessing the silver wasn't good enough for thermonuclear weapons?
Why is it a nightmare in thermography? Because it reflects heat well?I have never seen an explanation of the physics behind it, a polished metal finish is more reflective of heat radiation than a white finish, polished metal is a nightmare in thermography, which I was involved in long ago.
Exactly, the ideal is what is called a black box emitter, this emits most heat by radiation and reflects very little. With polished metal it emits little but reflects a lot, so basically you measure the temperature of anything hot nearby. A chrome plated mug will keep a drink hot longer than a matt black one. Heres some interesting equations and values. A perfect emitter has a value of 1, polished copper, tin foil and polished silver are 0.02-4. Emissivity - WikipediaWhy is it a nightmare in thermography? Because it reflects heat well?
So it protects against heat and UV, but as you go into X-ray and gamma, it makes things worse, whereas white paint tends to absorb gamma-rays, neutron particle radiation and protect against neutron activation and the like?Depending on the material (aluminum in this case) the protection against radiation will vary a lot on the type of radiation it is being subjected to..
Yes zipper, if you look at people handling ionizing radiation they just wear white clothes and a crash helmet painted white, its all you need. SERIOUSLY white paint doesn't absorb alpha or gamma radiation, neutrons can pass though all sorts of things, if they were stopped by white paint they wouldn't be dangerous.So it protects against heat and UV, but as you go into X-ray and gamma, it makes things worse, whereas white paint tends to absorb gamma-rays, neutron particle radiation and protect against neutron activation and the like?
BTW: From what I remember reading the radii of ionizing radiation doesn't scale up as much as the thermal and blast radii as the yield goes up: That said, I'm not sure if ionizing radiation is an average of the alpha & beta particles, neutron emissions, and gamma-rays.
So it's a very specific type of coating that would be used for this purpose?White paint (like we usually think of it) as such would not protect much against x-rays on up, or very high energy alpha & beta particles, high energy protons, or neutrons.
Actually, I would have thought silver would be harder for the most part (it reflects the sky colors back) except for the whole glint issue (that would be seeable beyond the distance you could normally make out a specific shape).Crazy idea here, white is harder to see at altitude than reflective Natural Metal Finish.
It is kidology, the most important attenuator of radiation is distance. The idea that a nuclear flash could make a planes roundels hot from a distance of many miles defies the laws of physics. The muted roundels were on the top of the wings too, how would they be exposed to the flash, which lasts microseconds.So it's a very specific type of coating that would be used for this purpose?
There is one thing I remember in particular regarding RAF V-Bombers: To avoid hot-spots, they used muted roundels that were a little lighter than the normal ones seen on their bombers. Provided it's not classified: I assume some of the air-tests of nuclear bombs carried out in the 1950's included air-dropped thermonuclear bombs?
Actually, I would have thought silver would be harder for the most part (it reflects the sky colors back) except for the whole glint issue (that would be seeable beyond the distance you could normally make out a specific shape).
The muted pastels were also used on camouflaged aircraft, there is little point in camo. if you have a high vis roundel on it. As I said, the flash of a nuclear reaction lasts micros seconds (in fact the flash is nanoseconds, the whole reaction is microseconds). To make a roundel hot from a distance of many miles in a few microseconds you need to be very close to the bomb or the sun. The building under ground zero at Hiroshima had its dome covering vaporised by the explosion, but not the metal lattice underneath, which was also subjected to the pressure blast and thermonuclear heat of dissipation. Enola Gaye was 10 miles from the explosion when it happened and 11 miles away when it experienced the shock wave.So they had another reason for the muted pastels, or they did it to make people feel safe when they really actually weren't safe at in the matter?
I was reading through some older posts of mine and I'm glad I stumbled on this. This is awesomeIt's too late at night to study the report, but here it is:
Operation Castle, Project 6.2a, Thermal Effects on B-36 Aircraft in Flight