 So, good afternoon, everybody. I hope you don't fall asleep. My name is Carlos Guerrero. I work at the University of Sevilla, since recently, before I've been working at CERN in the end of the experiment for the last six years or so. So, I'm going to be talking about, let's say, but the title is tricky, you know, but it's Challenges and Solutions to Radiative Capture Experiments. But I understand you've already seen some talks about time-of-flight experiments. We've even worked with data. So, already, even those that didn't know before now are familiar with the topic. Then there were some air-matrix formalism talks by Frank Gunsing. Also, you saw kind of resonances. We see how we treat the data, so on. Then this morning, we saw activities in Los Alamos. So, that was the part of the dance, calorie meter. So, you are in context. So, my goal is somehow to go through the radiative capture experiment, what are the observables, how are the different ways of looking at them, the different techniques, which one is better, what are the good and worst, let's say, characteristics of each technique, and to think a bit together about some solutions. So, you will see something like this along the talk so that you don't fall asleep. So, I will make a question, and then we try to talk. So, some people will know the answer. Some people will think of something new. Well, let's see how it works out. Let's try a list. So, course on radiative capture. What we measure, radiative-nation capture, this is all I'm going to talk is devoted to neutron capture cross-sections using time-of-fly. But there's also a radiative capture for thermal, and tomorrow there will be some talks, two talks by Thomas Belia. So, these I won't go into details at all. So, it's time-of-fly, neutron capture. Then, why using in different talks already? So, it's nuclear technologies, it's astrophysics, it's, well, some porters outside with very nice applications. Yesterday we saw one about hazard chemicals in the body and so on. So, there's plenty of use for this, right? But I will focus in the how. So, we have facilities, we have techniques. So, facilities, I will briefly mention some, but I will focus on the techniques to do these measurements and then challenge these solutions, right? And there's so much information that most of the times there are no references or acknowledgment, but this is not my work. I just take information from everywhere, okay? So, if you need to know more about something, just feel free to ask. So, what's neutron capture? This is trivial, right? There's a neutron coming, there's a nucleus, and then you form a compound nucleus. Once you form a compound nucleus, the excitator can follow different paths. You can re-emit the neutron. That would be elastic scattering, okay? You can remain in an excited state and emit the neutron. That's in elastic scattering. You can fission as we saw this morning, but you can also just get rid of the energy by emitting gamma rays. So, we will consider that all these gamma rays, that could be one or could be up to, I don't know, five, seven, eight, it depends. The path, the number of gamma rays, okay, will be every time different, depending on the number of levels available, okay, this we will see next. So, you have these nucleus, right? This set A nucleus, sorry, this one. You capture you are in a compound nucleus and this is in the neutron separation energy. So, now this compound nucleus can get rid of all these energies. So, it goes usually from five to 10 MeV. So, depending how heavy is the nucleus, you will have more or less levels. So, every time you will follow a different path. And of course, if the neutron energy of the incoming neutron is high, this five MeV, and you have an internal one MeV, then the available energy is not five but six. So, it's the neutron separation plus the neutron energy, okay? So, we get rid of all these energy with gamma rays. And now we have to detect them, okay? So, well, all these levels, pseudo-levels up here are the ones causing resonance. So, we have to look at them. So, how does the cross-section look like? So, well, using something like this, right? The one over V region. These are three different nuclei, aluminum, iron, and urinary. So, mainly what I want to show here is that depending on how heavy is the isotope and other things, this resonance region is not always at the same neutron energy range. So, for example, in our case, if we want to look at resonances and the resonances are up here because we want to study iron, then we need to go to a facility with very high resolving power. If we are interested in actinides, as you saw this morning in Los Alamos with 20 meters fly pad, you still get very nice resonances down here. But if you want to look at them up here, you will see just something smooth. So, it's important to keep this in mind, right? Now, I know you know about the motivation, so I just want to show a couple of things. So, the interest of N-gamma nuclear technology, you know that our fuel would start usually with U5 and U8. So, you capture and you do fission, but you can also keep capturing, producing other isotopes. You produce here, I put the quantities produced of spent fuel, what is going to be a nuclear waste at the end, right? And for new reactors, for managing nuclear waste, for using further the fuel for everything, we need to study all these isotopes in different energy regions, right? Because it depends if it's fast or thermal reactor. And what is common to all these isotopes? So, if you want to measure the nitrogen capture cross-section, what is the common thing here? Well, I'd say they're all heavy, right? Actinized, but the main thing is that they will always be available only in very small quantities. You're going to get three grams of plutonium-241, right? So, you always have to deal with very small quantities, they are radioactive. Always. You may have only alpha, mainly gammas, it depends, the energy of the gamma can be higher or smaller, it will kill your experiment or it will be easy to get rid of, but always be radioactive to some extent. And some of them are fissile. I mean, all of them will fission with high-energy neutrons, but if we talk about low-energy neutrons, there will be some of them sub-fresol, some of them will fission from the beginning. So, if they fission, more difficulties to the experiment. And this is what we're going to see how we do. Now, when we go to astrophysics, it's kind of similar, right? It's the same thing happening. We have iron, everything below is produced by fusion reactions and so on. And then we start with the chain of nitrogen capture, then you arrive to an unstable nuclei with very short half-life, you go up. Up, you keep capturing, so you produce all these up here, so I go a bit faster. You get to these fancy points. These are called branching points, right? So, here there's a real competition between capturing a neutron and decaying. So, these are very important because if you know the cross-section and the number of neutrons that you have in the star and the nitrogen energy distribution of the neutrons, then you should be able to predict how much goes this way, how much goes this way. And then later you can look at the abundances up here, down here, different contexts and so on, and you can learn about stars, about nucleosynthesis. But, again, well, I keep going with this, okay? So, you see another branching point here, selenium 79, for example, right? We keep going. Another branching point here, which is krypton 85. So, you have plenty of those. And, again, what's going to happen? These ones are radioactive. So, basically, you have the same problem than before. You, they're radioactive. They don't exist in nature. You have to produce them. Get them from a spent fuel, produce them at that reactor. They are different ways, but every time you will have very small mass, they will be radioactive, so the activity can be dangerous, can be high-energy gammas and so on. So, here, again, small quantities are radioactive. So, every time we measure, to measure a stable gold sample, it's easy. It's been, well, it's not easy. It's difficult, but it's been done a million times, and still we can do it every time a bit better. But as soon as you get to these complications, it's when starts becoming tricky. So, how do we see neutron captures? We said it's like this. Neutron comes, compound nucleus, gamma rays. So, how can we detect neutron capture? What would you look at? Just feel free to talk. Loud. So, you want to look for these gammas. What else? So, somehow you will look to this. So, you can, let's say, the outputs is two. It's a nucleus that can be radioactive or not. Okay? And some gamma rays. So, let's say we want to look at here. So, he already mentioned, if it's radioactive, we can look at the decays. And if it's not radioactive, then the gammas. No, okay. So, if you want to look at this, if it's radioactive, easy. You look at the gamma rays. Easy. Again, every time I say easy, take it with the, okay? Never easy. But what if you want to look at this? And it's not radioactive. Is there anything you can do? Charge particles from where? No, because this is, well, this is excited. It exitates by emitting these gammas is at the ground state. So, you can just bring your sample and do mass spectroscopy and see how many were produced. Right? So, you don't need it to be radioactive. If it's radioactive, it's easier. Otherwise, you just go into your machine and see a fraction of the original ones that became A plus one. There you go. Right? So, look from all the angles. So, we say, let's see. If we look at this, look in a mass spectrometer. Okay? So, accelerate our mass spectroscopy. AMS. This is done. Okay? Usually. An experiment. And if it's radioactive, we look at the signatures. So, we will, the problem here is that we will have to know, I mean, it's easy to find the gamma ray. A germanium detector uses a gamma ray. But then you need to know how often this happens, right? If you look at one, and how do you know that? So, you need a lot of input for this. But it's available in some cases. Otherwise, you have to do an experiment to see how often that decay happens, and then you measure the cross-section. Right? And what if you look at this? How would you look at it? One gamma ray, all of them, high resolution, low resolution, how do you count capture cascade? So, they will be from zero to 10 mm. So, if you take all of them, this is what we saw this morning with a calorimeter, right? If you put a detector that is ideal, 4 pi, high resolution, high efficiency, then you just get an energy, the positive, that is equal to this natural separation energy. So, this is called total absorption. Good. Any other way? You may not have a calorimeter. A calorimeter might be too expensive. So, the question is, yeah, sorry. So, look at one gamma. And sorry, gamma just means you look at one gamma, and you know that that happens 10% of the times. And that's it. That's what you meant or not? Right. But there's no one. Okay. So, the A plus decays. And sometimes it goes always to the same levels, no? So, it may be one gamma line that happens 5% of the times. Again, you could just, a small detector with high resolution, you look for that one, and you got it, right? Now, again, you need to know that that happens 5.5% of the times. It's another measurement. But you don't need to look at the whole cascade. You look at one, you're done, right? Anything else? Any other way? You could just say, well, if there's no background in the room, I don't care. I put a detector every time there's a gamma, it comes from the sample. No? And if they are background, then I just measure the background. And what remains comes from the sample. So, you don't need to detect the whole thing. If you detect the whole thing, it'd be better. Because you can, if you deposit 10.2 MeV from the separation energy, nothing else can give you that energy. So, you got it. If you just detect the gamma ray flying around, you don't know where it's coming from, but you can do a measurement with the sample in place, a measurement with the sample out of place, the difference in gammas. Now, what you have to know is the efficiency of detecting those gammas, okay? So, there's a lot of input needed, but there are different ways, no? So, I try to summarize like this. So, we can look at one characteristic gamma ray, and this is called prom gamma analysis, okay? Detect the gamma ray cascade. So, with a calorimeter. So, they are full cascade. Sorry. Detect one gamma ray. You'll detect the cascade by just seeing one of them, no matter what, okay? Or seeing all of them. So, here you have more or less the names, okay? So, this will be the talk of tomorrow morning, but in a thermal neutron beam. So, these, I will go in detail. These are called total energy detectors. If you see one gamma ray, you don't know the, really the energy. The trick is to see, when you see a gamma ray, what's the efficiency for seeing that gamma ray, and how probable is that if there's a cascade, there's such a gamma ray, and so on. So, it's a bit complicated. So, you have all this, right? Sorry. The signature will be the decay from this. So, this is eep radioactive, okay? You are activating this sample. From something that is stable, you are making it unstable. So, the signature that this happens is that you have a decay line that is well known. That's what I mean by signature, okay? So, it's the fingerprint in your spectra that that sample is there. Okay, so these ones, the problem is that they give limited information because you have a bunch of neutrons, and if you have an energy distribution of the neutrons, what you see at the end is a convolution between the neutron spectrum and the cross-section because all these reduce to one number, number of nuclei produced. Well, if you look in a time of flight to this, okay, to the only of these three, then you see that function of neutron energy. So, I will focus on this, okay? So, now, a bit about time of flight experiments to explain the data that we will see later and also to explain the exercises of tomorrow morning. Easy. Time of flight. You produce all the neutrons at once, ideally T0, but there's some spread here. As you fly along a beam line, then this neutron starts spreading because of different velocities, and then the top is related to the neutron energy. Easy. So, you just put a sample in your beam, and if you want to measure the total cross-section, you have the neutrons that go through transmission, right? If you want to measure capture, well, if you want to see scattering, you measure neutron scattering, and if you want to see a reaction cross-section, you just look at reaction products, gamma rays, alpha particles, whatever, right? So, you need a facility. This is obvious, but you have to think of everything, right? A facility providing the neutrons. A detection system. This is what we're going to be focusing. A sample that we're not going to be talking about, but it's most of the times the key and the difficult part. It's a difficult framework to analyze your data afterwards. So, briefly, the end of facility because I think it hasn't been explained in detail, so maybe it's good, okay? So, this is a turn, and we are a collaboration. I'm part of it, and some people around here is part of it. This is in Switzerland. So, it's a collaboration, Europe, Asia, and the United States. So, we have colleagues from India, and Japan, and so on. So, we study mainly nuclear physics, technologies, basically physics, and we're done with the neutron beam, and this is CERN. So, what you all know is this, right? Is this the LHC? CMS, Atlas experiments, but this accelerator doesn't live here alone. So, to say, there's a whole chain of accelerators that they all feed each other and bring the protons to these energies and these intensities. So, the two nuclear physics experiments that we have at CERN are these two. It's all there, here, and end tough. So, this is end tough, and it works since 2001. What we do, we are in the transfer line between this first accelerator and this second one, and the protons get out, and we use them to produce our neutrons, right? So, this is the top view, and so this is, well, Atlas is somewhere here. These are all the main buildings from CERN. So, there's an accelerator, goes to 1.4 JV, goes to 20 JV momentum, and then we launch these over a lead-spallation target. It's like one cubic meter, so to say, cylindrical. And then, spallation happens, and there you go. So, spallation happens, and then we look at this spallation target from two areas, let's call it. We could have experimental area one, it's nearly 200 meters, and it's horizontal, and this is 20 meters underground. And since it's 20 meters underground, we also have an experimental area that we call ER2, that is 20 meters above. So, we have 20 meters and 200. So, at 200, higher resolution, less flux, at 20 meters, more flux, lower resolution, plus backgrounds are different and so on, but that's the main difference, right? So, some pictures, we always show the experimental areas, I thought it was nice to show what is a beam line, how a beam line looks like, right? So, this is controlled axis, the beam line is only a tube. So, no, so fancy. This is our magnet. So, in spallation, there's also charged particles produced. So, especially the high energy ones are very harmful for us. So, we have a magnet here that deflects all the particles. And then, we have first the collimator, and this is what we call the second collimator. So, this is, no, no, this is the second collimator. So, at the other side of this wall, we have our experimental area. So, this is open, okay? This is half open. So, we have polyethylene and iron, okay? And then, the neutrons come from here, and this is our experimental area. And then, the beam comes here, and then here, outside the experimental area, we have our electronics, our changing room to go in clean and so on. Yeah, why? No, it's half open only for the pictures, it's nice. And mainly because we go there, because we have two modes. We change the size of the collimator. When we measure capture, we make it small, because samples are usually small, so we want all the neutrons in. The neutrons out, because they will produce background problems. When we measure fission, usually you have to make the samples very thin. That was mentioned this morning, so that the fission fragments escape. So, if you want to put enough mass, you have to make a big sample. And then, we change the collimator and make it 8 centimeters. So, the way we do it is that we dismount like this. So, when we dismount, we profit to take the picture, okay? So, two modes. Capture, we call them capture and fission mode, but sometimes we measure fission with a small one. It depends, okay? So, this would be our experimental area one. Okay? So, again, protons let target, and this just shows the different resolutions if you want of the two experimental areas and some pictures. So, this is the inside of experimental area one. This is our total absorption calorie meter, so I will explain later about it. It's if you want similar to the dance detector. It's a ball with a lot of detectors in with high efficiency. Okay? And then, this is the director general of CERN. When he was digging the first hole for the experimental area two to make the building, because this is only three years old. So, three years ago, he wasn't there. He came. We started, and now it looks like this. Now, it's built. We are running. There's one poster there about this. So, basically, the trick here is that the beam is vertical. So, it's quite tricky to put the detectors in place to hang things and so on to align. So, it's easier horizontally. So, we have this structure. We feed. These are our monitors. And then, between here and here, let's say, we can just make a puzzle. So, we put a neutron beam line, capture the detectors, vision. It depends on the experiment. Okay? And some preliminary measurements, this from last year. But, as expected, we have in this experimental area two, we have something like 50 times more flux than in experimental area one. So, in the rule of thumb, you can measure 10 times less mass. Right? In the same time, or 30 times less mass. So, new measurements become possible. Okay? Some of the things we do, but I will go fast just in case you work in the field and you want to know. When we measure vision reactions, most of the times we've used P-PAC detectors, either this configuration or one that is tilted. And, when it's tilted, we have different angular acceptance efficiencies. So, you can measure angular distributions and so on. And the best thing we do here is that some references here is that we are able to measure up to one JV cross sections because we have 20 JV protons. So, we produce neutrons up to 20 JV. And with very fast detectors and very low pressure gas so that we don't produce other reactions. So, we are able to go up to one JV. So, this is very nice. Then, this is something that is up and running now for the first time. This is, I think, more or less similar or the equivalent to the spider detector that we saw this morning. So, we want to measure, this is Steph, who was made at University of Manchester. It has been used already at ILL in Grenoble for thermal neutrons. And the whole point here is a bit different than spider in the following sense. So, maybe the figure is not so clear, but we get the vertical beam. So, neutrons come up like this. Here is our target. And then, we have two arms. So, again, we measure the two energies and the two velocities. We get the signature of the fission fragments. In addition, we get all this. This is a sodium iodine detector array. So, we have, I don't know if it's 8 or 12 simulators. So, what we want to look is, at the same time that we look at the fission, I mean, at the fission fragments, we will tag here. And with this detector, we measure the prom gamma rays from fission. So, we get, and we can do a correlation between the prom gamma rays and the fission fragments. So, you get a lot of information. The only problem there, of course, is that you cannot put so many gamma ray detectors because the fission detector takes a lot of space, right? So, this is quite big and it's running now for the first time in experiment area two, and they installed it like two weeks ago. So, no results, but it looks promising. Then, this is the experiment of Thanos right there. So, the poster is outside. This is measuring, this is what I showed before, right? The tube comes up to here. So, they put this micromegas fission chamber to make one experiment. It's one experiment of fission in plutonium 240. So, when we measure this in experiment area one, the activity of the sample was so high that first, the measurement lasted for several months and the activity damaged the detector. And second, the activity itself was very high compared to the signal. So, what do we do? We went to experiment area two. And now, there's something that I will repeat later because I'm going a bit fast, but if we have, I said, how many more neutrons in area two than in area one? 50 times? Yes? But, we are 10 times shorter. So, everything happens in 10 times less time, right? So, if you look at the flags as, let's say, neutrons per unit of time, you have an increased factor of 300. And then, what the activity of the sample was killing you in experiment area one, it's non-negligible, but it's much less of a problem in experiment area two, right? So, this, without showing any results, is just how the gamma flash looks like and how we look for signals, so it won't go into details. This is kind of proving how an experiment that is impossible at 200 meters, because the flux is not intense enough, you can go to this one and then you can make it, right? Now, we also measured N-alpha reactions with this is a set of micromegas detectors. So, for example, this is an experiment Sulfur-53 N-alpha, and this is related to Boronetron-Capture therapy because sulfur can be in some components, again, not going into detail, but we measure N-alpha cross-section with micromegas and with diamond detectors. So, if you want to know anything about that, you ask me later. And then we have Capture, right? This is where I'm going to focus the rest of the talk. We have our calorimeter and we have one C-66, low-efficiency detector that I will explain afterwards. And I put this down here only to tell you that samples, which is something that I won't be talking about, the samples that we are measuring now and also there's a couple of examples outside are very difficult to get. So, in order to get one milligram of Talium-204, for example, that you have the poster outside, it's tricky. So, we had to get a group of chemists, a nuclear reactor, CERN and ENTOV together to get this, and then we do this kind of experiment with this, the Texas that you will see later, okay? So, ENTOV is gone. Questions? How about ENTOV? So, let's say... well, let's say 50, okay? So, to get the numbers. So, we get 50 times more flux just because we are closer. So, geometric acceptance if you want, right? Now, the time that the neutrons need to travel 200 meters is 10 times longer than what they need to travel 20, okay? So, because you're closer, because of the geometry, you get 30 times more neutrons, but if you want to know the number of neutrons per unit of time, okay, everything happens much faster in year two than in year one, right? You know what I mean? So, for example, all the neutrons between relativistic to one electron volt take 13 milliseconds to travel to experimental area one, like this, okay? They only take 1 millisecond to travel to experimental area two. So, you get 30 times more neutrons in 10 times less time. So, when you want to compare the number of neutrons to the, for example, the activity of a sample that happens, you know, 100 disintegrations per second, then in experimental area two, you gain a factor of 300 because you get 30 times more neutrons in 10 times less time. Now, I mean 500. It's 10. You get 30 times more neutrons in 10 times less time. So, 10 times 30. 300, no? Okay. And, no, because it's, no. So, what you cannot do is the number of, that it goes with the R-square, the number of neutrons, because most of the neutrons are emitted forward, for example, then the geometry of the spallation target comes into play. So, the one thing that we know because we measure it is that you have 30 times more neutrons. They happen in less time. So, neutrons per unit time is bigger. So, the resolution is worse and that has to do with the distance, right? So, if you want, it's 10 times worse and the time production is the same, but they fly 10 times more. So, it's like two times the spread. So, two times more. When you go to high energies, you don't see resonance as well resolved, right? But then you can, so, you choose or you do the experiment in both, right? More about end-tough? Okay. Then we move to capture again. So, after these parentheses, we've mentioned that we want to measure these gamma rays. And, either we look for a catastrophic one or at least one gamma ray or all the gamma rays, right? So, the question is, again, we haven't talked enough. So, what kind of detector would you use for this? So, if you want to do prong gamma analysis or total energy detection or attack. So, we will do this a bit fast, but it's to keep you thinking. Okay? So, for example, if you're gonna do a total absorption calorimeter, this is obvious, right? Do you need high intrinsic efficiency? Yes. Because you want to detect the full cascade. So, the bigger the efficiency, I mean, the better. And, do you need geometric efficiency? Yes. The bigger the better, because you want to get the full cascade. So, what you're gonna do is a ball so that you get 4 pi. And, what material are you gonna use? Even in high intrinsic efficiency for gamma rays, you're gonna go for a high set material so that the interaction probability is high. Let's take, so you might, let's take a barium fluoride, lanthanum bromide, something like this, and you have to make it big enough so that the probability of a gamma transversing the detector and escaping is small. So, for example, in our case, the barium fluoride, they have to be 15 centimeters thick. Okay? If you make it 5, then they will escape. So, you think about this and you come, it has to be high set. It has to be big. It has to be thick. So, it's a lot of money, you find the money, you make it. Okay? So, for example, if you wanna look at the prong gammas that we, a characteristic gamma ray, do you need high intrinsic efficiency or not? Anybody? Not Thomas because he's the expert. You do, why? But he will say not. I think, I mean, the technique doesn't require high efficiency. It requires that when, what it requires is that you have high energy resolution so that when that gamma ray happens you don't confuse it with another one. But if you have low efficiency you just run for longer. No? I mean, the technique doesn't require high efficiency. But then if you have high efficiency, better. You save time, you save everything. But the technique as such, it doesn't, while the tack, you really need high efficiency for it to work. Right? Yes? So, usually here we use high purity germanium detectors. It's always used. Now, you could also try to do with lantern and bromide if it's a light nucleus or something. But usually that's what you use. While here, you would never make a tack out of germanium detectors because nice resolution, low efficiency. So, it doesn't really work. It's against the principle. Right? Now, these total energy detectors is a bit more tricky because you just need to detect one gamma ray. So, you don't need high efficiency or it only saves you time. You don't need high energy resolution because as soon as you detect it, that's it. It's more tricky, but it gives you an idea. Okay? Always energy resolution is welcome, always geometric efficiency and intrinsic efficiency are welcome, but sometimes you don't need them. So, these we will go later, exactly. The point with this technique is that you have to detect one gamma ray, but only one. Okay? So, it's one and only one, so to say. So, what you need indeed is low efficiency but not so low that it takes forever. So, if you want the probability of getting two is the product of the efficiency. So, if you get 1% efficiency or 3% efficiency, you're fine because the probability of getting two gammas at the same time is very small. Okay? So, you could fill up this table, think a bit and then come out with the actual solutions that we have. Okay? So, the choices are never random. So, the three techniques. So, this is an example at Japan. So, this is another espalation source. It's like in Toph, like Los Alamos. Right? So, in Toph Park, they have these facilities called ANRI. Okay? So, it's a 17... Okay, here. This is 21 meters fly path. So, it's like Los Alamos, like end of year two, more or less. And what they get, so I move here, they have two detection system. This is sodium iodide to make total energy detection and this is the one where they look for a characteristic gamma ray. So, they look for prime gammas characteristic of the decay after capture. So, one material is going to be made of, germanium. Right? But they want to have some efficiency. So, they make an array. But they don't make an array to detect everything. They just want to increase the efficiency. Right? So, it looks like this. They have two clusters, up and down and four, eight, coaxial germanium detectors. Beam comes this way. So, nice energy resolution at the many crystals. A lot of material around because you need the anti-compton and so on. But, in principle, it fulfills the criteria to measure this. How does it look? Well, if you tackle to a neutron energy resonance, okay, so these are not my data, so I just show a bit. Okay? This is the energy deposited in the germanium detector for a measurement of curium 244. Okay? So, curium 244, highly radioactive, levels not known so well and so on. You put the germanium detectors and the cascade always follows different paths. But, sometimes, it goes to the same level or the same transitions. So, this is what you see here. Some gamma lines are really clear. So, this is this 252, this 381 line and all the red lines have never been seen before. So, what people knew before are these lines from low energy levels. What they've been able to see is also these lines which I would say is the first transition from the captured state to the low-lying states. Okay? Since the low-lying states, there's only a few, this transition is probable. Okay? To the different states. So, you get this. And now, if someone tells you, this transition happens 10% of the times, you count the number of... the number of events where you detect this energy, you multiply by a factor of 10, you get your capture cross-section. Right? So, this will be the tech acro-statistic gamma ray. Okay? Now, clear? Now, this is more tricky. What is this total energy detection technique? What we're going to do is that after capture there, imagine that there are three gamma rays coming down. We just want to detect one. We don't care. Okay? But then the problem is once you detect one and subtract your backgrounds and so on, what is the efficiency of your detector? Not of the detector. Of the detector we can measure, but it's what is the probability that a cascade emits a given gamma ray, that this gamma ray gives you this energy and then you detect the cascade. So, here there's a mathematical trick. Let's see if I can make it clear. And it's the following. What is the efficiency for detecting the full cascade? It will be one minus the product of missing each gamma ray. Right? It's one minus the product of missing the first one, missing the second one, missing the third one. And what remains is that you've seen at least one of them. Right? So, it will be this. So, now, if the efficiency for each of these gamma rays, which was the condition that he was asking before, is small, when you do this product, all the cross terms, they vanish. You end up having the efficiency for detecting the first times the efficiency for detecting the second. And this is there are small numbers, they vanish. Right? So, when you expand this, it comes out that the efficiency for detecting the captured cascade is just the sum of the detecting each of the gamma rays. Okay? It's not trivial. So, you start from here and you end up here. So, now, imagine that you have a detector which efficiency is proportional to the energy of the gamma ray. Imagine that you have it. Okay? So, the efficiency would be a factor K times the energy of the gamma ray. Okay? Yes? The K comes out. So, you have K the sum of the energies. And the sum of the energies is always the capture energy. Do you follow? I'll do it again. Everybody? So, it's a trick, right? It works. It's an approximation, but it works. If epsilon is small enough, this product becomes the sum. And if, and this is the big, if I have a detector which efficiency is proportional to the energy of the gamma rays, this is K energy of the gamma ray. The K comes out. You have the sum of the individual energies and the sum of the individual energies is the energy of the cascade. So, you get something like this. The efficiency for the cascade is just proportional to the energy. Then it's very easy, right? Because every time you detect a gamma, you know that the probability for detecting this is proportional to the energy of the cascade. And this is how you get through. So, it's not simple, then you have to do other things. The question is, do we have such a detector? Is there a detector that, which efficiency is proportional to the energy of the gamma ray? In principle, no. Because the interaction probability changes because you have entrance windows, because you have thresholds, and, well, the cross-sections for the interaction of photons with matter changes. So, then it comes to the complicated part that I won't go into detail. If you do a mathematical treatment with simulations, you can change the response of the detector so that the detector fulfills this condition. So, you do mathematics behind, knowing the response of the detector to make the detector response proportional to the energy. And if you do that, then you got it, okay? So, this is a bit of information because you will have the slides there. You characterize with simulations the response of your detector and you find the response matrix and you find these, they're called waiting factors to be multiplied by the detector response, give you this thing. So, this complicated, you don't need to understand the details, but the principle, yes, okay? So, how are these detectors? Well, we said they have to be low efficiency, right? So, low efficiency, we just take any organic scintillator. Because it's going to be light, it's going to be cheap, it's going to have low efficiency, okay? If this was a crystal, the efficiency will be multiplied by 10 or so. So, we just take, this is inside what we have is benzene with deuterium, okay? Photomultiplier and then you got your detector. So, for 10 or 15,000 euros, you get your detector and then you can do these experiments. So, it's cheap. So, why do we say is deuterated benzene instead of this would be a normal molecule, right? But we changed the hydrogen by deuterium. Anybody wonder why? There are too many questions already. The question is, if we are measuring in a neutron beam, the neutrons are scattered, okay? And they can be captured in your detector. How do you distinguish between a capture happening in the sample and a capture in your detector? They will both emit gamma rays. So, since there's a lot of hydrogen here, you change it by deuterium and the deuterium is not willing to take more neutrons. Well, a hydrogen is just willing to take neutrons. So, by doing this, you just reduce the background induced by order of magnitude, okay? That's why they're always called the C6D6 detectors, which were mentioned also this morning. And they look like this. Another thing we do at NTOF is that usually when you buy a detector, it comes like this with all the aluminum housing. So, we do our own housing and windows and so on, all made of carbon fiber. So, again, instead of producing capture in aluminum, you collide with carbon and you scatter. And carbon is not willing to take neutrons either compared to aluminum. So, you reduce the intrinsic background that is going to be caused by your detector. So, these are tricks to get rid of the neutron scattering background, okay? Last one, this is the easiest, right? If we have a total absorption detector, we have this cascade. So, for example, the peak efficiency will be just the product or the efficiency for detecting each of the gamma rays, right? So, and ideally, if all the efficiencies are 100%, then you get a detector with 100% efficiency. So, what is the response of your detector? So, these you will see tomorrow, okay? So, pay attention. In principle, you look at the energy deposited in your detector, it's going to be equal to the neutron separation energy. So, perfect, beautiful delta Dirac, here. Of course, not the case, no? Two things will happen. Sometimes you have Compton and you lose the photon. If you make it thick enough after one Compton, you may deposit more energy, but you don't make it infinity. Go, or sometimes they will deposit the energy in the capsules of the crystals and so on in the photomultipliers. So, you lose energy, right? And, in addition, you have a resolution. You don't have a Germanic detector. So, this becomes something like this. You still have a peak, like the photo peak, it's not a photo peak, it's the sum when all the gamma rays deposit all the energies. So, the better the calorimeter, the more counts you will have in the peak and the better resolution, more looks like a peak. And then you have all these from losses. Still, if you look at all the counts and it's a good calorimeter, maybe they don't fall in the peak, but most of the times, if you emit two, three gamma rays, at least one of them will deposit some energy. So, the counts will be here. So, maybe the total absorption efficiency is not full, but the detection efficiency that at least deposits some energy is very high. And that's how a calorimeter response looks like. Why do you see the tail? Well, this is, in principle, it only goes down here and this is doing something that I will say later, which is, what if there's a capture somewhere else? That will, for example, if you have a capture in the aluminum that surrounds the detector, that has an 8MV separation energy and uranium has 5MV. So, you will have a 5MV, your peak from uranium and high energy counts from capturing aluminum, for example. That's the high energy background, not high energy from the neutron, but high energy gammas from somewhere else. So, it has to be fast enough. So, not two gamma rays. If you have two gamma rays, it's fine because they are part of the same cascade. But it doesn't matter because here, what I'm putting is the total energy deposited in the crystal. So, I don't, that's what I want. I want more than one gamma ray going together. So, I don't care in a sense, then you care, but you don't care if you deposit two gamma rays in two crystals, one MV each, or they go to the same one. You have two MV in any case. So, the sum will fall in the peak. What is different is if this tail could be from, if you have a high counting rate, then you can see the two cascades too close in time as one. So, the energy is bigger. And then you put these tails typical from pile up. We understand? OK. So, total absorption, this is the one at 10. So, we have 40 crystals. And this is the one at Los Alamos. They have 162 crystals. So, many more channels, better multiplicity. What does it mean? It means that since there are more crystals, they can know a bit better if there were two gamma rays, three gamma rays, one gamma ray. And this gives you additional information to remove background, to understand physics behind and so on. But it adds complexity too. So, it's a trade-off. It's just two options. So, to say. And they both have, this was mentioned this morning, they both have these balls here, OK? And they're both rich in lithium and hydrogen. Why are they there? Because we say the following. We say, well, one problem is that neutrons are scattered in the sample, right? And then, if they are scattered in the sample, they can be captured somewhere else. And they give a background. So, what we do is we put neutron absorbers inside. So, ideally, if you were able to absorb the neutrons and do nothing to gamma rays, you're happy. All the gamma rays go through, all the neutrons die inside. This is not the case. But if you put a lot of lithium inside, lithium-6, then lithium-6 will eat. Well, you put lithium and hydrogen. The hydrogen makes the neutrons to slow down. And as soon as they are slow, the lithium eats them. You got rid of the neutrons. And these are very light materials. So, the gammas go through almost without interaction. So, it's the best trade-off you can have, OK? So, these are neutron absorbers, OK, that we put inside. So, a future with the same technique is, what if we are able to do one of lanthanum bromide or anything like this? In that case, we would gain a lot of resolution. The problem is that these materials tend to eat are more, let's say, sensitive to neutrons. So, I mean, total absorption is what it is. You can only look for new materials. And new materials could be these. So, there are people trying to think if it would be worth or not and so on. You have better resolution. It helps a bit to get gamma ray lines, to get better total efficiency, total peak efficiency, OK? So, a quick example of the TAC, and these are the type of data that we're going to see tomorrow, OK? Is we have protons, expedition target neutrons. We have a collimator, a magnet to get out of the particles, another collimator that shape the beam. In our case, we also have a neutron beam monitor here that counts the neutrons. Also, we have a monitor here that counts the protons, OK? Neutrons come. We have a sample amidst gamma rays. So, what is the information that the TAC is going to give you? It's going to give you neutron energy, because you measure the reactions at each time. It's going to give you the total energy deposited inside. And we also look at how many detectors we're firing, OK? If it was everything in one, in three or four, which doesn't need to be exactly the number of gamma rays, because a gamma ray makes a scatter, or two gamma rays goes in the same one, but it's somehow proportional. So, it helps to remove background to understand and so on, OK? So, for example, Neutron energy spectrum, red is background, OK? So, this is plutonium 240 capture. So, you see all the plutonium resonances. We zoom in. We take a resonance, a 58 electron both, and we say, OK, let's look at the detector response for this time of flight corresponding to this energy. And then, you see the deposited energy. And it looks more or less like I said before, right? We have a peak at 5.3 MeV, which is the Neutron separation energy. And then, we have a tail, OK, of, if you want partial losses, OK? Makes, I mean, this is a real one. And then some high energy counts, so to say. So, these are very background subtractives and nicely treated and so on, but it doesn't look as different as a perfect total absorption calorimeter, right? Do you like this? Well, one thing I didn't tell you is that this is already for multiplicity bigger than 2. So, this is not really the cascade. It's how we see it when we remove the low energy gamma rays, OK? I mean, the low multiplicity events, OK? But the main thing is that this is not related to Compton. This is related to the number of cascades in which, for example, the difference between this and this is like 300 kV. So, if you lose this one in the absorber, so it's like a shifted peak, but it's not, I mean, it's smooth because the cascade goes through different paths, OK? Did everybody follow? So, it's not like you have one gamma ray and you have the Compton, I mean, you have the photo peak and the Compton. No, you have four gamma rays, three of them, if, for example, you have four gamma rays, all of them leave all the energy, the event goes to the peak. The 100 kV, then you come here. If you lose two of them, instead of multiplicity four, you have only multiplicity two plus a lower energy, so it appears here. If you lose three of them, it has multiplicity one, so it doesn't fulfill my condition. It's out, OK? So, it's very powerful, but you don't look directly at the cascade. You look from different views. And this is what you're going to do tomorrow, play around with this type of data, see how it changes, OK? So, multiplicity. So, you see the number of crystal firing, it goes, the maximum is around three and it goes up to seven or so. OK? So, the techniques, why and so on, yeah, you will see this now, OK? We will see how this background happens and how we solve it. About the techniques, questions, anything? Because we move forward. Because now we're going to see what are the main challenges and how we solve them. Imagine that we understand perfectly the techniques. We know how to measure gold, iron, if you want like easy samples with enough material. We choose our technique and what are the main problems now? So, to me, because I suffered them, but someone else can have a different set of challenges. The main problem is that you have a small mass. So, if you have a small mass, the number of capture reactions is small, you have to minimize the background, right? How do you minimize the background, right? That's the beginning for astrophysics and technology is the case in both. Well, in most of the astrophysics, interesting ones. You will need to eliminate this background somehow. For example, you put a shielding around the sample. Lead, that's it. You kill the low energy gamma rays. That's a choice. You need to eliminate or minimize the activity background, OK? Now, another one that is related to your question is, if we go here, what if the elastic scattering is much bigger than the captured one? Then the problem is that if you scatter a thousand, every time you capture one, you scatter a thousand, all you will see will be neutron events, if you want. How do you deal with that, OK? And the last one is, if it's fissile, then it's even worse because you scatter, you produce fission. Fission produce a lot of gamma rays, bigger energies, high multiplicities, there's neutrons too, so more background. So, this is like my list of headaches, no? And on top of that, you have efficiency calculation, dead time corrections, and so on. So, first one. If it's small mass, if it's small mass, you need to get rid of background. So you need to select only the events of interest. And here, the more powerful technique is, I don't mention here, but the, if you have one gamma ray, the transition at 352 kV, the background will be very small there, because it's very difficult that any background event gives you exactly that energy. So, if you look at a single energy, maybe you don't have this problem, OK? But, in our case, with the tag, for example, it's easy if you want. So, what you are seeing here is, in this case it's neptunium, not plutonium like before, what you see is the total energy deposited in the tag for different conditions in multiplicity. OK? So, this is if I take all the events, I get the black curve. If I say only the ones with multiplicity bigger than one, red. Bigger than two green, bigger than four, blue. OK? So, you see, if you put no conditions, you see a lot of peaks. So, what are they? You see them here, right? So, this is ambient background. Everybody that has worked with the scintillator uses the potassium from the walls. That is there. And it's there, and if you have a small sample it will give you more counts than from the sample itself. But, we are lucky because if we put a condition of multiplicity bigger than one, this is one gamma ray. So, most of the times, it hits only one crystal. So, when you go to multiplicity bigger than one, it's almost disappear. It's not fully disappear because you may come to and you go somewhere else. If you put multiplicity bigger than three, it's gone. Get rid of one background. What is this? 2.2 MeV. 2.2 is very famous, no? What is it? Capture in in hydrogen. So, we see it in the actors all the time, right? So, we put our absorber. We kill the neutrons but every time they say capturing hydrogen, there's a 2.2 MeV gamma ray emitted. Again, we see it very nicely. We get rid of it by putting condition multiplicity bigger than one 2.2. Is there any other way I can get rid of them if I don't want to put multiplicity conditions? No, but you have them. So, you have the data. They are like this. And now you say, well I don't want to put multiplicity conditions because I'm very interested in low multiplicity events. How do you get rid of them? No, no. The experiment is done. I have to treat my data. I have to live with it. Well, it's easy. You just put a threshold in energy above 2.2 MeV. That's it. Everything that is below, you don't take it. So, you have this in attack. You have this multi-parameter if you want selection tool. So, you say, okay, I take only events above, let's say, 2.5 MeV so I don't care about anything that is low energy. The only problem is that my efficiency drops. But if I'm able to calculate how much it drops, that's it. And what is up here? I see other peaks. This is my capture peak. I see others. This is because my sample is inside a titanium capsule. So, there's a lot of capture in titanium. And I see some energy peaks of titanium. How do I get rid of them? They are capture events. So, multiplicity conditions don't help much. So, what I do, I say, well, if capture currently deposits its energy up to 6, I kill everything that is higher energies. So, I remove part of it because the tail comes down here. Still, I have some background. So, I have to measure it, but I have to minimize the background. Okay? Now, if it's very active, how do I get rid of the activity? If it's attack, like before, it's easy. The activity I didn't mention is this that goes up at very low energies. So, I put a condition in energy bigger than this, or multiplicity bigger than 1 or 2, that's it. The activity is gone. The only problem is if it kills my detector because of pileup or something. Otherwise, it's gone. Otherwise, how do you do it? I mentioned this before. You go to a facility where the number of neutrons per second is much bigger. So, the activity of the background as a capture to background ratio is smaller. So, there are some measurements that you cannot do in every facility. If it's highly radioactive, you go somewhere else, and this is what we did with the plutonium. We couldn't get rid of the plutonium. We need the mass with the activities there. So, you go to experimental area 2, more neutron flux, that's it. Right? So, this is the showing the factor of 300 that I was mentioning before, but let's move on. What if I have neutron scattering much bigger than capture? So, this is the example of U8. Okay? So, you have in blue is neutron scattering, and in red is capture. So, you see that neutron scattering is already bigger higher than capture, and fission is down here. So, fission is not a problem. So, this is a problem. This is worse. Iron has three orders of magnitude. So, you have to scatter a thousand neutrons before you capture one. So, I told you we have these two detection system. Which one do you think is better for measuring these difficult reactions with very high neutron scattering? So, imagine a neutron scatter is here at the center. What's going to happen? There's so much material it's going to be captured somewhere. Background. While fat, this one made of carbon fiber with all the hydrogen made into the deuterium, then the neutrons going through, they're going to just go through or make elastic scattering. So, I will have much less efficiency. I won't be able to look at multiplicities. I won't be able to look at the deposited energy because it's a scintillator that you just measure the Compton. But, neutron scattering is not a problem. So, if you need to measure the other ones, you cannot go to attack because you will see nothing. You will see bad neutrons. So, you go to this one. Okay? This is done already. So, what I'm giving you here is just the ratio of the efficiency for detecting a neutron with respect to the efficiency for detecting a gamma ray. Okay? So, in this case, if we take this red one, the carbon fiber one, this is at the level of 10 to the minus 5. Okay? This is to the minus 1. So, it's 10 to the minus 4, 10 to the minus 5. While it's here, I tell you now. While for the attack, it changes with energy, but it's at the level of 10 to the minus 2. So, it's like 1%. So, it's three orders of magnitude difference between one and the other. So, high-netron scattering, you have to go to low-set materials, small detectors. Okay? And for astrophysics, most of the time, we are in this region where this matters. So, in astrophysics, many times, this is used instead of attack. Now, we don't have time. I will keep going. Now, this is uranium 5. So, this was mentioned this morning. This, on top of being radioactive, having a small mass and scattering equal than gammas, is fissile. So, it can be sufficient, more gamma rays, neutrons. So, what do we do? And this was mentioned this morning. How do we do? How do we distinguish between gammas from capture and gammas from fission? By tracking the fission fragments. Okay? So, if you have a way to... Well, if you know when the fission is happening, you just don't count those events. Right? So, what we do, exactly, well, this is... Yeah, this is with the nitrogen scattering on top. So, what you do is that you combine two detectors. You say, okay, I have my tack that allows me to measure capture cross-section. I just need to get rid of all the fission. So, this was mentioned this morning for plutonium. You just put a fission detector. This is a micromegas. You just put it inside. So, you put two together. And if you have a perfect fission detector, you're working what is called anti-coincidence, right? If there's fission, I don't look at the tack. Every time there's... So, every time I see an event in the tack, I say, is it consistent with the fission? Yes. Throw it away. No. It can be captured. And so on. But the fission one, you get rid of it easily. Right? Now, this is tricky because you have to put even more material inside. And inside here, you have to close the bowl. So, how do you... So, you saw this morning, they have these tiny P-packs. We have these tiny micromegas, so it looks like this. So, this is the tack open in two parts. A beam to go in through. And then we have a gas chamber going from here to up here. Neutrons come this way. And then inside this gas chamber, we have... We put an arm going inside and has three micromegas detectors with three samples. Okay? And then that's it. So, this is one of our volume fluoride crystals. This is the signals come out inside the tube. That's it. You measure. Then it's difficult because you're putting material, the detector induces background. Then the efficiency for this one is not 100%. So, you don't tack all the fission events. But we can do things. So, this is just to say, this again, the deposited energy in the tack. And this is the peak that we expect from capturing U235. So, nitrogen separation energy is here. Then this is from background in aluminum or something. And then if we look at the events that are in consistency with fission, we see this. And it's expected, right? The fission spectrum, the gamma rays from fission don't have a structure. They just have a peak somewhere here, which in the detector is seen here. They go to higher energies. If we put this in log scale, we see that it goes up to 20. And if we look at the multiplicities, also we see that all minus the fission, minus the background, has the multiplicity. And if we look only at the fission, it has high multiplicity. So, it makes sense. Now, of course, we have to validate, see how we do one, so on. Okay? So, then we put our conditions like before. So, we only keep events below the nitrogen separation energy. So, all these fission fragments are out by default. Okay? So, we still get 100% of our capture events, but we throw away already 30% of our fission events, right? And here the same. We made a cut to keep 100% of our capture events and remove most of the fission events and so on. Okay? Because we want to put these conditions because we won't always know when a fission happens. The detector will have an efficiency. We want to put conditions that will reduce the fission as much as possible. Okay? So, doing like this, one can see this is the counts from fission and this is the counts from capture. So, you see that some resonances, for example, look down here. Okay? It's the same with two conditions. So, we just look down here. We see some resonances are dominated by capture, right? You see here. And some resonances are dominated by fission or are equally probable, more or less. So, we are able to distinguish this. So, we did this and we made the measurement in the low energy region and where ENDF is well known and we were in good agreement with this. So, we just published this and it was fine. And then we do a more serious experiment. And this was nice because we made it to the front cover of European physical journal. It was a nice job. Okay? So, yeah. Sorry. The height. Sorry again. Again? Well, no. One is if I look only at events. So, in the red one, I'm not looking at the tack. I'm looking at the fission chamber. So, it gives me the fission cross-section. And in order to know the capture cross-section, what I do is I look at everything that is not fission, which is the blue, and then I have a normal background like in the other experiments. So, of course, when you analyze at the end, you will subtract the green from the blue and then you have pure capture and in the red you have pure fission. What do you do with this? Here? Yeah. Here, for example? Yes. But they are independent. This is just that the capture cross-section for fission, sorry, fission cross-section here is a bit bigger than capture. So, they end up being more or less of the same size. Well, for some of the resonance are strong capture and almost no fission and the other way around. So, every time it changes. But now you're measuring both independently or you can do the ratio. So, we have two masses with radioactive samples with neton scattering and last with fission. So, what's next? I mean, there's no any new technology here or anything. We do every time better because we have simulation tools because we have better analysis programs maybe, stronger sources, higher quality samples. But detector-wise, we haven't done anything new. This was done 50 years ago or so. So, to my knowledge, the newest thing that is going on is what if we want to reduce further the background? So, imagine that we get rid of the fission, blah, blah, blah, blah. Still, we have very small masses, very active but the background is killing you because you have very small number of capture cascades. So, what can we do to reduce further the background? So, this is from last year. This is the work from Tessa Domingo and he's also within NTOF. So, we're doing tests on this. What if we apply imaging techniques to our scintillation detector? So, this is used a lot in medical imaging. So, I don't know if you're aware but basically something like this. If you have two scintillators, here they are of the same size but usually one will be thin and the other one is called the absorbent, it will be bigger. But the point is if the first one is thin enough so that you have a Compton here and the second one is thick enough and high to stop this gamma ray to produce a photoelectric effect here. You can say, well, the total energy of the gamma ray is the energy deposited here plus the energy deposited here. And then you also know the energy that was deposited here. So, with the balance of energy you can know the angle of scattering. And if you know this direction from this, let's say from this channel it's a pixel, sorry. From this pixel to this pixel with the change of energies you know the angle so you know that if an event happens here and here with such an energy it has to come from a gamma source in this cone. While if it deposits so much energy here, so much energy here and so on, you know that it's from this cone. So somehow with this imaging what you do is that you have some information about where the gamma ray was coming from and if you were able to do this because you say, well, I have my detector here and my sample here. So I will put conditions so that I only look at what is coming from here. If something is coming from there scattering in the walls, I don't care. Potassium in the walls. If it's coming from back here because it was captured in my photomultiplier I don't care because it doesn't come from here. If it's coming from scattering in the windows I don't care because it's out of my region. So if you're able to do this and with enough efficiency and nice enough I don't care because you will only see the capture. So who cares if you have small mass? The only thing you have to take care of is that you're also, even if neutrons are scattered they will be capturing your own detector so they will not follow this. Only randomly there will be one background coming from somewhere that fulfills this condition. So if you do this, it's great. And well, yeah. Sorry, sorry again? Yeah, it could be. So my source will be here and if it means a gamma ray I will get it. But this angle compared to 4 pi is a factor of... I mean also, I mean the background is not homogeneous. It will come surroundings of the samples or from the floor we were mentioning this morning so all those will go away. They will only deposit in one of them. And if they go like this and like this it's not coming from the sample. So of course it's not perfect. You will not only get capture gamma rays but I mean the factor is huge. So let's look at the reality and see how good you can do this. But ideally you get rid of, let's say, all the background. So let's try it. So the plan, and you can even put many of them so you can do something like this if we want module 2, 3, 4 like not a calorie meter but you can make like a high solid angle because the efficiency is small. You have to detect both with the angle. So you can try this. So 2, 6, 6 and background coming from like everywhere with this I-TED imaging total energy detector then the gain is a factor of 10 or 20 or so. So it will be great. So what it was done and this already submitted for publication we did this year is to try to make a very simplified imaging detector of this type. So it was done like this. You made a pinhole collimator made of lead. And a cone in the other side. This is seen from the back. And you have a pixelated detector. So your first point of interaction if you want, you know it. It's this pinhole. And the second point of interaction is whatever happens in your detector. So you can see where it's coming from. Of course you have a lot of material here that will produce captures so it's not something to do measurements it's something to see to start learning about this possibility. So this more or less to see how good we can do imaging with this we put a gamma ray source in different position that we know of course and we try to reconstruct them and you see the reconstructing position as red circles and the real position as black so you can really tell where the gamma is coming from. The only problem is that you have so much mass that you start producing backgrounds and so on. So you just have to the technique works more or less you have to get rid to improve it somehow. So these are four C66 detectors. This is how it looks now and we just put our detector down here so we try to look at the gamma rays from capture. So this is how the picture looks like the four C66 detectors and this is the pinhole shielding with a small opening at the center and this is the detector right behind. So we want to know, if you want we want to look only at this direction. Anything that comes from here we don't want. And this is how it looks. So this is superimposed more or less. I don't know if you can see here. One, two, three, four detectors this where the sample is and this was a short measurement the only thing we did, so don't expect magic here, is we put a calibration source like a gamma ray source. This is the sample position. So we put a gamma ray source here and a gamma ray source here and we wanted to see if we see if we are able to say where the gammas are coming from from the sample, from the calibration source or from the other calibration source. So for example, this calibration source we see very well we can see, but here with these colors you don't see much some captures from the sample but the efficiency of this is so small that we didn't see much. And what we see is the detector here I mean here there's a gamma ray source and what happens is that it's making scattering in the crystals. So finally we see like coming from somewhere else because there's material in between our detector and the sample. So if you want imaging can be done even in this easy way and doing it like this we did only like a factor of 2 gain in background, but this is the worst we can do. So now the plan is to really do with these 2 pixelated detectors and try in the lab and then try an experiment and in a sense you will have total energy detectors, but with better background rejection capabilities because everything I told about background today was with attack. With the C6 you just get all the gammas that come in you cannot do much but setting a threshold maybe. So if you have this you have the good of the total energy detector and with some good of the background rejection so it may allow measurements that were impossible before. So I think that's it so 10 minutes in case you have questions. So basically relative capture is used in several fields main challenges for me apart from every measurement is difficult but would be this samples, radioactive nitro scattering and fission issues background is most of the time the main problem 3 main techniques used nowadays with this pros and cons and then imaging for maybe the future so we will try next year and so on and that's it. So now questions I think we still have 10 minutes for some.