While it's clear that
ERichardson hasn't even looked at the
school exercise that I
presented back on Page 1 of this thread -- unfortunate, since it demonstrates that an average American eighth-grade student can follow its argument -- the copy 'n pasted commentary above deserves its own reply. I didn't see if anyone else had tackled it.
For starters, the unit
rem is a unit of total dose, not rate of exposure. This unit has fallen out of favor, to be replaced with the more logical and easily converted
Sievert, also a measurement of total dose. Saying an astronaut absorbed "500 Rems" of radiation has nothing to do with how fast he traversed the van Allen belts, because it measures the total. It could refer to a long exposure at moderate levels, or a short exposure at extreme levels. Which it is doesn't matter.
The claim quoted above that astronauts absorbed 500 Rem is ridiculous, since this would prove
fatal in most cases. Furthermore, the school exercise I've linked above -- again -- reveals the correct answer to be in the range of 11 Rads, or using the more fashionable unit again, 0.11
grays.
Grays and Sieverts are similar. They differ in that Sieverts are corrected by a fudge factor depending on the type of radiation, and another fudge factor depending on the type of organism. For astronauts traveling through the van Allen belts, the primary form of radiation is electrons, and the organism is humans, so both fudge factors are = 1 and in this case 0.11 grays is roughly equal to 0.11 Sieverts, or 11 Rem.
Not 500 Rem, 11 Rem. Your source is lying. That's all there is to it. 11 Rem isn't good for you, but it's not particularly dangerous. And that's the
unprotected dose, i.e. the dose an astronaut would receive if he'd been sunbathing on the command module during the journey.
Now let's turn to film. It is true that camera film is sensitive to ionizing radiation, and just how sensitive is a complex function of the film type, grain size, and properties of the radiation.
Keep in mind, however, that film in space is nothing new. Many
spy satellites relied upon film. NASA has had plenty of opportunities to study the effects of radiation on film (and astronauts too) and come up with countermeasures.
A nice thing about film is that it isn't particularly large. This makes it possible to shield the film without incurring a huge weight penalty.
Also, the radiation in the van Allen belts, again, is primarily in the form of trapped electrons and protons. You don't need lead to shield from these. Aluminum works just fine. Indeed, rad-hard electronics (something my shop is deeply involved in, as we send robotic probes to Jupiter) typically use relatively thin aluminum armor to protect computer chips from radiation effects.
The Apollo capsules, therefore, were quite adequate to protect both astronauts and their cargo. Not perfect protection, of course, since weight was still a factor, there are windows, and there are other, lower intensity sources of radiation that are harder to stop. But certainly good enough protection, particularly when combined with intelligent mission design that minimized their exposure.
Finally, to
ERichardson: I present the above as a learning opportunity for you. But there is one thing more -- I am a NASA scientist. Is there anything you'd like to say to me? Anything you'd like to ask?
