Silver & White Anti-Flash

[Zipper730]

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?

 

[pbehn]

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?

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.

 

[Zipper730]

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.

Why is it a nightmare in thermography? Because it reflects heat well?

 

[ThomasP]

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. As pbehn mentions above, a material such as aluminum is quite good at protecting against infra-red and higher frequencies through the UV spectrum. Above UV it drops steadily until at the low-energy gamma ray level it does very little, and may actually increase the radiation types dangerous to humans at higher energy levels. The white coating often seen on military aircraft and space vehicles is designed to absorb/attenuate an amount x of gamma rays and neutron particle radiation, but also reduce the secondary radiation being emitted from the protected surfaces due to interaction with high energy alpha and beta particles.

Primary radiation is generally defined as the incoming radiation emitted by the source (A-bomb or thermo-nuclear bomb/sun in this case). Secondary radiation is generally defined as radiation emitted by the material (aluminum in this case) caused by the interaction of the incoming radiation (ie alpha and beta particles, gamma rays, and neutron particles) with the aluminum. In some cases the secondary radiation can be more dangerous to the humans in the aircraft/space vehicle than the primary radiation.

The protection a material provides against radiation is dependent on numerous factors, but the main factors are designated Z (effective Atomic Number), N (effective electron density), and ED (energy dependence), and the material's atomic/molecular arrangement(s). These 4 factors combine to create the S (total effective cross-section) of the material.

The importance of the S factor relative to this discussion, is in the area of prevention of passage and attenuation (reduction in energy of emitted radiation types, both primary and secondary). If the radiation interacts with the material it will either be blocked, attenuated, or result in secondary radiation. The S factor is a way of predicting the probability of any given type of radiation interacting with the material.

A quick example that applies to the white paints/coatings of this discussion is in the area of neutron protection. Neutrons have no electromagnetic charge, and can penetrate large amounts of relatively dense materials such as lead, due to having to actually hit an atom to interact with or be stopped. Materials such as high density plastics are more likely to stop neutrons than a similar thickness and much heavier layer of lead. The lack of a crystal structure in most plastics will produce a greater likely hood that the neutrons will interact with an atom or molecule and thus be stopped or attenuated.

If you combine the high density plastic with a compound such as zinc or titanium oxide (bright flat white in appearance) into a relative thick coat of paint, you will have a significant protective effect (how much I can not say) against neutron radiation, a very high effect against the secondary radiation caused by high energy alpha and beta particles, and probably some useful effect agains x-rays and low energy gamma rays. Just how effective the actual material used on the bombers was I can not say without knowing the specific plastic type and the additives. The white appearance may simply be a result of additives used in binding or for subterfuge.

 

[pbehn]

Why is it a nightmare in thermography? Because it reflects heat well?

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 - Wikipedia

 

[Zipper730]

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..

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.

 

[pbehn]

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.

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.

 

[ThomasP]

Hey Zipper730,

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. The very high energy alpha, beta, and proton particles have a tendency to cause secondary radiation when striking materials like aluminum (sometimes called the cascade effect, although the term technically refers to other aspects of the phenomenon), some of which can actually be more harmful than the original particles. But special types of materials combined to form a coating that looks like white paint can. If I had to guess I would say that the white coatings found on the nuclear bombers was for protection against both heat and radiation. I know that there were/are coatings (usually white, often ablative) used on aircraft to protect against thermal flash/heat. And I know that there were/are coatings used on aircraft/spacecraft that help reduce the effects of various types of radiation.

The effective lighter weight materials are not ones that I would (instinctively) have thought would do the job. It is easy to believe that water is a good absorber of neutrons. But relatively thin layers of plastic that absorb gamma rays? and or attenuate the effects of various primary radiation? and reduce the production of secondary radiation? See:

"Demron - Radiation Shield Technologies"

Optimistically described by the following: "RST Demron® W CBRN Ensemble is the only suit to provide total protection for CBRN threat; chemical warfare agents (CWA's), toxic industrial chemicals, alpha particles, X radiation, gamma radiation, high energy beta radiation and heat stress."

If they were also worried about thermal flash from a fission/fusion event, the suits would probably have an additional coating that was bright white . . . oh, wait . . . !

 

[mjfur]

Crazy idea here, white is harder to see at altitude than reflective Natural Metal Finish.

 

[Zipper730]

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.

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?

Crazy idea here, white is harder to see at altitude than reflective Natural Metal Finish.

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).

 

[ThomasP]

Hey Zipper730'

Yes and Yes

 

[pbehn]

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).

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.

 

[Zipper730]

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?

 

[pbehn]

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?

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.

You can pass your fingers across an oxy acetylene flame without burning your fingers, because they aren't there long enough, to heat a roundel or anything in nanoseconds from a distance of 30 or 40 miles or even the 10 of Enola Gaye is fantasy, it is just "bigging up" the power of undisclosed weapons in the cold war.

 

[Joe Broady]

"Project 6.2a was established to determine the responses of a B-36 aircraft to the effects of a nuclear detonation at levels approaching the thermal and blast limitations of the aircraft... The entire underside of the aircraft had been painted with white enamel to improve the reflecting characteristics of the skin. The standard procedure for painting B-36s involves spraying all magnesium surfaces with aluminized lacquer and leaving all aluminum surfaces bare. To determine the effectiveness of this new procedure, a portion of the wing undersurface was cleaned of the white enamel and refinished with the normal aluminized lacquer."

It'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

Also note related publications at the bottom of the page.

 

[wrenchedmyspanner]

DTICs are a fantastic but too often overlooked source of information.

(Provided they're not classified )