Stopping X and Gamma rays
Posted: Sat Aug 12, 2017 4:37 pm
I've been getting some static about "why are you taking so long doing all this remotely when you could just use a buncha lead and be safe?".
Answer - because the amount of lead my floor will hold up is useless against high energy gammas, and of course, neutrons - remember atoms are mostly empty space, and it's like spraying neutrons between widely spaced bowling balls - little neutron energy is lost, they are just scattered a little - for that, low Z stuff works better.
Anyway, I gathered up a little data so I have something to point the static-givers at.
So, what's that? 5 or so orders magnitude drop between low energy and 2 Mev or so? So it's not exactly linear (would be if that line were horizontal) with energy, right?
Here's a paper that goes into more detail why:
I don't have anything handy just now on neutron cross sections for lead and fast neutrons, but it's low for all speeds. Hydrogen slows them down the best, and various things like to "eat" the slow ones, most often giving off a capture gamma ray, and often that's up there in the half megavolt range which is getting hard to stop with lead.
Distance is my friend!
Answer - because the amount of lead my floor will hold up is useless against high energy gammas, and of course, neutrons - remember atoms are mostly empty space, and it's like spraying neutrons between widely spaced bowling balls - little neutron energy is lost, they are just scattered a little - for that, low Z stuff works better.
Anyway, I gathered up a little data so I have something to point the static-givers at.
So, what's that? 5 or so orders magnitude drop between low energy and 2 Mev or so? So it's not exactly linear (would be if that line were horizontal) with energy, right?
Here's a paper that goes into more detail why:
I don't have anything handy just now on neutron cross sections for lead and fast neutrons, but it's low for all speeds. Hydrogen slows them down the best, and various things like to "eat" the slow ones, most often giving off a capture gamma ray, and often that's up there in the half megavolt range which is getting hard to stop with lead.
Distance is my friend!