In space, a thin sheet of lead is not radiation shielding but a radiation amplifier.
The problem being that high-energy cosmic rays are unlikely to interact with the lightly built spacecraft, going right through it. But if you add a thin layer of a good radiation shielding material, then there is substantially increased chance that they will interact with that material, and produce a very large spray of secondary particles. And those secondary particles will also be going fast enough that when they hit more shielding material, they will also result in more particles.
Then some of those secondary particles will be neutrons, which will easily penetrate the thin shielding (lead half thickness for 4MeV neutrons is 68mm), and irradiate the surroundings.
This has been very clearly demonstrated on the ISS, any metal tool has substantially higher radiation levels around it.
Thank you for this post. I was wondering if a thin lead sheet would be beneficial for the cockpit ceiling and maybe aisles of jetliners to protect the crew from the prolonged exposure to increased radiation. Do you think this is a bad idea for the same reasons as the spacecraft? (Of course there are other materials besides lead, that was what first came to mind because I incorrectly thought it was a panacea for all radiation types).
Air pressure at airliner altitudes is still about 20-30% of the sea level value. That means 20-30% of the atmosphere is above that—a column of mass equal to 2-3 meters of liquid water.
A thin lead sheet would be a rounding error next to that.
This is an oversimplification that's rather wrong, but: a decrease in altitude of just 300 meters, at airliner levels, puts an additional atmospheric mass equal to ~1 cm of lead (Pb) above your head.
Have you seen the explanations of radiation where they say flying (as a passenger) is about equal to the dosage of a dental X-ray (or something similar)? Someone who spends their career getting exposed at that rate might be worth making them a shield.
It's *not possible* to make a shield. The cosmic radiation that reaches that altitude is highly energetic and highly penetrating—enough so to go through 3 meters of water—and would be completely unaffected by lead sheets. Any easily-shielded types of cosmic radiation have already been blocked by the atmosphere.
It's not worth it. Like, you could mandate planes fly 100 meters lower, but a lead coating would be so heavy. Let's say a 737 with a max weight of 70 tons. Covering the top half with lead would mean a 200 square meter sheet, and at 1cm thick it would weigh more than 20 tons.
The problem being that high-energy cosmic rays are unlikely to interact with the lightly built spacecraft, going right through it. But if you add a thin layer of a good radiation shielding material, then there is substantially increased chance that they will interact with that material, and produce a very large spray of secondary particles. And those secondary particles will also be going fast enough that when they hit more shielding material, they will also result in more particles.
Then some of those secondary particles will be neutrons, which will easily penetrate the thin shielding (lead half thickness for 4MeV neutrons is 68mm), and irradiate the surroundings.
This has been very clearly demonstrated on the ISS, any metal tool has substantially higher radiation levels around it.