 I will go into matter and explain you how we are doing the experiments. I will start and main topic of the presentation will be talking about transmission measurements, which are the principles, the base principles behind these measurements. I will try to explain you how we determine the background in the facility using black resonance filters and then I will pass to explain all of these in a example using the American 241 transmission measurements. And then if I have time I will enter, I started to explain also about the reaction cross-section measurements, the principles and how we calculate the reaction yield. So we can jump. So we pass directly to the transmission measurements. Transmission measurements is to measure the total cross-section. So we are, for measuring the total cross-section we are not adding all the channels that I show before, but that we are measuring is the other part. We are measuring which neutrons are not reacting with the sample. So those that are traversing, that is what we call transmission, the fraction of neutron being traversing the sample without interacting with it. So this is in opposition with the reaction yield, that reaction yield is the fraction of the neutrons that are interacting in a certain way with the sample. In this case that I show here is a capture experiment, no, you detect the gamas that are reacting in the sample. So you see here the type neutrons that are not interacting, while here you are detecting the products of the reaction. So these are completely different approaches. The interesting point, the first interesting point of this approach is that in the transmission experiment the theoretical transmission is directly related with the total cross-section. Like this formula, while in a reaction cross-section the reaction yield is not directly related with the reaction cross-section, but also at least you need the total cross-section to measure. So this is the first advantage of the transmission experiment. The second one is that we measure the experimental transmission performing the following experiment. The first we measure the neutron being without any matter on it, and then without the sample in the beam, and then we put the sample and we measure how many neutrons are still reaching the detector. Doing this simple ratio we already get the experimental transmission. And the main advantage of doing this ratio is that we don't care about the neutron flux, we don't care about the detection efficiency because both are canceling the ratio. And then, like this, this means that if we are fulfilling certain conditions, we have directly the total cross-section obtained from the experimental transmission. And this is possible to do when we have what we call good transmission geometry, which are the following conditions. First, we have to require that the neutrons that reach the detector pass through the sample. Then, the second, that if a neutron is scattered in the target, it doesn't reach the detector. And the third is that we have to collimate the beam to have a parallel neutron beam and the sample should be perpendicular. This we can get it was going to long distance and with a special geometry. And this is what we call a good transmission geometry. Everything is doing by collimation. The most important part of a transmission measurement is the collimation. Then, there is a... This is very fast. This is how it looks schematically. Then, the fly pass in a transmission experiment at getting at 50 meters. We have here the neutron source, the crown grade welding that separates the banker from the fly pass. The first part of the fly pass with the collimator here in black. Then, the half path of the fly pass is the sample with some filters that I will explain later. And then at 50 meters we put our neutron detector. In this case, the lithium glass detector that is already John explaining his presentation. But there is a fourth condition that we have to fulfill to get very nice cross sections in transmission that is that the sample should be homogenous. That means that it has the same thickness everywhere in the sample. We have the same thickness everywhere in the sample. If we fulfill that, we can get very precise, very accurate cross sections. These are some pictures of the experimental setup, the fly pass that I showed schematically before. Here I showed what we call the sample station at 25 meters. So you can see here the sample and some filters, the soulful filter and other filters down here. You see that we put then in some kind of tray that we can move remotely. So we can put it in and out of the bin very easy with only programming the engine. And then here I show the lithium glass detector that already John presented the schematic view. Of course you don't see. It should be inside the black plastic bag to avoid light entering in the detector and causing noise. And this is what you have. I mean you have only the samples with the filters and the detectors. And with only these two components, with the proper cylinder, you can do the measurements. This is the lithium glass detector. You use it in the region of the resonance and up to hundreds of kV. But you can also perform transmission measurements in the fast energy by using a detector, like a fast neutron detector for example based in the elastic scattering cross section in hydrogen. But the measurements that we perform in gelina usually are with lithium glass. This is what I will show. So now I will try to explain to you how we determine the background in gelina for these transmission measurements. What we use is that we call the black resonance technique. The idea is to put in the bin next to the sample. We put a material that has a strong absorption of neutrons at a certain energy. So for the time of flying corresponding to this energy we remove all the neutrons that are coming in the bin to the detector. And put in different filters. For example I show here the case when we put the sulfur that I show before, a cobalt filter and abismus filters. We have these dips here that are giving to you. The bottom of the dips provide you know where is the background. Where is the level of the background. And how it works. So exactly this idea is that the principle in this in gelina is a white source you have your bin, neutron bin with all the neutron energies. So for example if we look at the, we have neutrons that are coming at this energy, 132 electron volts. And these neutrons at this energy are coming at a certain time that is given by these formulas. If we now put in the bin a material like copper that has a very strong resonance at 132 electron volts. The cobalt will absorb all the neutrons that are coming in the bin with this energy with 132 electron volts. So in principle we should not have measurements here related with the bin. But what we will have is the background. What is remaining is the background. At these backgrounds comes because for example from natural relativity or contribution because as Jan explained we are a multi-user facility. So we have different flight paths that are, you will remember now there is like they are exiting from the target hole. So we can have neutrons that are scattered in other flight paths and come to our detector. Then we have, this is a background that is independent of the time. But then we have also time dependent backgrounds. The first one is related with the gammas that are coming with the bin. These gammas are not stopped by the cobalt filter. And the main contribution of gammas is coming from the capture of the neutrons in the water, that produce 2.2 mega-electron volt gammas. It results that these gammas cannot be distinguished from the neutrons with the lithium cis-glas detector. Because this high energy at these gammas deposit more or less the same energy that the neutrons. So it's a background that we have to take into account. Then the second one is neutrons. It's a background due to neutrons with higher energy but that don't reach the detector directly. But only reach the detector after scattering on the pipes or in the material. So after scattering they reach the detector at it results that because they have higher energy but also longer flight paths they reach the detector at the same time that corresponds to the neutron and to the 132 electron volts. So this also will contribute to the background in the deep. And then the last one is that this famous overlap neutrons that Jan started to spray. No, because we are a facility, a pulsar facility with a high frequency. Usually we work at 800 hertz. That means that between one pulse at the following one we have a separation of 12.5 milliseconds. You can do the calculation you want. So that means that all the neutrons in a pulse that arrive to the detector with an energy that applies that arrive at the detector after this 12.5 milliseconds will overlap with the following pulse. So some of them will arrive to the detector at the same time that corresponds to the 132 electron volts. So we have to also calculate to estimate this background and consider this background. In principle to avoid this background we usually use what we call overlap filters. Cascmion ou borontén filters that removes the low energy part of the spread flow. But mainly with the boron there is always neutrons that are remaining. And this is how it looks, a typical background for a transmission experiment, but it is composing in the different components. You have here the time-independent background, the constant background, that for example we can determine the background for an experiment if we close the shutter. So in principle there will be no neutrons coming in the bin, but all the neutrons that are coming for other flight paths and the relativity will come. So we have studied this background like this. Then we have the gamma background that is contributing mainly at high energies. This background, this is standing dependent also we can study this background by removing the neutrons from the bin and leaving gammas and that we can do it putting the polyethylene in the bin so we remove the neutrons so we can study the gammas. You can also have scattered neutrons, that is this component here, and finally the overlap neutrons that are coming here. This also we can study what is the contribution of the overlap neutrons by for example changing the frequency of the accelerator. If we change the frequency for example at 50 years, the next pulse will arrive much later. So we can study, if not we have to cut here. This is corresponding to a cut of the 12 milliseconds corresponding to the 800 earth. But if we change the frequency we can study this and we can see what is the shape. Usually when we are doing an experiment we can already taking this tail we can already extrapolate and estimate the overlap neutrons that we will have in the next ring. So this is more or less the technique that we use. The only thing is that this has some price. We have to be very careful when we use this black resonance technique Anything that you put in the beam of course will remove neutrons but also it removes background. We will see this because we will see what happens for example. Here I show you the transmission spectra that we obtain using a manganese sample that it presents already itself black resonance filter. So already with the sample we can have an idea where is the background. If we now put one germanium filter we will see that of course you get more black resonance, more here but also in the depths of the manganese you can see that the green is below the blue. That means that the germanium filter is also removing some part of the background that is reaching the detector at this point. The situation is even more clear if we put this big Sulfur filter you see here that the difference in the background after putting the filter and without the filters so we have to be very careful when we put the filters and to account for these effects we have two possibilities that is to correct it we can do two things. The first thing that we can do is use different filters with different thickness like this we can extrapolate the background that we will have if there was zero thickness filter. And the other option and this is also quite simple is that use fixed filters always in the bin so we don't care. They are there, the fixed filters are there when we measure with the sample and without the sample. So it's like you don't need to correct for them because it's already a characteristic of your bin. So I will try to explain a bit better now when doing the real experiment. This real experiment is a transmission experiment in the Amelicium 241. This Amelicium for the region of interest is the resonance region here. These are the resonance coming from the Amelicium and this is the spectrum that we obtain with the Amelicium in and this is the spectrum that we obtain when we remove the Amelicium. For this experiment the three fixed filters were used Sodium, Bismuth and Cobalt that were there in both cases in sampling and sample out so in the ratio they will disappear. And we can use these filters at high energies because this region is not of interest for us. We are interested in the region so we can leave it there and this is not affecting the resonance analysis that we will do. But for example if we want to use tungsten and silver this will affect. So what we do is to get the full shape of the background is do another measurement when we include apart from the fixed filters, tungsten and silver filters so in that experiment we determine the shape and then when we go to the real experiment we only need to adjust the background level using these points here and these points here. So that's the idea. So when you have already characterized your background you subtract it to the spectrum and you make the ratio and you obtain the transmission of the sample. And in this case for the Amelicium this transmission is as accurate as at the level of 0.25%. So with this number you can have an idea the powerful of this method not to measure cross-section that you can get cross-section well below the 1%. When you have already your experimental transmission that you have to do is to extract the resonance parameter so we go back to the theory I recover part of the jump presentation here we represent the refit code that is the code that we use to extract the resonance parameter for the resonance analysis. What we do is we modulate the transmission that we will have putting the sample characteristic putting the facility and detector characteristic in the response function that he explained in detail previously and what we do is less square feet between this model and the experimental transmission that we measure. This is done for by refit and we can obtain the resonance parameter the best values are just adjusted to the experimental data. So this is how we obtain the cross-section with a transmission experiment. If we now pass to the reaction cross-section in the reaction cross-section as explained before we have to measure the reaction yield. Now the situation is a bit more complicated in both sense. First for the theoretical reaction yield you have also to know the total cross-section as for example you can take from the libraries of doing dedicated experimental mission but if you are not but only in the case of a thin sample you can forget about higher order terms and use the first to encade the serial to this path. But in any case you will have to know also the total cross-section and the reaction cross-section both of them are affecting the reaction yield. And only in the case you have infinitely thin samples like it could be the case for example for certain efficient experiments that the targets are very very thin then in that case you get a direct relation between the yield and the cross-section but only in this case. In capture experiments this is not usually the case usually you have thick samples and if you have thick samples even the self-shilting correction is not enough you have also to apply multivase scattering correction or what this is multivase scattering correction what is happened? Part of this part of the gammas that you detect in your detector is coming from direct reactions direct capture in the neutron but for some cases the capture that you measure is not produced by the neutron daily but for the neutron after scattering in the sample once or even more than one time so in fact what you have is that the cross-section the energy at which the neutron has been captured is not the energy given by the time of flight that is completely different the relation between n and m-prime is given by this formula I don't know why it's not I think it's too simple so the energy between the neutron and the scattering neutron is given by this relation you see that is depending on the angle and in the atom and this implies that you have instead of having a clear resonance if you have a thick sample you will have things like this in your jilt how it's possible to explain this this is the case of the 56 iron resonance at 1.15 kV you see here that the big resonance is coming from the direct capture of the neutron but then if you have a scattering and then a capture you will have a contribution that is the blue curve and even if you have more scattering you will have a longer time and these shapes are coming from the following expressions that I showed you before the blue peak is coming because for the possibility of having a scattering and then capturing in the target there is a direction that is privileged that is the perpendicular direction because this is a pump cake like a pump cake sample the diameter of the sample is always much bigger than the thickness of the sample so that is playing this peak in the blue curve it's corresponding to this energy so the peak is corresponding to the energy you put in the formula 90 degrees and then this shoulder is corresponding to the maximum energy that the neutron the neutron in the scattering can give to the energy the neutron in the scattering can give to the nucleus and then the last shoulder is a combination between the peak and the shoulder and then also this is for the theoretical reaction gel but also for the experimental reaction gel it's also more complicated to determine for the reaction gel you have to determine not only the counting rates but all of these parameters that are the neutron flux you have to determine the neutron flux the efficiency of your detector the solid angle that you cover so you have to do all the calculations also you have to calculate the probability that the gamma escape because this is a probability that the gamma remains no exit from the target when it's thick then it's the effective area or the recent interception area the percentage of the beam that is intersecting with your sample and where you have to calculate all of these these are uncertainties so that is plain because in a reaction cross-section it's much more difficult to calculate a cross-section than without transmission and that's all from my part I will only finish with making publicity now for example the transmission to show now again the power full out the method I will show here that for the transmission measurement in gold at thermal energy you can obtain no point bar in a... well below the level of 0.1% if I'm not wrong 0.1% with the other reaction here we are talking about a few percent that's all Peter will continue later explain a bit more about how to calculate the flux no it's not I will be on Friday so on Friday Mr. King will explain how to calculate flux and all of these parameters that's all if you have any question if you have something like one minute