Apollo and Bremsstrahlung

[PhantomWolf]

I keep meaning to ask this.

I know that the CMD was shielded against the high-energy electrons of the Van Allen belts, but what about the X-Rays caused by the Bremsstrahlung effect as electrons hit the metallic outer shell?

I tried finding something on this, and come up with that most electrons in the VA Belts are less than 10 MeV and that electrons of 5 MeV and less are very inefficent at producing X-Ray radiation, but not what precautions were taken to prevent of lower this problem.

Also are there any good sources on the amount of radiation beyond the VA Belts? One argument that seems to come up every now nd then is that there is two much radition beyond the VA Belts.

I always thought that there wasn't a lot unless there was solar activity. What sort of figures are there on this?

[Indigo]

my understanding was that either just inside or outside the metallic shell was a polyurethene layer to reduce this effect. The shell was aluminium too, I think, which further limits the effect.

I may have some facts wrong, but this is off the top of my head. Did I get it right?

[JayUtah]

Secondary radiation from electron bombardment was simply too weak to care about. Polyurethane wouldn't stop it, by the way: the secondary radiation is electromagnetic; polyurethane would be useful against the particles themselves.

If you place an x-ray detector a fixed distance behind shielding and bombard it with a constant flux/energy of electrons, and vary the shielding thickness, when you graph detected intensity as a function of shield thickness you get an interesting curve. The detected intensity rises as thickness increases, up to a point, and then it falls dramatically.

Physically what happens is that too-thin shielding fails to absorb many electrons; they just pass through. As the shielding becomes thicker, more electrons are absorbed and therefore more x-rays are created. But as the shielding increases to the point were all electrons are absorbed, and then gets thicker, the inner portion of the shield is not absorbing any electrons. It serves to absorb the x-rays produced in the outer thickness of shielding.

The material I'm thinking of here is aluminum, and the shielding thickness is varied on the order of a handful of centimeters. The short version is that metal shielding works for secondary radiation, as long as it's thick enough.

[tlbs101]

There are not a large quantity of 10 MeV betas in the belts. I do know that the Argos (and other) high altitude nuclear tests in the late 50's and early 60's produced a large quantity of high energy beta's. They calculated that most of those had decayed by the time Apollo 8 was launched.