



S1: for the slight, delay. so everything went okay in my absence despite the fact that we had an overly voberse (sic) guest lecturer. verbose, guest lecturer. silence. okay homework, went okay...? Kelly what's up?
S2: uh, uh this week's homework was a little bit difficult, to finish with the project 
S1: with the p- yeah you do have the project tonight so we're all gonna be, buncha engineers in here talking about ethics from six to eight so this should be, a lotta fun. um, yep. well it's one of those weeks where you have a little extra, remind me which chapter the homework was on. 
S2: five 
S1: five which is? 
S3: interaction 
S4: interactions of radiation 
S1: hadn't looked at it yet. okay. what? 
S4: it's interactions of radiation with (xx) 
S1: oh it's interactions okay and we're just_ we're supposed to start charged particles today right? 
S4: yeah 
S1: okay so i'm still where, i think we need to be, um, we'll see how things go you've got until Thursday on that we'll try to, cover the charged particles today. we have some guests in the classroom so i'll let them introduce and say what they're doing. 
<MICASE RECORDING ANNOUNCEMENT> 
S1: okay? see at least we're not having this tonight when we've got the ethics, and you guys are all presenting. so engineers do i- do uh, do the humanities which is quite, quite interesting. okay. mm, we did charged particles already did we not? <P :10> didn't we? 
S3: we did 
SU-M: yeah 
S3: yeah 
S1: we did. <P :06> did we do, all of it? <P :06> the site has lost my bookmark. 
S5: yeah we did that [SU-M: yeah ] Thursday night 
SU-M: we always do all of it 
S1: we did what? 
S5: we did all of it 
S1: we did all of it i think we did because that's what i've got marked down here, okay. we'll do photons today. 
SU-M: woo hoo 
S1: hooray. so you've actually should be able to do the homework we did the charged particles before. oh before we start um, you happen to have had all the accident management you could possibly want the day of the criticality accident in Japan. i did warn you all that there's um, uh, the, that i had an assignment that i assigned about, patient triaging, and when i did that the next day Chernobyl happened, so i shouldn't have warned you about that were there any questions about, um, the plutonium accident discussions, uh things you've seen that you didn't uh, understand or that were puzzling to you from a health physics standpoint, or from a nuclear engineering standpoint... 
S4: have they determined the cause? 
S1: yes 
S4: i mean besides operator error i mean how, how you can possibly put in six or eight times too much uranium i mean 
S1: it's clear to me they had no engineering controls, in the first place so there were no engineering controls, and some kind of operator error why you put, effectively a moderator blanket around a tank where you're doing precipitation of enriched fuels, totally eludes me. um, i've been following, the Radsafe which is a bunch of junk, and um, also following as b- as o- as being on the board of directors of the, A-N-S there's a lot of email traffic right now about it, and it's_ no one really knows, but it's sort of, we don't understand it. there was a U-S accident about this in Idaho, similar to this in Idaho in the sixties or seventies. you've heard that? yeah, yeah. but um, also a friend of mine is the h- uh s- sp- sp- sp- is in the department of energy and happened to be in California last week on business and was the highest ranking, D-O-E official, on the west coast at the time and she was beeped, on a pager, and told uh can she get on a plane to Japan in the next hour. she's beeped sort of uh, at an odd time. so i expect if she, ended up going over there that uh, she'll tell me what the scoop is but i jus- i think it is just a, simple um, uh, accident, but it comes on the wake of last year, when there was a chemical explosion in a fuel processing plant in Japan. this though has obvious, reactivity implications. now i looked into Cember and there is a chapter on criticality safety, that um, we may or may not get to, this term i have a feeling we won't get to it this term. at any rate, in that chapter you'll look and there's a certain concentration, of U-two-thirty-five, in, aqueous solution, if you stay below that concentration and have no reflector, you cannot have a criticality accident. this was about twenty times that, it was also a precipitation tank so they're dumping stuff in, and stuff's precipitating, at the bottom. the most difficult part of the computation is to try to figure out, you're gonna try to get doses. to try to figure out, the, um the total, energy, and the completeness, of the fission process. this is not gonna work, like a bomb because it wouldn't have reached criticality fast enough, and as soon as you start getting it happen in the aqueous solution the geometry, is gonna change so i suspect, that they poured the stuff in, it started settling, um, and, reached a critical mass because it's twenty times the concentration that's safe, and then had criticality with a large rela- or large release of energy, which then would've blown up and made the hole in the roof. what could then have continued to happen in my opinion is if you s- didn't blow everything, that way you could still have other masses of U-two-thirty-five, forming additional criticalities so you might have had, second hiccups sort of like t- tremors, after- aftershocks after an earthquake. um, but, the other thing is that with the fission products, fission product decay, from fission which this would've been a a prompt critical, fission situation, the, radionuclides decay with the half w- in- inversely, to the one-point-two power of the half-life, which i think we covered in kinetics. so, you're not decaying exponentially because you have such a mixture. the other thing is you don't necessarily have a point, geometry do you? for the irradiation you really don't know what you have afterwards, and there was contamination. interestingly, in the Ottawa Globe and Mail, uh, they didn't cover this story except on the sixth page of the first section and had no reference to it, other newspapers in Canada, had, expressly uh, photos, on the front page dominating at least a half of the front page, including a photo of thyroid monitoring with simple sodium iodine probes of children. which i found a bit, puzzling but it immediately then revealed to me that in fact, um, they were concerned about releases offsite and immediate, through inhalation and other methods, uptake, of iodine. not something that wai- waited for the cow_ get in the food chain and get in the milk into the cows. um, they were a bit slow i think passing out potassium iodide. in class you would've seen, last week that giving out potassium iodide, will block the thyroid and in cases of large iodine releases actually will help, because half the iodine actually goes, to the thyroid the other half is excreted fairly rapidly. if you load the thyroid with stable iodine you've prevented that uptake and it's mostly then excreted. so there's very little dose, uptake. it's interesting because if you looked at what, Professor Shapiro said he covered acute radiation syndrome right? also you can read in Cember, the radiation biology chapter, right? well, the um, the um, acute radiation syndrome they were reporting seven Gray, which is seven hundred rad, so you would've expected possible, central nervous system syndrome. and as my way of checking whether the newspapers were reporting correctly was that they said seven Gray, but the, patients, three of them, were uh un- uh unconscious or one was immediately unconscious and didn't come to, till later and you had several other unconscious, situations. as a result of Chernobyl however, the lethal dose fifty, is probably less than that printed in texts. because they knew exactly what to do with, bone marrow transplants and the like based upon the experience, of the people in Chernobyl. uh Doctor Shapiro should also have given you the name REACTS, R-E-A-C-T-S did he do that? they would have been called over nearly immediately. i really don't know what the U-S government delay was on making statements which i heard indirectly that the government was making statements we're not gonna send assistance. and, if anything that team should've been in immediately, on the airplanes because they are the repository of information, or somebody who knew what they were saying. along the lines of public communication in Canada there, there were various sp- uh so-called experts from the United States who were, commenting in the Canadian press, i don't know what was going (on) down here, and i was asked by someone well do you uh, do you think uh, do you know this person? and i didn't know the person never heard of the person, they were clearly not an expert making some very sort of, uh, statements that were uninformed, but fancied themselves an expert because they were simply a radiologist. and it made it on the front page of newspapers in Canada. um, Professor Shapiro would be considered, an expert. he would be someone who could be called in to comment. but you really want someone with up to the date experience, practical experience on dealing with the, the victims. um, do you think this was one-over-R-squared...? do you think if you calculated the dose rates, at the tank and the dose rates at the edge of the, the plant, it would've been R, one-over-R-squared? why or why not? 
S6: cuz isn't all your uh, dose, going out the roof and just uh, floating around in the atmosphere? that's the impression i got, from what i read. 
S1: okay. we have to be very careful, dose, [S6: but mm well ] does not get airborne and [S6: okay, yeah ] fly around, but activity yes. [S6: yeah ] so we have to be careful how we speak, because then the press will quote us. did they report_ yes that's correct. i- also if it has stayed in the tank the tank itself, would not give a uniform, uh one-over-R-squared behavior. um, what else? but we don't know if all the activity went out or not. there's clearly a large contamination, contamination risk. now remember things will not also be, we we haven't done this, but you may have done this in or be doing this in your reactor safety course, about what happens when you have a plume of radioactive material, the chi-over-Q, relationships, that is in Cember for those who aren't taking reactor safety, but the chi-over-Q what happens when something goes up a stack, and it is distributed, remember all the stuff, about downwinders that was in the press that in fact in Michigan, we may have gotten more, radioactivity than was, was spread in p- places and points closer to the atomic weapons because of the transport, of the material, as a result of weather patterns? well, in this case though it, it probably had some real local contamination. i'm actually curious where people, detected if at all increased backgrounds. we could certainly detect when i was at M-I-T we could detect, a Chinese nuclear weapons test, using the environmental monitors that were were, uh controlling and monitoring for releases from our reactor. you could see it. you could also see weapons tests, in Arizona. and if you knew when the shoot schedule was, when they were doing above ground tests, you could figure out whether that was Chinese or a U-S test, yes Tom? 
S7: i read somewhere i'm not sure even what the source was or, whether it was reputable or not that, a half a mile away that they couldn't measure anything above background. 
S1: quite possible. again, what would be, far away? i don't know. it's clearly_ working from information reported through the press is extremely difficult. there was one thing that terribly bothered me is when they reported the doses, at various points like at the site boundary and so on, uh and they said_ gave the doses in Gray. this was in Canada. what did Ann Arbor Daily News do? 
S6: Sievert 
S1: Sieverts 
S6: everything in the U-S that i read at least were Sieverts 
S1: alright. you're gonna see that, w- at doses that high you don't use the Sievert, or the rem, because the weighting factors, the radiation weighting factors are based upon, nonstochastic effects they're not based on acute radiation syndrome. so the correct unit, would be the Gray or the rad, when your doses get that high. okay so that was one issue the other issue was, i was convinced that these numbers were dose, rates. and not doses when they talked about at the site boundary they'd say, s- eighteen hours after the accident the dose at the site, boundary was two, Sieverts. well integrated over what time? it was probably two Sieverts, per hour. so it it was very confusing to try to garner information in that way. so there probably was, acute, there was acute radiation syndrome, so the REACTS people are on it, there was central nervous system, (thing,) remember the L-D-fifties or that half the people, would die, and that the L-D-fifties are probably, conservative, in that the advances since Chernobyl, will have r- improved patient management. my worst-case estimate based on just newspaper data was that there could be as many as twenty, people, who have acute radiation syndrome and could die, but we're told nothing about the dist- physical distribution and the number of workers at the plant, we're just told there were, overexposures, at least the media_ i looked in about six newspapers, which didn't really, help me, we were also um, um, not told what the_ we were not told what the doses were. so conservatively, i'd say there are twenty, three would have had immediate effects, if their doses were higher but there're other people whose doses, would be lower. it's my understanding they've already done bone marrow transplants, on some of the, uh overexposed, individuals. the... um... but, e- the lower cases will not show severe effects, until sometime after exposure. and the degree of delay, and the lengths of the latency periods, are functions of, the total exposure and functions of, the individual. so my guesstimate, is between zero and twenty, individuals twenty being very conservative. based on newspaper information. now can such an accident happen, i told you it did already, can it happen in the United States outside, our weapons, compounds? fe- l- you had an Ida- I-N-E-L Idaho accident. can it happen outside, in say our, pressurized water reactor or boiling water reactor environments? i need the help of the nuclear engineers in the class. 
S6: i don't think so 
S1: why, Darren? 
S6: um, they said that they had procedures in place, at this place in Japan, and i thought that they, blatantly violated 'em. the procedures about criticality accidents are very carefully controlled. um, and they won't let you have, enough, uranium close to it, within a specified area and they're like really really conservative, on how much that they'll allow on a certain, range. like when we received new fuel, we'd have like, two fuel bundles in the crate, [S1: mhm ] so, i think it's pretty carefully controlled. 
S1: Mike, do you know the enrichment of commercial, fuel in the, pressurized and boiling water reactors in the U-S? 
S5: uh... two-thirty-eight 
S1: pardon me? 
S5: two-thirty-eight 
S1: two-th- yeah what's the uh_ two-thirty-five what's the enrichment? what's the definition of enrichment? it's what U-two-thirty_ for uranium fuel it's U-two-thirty-five per uranium, and natural, uranium is about point-oh-oh-seven-two percent 
S5: yeah it's like ninety-eight-point-something percent er- 
S1: i don't think so 
S5: (that's,) natural, and then, enrichment is_ i don't understand what you're saying 
S1: what uh what is the enrichment? sir i, you had a knowing look there. what's the enrichment of U-S fuels? 
S8: i know it's not ninety-eight percent <LAUGH> 
<SU-F LAUGH> 
S1: pardon me? 
S8: i know it wasn't that earlier ninety-eight percent 
S1: ninety-eight percent? Tom 
S8: no it wasn't 
S7: it's three to four percent isn't it? 
S1: that's correct. ninety-eight percent is weapons grade, enrichments you can make a bomb. remember though Mike the definition of enrichment is the percentage i think it's the weight percentage, of the fuel that is U-two-thirty-five. it also turns back going back to what Darren said, is it goes back to, when you can have a criticality accident and it turns out if you look in Cember in the criticality chapter, it has a table in it that tells you, the mass that you need, of U-two-thirty-five in various configurations to have a criticality accident. you need much much lower mass, in, aqueous solution than you do in your solid field, fuels. and you, you need that because, because why? the water is a moderator. your fuel sitting dry, is unmoderated. now they had a tank that had a moderating blanket, effectively around it. so i don't think, during our regular P-W-R B-W-R operations at three percent enrichment, unless the U-two-thirty-five gets higher than that at some point which i can't imagine why, that we have a chance of, criticality accident in our fuel processing. in reprocessing and so on we might, have a different situation. i think not, but, who knows? okay so the the solid fuel is even safer than when you have it in solution. 
S6: {TEXT EDITED FOR CONFIDENTIALITY} 
S1: okay, so even at fairly 
S6: {TEXT EDITED FOR CONFIDENTIALITY} 
S1: yep yep. now i'm not sure how hi- if i like this, conversation being recorded or not. 
<SS LAUGH> 
S1: this is really in the hands of a_ i i don't know. this is_ maybe we can like delete this part because this would get us in trouble, because we're ver- having a very comfortable_ we're having a very comfortable discussion and we certainly would have a different discussion with members of public present and i forgot y'all were here. but, in fact now i'm feeling like i need to, sort of, address <LAUGH> [SU-M: she's gonna delete it ] some of this now that he said when it's raining then, you might then ask the question and let's let's have the class kind of do this, someone from the public then heard this, and said, oh. so, if you have your fuel and and you have an accident and then it gets dissolved or we have, s- uh radionuclides leaking from a waste repository or the stuff that comes up to the stack, at the hospital here at U-of-M, i'm really trusting you guys. uh if if <SU-F LAUGH> then then uh, wouldn't it then when it gets into the water supply cause a criticality explosion? if i were somebody sitting, reasonable sitting around that's how i would respond to that. {TEXT EDITED FOR CONFIDENTIALITY} 
<SS LAUGH> 
S6: okay, well 
S1: but you're not in this class, cuz i know the answers. do you wanna try it? 
S6: {TEXT EDITED FOR CONFIDENTIALITY} 
S1: so it's just a psychological thing that we do as part [S6: yes ] of our safety culture. 
S6: exactly 
S1: in fact i would propose that was a meaningless, technically meaningless thing to do, but we do it anyway in case {TEXT EDITED FOR CONFIDENTIALITY} 
S6: that's correct 
S1: right? okay so. um, w- you would have gotten killed, the reporter would be gone already. 
<SS LAUGH> 
S6: yeah 
S1: and Professor Lee would be calling you up saying can you please write an article, like we had back in the other (xx) do- don't but ac- with this audience if we didn't have the outsiders in here, we'd be okay. any other comments on things we might have said where we would have gotten misquoted...? Marty? [S10: i don't know ] <SS LAUGH> i don't know. at least, you know someone might say well they don't know what they're talking about. they think_ they're not sure whether it's between three percent and ninety-eight percent or_ <SS LAUGH> what have we got? we've got graduate students at the best university in nuclear engineering in probably the world, and they don't know_ well, you would not speak, would you to a reporter if you didn't have that information. and you've not probably had that class yet, and you would not speak out of turn, i would absolutely hide and i was kinda glad i was in Canada, because i didn't want to hide, have to be [SU-M: oh ] hiding here to not talk to the press. but, if i were the only person at U-M who could do it and i couldn't refer to someone good, i would have grabbed my Cember or my notes, and looked over it and then be able to calmly handle the questions. it's not about, misrepresenting things, what this is about is that_ is trying to communicate, with the public that may not know as much as uh, you do about an issue so i'm, actually quite looking forward to our ethics discussion, tonight. yes 
S4: go ahead 
S9: oh. i [S1: Peter ] i was checking the A-B-C news web page that night cuz i didn't know what was going on, and they, reported, the radiation levels as three to four millimeters. 
<SS LAUGH> 
S9: they said, they said but natural, natural background's only one millimeter per year.
<SS LAUGH> 
S9: so 
S1: that's very confusing. Shelly 
S4: you mean Shari 
S1: uh Shari. Shelly's, Shelly's back there 
S4: that's okay. um, yeah. that's okay i'm gonna say something that is gonna sound really bad on tape but, [S1: they're gonna delete it ] i don't know, how you can say that it it, that that kind of an accident can't happen here. i mean we have regulations put in place and it's very strict but, i bet they thought they weren't gonna have that much uranium in one place either. you know and whether it was a mistake in, the person who prepared the concentrations or, [S1: right ] the person who was [S1: right ] putting them in [S1: right ] something happened. 
S1: i agree a hundred percent now i didn't really finish the discussion and i see you Tom so we'll get [S7: okay ] get you. lemme respond and then we'll get Tom. is is that, we probably said it wasn't possible, before, before um, our accident in Idaho. we had_ and we heard almost the exact same thing out of out of the reactor guys here, is it can't happen we're, really overk- doing overkill blah blah blah, um, well of course it can and we_ i didn't uh actually finish in that, our uh fuel, in submarines is high enrichment fuel, we still have high enrichment processes going on both, for the Department of Energy the Department of Defense, and other situations where you might want enriched uranium, we, we were not doing fuel processing here. the other comment that i wanted to make is the Canadian reactor system the CANDU, Canadian Deuterium Uranium, has a natural enrichment. so their probability, of having an a a a s- an accident, is, so much lower than ours, that it's not funny. i mean, but interestingly, the Ontario hydro people in responding to the press, said_ did not say they could not have an accident they simply said, well we're looking into s- making things safer. which was a real P-R mistake. uh the_ i don't think their guy is is really in touch he didn't talk to the right people before making the statement because, they at no point get, enrichments where they can have criticality accidents, now at Chalk River, they're, they're_ and they have no weapons manufacturing. that we know of. but at Chalk River they do have reactors that have higher, enrichments. there are no known processes in nature, that would concentrate U-two-thirty-five over U-two-thirty-eight remember they're the th- the element determines the chemical processes. and in nature we_ except in, uh the Oklo reactor, you don't, see, higher enrichments and you don't see fission products. so the press would then, jump on, there are naturally occurring things we haven't surveyed the entire surface of the earth, what if there's another, concentration like that somewhere and can't it change and become more concentrated? no it can't. it can't because U-two-thirty-five, is not created by anything higher up in the decay chain. if anything with time, it's going to be decaying, if it was undergoing fission since the big bang it's all going to be, gonna be gone. okay. Thomas 
S7: pretty much you covered what i was gonna say but, could, like this nev- this ex- like an accident pretty similar to this could never happen at a reactor because we don't process fuel at our reactors. 
S1: that's right. 
S7: you know 
S1: that's right 
S7: so, it's_ a- as far as looking at it as a reactor, at a reactor it's kind of a mute(sic) point. 
S1: now you could have, a criticality incident [S7: oh yeah ] in the core. 
S7: yeah. yeah but it wouldn't be anything of this magnitude or this sudden, you know where, suddenly you, put six, or however many times the amount of uranium, you're supposed to have in it, and it_ you know what i mean? 
S1: what if suddenly you pulled out all your control rods let me play Greenpeace here, <SU-M LAUGH> uh that i that you pulled out all your control rods, you lost the boronated, the boron in your chemical control systems, and you_ it just got run away, it's Three Mile Island... why didn't Three Mile Island explode...? 
S9: cuz once the water, vaporizes you lose your moderator and 
S1: that's right. once the water vaporizes you lose your moderator and it shuts down the reaction there's also the, what is it? negative temperature coefficient, inherent in our design which was not present at Chernobyl, that as temperature rises, the neutronics become, less, favorable, so the reaction will shut down... anything else...? okay. but this sort of making statements it cannot happen today it cannot happen in this country, can be ta- are taken with a grain of salt, because, they've heard scientists saying this before specifically they've heard people in the nuclear industry saying this before, and, it happened. i'm sure before our criticality accident in the ne- in Idaho, people may have said that. your your credibility, is far less, than your technical ancestors', credibility your great-grandfathers of nuclear. their, your credibility is much, less. and in fact some of those statements are gonna be interpreted to_ they'll s- just stop, stop listening, listening to you. okay? <P :05> well i'll i'll do some editing on that maybe. that's_ we could get picked up by the press. um, which w- or they_ i did not handle that the way i would've handled it in a press situation you have to really concentrate. now i sort of jumped on Darren a little bit about saying um, dose instead of activity, that was meant in a friendly fashion you have to start, <SU-M LAUGH> being careful. um and graduate students have to be careful you get in an oral exam and start misspeaking, then, um you can get uh jumped on, a little bit. okay, photon interactions, as for the charged particle interactions, we'll take a break at uh nine thirty as usual and then we'll come back. uh they're di- i we'll classify these in terms of the types of interactions, if you think of what can it interact with you'll get, be able to remember the different kinds, and the various approaches to, transmission through materials. i think we can uh manage this very well it should be review, for almost everyone, and you should look at the uh, notes. there is far more than you need to know, in the notes if you're starting out, if you've been here before you should know everything in the notes so there's gonna be a slightly different_ there's stuff for you to learn. okay. and each photon can be described as a particular class of interaction with a particular field, or, division of matter, and it's probably easier to look on your notes here, but you can have elastic scattering with orbital electrons on the faces of crystals, Thompson scattering is coherent scatter, with orbital electrons, we have Compton scattering, photoelectric effect then is a, a um complete absorption, wh- involving an orbital electron whereas pair production is complete absorption... wi- i- in the presence of an electrical field, so there's scattering it can be coherent or incoherent which has to do with the, angular relationships, of the photons, to the, um, the incident photons, you can have elastic and inelastic scattering. inelastic scattering is when kinetic energy, the energy of motion, is not conserved, elastic is when it is. some of the reactions we'll talk about here are technically, inela- uh technically inelastic but we can treat them as elastic because some of the terms are sma- so small relative to everything else, these are the minor forms of scattering Bragg scattering is scattering with a crystal face, it's sometimes called coherent scattering it is kind of a form, of coherent scattering, uh nuclear resonance and Compton scattering so those are the main photon scattering. with scattering it means you do not lose the incident photon. if you wanna get touchy with me, you could say the photon was reabsorbed and re-emitted, and the and the item re-emitted a photon at another, energy. that's splitting hairs for what we're gonna use this for. most important interactions are photoelectric Compton and pair production, photoelectric, you have the incident photon interacting with an atomic electron, the atomic electron is, spit out, so binding energy is used up and liberating the photoelectron, and there's a complete, disappearance of the incident photon. so the initial photon energy, this is the all the energy before the reaction, is equal to the sum of all the energies after, those energies would be the kinetic energy given an electron, the binding energy, used, up in liberating, the electron, and the kinetic energy of the nucleus it turns out to conserve, momentum, the nucleus must kick back a tiny amount. we c- if we neglect that then we can_ and neglect the binding energy of the electron, um we could, have some kind of um uh, classical mechanics treatment of this problem. but that doesn't turn out to be particularly, useful for photoelectric it will turn out to be useful for Compton scattering. things to know, it's negligible (xx) for photons greater than, two hundred K-E-V. relative to, Compton scattering, this does not mean photoelectric effect does not happen, above, two hundred K-E-V. now i wanna emphasize this so when you read the notes you don't get a misimpression, that, it's either one interaction or the other. these are statistical, processes, so you can always have a certain probability of photoelectric effect, unless there is no threshold, yes there is a threshold what is the threshold? technically? splitting hairs. you have to at least have the binding energy of the electron. so, above the binding energy of electron there's always some finite probability, you can have photoelectric effect. it's more probable at lower incident photon energies, but you have to be above the binding energy of the atomic electron. it's more likely in high atomic number materials, although it does occur in low atomic number materials, and the higher the energy of the incident photon the more likely the photoelectron is to be liberated, in the forward direction. there're a number of different ways of looking at the distributions, of photoelectrons as functions of angles, this again is from Evans the bible, of, physics for our purposes the bible of modern physics, and we have, here each curve is a different incident photon energy, and these are plotted, these are showing you the number that come out per unit solid angle, as a function of the angle, so at low energies, you have a broad distribution of electrons coming out of with many many interactions. you can have a few at, zero and a hundred eighty degrees and then you have a lot that are coming in between. now this is per unit solid angles so it distorts things in some way. at very high energy say here the two-point-seven-six, w- think of this as the number as a function of angle, you have strong peaking in the forward direction the peak, almost all of these, photoelectrons are scattered forward, at less than, forty, degrees. Compton scattering, you again supply binding energy, knock out an electron called a Compton electron and you have a photon coming off, at some angle. you can describe a photon as having energy or you can describe it as a wave, i'm tempted to remind you this could have a wave, wave nature, so when you're scattered, off, um, you can change th- think of it as a change in the frequency of the wave, lower energies are what higher or lower frequencies? 
SU-M: lower
S1: lower, of course. and it, with an a change in scattering angle. if we said we had a free electron binding energy of the electrons are the order of, what, Ellen
S3: uh free electron 
S1: in electron volts. 
S3: um <P :04> thirteen-point-seven? 
S1: thirteen-point-six you wanna say that's probably K-E-V for lead. so they're less than K-E-V, that's a lead X-ray it is is that amount so, the difference in energy levels, between the real estate of the atomic electrons, their R levels are like real estate, sitting out there, and you can have electrons occupying the real estate or not the real estate is always there, but the difference in, in uh neighborhoods, classes of neighborhoods is about thirteen-point-six K-E-V for lead, electrons, that's the X-ray you get, if you have something de-exciting from say the the uh L to the K shell, so K shell, so they're gonna be less than K-E-V. they can be the order of electron volts, for less tightly bound, electrons along the outside do you mainly get Compton scattering with, less tightly bound or more tightly bound electrons...? now i'm gonna ask Shelly... don't know i'm gonna tell you in a minute. anyone know? it's hard to remember all these things. let's treat this though first as a classic, mechanics problem, with the incident photon, and the free electron, that's sitting with no kinetic energy and no binding energy. we're gonna idealize this so we can do a classic mechanics treatment, and then we say afterwards we have a electron (scale,) uh and a photon, we can write down the conservation of momentum, the total energy, you can write this if you prefer, a- a- using Planck's law, Planck's law converts particle, particle treatments, into wave treatments, and back and forth. it allows us to assign a momentum to a photon, it allows us to assign, um, energy, a- r- in relationship to wavelength, so if i wrote conservation of energy, conservation of momentum in the two directions, just a little vector, uh vector stuff here, and photon electron, wavel- uh wavelength change we could, do a lot of, um algebra, and we would come down, to an equation that said the change in wavelength, between the incident and scattered photon, is gonna be proportional to, um, the, Planck's constant, and proportional to the rest mass energy in some way close to the rest mass energy over the wavelength that, is uh, rest mass energy times C not C-squared, times one minus cosine-theta so it depends upon the angle of scatter, and if you put in, um, some of n- the values of the constants, you get that delta-U, is point-oh-two-four-two one minus cosine-theta, where, this is the wavelength change in angstroms. if i plotted this you see the wavelength change as a function of angle scattering, if you completely turn the photon around, and it goes back, scatters at a hundred, and eighty degrees, it's gonna lose, maximum energy it's gonna have the largest wavelength, change. and, here it's just a curve folding over on itself, because you don't know if forty-five degrees this way is, three hundred and sixty minus forty-five degrees if it's above the line. so this is just the curve folding back all i did was plot that expression. things to know this is called photo- uh Compton shift, greater the angle of scatter, the greater will be its energy loss, the greater will be the Compton shift, and photons can Compton scatter at any angle. and if i tried to relay the electron in photon scattering angles i gave you the blow by blow no and then a miracle occurred type language. we get, a relationship on page twenty-three of the notes, of the flux being in an arctan relationship, and then here E is the incident energy, cotangent-theta-over-two. and i sat and put in extremes, whenever you get an equation you can play and see does this make i- e- uh sense in the extremes, i said okay if the photon scattering angle can have any value, which we established zero to two-pi, but this cod- cotangent function, only spans values from zero to pi, so theta is small, the phi, is near ninety degrees the electron, trav- the photon d- goes forward, and the electron comes off at a right angle. as theta increases to zero to a hundred and eighty, notice that the cotangent decreases from infinity to zero, therefore, you go from ninety degrees to zero. so my hand waving argument is, for the electron, recoil angle is always confined to the forward direction. by classical mechanics, the f- electron always goes forward. now it could scatter in some bizarre way and come back, highly unlikely. but there_ the photons, can go in any angle, electrons always go forward they go more forward, depending on the, uh Compton angles. here's electron angle as a function of photon angle, this is a cotangent, function and what i'm saying to you is for scattering between zero and three-sixty, of the photon, you only have electrons between minus-ninety and ninety degrees. more energetic incident photons forward scatter the Compton electrons, and you can't have electrons, more than plus or minus ninety degrees, scatter. so that's to know. i can do more on scattered photon energy i can compute the minimum photon scattering energy and lo and behold, it turns out that the minimum, uh photon scattering anger(sic) uh energy, is this, so you cannot have, a scattered photon energy that goes to zero. that's not possible. this equation will account for what are called Compton edges, that you observe, in your, nuclear instrumentation class. how many have ever worked with a spectrum of radiation and have seen Compton edges...? was that this last semester then? so it was three-fifteen or five-fifteen in a previous year. okay. here's the maximum photon scattering angle, uh you can lose, basically, lose no energy, a skimming reaction, and that's really not an interaction but that's where the equation's reduced which is fine. greater scattering angle, greater loss of energy again so you remember this, and energetic photons lose a greater fraction of their energy. they they uh uh Compton scattering you lose more energy, on an absolute (and relative) basis at higher energies, than you do at lower energies very good. i did Compton electron, maximum electron, minimum electron, energy scattering, electron energy versus angle and so on. the electron energy, mirrors the photon, the maximum energy is less than the incident photon, by a fixed amount which depends on those equations. okay. here are some things to know, about Compton scattering, you need to look at them, and the Klein-Nishina formula is quantum mechanics formula, beyond the scope of me deriving it for you, but it tells you the probability that you will get, a photon scattered, at a given solid angle. it's beyond me to, do that for you here, if you normalize it it says what the distribution for a large number of photons coming through, is, as a function of, the angle at which things come out. this is a probability, that you'll have scattering at a given angle, these are very high energy uh i'm sorry low energy going to higher energies, you what you see here is it's more probable, that, photons will scatter at higher energies in the forward, direction. so you're trying to dec- decide in a back scatter imaging method would you want lower or higher, energies? looking at this graph... Marty you wanna try it? 
S10: lower? 
S1: you would want lower energies because you would want more back scatter, at_ which is around a hundred and eighty degrees. they are using some back scatter ti- techniques usually with neutrons however, to, do things like look into, uh spaces that you can't normally look into and you can't get a detector on the other side of, I-E this could be used for looking into safes, for various spy things, as well as characterizing or checking materials, to see, uh, what the composition is below the surface. here's a polar plot of the same thing, again that's Klein-Nishina, you can do Klein-Nishina formula and figure out electron angles, here's another polar plot they all see the same thing. so you should know these things in summary, about angular distribution. alright we, these then should be clear these are the Compton edges, where you, you must lose a certain amount of energy in Compton scattering so if this incident photon, then your elec- your things are gonna come out in that area (and) you do see something that has, starts an edge, in a spectrum. yes, Mike 
S5: um is, is it always point-two-five-six for the Compton edge? cuz i know in the homework you gave us, it's completely off (in the end.) 
S1: where di- e- i- ch- it's varies as a function of the energy of the incident photon. where are you getting the point-two-five-six? wha- what [S5: in three-fifteen ] what makes you think it should be the same? hm? 
S5: in three-fifteen uh we always use like point-two-five-six 
S1: as what?
S5: the, distance from the incident gamma to the, Compton edge 
S1: alright let's see <P :05> wait a minute okay maximum_ minimum scattered energy okay. the scattered photon energy, if we took this, and subtracted the incident photon energy from it, 
S5: okay
S1: would you always get point-two-five-six...? let's look elsewhere. where's my um, i liked it in this form. the, wavelength shift [S5: i mean the gaps ] the wavelength shift is, a constant function of the angle to maximize this, you set this to zero, it goes H over M C-squared for wavelength change, i would say yes you were probably correct, it is a constant, the shift, in wavelength is a constant, so the shift, in, energy would be a constant 
S5: okay
S1: the shift. so to me that would say it is always less and you're that number is point? 
S5: two-five-six.
S1: two-five-six. and that would be in? M-E-V?
S5: yeah
S1: okay. that is correct. if that number is correct, this equation says there should be a constant. [S5: okay ] in the shift. now the total energy loss depends upon, the incident, of energy. but this would be the, the change in wavelength, the maximum change in wavelength (let it) be, with cosine of theta equal to zero, okay? which would be, what? ninety degrees, so the maximum wavelength shift is H over M-E-C, this is the maximum wavelength shift, if you put t- point-oh-two-four-two and use Planck's constant i bet you'll get the number you have. let's take a break and we'll come back, can we please come back at uh, ten, to ten. 
<BREAK IN RECORDING> 
S1: what's it say? 
S6: well ther- the spots that i picked up, one uh says that the three workers that did it they were on the assignment for the first time, it was the first time they ever did the job. 
S1: mhm <LAUGH> 
S6: um, two paragraphs here, that are exactly what you were just talking about <READING> for years Tokyo insisted its nuclear facilities were far safer than those in other nations, because of Japan's high technology and meticulous workers, and officials have often scoffed at the idea that an accident like the ones at Chernobyl in the Ukraine or Three Mile Island in the United States could ever happen in Japan </READING> 
S1: uhuh 
S6: and uh 
S1: Paul's point 
S6: the other one that i've got here is um, <READING> J-C-O a wholly owned subsidiary of Sumitomo Metal Mining Company has admitted that it had for years deviated from government approved procedures by having its own illegal manual </READING> 
S1: uhuh. uncool very uncool. 
S1: Darren can you share that with everyone please? 
S6: sure, um 
S1: just tell them 
S6: just reading the Daily, today, on the second page there's an article about what we were just talking about. and um, the couple of things that i noted were, that one one of these paragraphs say that the three workers it was the very first time that they had ever done the job, uh, the other paragraph, uh it says um, <READING> For years Tokyo insisted its nuclear facilities were far safer than those in other nations, because of Japan's high technology and meticulous workers, and officials have often scoffed at the idea of an accident like the ones at Chernobyl or Three Mile Island could ever happen in Japan, </READING> and the other item was saying that uh, J-C-O, the company that owns the facility <READING> has admitted that it had for years deviated from government approved procedures by having its own illegal manual </READING> 
S9: hasn't, Japan's had, had some other, uh decently-sized accidents that really haven't gotten out, uh i know they had a leak last year at one of their, plants that went undetected for, a couple months i think. 
S1: mhm mhm. now there's differences between something being technically possible, and assurances that something cannot happen, and in some cases it's technically impossible, i think to have an accident like this at a processing plant, for CANDU fuel is technically, impossible. mm, if they go to an aqueous phase which i don't know enough about to comment but, i would certainly_ in responding to the press i would certainly have found out whether, what the different processes are and made a few calls to be able to comment, um, and be seen, between something being viewed as improbable. remember though th- Three Mile Island, was, predicted, by a nuclear engineering professor at M-I-T, Norm Rasmussen, the lost fourteen-hundred port, uh report. it predicted that in so many, reactor hours megawatt years, of nuclear reactor, operation, we would have a small bu- so many small break locus, and other events. the focus was unfortunately, on, the catastrophic event, and not the s- the the bad event, bad from an economic standpoint, bad from public relations standpoint, certainly Three Mile Island was not a, a a, a health significant, event. but um... oh i lost it, but th- there it was probable it would happen and the predictions were that it should happen, and then it happened and everyone acted surprised. if you operate for so many hours, and th- p- you have these tiny probabilities, sooner or later it's gonna happen and it's statistics though, you can't guarantee, it wouldn't happen. if it's technically possible. the best thing that ever happened to the U-S nuclear power industry, from a safety viewpoint, in my mind, was the Three Mile Island accident. as a result in my opinion of the Three Mile Island, accident, you had, um, greater emphasis on operations, compliance, the Nuclear Regulatory C- Commission rode in in white hats and said we're now the good guys ha ha ha, in things about communications, they were trying to call the designers at Babcock and Wilcox Company, to get some information on what was going on, the phone lines out of Pennsylvania were tied up because the governor had made his statement, and they had no separate, phone, they had inadequate if if any, special phone connections and they could not reach, the chief, fellow who could've been able to m- uh'oh i know why this is behaving strangely, which in part was responsible for the melt. so, the communications improved, operator training, in everything was completely redone, and i think we now have much safer plants than before Three Mile Island. now we don't have new plants, but we have much safer existing, plants. so from the viewpoint of, safety of operating commercial power reactors in the United States, Three Mile Island was a key event in terms of improving them. the concept of operator error. and operator error upon operator error, upon operator error. we are human we make, mistakes. have i told you Three Mile Island was the reactor that cried wolf...? what ha- one of the things i heard_ and these are insider stories cuz i worked at, Babcock and Wilcox Company when they designed, the Three Mile Island, and knew the folks and so i called them i was in graduate school then and i called, called 'em up and said you know what's going on you know i used to rent a house from the main response guy, before, before the Three Mile Island accident, i rented a room in his house, and um, he said this is the reactor that cried wolf basically, because, it got, um, um, they were starting up and you know when you have a system like oh like a smoke detector, right? you got a smoke detector, it might be too sensitive if you put it too close to the stove right? and any amount of steam will set it off, sometimes dust will set it off, it's hypersensitive it's, it's crying out to you all the time there's a problem when there isn't. well one of their, um, systems kept_ when they were tr- first bringing things up to power, kept tripping things off and saying there's a problem here there's a problem here, and that kept, happening so they, took it out of the sy- system, eventually. but w- after this happened three or four times it went off again and they said oh just ignore it, that's that uh, that system again let's defeat it, and in fact that was, a real warning. this is folklore i don't know if it is true. it's folklore within, people who who were there. why were there releases to the environment? at all? well you had all these lovely systems, well there was some point where there was an override, they were taking the water out of the the, basement, and then they have all the water E-C-C-S water, uh emergency core cooling system water, was, gone in the basement and then they pump it out and put it in holding tanks, well something happened i don't recall whether it was that they, failed, to, take an action to switch tanks, or whether someone overrode the switch, but basically they filled up a tank, till it was overfull which caused pressure problems then they had to vent through the roof. that's other for- folklore, from, from the inside. but again i don't know what is true and what is not true but when you start hearing stories like that, from people in the business you say well what next? you know they're defeating, the safety systems. um, what are the qualification levels of a reactor operator? do you know, what kind of education do you have to have? 
S6: going in? um, not much. most of the training is done inside 
S1: have a high school degree? do you hafta have a high school degree? 
S6: yeah i think you hafta have a high school degree but i don't think you hafta have anything beyond that. 
S1: that's right. sometimes it's two year Associate's degree but, i- they they take people with high school degrees and they're the people who are running these things. but those were the people you probably want. i was lucky enough to get on the U-S-S Alabama, the nuclear sub, and while i was on the nuclear sub i w- s- looked at all around at all the people and the guy who was in charge of pushing the button, looked like he could've been any one of your all's, um, younger brothers. i mean he looked about seventeen. and someone who was doing critical steering for the entire sub, looked about, seventeen. these are not really, couldn't have gone through college much too young, well they can follow orders and directions, in general. you want someone who can follow orders and directions, but not just that, if something's wrong will call, they will call, and get help it's kind of like the, the woman from Brooklyn in the red dress that i hired in the PET Facility, told you that, story i think. is that she, she was the only one everyone else had all these theories how to deal with my, my interview question. she said i would call you first. cuz i'd know something was wrong i'd be scared, and i'd call you first. i then proceeded to train her what to do in the actual accident which did involve calling me, only i was being called, second. <SU-M LAUGH> okay. so, um, anyway and we posted procedures now if you post procedures. and nobody follows 'em, if you post procedures and somebody changes them... then, there you are. did i tell you the ethics case? my personal ethics case about fluoro units...? no, cuz we didn't do the ethics we had a guest lecture for the ethics. okay. this is what has inspired the thing that you're gonna you're going to do tonight. fundamentally, the, i was doing uh i was in Arizona and there were only three people who knew how to do these jobs, uh quality control mammography in Arizona, in quality control X-ray machines. and that was pre the uh uh American College of Radiology certification program for, mammography. two of us, did a pretty good job, and, we're no longer qualified we are not considered qualified to do this anymore, because the American College of Radiology said you had to be American College of Radiology board certified, and not Health Physic board certified and they had a much strong lobby, and got things done, and we stood back and didn't say anything. then that effect of that quality, who can check the quality of the machine is there's suddenly no one in Arizona qualified, to check mammography units, so a guy from outside set up a business he's never even there, other people go check their machines and he signs the results. anyway these involve a series of quality control, quality assurance safety measurements around fluoroscopy and mammography units. fluoroscopy you'll see next semester if you take five-eighty-two has very high doses so you can get skin erythema, from new f- modern fluoro units, which are, high intensity units that they do surgery under in real time. so you can get a, burn from fluoro units. they, fluoro and X-rays are primarily regulated by the states, N-R-C does not get into that, they get into, by-product materials. but regulated by the state government, Arizona Radiation Regulatory Agency happened to be the group that, that dealt with, Q-C. they had one inspector to inspect thousands of machines and they only got around every year, year and a half. my assignment was to do a bunch of fluoro units and mammo units, i only agreed to do it because the other fellow who was reputable, got thrown off the job and he said i could do a better job and he didn't want the other guy touching it, so he put my name in and said w- i hope you can do it because, um, the other guy does it, nothing's gonna happen, i'm warning you there's problems with this this uh H-M-O, and they had scattered clinics all over Arizona so, i um, had my own equipment and i went around and and ran these checks like, scatter, leakage, um, various things. i had a fluoro machine and there was an Arizona Regulatory, Radiation Regulatory Agency, um, rule, i think it was you couldn't have more than ten R per minute, entrance dose to the patient. well first thing i always do with the fluoro machine is watch out for myself, i check for leakage and scatter that could hit me in the face through all the rest of the tests. which is not proper order, but if i've got that i don't wanna then find out after being in there with a beam on for half an hour i've just fried my corneas and lenses and everything else. so i did that first that was fine then i checked entrance dose. and it was about seventy-five R per hour at the surface, [SU-M: jeez ] limit was, ten. okay when do you get skin erythema...? what doses...? oh come on. wouldn't you have learned that last week...? nope. okay. well skin erythema you could probably, that's per minute you could get skin erythema from those doses. now there are obviously some changes in to what you can and cannot do. plus it's downright wrong if you have to_ at that time if you have to jack up the juice that high, then, what you'd end up getting, is a bad image anyway simply turning up tube intensity would not improve your image there was something wrong with i thought the image intensifier tube. so i said okay well that's a short job. i'll write it up and i posted do not use this machine under any circumstances, i caught it only by accident, most people, checking a machine will check the highest intensity buttons. you set it on the highest intensity if it passes fine. i tried a lower intensity button, and it was even higher... it was higher, it was okay at the high intensity but the low intensity had the seventy-five. so i went around with the techs i said what do you usually set? oh the the button on the left is what we use. we're instructed to use that or we don't get good images. which was the button that had the high output, i said when was this machine worked on they said, oh it wasn't giving good images, i said did you kn- anyone complain about images? the techs are your friends they'd tell you what's going on, if you make friends with them. they said oh yeah we were getting terrible images then the service person came by, and we were instructed to use this lower button, and well all our images look better to the radiologist. intentional rigging, to violate the law, so they didn't hafta to um, have, a new im- image intensifier. who was involved? illegal. who was involved? the H-M-O, and the repair company. wanted to save, a couple, thousand, dollars. they knew they wouldn't get inspected properly, these inspectors'd come in and they'd have a a detector with_ you know you're learning, in five-fifteen or you've already learned in three-fifteen, you've got detectors with time responses, one minus U minus, um, tau, over, T over tau <WRITING ON BOARD THROUGHOUT NEXT :32 OF UTTERANCE> responses, that if you have a detector, if you have a detector, here's time, and here's the response, some of them go like that, this could be the order of say a second... the inspectors'd come on they'd flip an exposer for, a hundred milliseconds... that's secant, seconds, and, really actually milliseconds is properly abbreviated that way. and, they'd flick it on, for that amount of time, they'd have their detector out there, and they wouldn't see anything the needle would not deflect. if it were digital it would it would bubble around a little bit but you wouldn't see it. so, they were going in and saying there's no scatter and the shielding is fine and i was going around finding out that there was and there was no shielding, and, there was scatter, because they didn't understand their detectors, so the probability that the inspectors would actually catch, this, what i consider to be a crime, was pl- practically negligible. so here was the ethical dilemma. i was scheduled to do mammography units, in several of the other clinics and i had done some mammography units, that i had found for the H-M-O where they_ this is before all the extra assurances and are you a certified mammography clinic, that were causing more cancers probably than they were finding because it was subdiagnostic, this is ten years ago, fifteen years ago, subdiagnostic images, which were, at ten times the normal dose. cuz that's what you checked, image quality and dose. and they had fixed them... and Rod had warned me go for their mammo you've gotta fix their mammo Jill I'm telling you. they fired me because i i um, i_ you've gotta see their mammos are fixed. so my friend said. so then i was there, and uh, the dilemma was, if i, really pitch a fit, on this, then, they'll go to the other guy and they won't get their other mammo units fixed. sorta trying to weigh, how am i helping the most? should i call my friends at the Arizona Regulatory Agency and place it. well i went about my business and i sent 'em the report and then i called up later and said did you fix it? there's a problem, it's illegal did you fix it? they said yeah yeah. so i went back the next week, and they were using the fluoro unit. i think my posting do not use lasted about one night. then they were back making money with their fluoro. and i said okay, um, i went o- and the techs were using it and then i said oh did they fix it? they said oh yeah they fixed it. i said well what setting are you using? they pointed to the same button. i said well what did they do did it take long? they said no it didn't take long they just told us to use it again. that it was fine, that this was bad reading on my part. so they were still using it. what would you do...? what would you do...? that's a good ethics thing that uh, after you get your quiz done, for r- for uh Professor He's class then we could think about, what would you do? that was the ethical dilemma that i was placed in. everyone would decide differently, and, there's no right or wrong answer. i was not doing it for the money either, mkay, certainly did not justify it i was doing it out of professional courtesy to my friend who had a health concern, about the system. okay. i don't know how we got there. interesting. <SS LAUGH> yes because of the newspaper, and what you say and what you don't say, and when are you're a whistle blower or not, we have whistle blower laws under N-R-C whether or not to blow the whistle, there were a lot of people who knew that, who were quiet. and the event has international implications. the board of directors of the int- American Nuclear Society i would characterize, the officers of that board as being outraged at the moment, suddenly occupying all their time, because how are going to, they gonna deal with this international incident? as a result of Three Mile Island also, we had WANO, forum the World Association of Nuclear Operators, which goes around and helps everyone with safety culture. clearly safety, culture, is, different, from place to place. even from, facility to facility within the same state. part of the health physicist's job is to impart safety culture, so that might be, the the hardest part of your job. Darren told us about covering, uh, fuel assemblies with a tarp, we informally concluded it doesn't make that much difference, well, for a tarp, it doesn't. but if you don't do it, your safety culture, is hurting. what about regulations that people think are stupid...? now it's just now getting getting cold, enough for me to start wearing long-sleeve shirts, and we're gonna start seeing bolo ties. does everyone in here know why i wear a bolo tie...? kind of a trademark i've kinda been out of it, in the summer. i- who who's seen me with a bolo tie? okay. now, why do i wear bolo ties? s- i- it makes a point for me several points every time i put on a bolo tie. and this is also about your responsibilities as health physicists. when i lived in Arizona we, we went in T-shirts and jeans and taught class, and the call ads had been written up as this is the university to go if you wanna see scantily clad coeds year round. the guys would show up in swim trunks regular basis, and, the, coeds, and it was part of our culture. it was that something everyone there appreciated. you didn't have to dress up you didn't have to wear suits, it wasn't like M-I-T, it wasn't like Georgia Tech. m- the faculty in engineering had all come from, that, culture. we'd come from very fancy universities. Arizona State is, engineering is always ranked as the, most underrated engineering college. that was starting to irk, the deans. well anyway the regular dean went away and someone was left in charge and, for a year and, he said well, i'm gonna do something we can't get our rankings up if we don't look like a highly ranked place we will never get highly ranked, we'll always be underrated, i'm sick of being the most highly underrated engineering college, in the country. and we get singled out every year in U-S News and World Report for that. p- still happening i saw a couple years ago they were still naming Arizona State as the most underranked. <SU-F LAUGH> so, he sent out a memo to everyone. we were young whippersnappers from top schools. from the coast, and Michigan. heh heh. and, we, we uh got the memo the memo said from now on in the interest of professionalism, all department chairs, will wear suitcoats and ties, and all engineering faculty must wear ties, at all times when they were on the property. you shoulda heard, what happened in the hall. i may as well be working at M-I-T, i'm going back to U-C-L-A this is ridiculous we could wear p- flowered shirts like Professor Ewing, all the time, and what is this? you know, wha- w- they can't make us do this, and our students are showing up in swim trunks and shorts year round sort of like, everybody was a Jim Bachek. <SS LAUGH> you know Jim? he's from the U-P he always wears shorts. so, he he comes and you will remember this about regulations. so i'm sitting there puzzled. i was the only woman. i always thought however i dressed was how women engineering faculty dressed. i'm like well you know, i was a good girl then, young, not spoiled, not bitter and angry, i thought i'll just comply with the regulation now what should i do to wear a tie. so i went down i said the oh the state tie of Arizona is a bolo tie. so i went over to Chief Dodge's and they wouldn't sell me the official state tie because that was for men only, but they go- received so much flak they sold me the women's version <SS LAUGH> Barry Goldwater, wears the state tie of Arizona. i now have two copies, of the official mens' version of the Arizona state tie. and they have secret meetings in Monty's, which is on the dry river that runs in between Tempe and Phoenix, and have state dinners and if you wear your bolo tie, you can go there and a- hobnob with Barry Goldwater i don't think women are welcome thank you but i don't know anymore that's for the wives, girlfriends to wear this, the state tie. so the official state tie of Arizona, i plunked it onto my T-shirt, wore my holey jeans and proceeded, complying with the regulation... mocking, the regulation. mocking it not only in what it was trying to do which would not have been effective in accomplishing the end, but in it not taking into account special cases. so for me when i put on, my bolo ties, i, think of, different things in in what i had learned and where i had been, and, though, all of my colleagues were so delighted that i would wear the, the tie for them, they didn't have to wear ties, it was sort of like being the designated wearing the pants, but it was sort of wearing the tie, and they were just gonna say well, Jill's wearing the tie for everyone. and th- and the T-shirt and the holey jeans. and um, they all started giving me bolo ties, so i have a very large collection of bolo ties because they were in agreement this was very stupid. um, now what you do though, on the topic of ethics if you don't like a particular regulation... do you mock it? thumb your nose create your own manual? bad safety culture. is- i had a ba- that's the beginning of the development of my bad attitude. <SS LAUGH> in case you were wondering how long i'd been nurturing a bad attitude. but, what you should be able to do, is comment on the regulations. if there's some case it doesn't fit for and makes no sense whatsoever this was way before that, that little trend of women's, women's ties and we've had recently a women's necktie trend and things, way before any of that. you try to influence the regulations, if, it is truly a regulation, that's presumably relates to something which i don't think our d- faculty dress code was, then you ha- should comply out of courtesy to safety culture. you can make crass comments, about it and try to fight it and write letters, the best time to do that is when things are out for public comment. it's professional responsibility to respond. your workplace will not generally require you to respond to new regulations. you could become a regulator and try to fix things. when the market was tight, in health physics which right now it's not, when it was tight about five six years ago, i had s- two students actually stoop and take jobs at the Environmental Protection Agency, okay? i like E-P-A. E-P-A though had this little problem about not paying people going rates for radiation protection so no one wanted to work there, E-P-A has a few other difficulties right now, particularly in its regulations concerning radiation are not consistent, with other, agencies, but, i feel very confident that because they went there, they will change things. now one of 'em subsequently left the other one is goo- gonna probably be by the time he reaches thirty-five, in the main office in Washington. this young man will, really take over E-P-A. so that's another way of dealing with it. at least i know in the New York region, there's some reasonableness, with the E-P-A's treatments of radiation. well that's sort of our moral story du jour, but it does relate to, silly regulations, complying to regulations, ethics choices, i'd be interested in, tonight what you would have done though with my fluoro mammo, moral dilemma, and then i'll tell you what in fact i did do. we've got only one more kind of interaction to cover which is pair production. you have an incident photon it disappears it must take place, uh, in the electric field of a nucleus why? because the nucleus has to, conserve momentum and get a little bit of, recoil. well does it? if these always came out, after the interaction the, initial photon disappears and you have two, um, electron, photon positron pairs, do not confuse this with annihilation, reactions which are charged particle interactions, pair production produces positron electron pair, it turns out these don't come out at exactly a hundred and eighty degrees, because there is the nu- the uh nuclear recoil happening. they do not come out, with exactly, uh the energy, the energy difference. the same as for annihilation interactions. if that were the electric field of an electron, the electron could also be liberated. you're actually still producing a pair but they're calling this triplet production, cuz you've liberated an electron. so it's near an electric field, you have a threshold which is equal to the sum of the rest masses that you need, you can get three, which are called triplet production very rare, not significant from radiation protection viewpoint, and it's more significant for higher... atomic number, higher atomic number um, materials. there's clearly, a deletion on page fifty-two. <P :08> and you always get, five-eleven K-E-V photons. always always. because why? positron. you created a positron. photodisintegration gamma-N reactions, i'll give you some examples of when those happen. what you basically end up getting is many many photons, interacting, you get, a photon comes in it could have nuclear reactions nuclear excitation coherent scattering, i won't follow those, but i'll follow the three main ones Compton, photoelectric and pair production, it is better to actually look on page, fifty-five which is more legible than the overhead is, it's also more legible than my com- computer screen but i will do pointing here. so, when you have Compton process what do you have? Compton electron, Auger electron. Compton photons you could have X-rays. if you had a liberated electron, a liberated electron, from a lower shell, higher really bou- more h- tightly bound, higher binding energy shell, and the less tightly bound electrons jump down you have, atomic deexcitation which would be Auger electron emission competing with, with uh X-ray emission, and a col- and Compton photons. with photoelectric, effect you'll produce the photoelectron, your initial photon goes away but you could have Auger electrons in X-ray line spectrum, in theory, and maybe very low probability, and you have pair production, where you have, more charged particles. so all your charged particles will undergo charged particle interactions, excitations, ionizations and Bremsstrahlung right? plus your photons all these secondary photons, here, will come down and they will repeat all these primary processes. so you'll get more photons than charged particles. from all of these you can have the the uh the positron have annihilation so you've got more photons. then all of these can interact through, excitation, a- e- ionization and Bremsstrahlung for the charged particles, or all of these interactions, so what you basically have going on is a single photon can produce a whole lot of different radiations in material, having different energies, and it turns out the probability of interactions of these, is going to dramatically vary, depending on their energy. so what in the world can you do? how can you possibly, do this problem? i will show you the easy health physics solutions, coming up soon, but, what you really would have to do is use Monte Carlo techniques, where you take a photon you assign random numbers. if you have a hundred random numbers and a particular event is sixty percent probable, you assign sixty of the random numbers to that event and forty to the other events, you generate a random number for that event if it comes out within the first sixty then you say that event happened, if it came out in the other forty you say whatever those other possible reactions are. so you map the probability of interactions with random numbers, take a history, trace it through using the computer through steps, points, in time and space, move at tiny increments and keep asking rolling your random number generators like you're gambling, in Monte Carlo, and you repeat this, until, the charged particle or photon or neutron comes totally to rest. then you take another one, and do it. and you would even map Klein-Nishina to say what the probability you could say is it Compton scatter? if you say yes then what's the probability, it will scatter at a particular angle, okay. then what's the probability that your electron will come out in a particular angle okay. you roll dice for each probability. and you do this, oh do it five hundred thousand times, sum up the results and pray a lot. you can't do that for the most point (sic) so for the most point we'll di- do variations of one over R-squared, we will do external. but you take a photon source, and follow each photon to see what you ha- what happens and tabulate. we will start, i think is it tomorrow night...? i'll email you. in the next lecture that we have i will finish photons, and get you fairly much through, interactions. okay? thank you very much. see you tonight. 
<P :04> 
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