Placeholder Image

字幕表 動画を再生する

  • The following content is provided under a Creative

  • Commons license.

  • Your support will help MIT OpenCourseWare

  • continue to offer high quality educational resources for free.

  • To make a donation or to view additional materials

  • from hundreds of MIT courses, visit MIT OpenCourseWare

  • at ocw.mit.edu.

  • MICHAEL SHORT: So as a quick review

  • of all the different biological effects,

  • we've pretty much taken it up to here.

  • We've explained the physical and chemical stages

  • of what happens when radiation interacts

  • with mostly bags of water with some solutes in them, better

  • known as organisms at dynamic equilibrium.

  • Everything from the sort of femptosecond level, ionization

  • of water almost certainly, because that's

  • most of what biological things are,

  • to the formation of many, many, many, many, many different

  • radiolysis byproducts eventually that end up as just a few

  • that we care about, the longer-lived radiolytic

  • byproducts that will then diffuse away

  • from the original damage cascades

  • and go on to eat something else, likely DNA or something

  • that you don't want to get oxidized or chemically changed.

  • We talked a little bit about radiolysis in reactors

  • and how you can actually measure it directly

  • which was only done really a few years ago which is pretty cool.

  • Just to remind you of this experiment,

  • there's a tiny high-pressure cell

  • of high-pressure, high-temperature water.

  • There is a foil sample with a very thin region and protons

  • firing through it, so that they both irradiate the sample

  • and induce radiolysis in the water at the same time.

  • And this way, you can test the effect of radiolysis

  • in the water here versus just plain, old, high-pressure,

  • high-temperature corrosion here.

  • And the results are pretty striking,

  • where you can clearly see the boundary where the proton

  • beam was as well as the increased thickness

  • of the oxide and corrosion layer formed when radiolysis

  • is turned on, so to speak.

  • We went through DNA damage, and we ended with pseudoscience.

  • So I want to bring up a couple--

  • no, we don't have time for that.

  • But we spent the last 15 minutes of class railing

  • against pseudoscience and making sure that you check your facts,

  • but we pointed out a number of things

  • wrong with some of the studies.

  • So aside from just that guy misreading everything

  • on that entire blog, of the studies that you felt

  • weren't very convincing, what do you remember about them?

  • Some of those studies were totally fine, but some of them

  • were not.

  • AUDIENCE: The ones with particularly small sample

  • sizes.

  • MICHAEL SHORT: That's what I was hoping someone would say.

  • Yeah, the case study of four women

  • who got breast cancer in the pocket

  • where they held their cell phones, four, right?

  • Or in a study of 29 humans, 11 of them got brain tumors here.

  • It's pretty easy to cherry pick small amounts of data.

  • I did want to say that just because radio frequency

  • photons aren't ionizing, doesn't mean they can't hurt you.

  • If you've ever-- no, no one's ever been inside a microwave.

  • I wonder if anyone's ever felt the effects

  • of an external microwave being by something like this,

  • the active denial system.

  • One of my favorite weapons ever, because it doesn't actually

  • permanently hurt anyone.

  • It just heats up the outer layer of your skin.

  • It fires these non-ionizing photons at RF frequency

  • and effectively makes you feel like you're on fire.

  • So if there's a whole mess of troops charging at you--

  • let's say at the DMZ from North and South Korea--

  • all you've got to do is turn on this thing,

  • and they all think they're on fire,

  • because their body is sending them signals that I'm on fire.

  • And then you turn it off, and they're OK.

  • So no loss of life, no permanent damage,

  • a lot of maybe psychological, but whatever,

  • you can't see that.

  • AUDIENCE: Active denial.

  • MICHAEL SHORT: Active denial system, great name for it,

  • isn't it?

  • Yeah, I think non-lethal weapons are really the way

  • of the future is just make it unpleasant to engage

  • in warfare, and people probably won't.

  • But then no one has to get hurt, which is nice.

  • But then onto the sources of data, because like Sarah said,

  • sample size is everything, especially when you're

  • trying to figure out, are small amounts of radiation

  • bad for you?

  • This simple question hasn't really

  • been answered suitably yet, and that's because, thank god,

  • we don't have enough people exposed

  • to small but measurable amounts of radiation

  • to draw meaningful conclusions from this data.

  • I think that's a good thing, is if we were certain about

  • whether small amounts of radiation,

  • like one millisieverts, could cause cancer,

  • then there would have been millions or billions of people

  • exposed, and so it's kind of a good thing that they weren't.

  • But the sources of this data, the first source

  • was radium dial workers, like you may have heard of,

  • the folks that would lick the paint brushes with glow

  • in the dark radium watches.

  • They ended up setting the first occupational limit for dose,

  • because they were the first large group

  • to be exposed to radiation in a controlled setting.

  • Things like uranium miners, radon breathers, better known

  • as us, but especially folks that smoke anything.

  • Medical diagnostics, so anyone that gets a medical procedure,

  • you can follow up with them to find out what's, let's

  • say, the extra incidence of cancer and figure

  • out, if you have a high-dose medical procedure,

  • does it induce secondary cancer down the line?

  • But like we said last time, down the line is the key here.

  • I'd take a whole bunch of radiation

  • now, if it was going to save my life now, and maybe

  • make it messed up in 20 years.

  • Because then you get 20 more years of life

  • or however long you get.

  • And then from accidents, survivors

  • of the atomic bombs, not just the folks at the epicenter,

  • but in the whole fallout regions and nearby, as well as

  • nearby nuclear accidents and the criticality events

  • like the demon core that you guys analyzed on the exam.

  • Luckily, there aren't a lot of those, either.

  • But they were pretty severe, the ones that got exposed.

  • And speaking of accidents, has anyone ever heard

  • of the Kyshtym disaster?

  • This is the third-worst nuclear accident

  • that we know of in history, after Chernobyl and Fukushima,

  • and worse than Three Mile Island,

  • because Three Mile Island was an almost accident.

  • There was some partial melting of the core.

  • There was almost no release of radioactivity.

  • And the definition of a nuclear accident in the public sense

  • is release of radioactivity.

  • There's actually two quantities that folks

  • in PRA, or Probabilistic Risk Analysis,

  • are most interested in.

  • Has anyone heard of these terms, CDF and LERF?

  • Core Damage Frequency and Large Early Release Frequency.

  • All the fancy probability fault trees and everything

  • goes into calculating the probability

  • that the core gets damaged.

  • So that could be an accident in one right.

  • Or the probability of a radioactivity release.

  • And that is an accident.

  • So if no one's ever heard of this,

  • there's a city in Russia--

  • I don't know why it says Russland, maybe came

  • from a different language--

  • called Kyshtym, where they had the Mayak

  • nuclear and reprocessing plant.

  • And there was a tank full of radioactive waste

  • that was exploded.

  • It was a chemical explosion, but full of strontium,

  • all sorts of other radionuclides that

  • blew up with about 100 tons worth of TNT,

  • and ended up contaminating a rather large area

  • with this plume called the--

  • I think it's called the East Chelyabinsk Radioactive Trace--

  • or the--

  • what is it?

  • The south-- South-something Urals Radioactive Trace.

  • And that area is still contaminated today,

  • because the disaster was covered up, or rather wasn't--

  • nothing was said.

  • These towns here, they didn't--

  • weren't actually towns back in 1957 when this happened.

  • They were just given designations,

  • like Chelyabinsk-40 or Chelyabinsk-65,

  • because the largest nearby city was Chelyabinsk,