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Chemistry: Applications of Nuclear Chemistry

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  • Type: Video Tutorial
  • Length: 13:47
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 148 MB
  • Posted: 07/14/2009

This lesson is part of the following series:

Chemistry: Full Course (303 lessons, $198.00)
Chemistry: Nuclear Chemistry (8 lessons, $12.87)
Chemistry: Nuclear Fission and Fusion (3 lessons, $4.95)

This lesson was selected from a broader, comprehensive course, Chemistry, taught by Professor Harman, Professor Yee, and Professor Sammakia. This course and others are available from Thinkwell, Inc. The full course can be found at http://www.thinkwell.com/student/product/chemistry. The full course covers atoms, molecules and ions, stoichiometry, reactions in aqueous solutions, gases, thermochemistry, Modern Atomic Theory, electron configurations, periodicity, chemical bonding, molecular geometry, bonding theory, oxidation-reduction reactions, condensed phases, solution properties, kinetics, acids and bases, organic reactions, thermodynamics, nuclear chemistry, metals, nonmetals, biochemistry, organic chemistry, and more.

Dean Harman is a professor of chemistry at the University of Virginia, where he has been honored with several teaching awards. He heads Harman Research Group, which specializes in the novel organic transformations made possible by electron-rich metal centers such as Os(II), RE(I), AND W(0). He holds a Ph.D. from Stanford University.

Gordon Yee is an associate professor of chemistry at Virginia Tech in Blacksburg, VA. He received his Ph.D. from Stanford University and completed postdoctoral work at DuPont. A widely published author, Professor Yee studies molecule-based magnetism.

Tarek Sammakia is a Professor of Chemistry at the University of Colorado at Boulder where he teaches organic chemistry to undergraduate and graduate students. He received his Ph.D. from Yale University and carried out postdoctoral research at Harvard University. He has received several national awards for his work in synthetic and mechanistic organic chemistry.

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Thinkwell
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Finally, let's talk about how nuclear chemistry and radioactivity affect your life in both good ways and bad ways. And to do that, we need to come up with, or talk about, a unit of exposure of radiation, and there are two common ones and neither of these turn out to be the SI unit, but they are much more common than the SI unit, so it makes more sense to talk about these units. The first one is the rad, which is short for the radiation absorbed at dose. And it's the amount of radiation that deposits 10^-2 joules of energy in 1 kilogram of tissue. So in other words, it depends on how much stuff you've got here and then how much the radiation hits that amount of stuff. Now, not all radiation is exactly the same. That is, some radiation, like alpha particles, is extremely damaging. Alpha particles are the most damaging. When they are in your body, they cause a lot of damage as a result of ionizing events, and I'll talk about that more in a second. But the good thing about alpha particles is that they're very strongly absorbed, and so clothing will typically protect you with no problem. The problem with alpha comes if you happen to ingest it - either swallow it or breathe it - because then you don't have the safety net of having clothing. Now it's inside your body where it can really do some damage.
Now, in contrast, things like gamma rays and beta particles are much less strongly absorbed. So, in other words, clothing doesn't protect you as much, but they turn out not to be quite as damaging as alpha particles. And what we need to do is differentiate. So, in other words, an amount of radiation that deposits 10-^2 joules in a kilogram of tissue, it depends on what gave rise to the amount of radiation that was absorbed. And so, we defined something called the ren, which is short for the Renken equivalent in man. And it is the number of rads of radiation times what we'll call the "bad-ass factor" or how damaging that particular kind of radiation is.
Well, for gamma rays and beta particles, it's roughly one. And for slow-moving neutrons and things like that, it's closer to five. For alpha particles, it can be as much as 10 to 20. So alpha particles, again, cause the most damage, but fortunately, your clothing can protect you for a bit.
Now, what is it exactly that these radioactive particles do? What is that an alpha particle or a gamma does to you? And the answer is - and I've talked about this before - it has enough kinetic energy to ionize things. And your body is about 70 percent water and what being struck by a gamma ray can do to water - or having an alpha particle go by with a lot of kinetic energy - is that it can actually strip an electron away from water. To form a species that you haven't seen before, this is a water molecule that's been ionized by one electron, and that costs an amount of energy - 1,216 kilojoules per mole of water. Well why are these things bad? These things, which are water molecule radical cations, can react with another water neutral molecule to form a hydronium cation. And what this is, it's a hydroxyl radical. Understand, this is not a hydroxide anion. It's a hydroxyl radical. It's missing an electron to become a hydroxide anion. And what this guy really wants to do is he wants to go back to being water. And the way he can go back to being water is to grab onto a hydrogen atom from something. Right? This guy plus a hydrogen atom gives water back. Well, if this happens to be inside your body, what this hydroxyl radical does is it grabs a hydrogen atom from whatever it can find. And if, unfortunately, that whatever-it-can-find is DNA, it grabs a hydrogen atom off of your DNA. And what you've done is, you've changed your genetic code.
Now, it's not necessarily the case that you're in for cancer right after that. And this is subject to debate as well - how much can you tolerate of these sorts of ionizing radiation events - because, in fact, these go on in your body all the time. You have potassium-40 in your body. It's radioactive. I'm going to talk in a second about radon, which you have to deal with. The point is, things like this go on all the time, and we wouldn't have gotten as far as we have as a species if our body didn't have repair mechanisms for dealing with bad things like this.
Another way that your body deals with these free radicals and this is something known as a radical. And you've probably heard the term "free radical" in the popular literature. These things are continuously generated in small amounts. And we take things like vitamin C, which is a free radical scavenger, and vitamin E, which is a free radical scavenger. And what they do is they go in and they glom onto these things and they take them out before they can go and attack something like DNA.
So your body knows how to deal with these things. It's a matter of, in my opinion, a question of how much this happens. And so, in other words, we're dealing with a low level all the time. It's if you get a really high level that you can really get hammered. What's a really high level? Well going back for a second, it turns out, to calibrate you, that the LD[50 ]for radiation is thought to be 500 rads. So in other words, LD[50 ]stands for "lethal dose 50." It means that if you had 100 people and you hit them each with 500 rad of radiation, half of them would be expected to die. And so, a rad is a pretty big number if half the people are going to die by getting hit with that amount of radiation.
But, again, all day, all the time, we're being hit by little bits of radiation here and there. And one of the places you get hit by radiation is from radon. Radon is a noble gas, and so it doesn't react with much, which means it hangs around for a while. And in particular, it's relatively dense, so it collects in your basement, and basements are where you'll sometimes find high levels of radon. Where does radon come from? It's a daughter of the uranium-238 decay. So 238 goes through a series of alpha and beta decays to get all the way to lead and one of the daughters is radon-222. Well, so how do you know if you have Radon in your basement and if you have something to worry about? And the answer is, you get yourself a radon detection kit. And what this is, it's something that you put in your basements and you leave it there for a few days. And then you seal it up again, and you send it off to some lab, which analyzes it to see whether or not you have radon in your basement. How do they know if you had radon in your basement? What you're collecting are the daughters. So if the radon is in your basement and it hits the detector and it decays, then it leave a daughter and that daughter can be detected by chemical methods. So it's not that you have to take a sample of radon from your basement and send it off to the lab. What they do is they detect the daughters and then infer that there was radon in your house.
Now, what's the problem with radon? The problem with radon is it's a gas, and when you inhale, some of it goes into your lungs. So long as when you exhale, it leaves your lungs, everything's fine. But remember I said that radiation is really bad, particle alpha emitters. And radon is an alpha emitter and is really bad if it gets inside your body, because you don't have your clothing to protect you. And furthermore, when radon decays, it decays from radon-222 to polonium-218. And polonium-218 is not a gas anymore. So now this thing is not only not going to leave your body but it's also an alpha emitter and beta emitter and it's sitting in your lung where it can do a lot of damage. So a lot of lung cancer is probably caused by radon that's being inhaled. It's part of living. You've got to deal with it. But on the other hand, you can minimize the risk if you happen to find that you have a lot of radon in the basement. And places like Colorado that have a lot of uranium in the soil are places where there's a lot of radon in basements. What you can do is you can set up fans or you can have a contractor come in and basically vent your basement - continuously suck air out of your basement - and hopefully decrease the amount of radon that you have to deal with.
Now let's talk about a couple of places where radiation is useful. And one of those places is in food irradiation. And it's a form of pasteurization, or at least you can think of that. When we take milk from the cow, it typically has some bacteria and things in it that aren't good for you. But if we heat it up to boiling, or to a temperature at which we kill all the bacteria, then the milk stores much better, lasts a lot longer, doesn't spoil as fast. And that's what we do. A few years ago, in fact, there was a juice company that had a problem with their apple juice. Their apple juice had bacteria in it and it made a bunch of people sick. And what they do now is they flash pasteurize it - meaning that they expose it to hot steam, and that kills all of the bacteria. And that's really all that's going on in food irradiation. What we're going to do is we're going to take our food - say our pork chop here or, not typically a hamburger, but more often, raw meat or vegetables. And what we do is we're going to hit them with radiation that's going to kill all the bacteria on the meat. And the particular radiation we use is gamma. So cobalt-60 decays to nickel-60 plus a beta plus a gamma ray. And that gamma ray will strike the meat and if there are any bacteria on the meat, it kills the bacterium. And then, if we package the meat very carefully, so that we don't let any new bacteria in, this piece of meat is going to last a long time.
Now, you might say, "Why do we want to do this? Why do we want to even mess around with radiation?" And the answer - and this is somewhat my opinion - the risk of getting sick from food poisoning is much greater than the risk, which I consider really small, but probably not nonexistent, that something like the radiated meat is going to cause cancer. So the idea is that it's a calculated risk. You have to deal with the cost and the consequences. And the cost is that you can avoid getting sick from food poisoning, but the cost on the other side is that there's probably some risk, although I think it's really small, of getting cancer from this process.
Well, interestingly enough, I looked up how much irradiation they use to hit the meat and it's on the order of 1,000 kilorad. And remember, 500 rads was enough to kill a person, but of course, we're just talking about a piece of meat, and this radiation doesn't linger in the meat. It just goes in as a gamma ray and it either ionizes something or it passes right through the meat. So the meat is not left radioactive, and that's an important point that I wanted to make. I think this is the wave of the future. I think you're going to see a lot of this. There are lots of countries that are already doing a lot of food irradiation.
And finally, the last topic I wanted to talk about are some medical applications. And in particular, I wanted to talk about positron emission tomography which is an imaging technique - a way of looking on the inside of your body. X-rays, for instance, is another way of looking at the inside of your body. But positron emission tomography, or a pet scan, is something a little more high tech in which they take something like carbon-11, which is a positron emitter, and they incorporate the carbon-11 into a molecule that your body uses - for instance, glucose. And then, what they do is they feed it to you and then they monitor where the glucose goes. And it turns out that your brain uses a lot of glucose. So they'll give you a task like looking at things or picking up objects or something like that, and the glucose will go to that part of your brain that's really active - where it's metabolizing a lot of glucose. And that carbon-11 is going to emit a positron and turn into boron-11. And then that positron can annihilate, with an electron, and give off two gamma rays. And then the doctor will pick up those two gamma rays in a gamma ray detector, and by looking at the emission of gamma rays, figure out something about how your brain is working, like what part of it is working if you have brain damage or something like that. And that part of your brain is not going to light up on the scan, because glucose is not going to be consumed at that part of your brain.
So what is this? It's a way to look at the inside of your brain. And there are lots of radioactive nuclei that doctors have very cleverly figured out how to use in order to scan your body without having to go in and do surgery, which is an invasive technique. This would be considered a non-invasive technique - well bordering on non-invasive, because you do have to inject something into the person. But in any case, you don't have to do surgery.
So obviously radiation has its good points and its bad points. Another sort of controversial topic that we talked about earlier is should we have fission reactors to generate electricity or shouldn't we have fission reactors to generate electricity? But the bottom line I'd like to make is radiation is part of our lives, because it just exists and you have to deal with it. And fortunately, your body has come up with ways to deal with it. And ultimately, what we have to do is consider cost-benefit analysis. Are the techniques that we use that involve radiation worth it? Is it worth it to not have global warming? I don't know. Is it better to use things like irradiating food so that people don't get sick? I don't know. But, as informed scientists and informed citizens, these are the issues - there's obviously more - but these are the issues that you're going to have to deal with, by voting and by just living. Go to the supermarket, buy irradiated food or not. It's up to you.
Nuclear Chemistry
Nuclear Fission and Fusion
Applications of Nuclear Chemistry Page [3 of 3]

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