2. Radiation Utilizing Technology

2. Radiation Utilizing Technology

Show Video

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. So, I wanted to give you guys a survey, of radiation, utilizing, technology and, tell, you a little bit about the way this department, has changed, the way it teaches, it used to be in our department, and probably, everywhere. Else around the country that, first we teach you the theory of how, things go down and understand. Them and then, we can teach you the context, in which they're placed this. Resulted, in a rather boring curriculum. In my opinion, having, been one of the ones that went through this actual curriculum so for those who don't know I was an undergrad in this department and while. I learned a lot of great things from folks I also kept some mental notes on what I would do differently and now, it's the chance to do this so, instead we've adopted a context, first Theory, second approach which, means we tell you where we're going to show you why should you pay attention to the rest of the semester then. We fill out the rest of the theory that fill in the gaps and then revisit, the context, to show you what you've learned and how you can understand, it that's, why today is gonna, be a rather light class so don't take any notes just listen, enjoy ask questions, and I'm going to show you some of the applications, where we use radiation. And the principles of NSA in technology, today and for. Recitation, today since we haven't gone over any technical material, we're going to be heading to my lab to demonstrate, one of these things a sputter, coder which is a controlled, system for radiation damage which, applies one material to the other via the process of sputtering, or actual. Nuclear. Or ionic collisions, that blast material, in this case gold on to whatever you want to coat which, in this case is a pile of pocket, change so. We're gonna make some gold change today. So. The motivation today is really to get over to questions. Is how. Can radiation, be used for benefit and what. Is the physics behind how it can be used I'll, be using a circle, a fuel rod the same kinds that you'd see in a nuclear reactor as the pointer cuz I'm not a fan of lasers and this, is actually incredibly light like, I can hold it out at the end not. Much visible, shaking and I, wanted you guys to see and feel. And try and Bend what Zircaloy, actually. Is like that's a piece the. Same diameter, and dimensions, and stuff that you would see in, a nuclear reactor so give, it a slight Bend you know if you try really hard you can bend it but, notice how light it is notice. How strong it is it's. About midway and. Between stainless, steel and aluminum but, it's a hell of a lot stronger than aluminum it. Also has the added benefit. That it basically doesn't absorb neutrons, the real reason we use Zircaloy, or zirconium, alloys and reactors, is that, they have very low interaction. Probabilities, or cross-sections. And, for those who don't know what those are in a couple of weeks we'll be defining, what a cross-section, is. This. Stuff's pretty cool also what makes this nuclear, grade Zircaloy, and not just regular zirconium. Is that. There's no hafnium, in it hafnium. Is chemically. Very similar to zirconium, it also happens to be one of the highest cross-section. Elements that there is so. You'd hate the stuff that you need to be Neutron eclis transparent, in reactors, it, happens to be found in the ground with, the last thing you'd want in your fuel cladding in fact you, can use hafnium, as a control, rod or control blade so. The difference in in. Chemistry. And and cost between nuclear zirconium, what you've got there and regular.

Zirconium, As the hafnium, has been taken out by some very painful chemical, separation, usually. You'd find about three or four percent hafnium. So. There's all sorts of technologies, that we use the, principles, of nuclear science and engineering, I'm just, going to say NSC from now on you're, all probably pretty familiar with power and may, be familiar with some of these other ones like medical isotopes, are, the backbone of a lot of imaging techniques to find and treat different. Maladies space. Is basically a giant maelstrom. Of radiation, so you can both use it and you have to shield from it we'll go over some of the crazier ways of shielding from space radiation actually. Today. Semiconductors. The. Way that the MIT reactor, made about 60%, of its operating, budget until, recently, was, by irradiating, crystals. Of silicon single crystal, bulls or ingots of silicon to make what's called an n-type semiconductor. Via. The following reaction, if I can find an eraser. I'm. Gonna use the shorthand that we talked about last time normally. You would take. Silicon. And. You. Add a neutron, and, you. End up forming, phosphorus. I've not memorized, the masses. Of the isotopes but in the end this. Is actually, a neutron, capture reaction, and then a resulting, decay which, produces, phosphorus. Which. Is what's also known as an n-type dopant. It's. A sort of extra, negative, so. Does that a negative charge type dopant, that changes, the conductivity, of the semiconductor there's. Lots of different ways of doping semiconductors, one, of the best and most uniform, is to stick things in the reactor so back, when silicon. Ingots were smaller, like four or six inches in diameter there, was a constant train of these things traveling, through the reactor getting. Irradiated and being sold and then cut up into wafers to make devices and it. Used to be student. Or you're off jobs to. Load and unload those, things from the reactor now it's not that dangerous as long as you use the right handling, procedures like put them on a cart pull.

The Cart, at arm's length and push like that your, dose is very low and that's, because for a given point source emitter the, dose you receive, drops off as one over R or, the distance squared which, means that your arms length let's say your arm is about a meter you can drop the dose by quite, a bit compared, to what's called the contact dose well. This poor fool held, the silicon ingots up to their chest like that, they. Were okay they. Got about ten months of their yearly allowable, radiation, dose that. Won't induce any additional risk of cancer but, to insure that they would not exceed, that allowable, dose they. Became, the administrative assistant, for the reactor for the next ten months so their, job at the reactor was to answer the phone which, is not a radioactive. Activity. Including. At the reactor. First. Nuclear power the reason why I know a number of you guys are here is pretty. Simple it's just a hot bucket of water the way we make that bucket of water hot is by. Putting uranium. Or other fuel into these rods, assembling, a lot of them in a small space where, they then heat up by, producing nuclear fission, capturing. The resultant kinetic energy of the fission products and neutrons and everything else that comes out and using. It to either heat up or boil, water that's, then just driven through a heat exchanger and a, turbine so aside, from everything on this, side it. Looks basically like any other water-cooled, power plant, the difference is things get toasty, in a radioactive sense but, also pretty well under control and, what's. Inside, a reactor if you, say this is the diagram. Of a typical pressurized, water reactor, or PWR, where, the water is pressurized, enough so as to stop boiling, from occurring keeping. The water liquid, which, is has, a number of safety implications. You've. Got the core of the reactor right here and these. Things right here are called steam generators, it's nothing more than a heat exchanger, that generates steam and the, steam generated. In here goes off somewhere else and drives. The turbine if you, look inside this reactor you'll notice a lot of different fuel. Assemblies, or fuel rods, including. Things like control, rods or shut down rods, rods. Made of Neutron, absorbers like hafnium, that we talked about or gadolinium. Or boron. For carbide, or any other material, with, a high capture, cross-section, meaning. A high probability for capturing a neutron rather. Than letting it go from one fuel element to another to. Produce more fission to produce more heat that's. Effectively, how a reactor, works. So. We went over a little bit about the fuel the, fission and the energetics, is kind of cool, so. Let's say you start off with. Uranium. Probably. The fissile isotope, 235. And. You. Send in one. Neutron think. It's 92. Don't quote me on that though, and. Instead. Of undergoing some sort of a capture reaction, or something else it can split into what. We call different. Fission, products, and. Plus. Anywhere, between 2 or 3 neutrons, the. Usually accepted, number is an average of about 2.4. For neutrons, plus. Gamma rays plus. Anti. Neutrinos, plus other energy, and. Some. Occasional other stuff the, main point here is these fission products. If. Let's say you had a uranium nucleus, and it were to split, in half fission. Products go in other directions. They. Carry with them quite. A lot of kinetic energy and what, we'll be doing a lot in the second half of this course is watching, to see how.

Do These highly, energetic nuclei, or atoms when they slam into other atoms how quickly do they lose energy how. Far do they tend to go these. Fission products, tend to stop in the fuel their, range is going to be on the order of nanometers I don't, even think it reaches microns, but. The neutrons, however as we saw from looking at Chadwicks, paper they, can go pretty far usually. On the order of around 10 centimeters, in, a reactor, before they go do something else so it might make it a few, fuel rods over and chances. Are get captured by another uranium. Nucleus, making. More fission more. Neutrons, and some other fun. Stuff like gamma rays and neutrinos. Anyone. Not know what a neutrino is. So. A neutrino, is a very. Very low mass but not massless, as was found I think like last year, almost. Speed of light particle, that's released as part of radioactive, decay they. Basically, don't interact with matter but once in a while they do what. That means is that they, travel straight through everything it's been estimated that, trillions of neutrinos from, space are passing through us per second and on. Average you won't get a single interaction during a day in fact. To detect neutrinos they've. Had to fill old hollowed out salt mines with water and fill them with photo, tubes in the hopes of catching two or three a day what. That means is if someone turns on a reactor, somewhere anywhere, in the world it's. Releasing tons and tons of neutrinos, and if, all of a sudden you start to see two or three coming from the same place that's a rare event that's. Something, with some statistical, significance, and there's, been projects, in are still in our department, using. Neutrino, detectors, to try and detect where, reactors, are turning on anywhere. In the world so we've, been able to sense that the MIT reactor, is next door from the building next door I don't, know how well this is going to work when you get to farther distances, but, the physics is, pretty much there it's, an engineering problem to figure out well how. Do you detect. Neutrinos, to get a statistically. Significant, signal that's. Far as I know has not been solved hopefully. By this time next year it will. There's. Also control, rods rods. Filled with absorbers, like I mentioned before if you want to stop this nuclear reaction you, send in something like hafnium, or gadolinium, or boron so. Let's say boron. 11 like chadwick knew would, be able to capture. A neutron, and then, it would turn into what's, the next one over well sorry. That's a 1 and a 0 that's. A 5 that. Should turn into carbon-12, and then. You've captured, the neutron instead of letting it get into more uranium and cause, additional fissions so. When something's going wrong or you want to control the power level and the reactor you, insert control, rods they, soak up the neutrons and make the reactor go subcritical, and we'll go over what all these words mean in due, time various. Points in the course, there's. Also coolant, and what's called moderation, does anyone know what I mean by moderation, of neutrons. Yeah. What. Do you mean. It's. Thermal eise's them and in other words it slows them down because. The probability, that each. Uranium, nucleus can capture a neutron, depends. On the energy of the neutron the. Cross-sections, for interaction, which we give the. Symbol Sigma for. The microscopic, or sort of mass independent, cross-section. They're. Functions, of energy they're extremely, strong functions. Of energy over. The energy ranges, were interested, in because, we're interested in an extremely, large energy, range these. Neutrons, tend to be born at around, one to ten MeV or mega electron volts, and by the time they thermalize like you said or reach roughly, room-temperature, kinetic energies of about 2200. Meters per second they, can be a what. Is it a fortieth or point oh two five evey fraction, of an electron volt so we're, interested in nine orders of magnitude, of energy, and the, cross-sections, vary wildly. Over. These nine orders of magnitude, and I'll show you what some of these look like pretty, soon and in. This case in the case of light water reactors, like the PWR we saw the, coolant and the moderator, are basically the same thing, you. Guys remember how when Chadwick put the paraffin, in front of the neutron, source he, started to see more ionizations. That's. Because the paraffin, is a great source of hydrogen so. Is water water. Is an ideal coolant, because, it takes a lot of energy to heat it up and a lot to boil it so, you can store a lot of energy with less of a temperature difference in water and it's, full of hydrogen and, kinematically.

It's, Easier, for something. The size of a. Neutron and the mass of a neutron, to. Slow a neutron, down because. A neutron, hitting a proton, can transfer, up to all of its energy, ballistically. Then, that proton, won't move very far because, it's also got, charge. On it if, a. Neutron hits something heavier like stainless steel or other stuff in the reactor it cannot by, conservation of energy and momentum transfer, all of its energy that, fraction, is actually pretty small so. You'll. See we'll actually calculate, what that fraction is but it drops. Off pretty precipitously, as you, start to get heavier than hydrogen and, finally. There's a reflection and shielding, we'll. Get into shielding and terms of how much stuff and how much matter does it take to stop radiation, from, getting through in. Some cases you could stop at all in, some cases like gammas, you technically, never can you'll. Just get what's called attenuation, or continuous. Removal of gamma rays but. Chances are you can't remove every single photon from getting out it's, only a matter of how much do you need it to get down to and. There's. A neat aside who here has looked down into a nuclear reactor before. Three. Of you Wow four okay what. Did you see. Not. That much this is a particularly, powerful reactor. Known as the advanced test reactor, or ATR, at the Idaho National Laboratory, you, won't see any others that look like this one because these crazy. Shaped, fuel elements, are not that easy to make this, is a test or a research reactor where. Things get irradiated it's about a hundred twenty-five megawatts, and the, blue light being produced is called, Cherenkov. Radiation. It's. From. Electrons. And things moving or beta particles, electrons moving. Faster, than the speed of light in water, now. As you know you can't exceed the speed of light in a vacuum but. Things can move through other media faster. Than the speed of light in that medium, effectively. Producing, optical, shock waves given. Off as little blue cones of light for each particle so. When folks say Oh am I going to go green when I get near radiation, you can say no you'll glow blue. They've. Just got the wrong color on all the TV shows and then. Onto fusion energy since most, of us tend to talk about fission a lot of the time but how many of you here are interested in going into fusion. Usually. It's at least half the class and so I figured this, used to be a fairly fission. Centric, teaching. Style in the department and I think fusion deserves equal time because, about an equal number of you want to go into fusion to make it a reality these. Reactors are laid out fairly, differently, what. They'll be is a big hollow vacuum, chamber that shaped like a donut or a torus, and lots. Of magnets, to confine, a plasma, or. Sort of a charged mess of separated, ions and electrons that. Whirls around at millions of meters per second once, in a while these. Ions, and electrons are, the especially these nuclei will collide, with each other and undergo. A fusion. Reaction or one of a few fusion reactions that I've written up here for you so. In this case there's. No elements, with a symbol D or T we're, just using those to refer to deuterium, or tritium as a visual, aid but. You should know that they're deuterium, and tritium from, their, atomic. Numbers 1 which means it's an isotope of hydrogen and their. Mass numbers 2 and 3 which is not the mass. Number for a normal hydrogen and in. This case when you fuse deuterium, and tritium you. Can produce helium and another, neutron and so, then those neutrons, can. Be used to. Hit lithium, what they'll usually have in what's called a breeder blanket, around the outside which. Releases more. Tritium, so, fusion reactors actually can produce their own fuel the, trick is they're radioactive, gases so.

Containing, Them can, be kind of tricky you. Also need a way to get the helium out of the, reactor but. We have one of these on campus, we have one of the only three in the country it's called the Alka tour ciment have any of you guys seen a tour, of this place yet. Almost. All of you so forever who hasn't do, it this year because this may be the last year of Alka Tour seen mods operation, that's, not to say there won't be the next fusion device on campus but there's one here right now and it might be a while before the next one's built so, if you haven't seen it yet go and, see it this semester definitely. The. Reason why fission, and fusion work, from, an energetic standpoint. Is we. Look at the binding, energy per nucleon, remember. Last time we mentioned the binding energy is, the. Difference in energy if you were to take let's say a, proton. And a neutron from. Infinitely, far away and bring. Them together. To. Create a nucleus, of deuterium. We'll. Call this D. These. Two, the. Energy of the proton, plus the energy of the neutron, the. Rest mass energy rather would be greater than the energy of just deuterium, and that, little bit of mass that's change is converted, into energy and this is what's known as the binding energy if. We look at the binding energy per nucleon, or. Per proton, or neutron we. Can get a relative, rank, of how tightly bound each, nucleus, is so. For the light isotopes. Smashing. Them together should, liberate, excess. Binding, energy or, sorry excess energy because you'll gain. Back some of that energy by the conversion, of mass to. Energy same. Thing over on this side there's not as extreme, of a gradient if you, were to split apart heavy nuclei like uranium-235. You, can release a little bit of energy in, fission and once, you get up here to iron you, can't go either way which. Is why if you think about the biggest fusion reactors that exist in the universe anyone, know what they are. Stars. Right they. Tend to hit cores of iron before they either die out or go all gravity crazy, and become black holes of supernovas, or whatever, you will this, is kind of the energetic, limit for, normal nuclear processes. Or if, they become a neutron star then things, get beyond the scope of this course I won't, be explaining, neutron stars. There's. A lot of medical uses of radiation, I don't, know if any of you guys have seen these things it's the only time I'll show a tricky. Looking biology, diagram, because it's kind of interesting. Just note these, are what's called brachytherapy seeds. Little. Seeds of isotopes. That remit, a certain, type and energy of radiation, selected, for their applicability that can be implanted in the body at the site of a tumor to deliver localized. Radiation. Treatment, you, can either go in through existing, ports on the human and not having to drill or cut a hole in someone or they, can be implanted, laparoscopically. Or surgically so, this way if you don't want to subject someone to a whole body radiation, dose or chemotherapy. Or if you want to use it in conjunction with chemotherapy, you. Can implant a tiny little seed of a radioactive material in there to, deliver a certain dose to a tumor and then take it out and that, way you know very very well what the dose is going to be because, you can measure the activity or, the, number of decays per second of that Brockie therapy, seed and you, know how it's going to change over time because.

You Know the half-life, of the particular isotope, that. You've looked at there's. Also things like imaging, you, can have someone ingest, an isotope. Like, technetium-99. Metastable, to. Highlight, certain organs, or things in the body that you then image later by their decay gamma rays or other phenomena. It's. Also one of those reasons why when you go in an airport you have to tell them if you've had a medical imaging procedure because. A lot of these places have radiation detectors, and if you are radioactive and don't identify yourself. You, will quickly be identified, and taken into the backroom to the probe you later or, whatever they're going to do with the airport's I don't, know I've never been searched I don't, plan on that happening, there's. Also x-ray, and proton therapy sending. In well, known well. Energy, characterized radiation, to, fry tumors, or other things in the, case of x-rays, you, are relying on what's. Called exponential, attenuation if, you, look at the distance into a material and you. Look at the intensity, of the. X-rays. Say. At x equals, zero this, is your x-ray source. This. Is your incoming, intensity, it, falls. Off exponentially, with distance. You. Might then ask yourself all right if my tumor, is this deep and I, apply that radiation, dose to the tumor. What. About the rest what about the part of the body that the x-rays have traveled, through in. Order to get to that site. Anyone. Know how you would deliver more x-rays to a tumor than the surrounding tissue. Anyone. Have any ideas yeah. Exactly. Go from different angles so, the Rays would intersect, on the tumor I'll have, a better diagram, but I'll draw one for now. Let's. Say that's the eyes and, that's the tumor. You. Can wear this helmet wear, x-rays. Can come in from all different angles and. The. X-ray emission emitter, would, have to come in from different angles, so that as all the Rays intersect, this, part gets fried the most, while. Keeping you from, getting too much radiation to the rest of your brain and ceasing, to function, there's. Also radiotracers. I think I already covered. Those so. Imaging we already showed an image of what this looks like the, first x-ray back in 1895. Didn't. Have that good resolution, but it was kind of striking in that you could see the difference, in contrast, between bones and tissue I should. Replace this with the x-ray of my foot that was my signing bonus at MIT, my. First day on the job I went down to clean one, of the old rooms in Northwest 13 which is now where my labs are and I, moved a bunch of boxes aside and a 200-pound, steel plate, jagged. Cut with plasma torch went. Down and smashed down on the bones of my foot and I. Had one of those you. Know temporary. Feats of superhuman strength, and was able to lift it up I went back to trying to lift it up and couldn't move it an inch I don't know how I got out of the plate the next thing I remember I was crawling up the stairs to, go to the hospital but. I did get an x-ray and they, were able to sense that the pain and my foot was due to a hairline, fracture it was like a fracture. In the bones that basically came back together but. The improvement, in contrast, resolution, and x-rays is what, differentiates, the ability to see a hairline fracture from. Just the ability to see that you contain bones. And. The. Reason for this and, we'll be looking at a lot of these curves in this course is the, differential, absorption or, attenuation, of x-rays, or any photons, of any energy through.

Different Types of matter and so. For example here we have the ICR. You standardized, average soft tissue attenuation. As well, as bone. And you, notice that there's a few differences, in these curves so also. There's some similarities, I'll note, that these actually have the same axis, of the same units. What. Do you guys notice that's the same about. These curves. How. About the value, they're, basically the same, mass. Averaged. With. Very little differences if you look at where it hits the y-axis. About. 3 times 10 to the 3rd 3 times 10 to the 3rd the, curves follow, basically. The same shape. What's. The differences, so, Sean what do you think. These. Jagged edges right here anyone. Have any idea why and, these, reasons, go back to what you learned in high school in 802 in terms of atomic transitions. Not nuclear. Anyone. Here remember the K lines or the L lines or, though it was, at the, which. Emissions series were they called the, different emission lines that you can get from missioner absorption, spectra, it. All has to do with allowable, electron, transitions, and. Notice. The units here are in centimeter, squared per gram what's. The main difference between soft, tissue and bone. Say. It loud enough so I can hear, density. Bone, tends to be a fair bit denser, than, soft tissue so, these are mass. Outwards. That mass normalized. Curves, but the fact is if you have bone that has a higher density then. You're going to end up with more absorption. In, addition, you, can use some of these features and differences, to your advantage like. If you choose a photon, with energy here. It. Might not be nearly as absorbing, in soft tissue as it wouldn't bone so, by selecting the mass of the thing you're trying to image what you don't control and the. Energy of the photon which you can control you, can produce as much possible contrast, as you can between two different things, is. Everyone clear on how that could work. Cool. We'll, be going over why the kerbs has these shapes especially, these jagged edges pretty. Soon, and. Like. You said this, is how you irradiated. With, x-rays, because, you can't quite control. The amount of dose to any one. Part and you split it up into a whole bunch of different Ray's. Proton. Therapy is quite different it's a newer technology, and it relies on very, well-known and distinct, ranges, of charge particles, to, enter the body with very little damage stop. And do their damage in the tumor and not come out the other side they, just require significantly. More expensive hardware. There's, one of these at Mass General Hospital or, MGH down the road it has, consists, of a cyclotron, or a particle accelerator which, injects, and speeds up protons, so that they're moving very fast then, sends, it in a beam through a bunch of bending magnets and up, to deliver the. Protons, to the patient. The. Way this works is you start injecting. The. Beam and as. It goes through these two magnets, or what's called DS every, time it moves through the magnet it's, a charged particle in a magnetic field, it. Has a fixed curvature, but. Every time it's accelerated. Through this electric field it speeds. Up so the curvature gets greater and greater and greater and it spins outwards in a spiral until. They exit the beam and by, deciding, how long they get to spin you get to choose the energy of the protons. Why. Depress proton, therapy work this, has to do with the difference in interaction, between charged, particles and, photons. Which have no charge charged. Particles will lose their, energy in a very well-known, way what's called the stopping power formula until, they actually stop, in the matter that they, are going through photons. Either scatter, or attenuate, or they don't and, you. Can't stop them all so, I want to run a quick Monte, Carlo simulation, for you guys and, show. You what, proton, stopping, in matter looks like so, this is a program called srem or the stopping range of ions and matter it, uses the formulas, that will be deriving, and developing in this class to, calculate, the trajectory of, protons. In anything, so. Let's say you are made basically. Of water so, let's say you consists, of hydrogen, and oxygen. In, a. Stoichiometric, ratio, of 2 to 1 I think water approximates. Humans pretty well so, we'll find out what the range of these actual, protons, is in humans. So, what. We do know is that it's a proton accelerator, and I. Know that, the MGH accelerator, has an energy of 250. MeV or, 250. Thousand. Kill, electron, volts and. Finally. We decide how, thick is the person so how thick is a person. Typically. How, many what. Units do we get, how. Many centimeters, thick is the average person. Let's. Go the the shortest, distance in so you know front to back maybe.

10 Right. 10. Centimeters, about. That much they, get halfway through you only. Have to go halfway because you can always lie in your stomach all. Right let's go ten centimeters. Most. Of the protons go screaming, right through you you notice they don't actually stop, in the person so. You don't tend to irradiated. Two hundred fifty MeV protons, directly. You'll, actually slow, down their energy to something a little more reasonable. Maybe. Fifty, MeV. And. Then. You can actually watch each of these charged particle, tracks being. Computed, as it, hits. Let's, say imaginary, nuclei or electrons, the paths will be slightly deflected. But. What's really striking is they all tend to stop at about the same place that's. The really cool thing about charged particle, interactions, is if you know the charge you, know the nucleus you know the energy you. Can calculate the range to within a very narrow margin and, what, this is doing is just flying looks like it's done 70 ion so far and it will keep on flying, them until. Either you hit the, end let's. Say we set it to do a hundred thousand atoms or you just tell it to stop. Also. When you don't have to draw the lines it goes way faster so, let's let it get maybe three or 400 ions and we'll, show you what the average range of the protons, looks like how, far do they go before they stop, if. We look at the ion distribution. It's. Pretty striking, all of the protons, except it looks like one of them stopped. At a very fixed depth of, forty-one, point, nine millimeters, with, very little, straggle maybe point six millimeters on either, side so depending. On the depth of that you can even get a deep very, shallow. Very small, tumor if you get the distance, just right in the proton energy just right this, is why proton, therapy centers, are popping up all over the world this. Is a much more effective, though expensive, treatment. For, certain types of tumors. At. The same time since we're nuclear engineers, we may be concerned with the amount of radiation. Damage, being. Done to different materials and so. This is kind of a measure of how much energy the protons are losing as they travel through notice. It's not zero as, soon as the protons, enter the person they start to scatter around undergoing. Some different interactions, but, they mostly don't lose much energy until, they. Reach almost their target depth and what's, called the stopping, power is very low at high energies, very. High at low energies which means once they get slow, enough they. Almost all stop right there what's called the Bragg peak and that's. The basis behind proton, therapy and, you'll be able to understand, why every feature this curve looks the way it does by. The end of this course probably, by the end of this month. So. Let me stop that simulation, because, you. Really could go on forever what. We won't. Then. The question is what do you do if the tumors too big if. The tumor is larger, than that struggling, you, actually have to sweep the energy of the proton beam so you can vary the energy continuously, what's, called intensity, modulated radiation therapy, where.

You Change the energy of the proton, sweep, it back and forth across the tumor to cover the whole thing so you can sweep out in 3d, space the, size of whatever you want to die without, affecting, the stuff that you don't want to die. So. In this case let's say you'll apply protons. Of a certain energy for some point and then another energy that another energy and you, can maximize the dose to a pretty flat level while. Minimizing. The rest of the dose to the patient so, even while changing, energies the, most dose is done to the tumor and as little as possible is done to the rest of the person. We. Already talked about brachytherapy but, we didn't say why it works this, is the first major topic, we'll be talking about in this course it, relies on natural, radioactive. Decay and for, natural radioactive decay you need to understand, decay, diagrams, which. Are energy level, diagrams, of which isotopes, turn into which others by, which methods, and how, much energy they, release in each type of decay so, for example a common run is iridium, 192, a pretty, bio compatible, isotope because, it's well it's like a noble metal and iridium. 192. Can, decay by one of three pathways, and, become. Platinum, 192. Gaining. A proton. Gaining. A proton, what. Has to happen for that to be conserved so let's think about this. Let's. Say we have platinum. 192. Which. Decays naturally. Into. Iridium. 192. I can. Tell you because we've drawn the diagram to the right it's, going up one. Atomic number so, let's just say that it had n protons, and it, now has n. Plus. One how. Do we balance this nuclear reaction what. Are we missing. Yep. It's, in the new okay so there's a neutron somewhere, in this nucleus, that, turns into a proton what. Are the three and what are the things that we have to conserve in any nuclear reaction. Yep. Yes. Thank you I got. That backwards but, the numbers are right the symbols are wrong. Something. Else I'll mention about this class please, do stay on your toes to correct silly things like that, I don't. Do scripts, because you didn't come here to see me read off a piece of paper everything's. Live all, the derivations are gonna be live because it's more interesting certainly. More interesting for me to teach so thank you for catching that and please, do stay on your toes if you see something silly especially if it's just not the same as on the screen so. Like. Luke said, we. Made a proton or, a neutron turned into a proton what's. Not conserved, in this reaction. Yep, charge. How, do we balance that. Well. Let's add some other particles, there's. Got to be some sort of radioactive decay. So. Wonder what are our choices of particles. Yep. Sure. An electron, or. More specifically. We'll. Call it a beta particle just. Like a gamma ray is a photon, that originates, in the nucleus a beta, particle is an electron that originates, in a nucleus you, can't tell it's, a beta particle just, by looking at an electrons, and electron the, only way you'd know is either.

By Its energy or by cuz there another source of electrons, nearby so. In this case we get. Beta. Decay. This. Looks fairly balanced. One. Thing that I'll put in is beta, decay is. Accompanied. By an anti neutrino but I did not expect anyone, to know that I just want to make sure it's up there for completeness so. What we're relying on, is. The. Movement of these electrons, which. Are high charged and low mass which. Means they're very low range which, means when you implant, a brachytherapy seed, into a person, the, irradiation, volume, is only, as large as the energy, of that beta particle, will allow the. Maximum energies, for these beta particles, are given by the differences, between the starting, and the, ending energy. The. Way these diagrams, are constructed, is your ending energy is usually has an energy of zero which we refer to as the ground state of that isotope and all, of these are relative, energies in MeV. Or mega electron volts, so, for example this. Iridium, 192, has a 40%, chance of decaying by beta. 2. Platinum 192, which. Means the electron can have up to one. Point four five nine seven MeV. And if. We know its energy we know its maximum, range, so. Selecting, the right isotope, and the right activity, for, the right tumor is quite important, notice. That there's also other ways in which this thing can decay it, might release a beta particle of, a lower energy and reach, what's called an excited. State of platinum. 190, - which. Can then decay. By just giving off this extra 612. KV of energy to the ground state, so. Let's write that nuclear, reaction let's say we have, Platinum. 192. And. I'll. Put a star to. Mention that it's excited. Becomes. Platinum 192. Where. The energy go. Gamma. So why do you say a gamma ray. So, you said it's because it's the biggest source of energy that could be released. Okay. What, do you think. Indeed. If an electron, drops, down in energy levels that review will have release an x-ray or a photon but. That's not a gamma-ray it's not coming from the nucleus yep. Exactly. So the question, with this is what. Do we have to conserve mass, momentum, energy charge, we. Have Platinum 192, going to platinum 192. The, mass is pretty. Much the same yep, question, Luke what is. It. Means it's at a higher, energy nuclear, state it. Means that there is excess energy in this nucleus, so the difference between ground, state or whatever of iridium 192. And the, ground state a platinum 192, is one. Point four five nine seven MeV, notice I'm not rounding don't. Round and, we. Can end up with a beta particle that doesn't quite release all that energy leaving, some in the nucleus in what's called an excited state it's. Analogous, to if. You have let's say an. Atom of a, whatever that happens to be and since, you started talking about different electron, energy levels. Maybe. This, atom is helium and. It only has two electrons and. One. Of them gains some energy. Becoming. Excited. Up. To the next energy level same. Thing but on the nuclear level. These, excitations, are not in the easy range there in the MeV, range but, you can think of it as a precisely, analogous, process, for the time being there are excited, nuclear energy levels, and they, can also decay, by, photon, emission in this case gamma emission. Because. The. Masses, are basically, the same remember that the rest mass energy might be slightly different but the charge is the same there's. No real change in momentum because this is a nucleus, that started at rest and. This. Way the energy can be conserved, yeah. Sean. In different cases. Absolutely. So. There are multiple isomeric. Transitions. Or gamma rays so if let's chart one of the paths through here there's, a 14 percent chance that iridium decays to this excited, state and it.

Can Then decay by a gamma ray to another, excited, state and then. Decay to ground so, there are lots of different, possible, pathways, I've chosen, a particularly. Simple, isotope, because it fits on the slide in. Your homework you're going to get to look at the decaying diagram, for, plutonium-239. There. Are not enough pixels, in this projector, to show the full complexity, of that so. You'll. Have to zoom in a little bit but I'm not going to ask you to do anything with it except. For look at the three most likely, transitions, out of, dozens. Maybe. Scores, who knows you. Guys will see so that's a good question yeah it can decay from an excited state to an excited state to an excited state whoo an excited state to an excited state and. So, on until, it reaches the ground state. It. Wouldn't be fishing products but everything else you said is yes it can continue to lose energy by continuously. Undergoing, radioactive, decay and. We're gonna go some of this when we explore, the orally early, origins of the universe to. Say if you just started off with a soup of protons. And other things you'd. Start to form all the isotopes possible, and the shortest half-life, ones would then decay, successive. Decays. May be multiple, gammas, are multiple, betas or multiple alphas at the same time I'm. Sorry in sequence, until it reached something that was stable, or stable. Enough that it's still around now for. Example there's no stable, isotope of uranium, there's. No isotope, of uranium that will not undergo. Alpha. Or, spontaneous. Fission it's. Just that the half-life is so long that, there's still some left since the universe began, there's. Still a fair bit left but. You guys are going to actually calculate as part of your homework later. In the course how. Much uranium-235. Was there when the earth was born and how, much has just disappeared because, of the passage of time so.

Right Now it's typically about. 0.7%. U-235. By, ASSA topic composition, it was not the case when, the earth was born but. You guys will be able to figure that out yeah. It's a good question and. Have. A rant from me I think has been in response I'll, try and keep my answers a little shorter, oh here's, a crazy one not. Particularly crazy though so. This is, molybdenum-99. Decaying. To. Technetium-99. Metastable. There's, lots of possible, decays but the most likely one is. Right. Here the state above the ground state at about a hundred forty KETV a fairly. Low energy and therefore more easy to detect Photon. So. If you notice almost. All the other excited, states with a couple exceptions decay. Down to this. Point one for, MeV. Excited. State at which point you get two caves to the ground state those, also have a rather long half-life, it's a few days so. You can make Molly 99, in a reactor, transported, to a hospital feed, it to someone. Use these hundred 40 ke V gamma rays because, they come from the nucleus to image, whatever the technetium, will bond to. Yep. Touching. The. M stands, for metastable. Now. Where do you see it this one yep. Because the direct, decay you don't you never go from molybdenum-99. To. Technetium-99. At the ground state the, M stands for metastable, so it's an excited, state and metastable. Tells you that it's got a pretty long half-life, all. Of these other states are excited, States metastable. Means it's kind of sort of stable on like a human, time scale of things it's. Not technically, stable, because stable would mean infinite. Half-life close, enough, but. Metastable means long enough to be detected or used or. Significantly. Longer than the others. Any. Other questions before I move on. Cool. So. You can use these to, image where something, is in the body for example you can use this to. Highlight, certain organs, highlight, anything that you can that, will absorb technetium. Or if, you attach let's say the technetium, to a type of sugar or something else that will be up taken by the body you, can see where it goes and you can use gamma ray imagers to, make kind of heat maps or radiation, maps of where the technetium, is going to, find what could be causing the problem. The. Problem is well our main problem is there are huge, mali 99, shortages, right, now the only economically. Viable way to make molybdenum-99. Is, in reactors, and there's, only a few of these places in the world that actually make them and, yeah. I don't see any on the US, we. Get ours from Canada and these. Are slowly, getting closed down as, we go so, the question is with millions, of these diagnostic, procedures, per year where, is the mali 99 going to come from that. Might be where some of you guys come in you. Can use the knowledge from this course to figure out an energetically, and economically, feasible way to, make more mali 99, you're. Rich that's, you know life. Goal achieved. Space. Applications. If we ever want to get off this earth for a significant, amount of time, we have to deal with the fact that there's no atmosphere in space to, shield us from the, high-energy protons, and other cosmic, rays that would otherwise. Well, destroy, life so. There's a lot of interesting. Ideas and a lot of problems with astronauts shielding one, of them is that the protons are so heavy. I'm sorry the protons are so energetic.

That. They're difficult to shield just, by mass attenuation. The. Trick here is well, different. Radiation, has different, penetrating, power it depends, on its energy but it also depends a lot on its charge for. Example alpha particles, can. Be stopped by a sheet of paper these at the MeV, level, helium. Nuclei like if, you hold an alpha particle source, in your hand the dead skin on your hand stops, the alphas from getting in remember. That because I'm gonna be asking you a question later. On to see who your friends are and who they aren't I don't. Know if anyone knows what I'm talking about but if you do don't give it away beta. Particles or electrons, have, low mass and half, the charge of an alpha particle they, tend to be able to get through paper even through a little bit of plastic but, a small bit of metal can stop them gamma, rays go. Right through and notice that they've been drawn not quite, being stopped by the concrete, which is a great shielding, material, because, like I said before you. Can exponentially. Attenuate, gamma rays you can't, with all certainty, stop, every single one. So. Then how do you stop these high-energy charged, particles if, the more energetic they are the, more range they are boost. Your electromagnetic field, so it's, actually been proposed, to have spaceships, with enormous. Magnetic. Fields, or electromagnetic, fields around them to deflect the protons, away or around the ship because, if you can't stop it by putting matter in the way rely, on the fact that they're charged particles, and will. Curve. Around whatever's. Got a high electric, field around it so. This is one way of let's say shielding, deep-space missions, you, can't put more stuff in there because stuff is heavy and launching, stuff into space is expensive. Rely. On electromagnetism. And there. Are also RTG. Their radio thermal, generators. Or radioisotope. Thermoelectric, generators. Which. Are little balls of things like plutonium, or strong tea that, give off so many alpha particles and, the alpha particles have very low range they, deposit, their kinetic energy as heat in the material, and cause, them to glow on their own if, you produce enough heat if something's glowing red, you, can use thermoelectric. Generators. To capture, that heat and turn it directly into, electricity, this. Is how things like Voyager and, let's. See all the other space probes with, interesting names are powered once, you're too far from the Sun for solar power to work you, need something that doesn't turn off, so. You can use RTGS. Which, have long enough half-lives, to produce. Significant. Amounts of power for a long time but. Short enough half flies so that their activity is pretty high and they, release a lot of energy as radiation and that radiation. Is. Heavy, charged particles, but you can capture as heat. So. Yeah an actual little sphere of plutonium that. Produces a hundred watts just sitting there there, is no way to turn it off, that's. The end of the sentence it's, plutonium, and. Finally. There's nuclear rockets, if. You think about using a reactor, for thrust instead, of electrical, energy the, design, of the reactor gets very, different, for example you. Can start to let things get a whole lot hotter when there's no oxygen in space to oxidize, things and your, propellant, maybe, would be liquid, hydrogen that doesn't burn but, goes through the reactor gets accelerated turned, into a gas with a high kinetic energy to, fire out the back of the rocket nozzle and provide the thrust that you need and so, it's nuclear, rockets, that would really be the only feasible way without, bending space-time which I don't think we've really done yet -. In order to get to very distant stars like that planet they just found orbiting Proxima, Centuri 4. Light-years away pretty close right no. Not. Really if. You think about how a nuclear, rocket. Mission, would would. Work well it. Doesn't have to have nearly, as much thrust, especially. If you start from orbit maybe, use a chemical rocket to launch yourself into orbit, and, then spend half your journey accelerating. Very very slowly and then, turn the rocket around spend. The other half of this journey, decelerating. Very very slowly so you need a long constant. But low level thrust for, these long-lived nuclear mission. I'm. Gonna stop here because it's five minutes before the hour we. Only have a few more of these things to go through but, what I will ask is you guys hang tight for the next few minutes while these guys take the cameras apart we're gonna go to my lab and see an application of nuclear which, like I said is plasma sputter, coating.

All Right everyone so welcome to my laboratory this, is the mesoscale nuclear, materials, group where, we make and break materials, for nuclear technology. Usually not, in that order but. Whatever, we get it done somehow and this, is read to knock out one of my graduate, students who's, actually repaired, I'm going to show you the physical principles, and operation, of a sputter coder which, is nothing more than a controlled, radiation, damage machine and he'll, be making, some interesting door, prizes for you guys oh. My. Kurt said this, is Professor, Mike sorts, calling, something else I call it the. Home the rehabilitated, home for old orphaned. Equipment, and old, friends. And. So this is actually this piece of gear here and. Did a little research on it and I think, it. Was built, about. The same time as, I. Was entering. College. 35. Years. So. About. 1978. Maybe, 98. That's policy. Now. So. That's. A short goes. Around as all, of us that we sprouted, we scavenger, and. If. You look at it and talk. To a little bit but there's a procedure of this that, we've gotten rich out we, don't know. So. What you're gonna see is, a. Little demonstrate, fitter smarter cutter it allows. Your scooters. Wheat. Under vacuum right now back is pressure there's our vacuum are, there. Come right here so you can see both or again. There's another. Reputation. But we don't discuss that one. Alright. Without, further ado like we did power, off we're, gonna put up the center of high-voltage, its. Argon in here we've got hard on supply sand that bottle over there. We're. Not gonna - charts, why turning it up so we get the lights read. I'll. Go get him. I'll. Just get him right over where you are. You. See, through this glass bar. Oh yeah, come. A little closer from where I am you start to see the glowing purple plasma. So. That's the ionization of the argon causing, it to electrostatically. Accelerate, towards the gold target and that's. Blasting, off gold atoms that are then coating, the stuff that reads coating that you'll see in a second but. This is a controlled, application of, ionization and radiation. Damage using a couple. Of kilovolt, argon. Ion, don't. Know if you call it a beam but at least an argon ion plasma. So, there's a few other things to note remember how we talked about charged particles, having a certain range and matter well. Charge. Particles and let's say low energy particles, and the kv range do, not have a very high range even in gases, which, is why reid has this vacuum pump connected otherwise. The argon wouldn't make it to where it has to do the damage so. When there's too much gas in there shuts. Off when. There's not enough argon, in there there's no argon to do the damage so. We're actually exciting, about two kV ions and their, range is higher than the distance they have to travel so they actually make it where they're supposed to go, this. Is a kind of direct application, of NSE along, with a fair bit of high voltage electronics. And. That's. Pretty much all there is to it. Yeah. They'll. Get right in there. If. You want to see if you look underneath you'll. Actually see that a blue, glowing ring that's actually a ring of gold that's. Being hit by the plasma and that's causing gold ions to fire on to the target. Oh. You should know that only, the nukes can do that right, really all you got you got to get away from all the electrons, and all that other chemistry stuff and only the new so if, you really want to turn something to gold you. Got it to learn the different. Does. Everyone had a chance to get a close-up look. Okay. Anyone. Have any questions about what you're seeing here. It's. A good question the temperature, does not go up that much, there's, certainly kinetic, energy turned into thermal energy as the argon hits the gold and the gold hits whatever you're trying to coat but, the total amount of energy the density, of that gas is extremely, low that's. Another reason why in fusion, reactors, the, plasma, is up to like millions, or tens of millions of Kelvin there's. Just not a lot of it so if you look at the total amount of stored thermal energy in a fusion reactor it's quite low even. Though the temperature, or the relation. To the average kinetic energy of the molecules is extremely. High. Yeah. Good question you, want put, your hand up to the side of the chamber. It's. A warm. Not, at all yep. The. Plasma, is. There. We go. Yeah. We'll open it up and show you so I'll get the lights on now. Yeah. From. The point that we when you walked in and saw that yeah okay, the first thing the, first thing so this had a sort, of a static, amount. Of argon in it and when. I turn on the voltage the high voltage. That's. Thick that's it to create the plasma, but then it has to get fed so, what I ended up doing with this little knob for a price to explain that it's, out speeding in argon but, they are got bottles of coke in here it's going into this when.

You're Feeding the argon into the pressure p1 if, the pressure comes up too high on, this particular instrument and. It has an automatic cutoff, for the Michael to spits out because otherwise, you. Know one. Of the reason why it works is because we have so few atoms, in there. Deal. With what, happens, when director is important. 7:16. Right. Have. A little bit although. This. Is that, that's. The goal. In, the chamber you. Can, put the you can put the ring facing down for stability if you wanted that I said you can just put the ring lying flat down if you want for stability. Yeah. Anger. Purpose, of happiness, actually this machine, the, main reason. Is. If you have something that you want to put into a scanning. Electron microscope. And. We're. Actually gonna use one of those in plots so. You, have some kind. Of. Coating, on it. So. If you're looking at nothing like the fire log. Something. That's. Conductive. And. So there you see. About. I would guess I think, as, long as we did it for something on the end on, the level above 200. That's. All you need though yep. Remember after quiz number one we will be piloting, or well two of you guys will be piloting, a scanning electron microscope, down in the basement and before. We look at whatever samples, you want to see whether it's your one of your eyelash there's dust on the floor or a bug you found or something we'll, want to coat it in gold so that the electrons, that we use for imaging, will have a place to go, well of a conductive, path and, they won't charge up ruining the image I have. A question, yeah as, anybody, was anybody, here for this. Millennia. One. 2000. Or later, nobody. In, one 1999. Nobody. In 1990, honey. How. About 98, Google. For 298 there we go alright. That. Would be. At, the 1998. Die. Now. Gold-coated. That. Right. So. You win this. It'll. Rub off okay, so thank, you guys might you put it up on eBay and. Build, teams yes. The other ones go to people that. Oh no. 97. Out of 96. Oh. There's. 396, okay you guys. All. Right what's the nipple at the 96. You. Know oh yeah right fun you read. You, got the armwrestling it's a quarter and it's parked. Out there for ya. That's not a nuclear thing but it's, fun. Actually. Breathe into it that's just. Okay. Yeah so, there's the goal deposited, anywhere else yeah. If you look actually if you look at the neighbors, I mean, this is all this. Is all being, smarter than if you look around. So. It actually it, gets, everywhere. But it's mostly directed in that area that you saw them. I. Have. Another offer. Are. All going to be in all but one. But. We have a new kethu Xia so. Otherwise, wouldn't, be in this class and anyone scared of nuclear is probably not in this class so. Obviously. Is pretty easy for us to do we have this machine here. I. Mean. I can even supply, I'm I feel rich enough I could, because. All those graduates. Graduate, school. But. Aren't, anything else any. Questions for Reid. What. You just saw, the. Goal is to sort of give you a real life you know learn, 2201, you'll understand, how these things work and how you can modify. Them create new stuff that's. A general idea same. Thing behind looking at the electron microscope, or the focused ion beam, EDX. Elemental, analysis, I want, to bring what we're teaching you to life as often, as we can since, we only got one recitation, a week we'll be doing it about that much once, in a while I may schedule, some extra stuff as, long as folks who are available but we're, gonna try all we can to have days like this we get to see what you're learning in, real life. Because. The process, of the argon hitting the goal is actually known as sputtering, which, is the blasting, off of surface, atoms by. Energetic particles, it's a controlled form of radiation damage. Swagelok. They're. All in UV what Swagelok, companies, oh here we go yeah. This. Is Swagelok tubing it's. Got a two-piece, ferrule, which. Does make some metal to metal seal for moving liquid or gas and it takes an insanely high pressure. So. Actually over in the next room we can look on our way out we've built a reactor, simulator, like an experimental. Reactor. That, replicates, all the conditions, except, for the radiation we have to make it entirely out of Swagelok, tubing because this stuff can hold the pressure and the temperature without, deforming, too much. So. When you want to make an absolutely, airtight seal. Use. Things Swagelok, or things like it. This. Is stainless steel yep they, make it out of titanium or other things too but stainless steel works for us. PWR. How much pressure is in, a PWR there's a hundred and fifty atmospheres, of pressure it's. Also 150, atmospheres of pressure over in the room next door. Like. I said it's all the same conditions, as a reactor except the radiation, the, pressure is what makes it really dangerous. Yeah. We'll look through the one of the few bulletproof, glass shields, because, if anything blows on that loop it's like it, is a projectile. We've.

Only Had one explosion, there. Was no temperature, at the time but, it sounded like a like. A shotgun blast over the side of your shoulder it, was loud. The. Loop was right here and we were right in front of it then the loop jumped up maybe an inch and we jumped up about three feet, we. Got scared. That. Was what happens when you improperly, torque a high pressure fitting because you've actually got to tighten these nuts down to. Not too low and not too high of a torque otherwise. They don't seal, and usually. Only find out that they don't seal when they're approaching, close to their rated thing you're, like great it's not half pressure it's all okay you reach 99%. Pressure and kaboom, that's. What happened. Cool. Thanks, a lot Reid for showing this to us and taking, time out of your day, anytime. Hope. You guys enjoyed it so no. Problems, to work through this week that's gonna change starting, Tuesday. Next, class so. Have a good weekend and I'll see you guys all on Tuesday in room 24, 115. Next. To the room where we were just in. You.

2019-09-22 19:54

Show Video

Comments:

i am a student of electronics but these lectures are making me fall in love with nuclear physics

I'm just glad this kind of stuff is available online for people like me who are not students. This is remarkable.

Other news