13. Practical Radiation Counting Experiments

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 view additional materials from hundreds of MIT courses, visit MIT opencourseware at ocw.mit.edu. I think things have gotten pretty difficult lately so I wanted to change the subject to something a little more

practical

so I started alluding to this hypothetical

radiation

source that you might have here and things like do you have a known source of activity that we calculate. yesterday and you have a detector of unknown efficiency, how do you know what the efficiency is?

How do you know what, let's say, your dose-distance relationship is and how do you calculate all this? So let's take the general situation we were starting to solve. Let's say we have a Geiger counter right here, which is our GM tube, and we have a point source that emits things in all directions. Let's go with this from yesterday, let's say it's a source of cobalt-60. Now it is zero point five two micro Curie. the question is how many counts do you expect on this detector when it's at a certain distance, so I laser cut a small Geiger counter template from a previous class and all of you who have been to the IDC can do this too. before I joined the International Design Center so they have a laser cutter that you can sign up to use, which is where I did this and it's set up to just take a Geiger counter and place your sources at a fixed distance so you can figure out the dose distance relationship with things talking, does anyone know what the relationship is between dose and distance or measured activity and distance?

Yes, Luke, close, let's say the measured activity would be proportional to one of 1 over R squared, now who knows where this comes from. I'll move the source a little further away to decrease the beeping, yes, exactly, if you were to draw a hypothetical sphere around this source right here, then you would have a detector that is approximately rectangular with a fixed area. Let's say it has half a length L and half a width W, then the area. Sorry, let's just say length L, that W, the area would just be L multiplied by W and actually, what is it that Chris mentioned as the solid angle subtended by this detector here?

In other words, at a certain distance R, how much of this sphere? How much of the area of ​​this sphere does this detector occupy? In other words, how many of these gamma rays are going to go in a different direction than the detector versus how many? many will actually get into the detector and a simple formula for the solid angle is just the surface area of ​​whatever you have over R squared, it's kind of a pretty good approximation to the solid angle of something for very long distances and it's probably which you'll see in the lecture, but I wanted to show you the actual formula in this case for a rectangle solid angle comparison.

Well, that's up there, so let's say on the x axis right here, this would be the distance from the source. to the detector in meters and I said that we have a kind of detector that is 2.5 by 10 meters in size which is a huge detector, actually let's change it to the units here, so this one is about 10 centimeters long, so we change our length to 0.1 and what do you think the width of this Geiger counter is in meters centimeter 0.01? We're going to have to change our axes so we can see the graph, so instead of looking up to 15 meters away, let's look. a meter away maybe less, all of this is probably 50 centimeters and we'll take a look there and what we notice is that except for extremely short distances, this approximate formula for the solid angle or in other words, if you were to draw a sphere around This source that is the radius of the distance between the source and the detector.

How much area of ​​that sphere does the Ted Tector occupy? this actual formula approximate formula the blue curve is a pretty good approximation of the red curve until you get really close to like five centimeters away or about this distance here, so it's anyone's guess why this formula would break down what happens when R goes to zero, which happens to our solid angle or our approximation for our solid angle goes to infinity, to the right. The Kenneth detector actually occupies an infinite area. in any case, it doesn't matter that the unit sphere is not quite if you were to take this detector and reduce the radius to zero so that the source and the detector, if you didn't count the thickness of the plastic, would be next to each other if that solid angle out to want infinity, then the count should go to infinity and it is not calculated, does anyone know how many, first of all, those of you here have heard of the solid angle before, so a little more than half of you, Solid angle is something that is becoming clicky?

I'm going to disable that. The solid angle is sort of analogous to the old normal angle, except in 3D, so instead of looking at things in radians, this has the unit of what's called ester radians d radians with a full sphere taking the place of pi ester radians, curiously. enough for pi is also the surface area of ​​a unit sphere with radius of one, that's where this comes from if something completely covered a unit sphere, like we would say in the case of a light source in aluminum foil completely and say how much of that solid angle is made up by the aluminum foil in case it's 4 pister radians, regardless of the size of the sphere, how much aluminum foil did you have to use, so this fairly simple formula is not the best approximation and I'm not going to go through the derivation because, as I said today, it will be more

practical

in nature, there is a more complex and rigorous formula for the solid angle of something, let's say in this case a rectangle of length L and width W from a certain distance R or in this case on our chart yes I take this source and hit it right next to the detector.

What part of the detector is there? Sorry, how much of that sphere does the detector subtend to PI half of the sphere because it's this, let's say this entire side of the source is completely obscured? by the Tector and this whole side is free to move and if you look very closely, yes, at zero, the correct formula gives you 2 pi lord radians, which means that half of the gamma rays coming out of this source would enter in the detector. I did not do it. I can't say anything about being counted, but that's where detector efficiency comes into play and that's something we're going to measure today, which is why I have my big bag of burnt bananas.

These are the ashes of about 50 pounds of bananas charred to about a crisp. 250 Fahrenheit for 12 hours in most dorms and a couple of frat houses, so last year I had students take home about 50 pounds of plantains or 50 plantains. I don't remember which one was a lot and we did some distributed work, so we all peeled the bananas and put them in the oven, baked them, separated the aluminum foil and baked as much water and sugar as possible to concentrate the potassium-40 in the bananas, so there's a reason I've been using potassium-40 because it has a lot of examples in this class because you're full of that is pretty much the short answer: if you eat bananas, which I think most of you do, they're taking in a good amount of radioactive potassium, which is a positron emitter and also does that. electron capture and all that fun stuff, so today what we're going to do is calculate the activity of a banana, but that's a very difficult thing to do, so it's anyone's guess how radioactive a banana is in any unit, whatever. be. is very, very, very small, a banana contains a tiny but measurable amount of radioactivity and one of the ways to increase your confidence in any type of

radiation

measurement is to increase the signal intensity or increase the

counting

time and why not I want to count for the next seven years, we have concentrated the ashes of 50 pounds of bananas and it to increase the strength of your signal, which will increase your count rate, which is the introduction I want to give to statistical certainty and

counting

, so let's take the one of the homework problems as a motivating example, guys, does anyone notice the extra credit problem in homework?

Let's start talking about how we do it, that should motivate the rest of the day, so I'll pull out problem set number four, which by the way, is due on Thursday, not Tuesday because we don't have school on Tuesday, that was a surprise to me , but whatever it is, I'll still be here, we don't have a vacation, just you, so one additional question, do this so we all know to smoke. is a major source of radioactivity and if you think about it, it's not just smoke that contains those radiation particles, it has to be cigarettes, cigars and other smokeable products, so I was thinking that there is no better concentrated source of radioactivity for smoking than a smoke shop, there's a brewery one at the end of the teeth, it's probably closer to campus but I know there are plenty that are accessible for tea so I thought it would be cool for us to find out How radioactive is it to work in a tobacco store because there is all this radon decay?

Oh yes, actually you know. Are you serious? But you must be 18 years old to smoke. Interesting, we might have to leave town for this. What about Somerville berries? Yes, I don't think so. It's where I'm from, Swampscott. I don't think it's uh, I don't think it's the 21st, but that's on the commuter train, so you shouldn't go to Swampscott anyway. I think that's okay, it's probably a pretty radioactive place to work, but the question is how long would you have to wear a detector and count to be sure that there is some kind of measurable difference and so on without deriving everything from binomial poison? and normal statistics.

I will say that that is in today's reading. I want to show you some practical uses and applications of these things. Let's say you measure a count rate in some experiment and we'll put it in units of counts per minute, which would be the number of counts divided by the count time, which is as simple as it gets from Poisson statistics, you can say that the standard deviation of that count rate is actually just the square root of the count rate divided by time and that's kind of simple, right? here, but normally in these types of

experiments

, if you want to know how much more radioactive one place is than another, you have to do a background count, so if you wanted to know how much activity that source emits, there is a lot of background radiation that we will be going over in about a month.

I would have to sit here for quite a while and wait for the slow clicks of whatever background radiation in the room we are going to to get a sufficient count rate, as you can imagine. The slower the count rate, the less sure you can be that the number you're measuring is actually accurate, so the idea here is that this standard deviation is a measure of confidence that your values ​​really are correct, so the two things you can do, Yes, the two things you can do to decrease this standard deviation are: you could increase the counting time.

It seems that way, why is there a C at the top that doesn't look right? Actually, okay, yeah, there we go, so counting for more time. you can decrease your standard deviation, this will take forever, it actually takes about 67 minutes because we've already done this calculation to get 95% confidence over 5% uncertainty for this type of background count. I mean how many concepts we had until now. like 12 14 yeah, not many, so you have to be able to subtract that count rate from whatever your source is and the way you actually measure this is pretty simple, but the way you subtract errors may not be as simple. so let's say we are going to separate these two

experiments

into a background experiment that we are actually going to do in an hour when we want to count these banana ashes that we will have to put in, we will have to count the radiation coming from the detector itself, which will represent the contamination of cosmic rays into the detector, anything else that may have spilled in there from previous samples and we're also going to take some sort of gross count rate background which will be our background plus the net count. rate from our actual source and that's what we're looking for, so the net count rate is pretty easy just the gross count rate minus the background.

Let's keep the symbols the same minus the background count rate. Does anyone know how to quantify the uncertainty of this? net count rate, just add the two, either, in this case we have to take into account the fact that the emission of radiation from anything is a truly random process, so it is actually random, there is no correlation between the moment when one particle leaves and the next particle leaves. exit and because it is a truly random process, these errors in the background rate and the growth rate could add or subtract from each other; In other words, one might be a little taller than one shouldbe, another might be a little lower than it should be.

If you simply add the two standard deviations together, you will actually always get an overestimate of the true error because you are not taking into account the fact that these two experiments may have partial cancellation errors, so in this case this would be the worst case . scenario that is not the most likely scenario, what you really want to do is do what is called quadrature uncertainty, where you actually add the sum of the square roots of those errors, it looks like the magnitude of a vector, right? exactly like the magnitude of a vector, this way you are taking into account the fact that more error in each experiment increases the error in any net experiment you are doing, but not linearly because sometimes you have partial cancellation errors and with enough statistics if If you count for long enough or count enough counts, then these things on average will add up to quadrature, which will result and I want to make sure you don't have any typos, so I'll keep the notes with me. you need the fund count over the fund x squared plus those, here we go, so now I would like to ask you a question, the same one that is here in what is and in the problem set, how much time do you have? count in the smoke shop to be 95% sure, let's say your counter has 5 percent uncertainty and we're going to spend the rest of today's class dismantling that statement and coming up with what it should be, so again what we mean is How do you know that we are 95 percent sure of our count rate plus or minus five percent error?

That is the main question today. Does anyone know how we would start? Does anyone come to the reading today and see some smiles? Okay, we'll start from scratch, so okay, who here has heard of a normal distribution before Wrigley LA? Great, the idea here is that with enough count statistics, this binomial distribution of very rare events approximates a normal distribution where you can tell whether a certain count rate is measured. Let's say this would be your mean count rate and if you measure some other count rate up to limits of plus or minus 1 Sigma or one standard deviation 1 Sigma gives you about 68% confidence in your result, confident that you wrote it correctly, The reason is that if you move plus or minus 1 Sigma away from your true average here, you filled out 68 percent of the area under this normal distribution.

Similarly, if you move plus or minus 2 Sigma or minus 2 Sigma, there are about 95 percent of the area under this normal distribution. % confidence that 3 Sigma is close to 99. Point out what the number was again, I think it's 6, maybe it's more like 98.5 percent and so on and so on, there's actually a society called societies Six Sigma and the way they get their name is that we are very confident in things. We can predict them with Six Sigma, which is about ninety-nine points, a large percentage of nines from the area under a normal distribution, so if I ask you how long you have to count to be 95% confident in your result, you should give an answer that relates twice this standard deviation and now we know the formula for the standard deviation of this net counting experiment, so we can formulate our Li powder equation, let's say, to be 95% confident in other words: Sigma of that our count rate is within five percent of the true value, in other words, plus or minus five percent error.

We put our error percentage here and our true net count rate there, so this part here tells us the 95 percent confidence. This part here is our five percent. error, that part over there is our count rate, so we can substitute into our Sigma expression our quadrature uncertainty and figure out things like it depends on the information that was given, let's say before you go to the smoke shop, you take your Geiger . counter and for an extremely long time you count the background counts somewhere so let's say in this problem the known quantities we know our background count rate because you can do it in your free time at home and when I did this the result was about 25 counts per minute and the background counting time is known and when I did this to get 95% confidence of 5% error I had to do it for 67 minutes and now all that's left is to relate our count rate net and our gross count. time or our raw count rate on our raw count time because it's the same thing, so that's actually how you decide how long you have to sit in the smoke shop to count to satisfy what we ask of you. 95% confident that your counter eight is a five percent error, so let's start substituting this that's not mine so we can get rid of that, so we'll take that expression and substitute it as much as we can so that 0.05 CN is equals Sigma and there is our expression Sigma, everything is rewritten here. so we have C V over T V squared + cg/TG squared well what's next?

How do we relate TG and CG? Well, let's start with the easy part. What can we cancel or square or whatever? Just have someone shout it out. Yeah, so we have numbers for C B. and T B but not C G and T G we still haven't answered the question when you walk into the smoke shop and you talk to the owner and he says, well, you're going to sit here with a radiation detector. How long do you have to stay here looking at everything? It's strange that you want to have an answer, so if you get an initial estimate of CG, you can tell him or her that this is my approximate T G, at which point he or she will say yes or no depending on how they feel, so why not ?

We just start / - right / - 0.025 we can square both sides and there is a CN there we square both sides and we end up with 0.006 - 5 CN squared equals CB/TV squared plus C G/TG squared there is many ways to do it I want to make sure we do the efficient oh, sorry, those are not squares because those are already our standard deviations that had the square root there we go, that's more like, what's next? We have too many variables, yes. Come on, there's still no what? Because in this case the standard deviation is the square root of the count rate over time, so the squared standard deviation is just the count rate over time.

It was there in Perley or the expression that we have to correct, yes. that's where it came from that's right, that's not because it's there we're going well, tracking that's fine now that everything is corrected here what's next we have too many variables yes, not at all because there is a count rate here, so the units of standard deviation if this is the square root of the count rate over time, which is the same as the number of counts multiplied by time, sure, yeah, because again the count rate is, I'm sorry, it's a number about - uh, where did he go?

Yes, number over x squared. Although it doesn't sound good, let's see, wait, I think that although standard deviations should have the same units as the count rate itself, because they are additive, because they usually express some count rate plus or minus Sigma or two. Sigma is that they have to have the same count rate, so standard deviations are expressed in counts per minute, if your counts are expressed in counts per minute, okay, then you have too many variables, but it's also easy to get rid of one of them. CN or CG, do you have a question?

Great, so you're going to say the same thing I was going to do, great, so we'll take out our CN and put in a CG minus CB, okay and we're trying to isolate T G as a function of CG or vice versa, there are a lot of CG and not a lot of T, so let's keep the TG just so we have 0.000 six to five cg minus CB squared and I. I'm going to subtract CB over TB from both sides minus CB over TB equals cg/TG and I have to go over the rest of the calculations with you.

I think at this point we have it pretty much figured out, we divide everything by CG, turn it around and you end up with: Actually, I already wrote the expression I want to show you here, back at the tobacco shop, counting time, so I want to show you some of the implications of this expression, that number is there. just a more exact part a little bit of Sigma instead of 0.05 and let's see, yes, instead of 0.05 we had something much closer, so what I want us to see is this graph here, we have a good relationship now between the count. rate in counts per minute and the requirement was the raw count rate and the count time required to reach that five percent uncertainty.

Well, there are a couple of interesting parts about this equation, what are some of the characteristics that you notice? Yes, yes, if the count rate is extremely low, it will take an infinite amount of time, you're actually right on some levels, so if we have that expression right there, let me take it out completely so we can see why I want to show you something. of the math related implications for this, so if we had our counting time, what do we have CG over 0.0, say 2 5 CG minus CB squared minus CB over TB, at what point is this equation undefined?

Yes, that's correct for the condition, like Sean. said for the condition where 0.025 CG minus CB, let's call it C net squared minus equals CB over TB, these equations are actually undefined, which means that if your CB and TV, let's say, if the uncertainty, you stepped on the wire , if your background uncertainty counts A great experiment is such that you can never reduce the total uncertainty to, say, a five percent error with 95 percent confidence. You can't actually run that experiment because these uncertainties add up in quadrature if you try to reduce Sigma to one value. below that already, how can you do that?

You can't have a negative standard deviation, right? So what this really means is that when you're designing this experiment, even if you count for 67 minutes at 25 counts per minute, like we can do now. air that might not be enough to discern smoke store activity or source or whatever you're looking at with 95 percent confidence within 5 percent error, so let's look at that on the graph if We keep scrolling up. just by adding things to the axis and eventually we see that everything becomes straight and right here, about 49 counts per minute, suspiciously close to the background counts, you will never be able to get within this confidence and error interval, so there are always some concessions you can make in your experiment, let's see what's there, so sometimes you necessarily have to be 95% confident in your result, it depends on what you're doing or you necessarily have to be within 5% error, that's probably be the one that you can start sacrificing first, so you generally have to be confident in whatever outcome you're saying and be sure that you're giving an acceptable bounce so you can stay at 95% confident, which means where it's going to go. that heart, yes, here. which means staying at Sigma but then you can increase your allowed error percentage, so if you can't be within 5% error and I think the assignment doesn't actually say that for a reason, yeah, we don't tell you what to choose. but we do say try to get to 95% confidence, then the question is, over a reasonable counting time, how what: what error can you get with 95% confidence, the more air you allow, the less time you have to count and I want show you graphically how some of those things interact with each other.

Let's say you increase the count time, which we can do here with this slider to get the same background count rate, if you increase the count time, what happens to the uncertainty in your background? experiment, it goes up, it goes down or nothing, it's going to go down, yes, count for longer, the uncertainty decreases. I'm going to have to change the limits here to something more reasonable, so we were at 67 minutes and now notice as you increase the count time. although you haven't changed the counting speed, so it takes less time to distinguish what your source is, so let's say you count for less time in the background, you have to count for longer in the experiment until it just explodes, count for longer.

In the background, you have to count less time in the experiment to reach the uncertainty with confidence that you want to reach, for example, if you double the background counting time from 67 minutes to 134, then you can measure count rates as low as Growths of 42 counts per minute, so when you start going to the tobacco shop, let's say you count for a few minutes, get a very rough estimate of the count rate and then decide how long you have to let your fund build up to be able to distinguish the activity. in the smoke shop - with some confidence in some error, yes it definitely depends on location, so we will get into background counts and background radiation sources in about a month, but to give you a fast forward, it depends of its elevation to tell how much of the atmospheres protect you from cosmic rays definitely depends on location, so in New Hampshire the bottom counts a little more because there are a lot of granite deposits and granite can contain more than 52 parts per million of uranium and radium.

Granitesince I take a couple samples, I throw them in a lead hog, so I got a bunch of these. floating and I pass it down the hall and throw it into a detector and we count it, when are we shorting? I will irradiate two samples at a time because I have two detectors, which used to have four detectors. I ran four samples at once, so you irradiate, repackage it, count it while that sample, that couple of samples are counting, come down here, irradiate the next two so you know you're always irradiating and counting. I usually do ten minutes of radiation. for the short ones, I'll do it pretty quickly, I'll count five minutes right after I get the sample there and that's looking for things with half lights under 10 minutes.

The shortest half-life I'm looking for is for aluminum, it's two and a quarter minutes, but things usually have a lot of aluminum in them, so if I see aluminum pretty good for the short ones, I'll count up to about sodium, which is almost fifteen hours of life. longer average. I'll do a longer radiation account. a little overlay on my shorts and longs that helps me do quality control on things and if I run two standards I'll check that you know the concentrations of one of the standards and the other, there's another little thing q8, I don't know what else we have questions. pretty simple, yeah, what do we have, oh, yeah, yeah, okay, yeah, there was a lot of archaeology, did you know naa got really used to that?

I don't think we've ever done that here. Fred Frye, who is a retired EOB professor now. Earth's atmosphere. and Planetario did a lot of geological samples and yes, I forgot where it was. They did all the archeology. One of the things that na is really good for are rare earth elements that are difficult to measure with other methods. I mean, I didn't. you get very low limits on that and by selecting various rare earths and the ratios you can help identify where things are from in the world if you give me a tiny little bit, I mean, you know, I mean see, that's the rabbit, so it definitely has to fit in there, which I really like, yeah, excuse me, where are my vials?

Yeah, I used to have some smaller ones here, but you know, I should definitely fit in one of those. I like to see that guy, my usual description of what The sample size I like is if it's a piece that you would pick up with a pair of tweezers so it's not too small to pick up, you know you'll be able to find it, so no. powders, but you know, and maybe you could get them with your fingers, but 20 milligrams, 50 milligrams, 100 milligrams is right in the right ballpark, no, it doesn't matter, but we'll see what's coming and yeah, I might veto some things or not. .

I'll see, well, we have bricks everywhere, so when I take the sample out of there, I do the repackaging here and this is just a buffer between me and the samples that I'm working on. I don't have simony in the toe. now but usually I have the symmetry and a ring badge and then it comes here and I do this is where the heat sealer is so I can seal it here and then I'll have a pig over here oh yeah these are just painted lead bricks and you know who have been here longer than me so sometimes things just sit somewhere and you never move them yeah they think they're older than me too so this lab has been doing something I don't know since the 70's, I think someone else, full size bricks this size, 2 inches by 4 inches by 8 inches, weigh about 25 pounds, there are usually a ton of them floating around, not that one.

Pretty full size, you know, they're heavy, they're lit, okay, when people ask me because I work in the reactor too, they say if there's something dangerous in the reactor, the dangerous thing is dropping wet bricks on your feet, that's why I have a piece of steel if I put my toe wrong, yeah, I'll probably break it. I don't want to think about that and they move much bigger things in the reactor when you go to the reactor, still yeah, so I mean, there's that giant crane there and Move, you know, five tons of armor pieces and that's the other one. dangerous thing and really big things are falling.

We've never dropped anything that big. I think someone dropped a steel plate on his foot once, that was the worst, you know, like four. one foot and a half inch steel pen yeah, okay, yeah, you know, when people trip and fall off ladders and they're the usual industrial accidents, okay, yeah, yeah, I mean, I've broken a few , but no, I'm not here, for sure, and I'll see you in a month or so and have fun running the reactor. Oh, good morning friends, you are here to do an experiment in the reactor. It is in two parts, the first part increases the reactor power and the first increases the reactor power using a low ground absorber called a throttle rod. and then the second part will be to reduce the power of the reactor by using a high value absorber and the high value absorber would move much faster and we don't want to run the chance of it accidentally going too high, so we use the low value one. absorber on the way up and a high value absorber on the way down, okay, and I just want to show you the controls with me today, it's Tim to do this experiment, we need to license the people here, one that has less of an operator of senior reactor in both.

Tim and I both have senior licenses, so we've got that covered. The only way you can really do these manipulations is if you are in my training program as a facility training supervisor or if you are in a program that needs them to actually operate the reactor and the program they are in fits that definition , so I just want to show you some of the reactor controls first. We have our Shin Blade controller, which basically moves one of the six Shim blades at a time, whichever one is selected. it has a slide and we can change which one is selected with the wedge blade selector switch this switch here is a governor rod that will allow you to move the governor rod up and down our blades are fixed speed which means they can only move at a speed at exactly the same pace all the time moving the wedge blade up or the regulating rod up grip with your hand up and pull up or turn up until it stops we get just a little bit it doesn't move anything, It has to move everything. the road until it stops and then the damper will move outwards if you want the blade to stop just release it it is spring loaded and it will go back to the neutral position and stop moving if you want to drive something in the inward position take a grip above your head and turn down and that will bring the damper back in, release it, it will go back up and stop the blade from moving while the governor rod, the experiment we're doing, basically changes the power by half a degree. megawatt and we are currently at 500 kilowatts, we are going to take the reactor up to one megawatt and then bring it back down to 500 kilowatts, so before we can do this you need to log into our logbook as a trainee in the console.

We will show you the correct way to make entries. As you do them, it will continue and then do the actual movement. So the first one will use a regulating rod to move the rack and turn on what's on. reactive power we have about nine different instruments that tell us what the reactive power is at all times, but those of us who are going to pay attention to our channel 7 and channel 9, these two channels are the ones we use to basically tell us what the power is. reactive is channel 7 it is what we control our act of automatic control if you look at the regulator rod you will see that it moves up and down on its own that is because it is changing the power according to what channel 7 sees it does if the channel 7 sees that the power level is going too low, it will cause a normal rod to move outward to increase the number of neutrons, making the rack part of the world.

Channel 9 is a linear power channel and basically tells us what the power level is based on. in our graph that we created, it doesn't show megawatts or kilowatts or anything like that, but rather it shows a current coming from a chamber and that current is then converted to megawatts, etc., so now we are at 500 kilowatts and 8.5 microamps . on this channel and that's 8.5 micro amps equals 500 kilowatts you're going to take the rapper to 1 megawatt and since it's linear it's going to be double that so 17.1 now you have to be careful when you increase the reactive power so when you start adding power to the reactor by raising the regulator rod, you don't want to bring it in, you don't want to keep raising it until it reaches its value because you also have to stop the power increase, so we have two rules. that we have to follow one in the power level or in we have a period there in the period the period of the reactor is the amount of time it takes to turn off the power to increase in the power level that we are in, we cannot go period less than a hundred seconds, okay, here's one of three period meters, one here and one here, which can be selected from two different meters, so as you lift up the regulator rod, one of the things you need to keep in mind Note is to ensure that the reactor period is not less than 100 seconds.

If so, you have to stop following the blades. The other thing we need to keep in mind is to make sure the Channel Nine power level doesn't exceed where you're going. not exceed, but we also want to make sure that you can actually control the reactor, it's called control feasibility and what that means is that when you get to about 80 percent of the power level that you're going to get to, since We are going up to one. megawatts, that's about 800 kilowatts, you want to be able to put the absorber in and hold it, you'll buy the regulator rod in and you'll watch the channel nine value, it'll slow down until it actually starts going down again once it hits that value and you see it go down, Now you know that you can control the reactor and prevent it from disappearing.

The power of the rack increases continuously, so what we are going to do is have you when you reach 80% of the power level you are going for. at what turns out to be 800 kilowatts, you will begin to increase or lengthen a period by pushing the damper back on the regulator rod and continue to hold it down. You will see that the number not only stops increasing but actually goes down a little. a little as soon as you see it go down a little release the throttle stick, you haven't stopped the power at this point you just increased or decreased the speed at which it goes up and then the power level still goes up but a lot. at a slower rate than before and once it reaches the power level you want to stop at one megawatt, keep pushing the regulator rod in to keep it at that power level, once it is at that power level it will do a entrance. in the logbook that basically says you've reached the power level you're going for and then we'll go down in power, so once again make an entry in the logbook that says: I'm going to reduce the reactor power to 500 kilowatts and then this time we will use a wedge blade, the wedge blade is worth a lot more than a regulating rod, about ten times more than the wedge blade, excuse the regulating rod, so things will happen much faster so you can enter this and the power of the frame will change much faster than before.

Same thing as you get closer to the power level, start with 500 kilowatts, you don't want to go too low and go too low, so around 600 kilowatts or so start to wedge it. Take the blade out to slow down how fast the power levels go down, that's fine and once it's back to where you started, we'll use a regular dipstick to adjust it and keep the amount of power where we want it to be. There will be another entry in the logbook and your round of time at the console will be completed, so with us today we have to go to MIT soon, so it's actually my training program and they have already done a lot of these manipulations, Sarah Come on, I'll take it.

I'll take them, so we usually sit back and watch, if at any point you don't feel comfortable doing something just let us know, we'll ask you to take your hands off the console and we'll do whatever needs to be done. to keep the reactor safe, but keep in mind that we are a factor of 10 below where we would launch automatically, so it would be very difficult for you to get somewhere where it would cause a problem without us being able to stop you, okay? So it's normal, I don't know if you want to move or something, but we, the supervisor, usually sit right in your way so they can keep an eye on what's going on.

Well, you can go ahead and make the announcement that you are like that. We were starting the power manipulations and then the last verse announcing that we are done with our manipulations at this time, the reactors in automatic control and when we do these manipulations, the reactor operation will take manual control, which will cause an alarm to sound. and this only happened for the first time, so one of the things he will do nextto enter into our logbook, no we will do it at the end, is that she will take manual control of the reactor and the alarm will go into the console and she will respond and that should be the only time she hears this alarm because we will leave her in control manual until the last participant has done his manipulations.

Okay, now she's raising Reg's rod up to where she sees the number on Reg's rod going up, the period is getting shorter, it's not at infinity anymore, it's getting closer to one hundred seconds and channel seven and channel nine They are increasing in value. Another way to look at it is that we have one screen in front of the operator, those three screens two. of them are just for evaluation, we don't actually use them to control the reactor, they are based on a system that has not been approved yet, but we are testing them to see how well they work so you can see that the level of power on the far left is going up, the one in the middle shows what the actual power level is that we saw: 500 kilowatts, sorry, up to 630 kilowatts and increasing, and the period that was infinite is now around 160 seconds, so She is looking until she sees. the value of 800 kilowatts here on channel 7, channel 9 and she started driving with the normal rod, so she is slowing down the speed with which the power increases, leaning and you see the period lengthening, it is no longer in 150 160 seconds, it's approaching infinity again, so she's demonstrating that she could stop the reactor power if she continued to wield this regulator rod.

No, she's approaching megawatt. One of the things she notices is that when she started the wrecker I was around Oh 300 oh three ten and she's almost back. up to there when you increase the reactive power you basically open a valve and let more neutrons in and when you get to the place where you want to be you basically close that valve again so you basically add reactivity and then you stop that reactivity plus by bringing the absorbers back about where they started from now on, okay, one megawatt, go ahead and make an entry in your logbook so that once again she has experience, she's been doing power snatches and manipulations for a while, when the rest of you sit here, it will guide you through them. logbook entries you are making etc. yes 30.6 yes so one of the things that could change the reactor is xenon it is a poison that is added to the reactor while we run the poison as it absorbs neutrons, does not lead fission and has to open paths. of being made in two ways to have it removed, one is direct fission and the other is decay, that is the way it is produced, the way it disappears is basically absorbing a neutron and decaying into another isotope and it's fine , yes your sword sucks and what happens is when we reduce the reactive power the way we remove most of the xenon from Verna, basically the neutrons are absorbed by the fission process.

The fact that we don't have the reactor at a very high power means that the amount of xenon in the core. it's not being removed, so we actually start, the energy would actually want to go down the tunnel, so it would have to do a lot of regions and over a period of time, that's a very large amount of reactivity that needs to be compensated for for this experiment. although we shut down the reactor yesterday and started it up early this morning, so it's not as big a factor as it normally would be after doing a denow that the reactor is running out of power, I think we could get at least one more person , so once again the reactor power is long, you can see on the period meter, it is in a negative period and the reactor power is decreasing, it is almost at 500 kilowatts. uh taking the shock out again to slow down how fast the power levels go down and when you're done the shin will end up at about the same point where it started at thirteen point four and two inches from the bottom of the core, cops say closed.

What's wrong with you two? 30.8 is fine and that's the end of the exercise.