Two shields were identified in this analysis that are of primary concern for the launching of a space nuclear reactor. A W/LiH* configuration was found to be the lightest weight shield. Its mass was calculated to be 528.39 kg. The SP-100 shield was calculated to be about 681 kg. The difference in mass can be accounted for by noting that the LiH in the SP-100 is in a stainless steel honeycomb, and there is aluminum in the shield for thermal conduction. There is also much more W in the SP-100 shield. Also, the shield has an insulation material which adds more weight. The shield with the smallest volume was found to be a W/B4C** shield with the W at a position of 10 cm from the core. This shield's mass was calculated to be 655.35 kg. The volume for the W/B4C shield was found to be 211,176 cc. The volume of the W/LiH optimum weight shield was calculated to L)e 437,407.84 cc. Since the W/LiH shield has twice the volume than that of the B4C shield, the 126.96 kg difference in mass may be more acceptable when considering a volume constraint for the launch vehicle or the material characteristics of the different shielding materials.
Table 2-2 shows that at energies above 500 keV the tungsten alloy has a significantly
higher linear attenuation coefficient than lead because of its higher density. Thus,
the same shielding effect can be achieved with a thinner shield. At energies below
500 keV, the difference between the attenuation properties of the two materials is
less significant; the higher density of the tungsten alloy is offset by the lower atomic
number. The tungsten alloy is used where space is severely limited or where machinability
and mechanical strength are important. However, the tungsten material is over
thirty times more expensive than lead therefore, it is used sparingly and is almost
never used for massive shields. The alloy is often used to hold intense gamma-ray
transmission sources or to collimate gamma-ray detectors.
Table 2-2. Attenuation properties of lead and tungsten
DeltaV: thanks for that shielding pdf. It looks like it will be an interesting read. I should be able to do a better (more accurate) shielding design for my ships
Glad to be of help. Radiation calcs are not really my gig, but, assuming Polywell works, shielding mass seems to be the biggest hindrance to putting it in a flying machine. I'm still hoping for some sort of nanotech breakthrough that results in drastically lighter shields. Layers of different materials seems to be a step in the right direction.
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Probably. You can work back from B10 loading density. Hydrogens/cc. To get a rough idea.
And since this is more or less out there: the secret to low weight shielding is layering. And getting the order of the layers and their thickness right. For instance B10 gives off X-Rays when it absorbs neutrons. OTOH poly is low melting point. So you have to allow for that.
The most secret thing about Naval Nukes is how the shielding is done. The Ruskies tended to kill their crewmen. The USN did not.
Engineering is the art of making what you want from what you can get at a profit.
I was reading in a NASA report on space shielding options that they wanted more research into carbon nanostructures loaded with hydrogen (compounds?). One idea was that carbon composites might do double-duty; load-bearing structures and radiation shields.
Maybe boron buckyballs or nanotubes could also be used. It would have to yield a really big improvement, however, to justify the added hassle/expense of nanostructures vs. macroscopic layers.
Enough to build my VTOL SSTO space hopper.
So it's a chicken and egg situation. I need the gadolinium to build the space hopper, but I need the space hopper to mine the gadolinium asteroid to get the price down.