 So, good morning for everybody. We will begin the lecture. Unfortunately, the director is not here. I mean, Danasri, because he's not here. But anyway, it's time to start. Let me tell a few words about myself. I am a nuclear physicist. I worked on this field over 30 years. And then now I will talk about measurements of nuclear data for promdegalm activation analysis. What does it mean? It means that to be able to analyze different kind of samples in terms of elemental composition, we need to have some kind of comparison to either to similar sample or some database. And this approach, what I will talk today, is using a database and I will present you that how it was built up. But before we begin all of this, let me have some introduction about nuclear analytical methods. The main purpose of all kind of analytical methods is to measure elemental or isotopic compositions or some other fields people want to measure chemical composition of some unknown samples. The nuclear analytical methods are analytical methods which are using purely nuclear technology. And what you can see here is a list of existing analytical methods. One of the most earliest one of it is the instrumental neutron activation analysis. Then there is a version of that which is used as a radiochemical separation at the same time neutron activation analysis. This is called RNAA. Then today's talk will be about the so-called prompt gamma neutron activation analysis. Many times we drop neutron, but it could be proton, for example. So some people like to make difference between the two things. So most of the time I will talk about PGAA instead of PGNA. Then there is the so-called atomic mass spectrometry which is one of the most sensitive method between all of them, which what sensitivity means. Sensitivity means that one method is very sensitive if it can observe very little amount of the element or isotope which we are interested in. Then there are some other methods which is based on accelerator induced spectrometry. One of it is the so-called proton induced X-ray emission. In this case the samples are irradiated with protons which induce X-ray emission of the atoms within the sample and we analyze the X-rays. Then there is another version which is called PGI, this is the proton induced gamma ray emission and this method is able to get information more depth from the sample because the gamma rays are more penetration power through the material than the X-rays. Then one can use instead of proton alpha particle and it is called alpha induced gamma ray spectrometry. There is also another method which is not so sensitive. This is the instrumental photon activation analysis. There is some reference at the end. You can look up if you wish. What are the advantages of these nuclear analytical methods? The non-destructive feature is a very important thing. If somebody do not want to solve the sample or do not want to take any part of it then this method must be applied and there is a list of the PGA, the Pixie-Piggy, and the high PAA is such a method. You do not need to prepare the sample, you simply put into an excitation beam then you can get the analytical signal out of the sample. The analytical signal is of course induced by the incoming particle and it can involve either the nuclei interaction or the atomic interaction or both. There are some very sensitive methods. These are the neutral activation analysis, the radiochemical neutral activation analysis, and the atomic mass spectrometry. For bulk analysis, the best method for bulk means that if you want to penetrate deep in the sample then we need to use the features of neutrons instead of inducing the actions with a charged particle. The charged particle range in material is usually a few micrometer or the X-ray has a similar feature so we can only study the surface of the sample. But these methods are able to study the internal region of bigger samples on the order of centimeter. There are two of these. This is the prompt gamma activation analysis and the photon induced activation analysis. There are also disadvantages of these methods. Of course there are many other methods. For example, most of you probably heard about the ICP-MS which is able to analyze very small quantities but this is a very painful process to solve the samples many times. Especially for example geological samples can be solved very difficult without having any residue of the material unsolved. So if you want to make it right then you need to make sure that you digest all of the samples and you can make some experiments with ICP-MS. Then there are many versions of the ion coupled plasma spectrometry that stands for ICP. There is the optical emission spectroscopy and there are many other versions. The nuclear methods are usually slower than some atomic methods. The atomic methods which use only the electronic feature of the material is the X-ray resonance fluorescence or the infrared Fourier transform spectroscopy or X-ray induced electron spectroscopy. These are already able to distinguish between the chemical composition of the material, chemical surrounding of the material. Now we switch to the PGA method and what are the basic features of the method. You can summarize on this picture. This is the principle of the neutron activation analysis. So once we have a neutron beam then we can put some target into the beam. Then the target nuclei can be captured neutron and get into highly excited states. The excitation energy in this case is between 7 to 6 to 8 MeV. Then this highly excited nucleus always emits gamma rays or 99% of the cases emits gamma rays to de-excite from this very highly excited state. Via cascade of gamma transitions which is depicted here in this simplified level scheme so a cascade would be if this is the capture state then you have a cascade of two is drawn in this case. This is going to be a direct transition to the ground state of the nucleus which is called primary transition. All of the transitions are coming from the captures. That is called primary transitions. All the others are called secondary transitions. Once this highly excited state is de-excited to the ground state then there are two possibilities. One is that the ground state is stable then we don't get any more information from the reaction. However, if the ground state is not stable then it can be followed, for example, by beta decay then we get more information from the beta decay and in fact this part the analytical signal is called prompt gamma analytical signal and this one is delayed and it is used in the neutron activation analysis. Delayed means that it can come within a second or to several days or even years. So from this point of view the neutron activation analysis is usually a very long process. Once you excite atomic nuclei of the sample in the reactor then you have to wait for a long time to get all of the analytical information from the sample and measure it time to time to be able to resolve the long-lived components of the analytical signal. Ok, then how is it sensitive for the elemental or isotopic composition to the sample? The gamma rays which are emitted from the various nuclei in the sample has gamma ray energy so we take a spectrum of it then it shows up in the spectrum as some peaks gamma ray is characteristic to the element or isotope inside the sample while the intensity of the gamma rays is proportional to the mass of the nuclei in the sample. One of the most important governing things which influences the problem activation analysis is the cross-section of the materials. You have already seen yesterday some presentation from X4. This is a very simple cross-section curve against the incident neutron energy down here and this one was collected for 59 cobalt neutron radiative capture by the way this process is also called radiative capture and the signal which is coming out is radiation of photons. So as you can see here this part of the cross-section in function of energy is fairly smooth can be approximated very well with the line and this part in most of the nuclei follows the 1 over v rule so the cross-section is decreasing as a function of the incident velocity of neutrons. Larger the velocity the lower the cross-section larger energy is lower cross-section. In fact this part is always going through all of the spectra at some places then resonances appear that you also heard the air-arm matrix treatment of these resonances and the way you describe the resonances in the Wigner-Brate salary which actually states that all of the resonances has a very distinct shape and similar shape for all of them the only difference is the height and the width of the peaks. Now what are the other consequences of the radiation analysis we need neutron sources. There are many different kinds of neutron sources the simplest cheapest way to create neutrons is via radioactive sources in which for example the plutonium berylium source or americin berylium source from the point of view of neutron creation the plutonium berylium source is consisting of plutonium which is an alpha decaying nucleus and berylium which is able to produce neutrons via the alpha n process and they are usually mixed in powder form and put into a small capsule which is then placed into the source the californium is different the californium is able to fission without any odor excitation so this is called spontaneously fissioning nucleus this produces also neutrons via fission then the other possibility to produce neutrons are the various charge particle reactions so most famous, two most famous are written here the DD Helium III neutron production is useful in the MEV range while the DT alpha n reaction is giving an energy about 14 MEV then instead of having these simple reactions one can use more complicated reactions using accelerated particles in use spallation in this process one can use for example high energy protons which then hits heavy targets with a lot of neutrons and also very dense and targets which can stand high temperature because usually to produce large amount of neutrons you need a lot of energy the energy can be go up to megawatt on these targets and in fact in the newest facility which is just under construction the European spallation source is designed to have 5 megawatt on the target which is already very substantial and the cooling must be made for this kind of targets as we learned also yesterday that each of these protons can produce on the order of 25 certain neutrons in these heavy targets for example tungsten or tantalum or some other targets can be liquid or liquid lead target then also has some other reactions which is the photo induced fission and a very good example is the Gale linear accelerator with this process electron beam hits the uranium target then it makes a brainstorm in the uranium then the brainstorm produces gamma rays and it produces a fission of the uranium target then from fission we obtain the neutrons this facility can be used in pulse mode and so we can perform time of light experiments just similar to one we already heard in the case of sun the alternative to these creation is the regular term of research reactors there are many research reactors in this school there are about 200 to 300 reactors many of them are producing radionucliase for medicine and very few of them are really doing experimental work around the reactors in this reactors the source of the neutrons is the fission of the 235 usually put in the reactor core and these reactors are called research reactors what are the possible geometries to do such an analysis so if you want to excite some sample and we ask what does it contain it can be understood as proton spalation source or reactor internal part so once we put a sample closely for example reactor core then we can make activation of the sample then if we have corresponding cube which let the gamma rays from the sample then we can measure it at the end of the tube the problem with this geometry is that there are many other gamma rays which is created in the environment around the sample which is very difficult to distinguish from the sample we actually put into the activation place another alternative is that we try to lead the neutrons out from the reactor core then this is also a tube and it can be now a very specialized tube then later I will talk about that then we can put the target to the end of this tube then the neutrons are hitting the target then we can detect it with some detector this geometry is called external geometry while the other one is the internal target geometry there are examples for that in life one of the most famous internal target geometry reactor was constructed in Oakridge and in fact it was designed in such a way that it had minimized amount of gamma rays coming from the structural materials of the reactor so the samples produced excess gamma rays compared to the background gamma rays which is coming from the structural material of the reactor and people could do rather good experiments at this place of course the advantage is that the flux neutron flux is very large but then the gamma rays which are coming out follow basically the one over R square rule so then it will be at the end of the channel it will be attenuated in the other geometry external geometry the neutrons are following the R square rule but we can go close to the target so the gamma rays basically can be all of them captured with suitable detector system so this is what people are using the most and the most advanced guides which let the neutrons out from the reactors are the so-called cold neutron guides the advantage of this system is once we cool down the neutrons then the neutrons can be guided by some so-called mirror guides with very small losses and if we curve the mirror guide from the straight line at the tube which lets the neutrons out from the reactor then we are able to get out from the way of the direct beam coming out from the reactor and make a very nice environment very low background environment at the experimenter stations the other important factor is of course the detectors the gamma rays coming out from the sample then we need to have good detectors for that in the past before the germanium or the diode kind of detectors people used the sodium iodine reactor sodium iodine detector however the resolution was not so great it has rather good efficiency and everything now is compared to the sodium detectors if we are talking about a 20% high purity germanium detectors then it is in a fixed geometry the signal is 20% of a sodium crystal efficiency so then once you get a hundred count in a peak from sodium crystal then with a 20% germanium it means that you get only 20% so this is a relative number then there were some more works to enhance the resolution of the scintillator crystals and now the most advanced crystals are the lanthanum halide crystals there are two versions of it lanthanum halide crystal both of them have a rather good resolution 2% so what does it mean at 1 MeV the resolution of this detector is 20 keV if the resolution follows the square root of the energy for these reactors the efficiency is higher than in the case of the sodium iodine anybody knows why it is higher what do you think you can see the composition here why this one has higher efficiency not only the density but the charge photo absorption of the peaks which is the most important process in gamma ray observation detector is going with the high power of the charge the highest charge number of the consequent in the reactor the higher the efficiency and the lanthanum has higher Z than iodine in the sodium detector to produce more efficiently gamma rays now we arrived to the modern high resolution detectors which is called high purity germanium detector in the past it was activated with lithium so they were called jelly germanium lithium detector most of them has a very good resolution it's on the order of 0.5% it means for one MEV that you have one keV then due to the again to the charge of germanium is lower than iodine in the sodium iodine detector the efficiency is lower but the resolution is much higher then there are so called composite detectors so the simplest one has only one crystal of it the composite detectors has many crystals the advantage of the composite crystals is that once one of the crystal is hit by a gamma ray then can go through two processes basically or three but the most important is the comtons scattering and the other important is the photo absorption but most of the time or 50% of the cases it will be comtons scattered and arrives somewhere in the neighborhood but if you put detectors there then you can catch them so the composite detector is able to produce photo full energy peak so to say even when the two crystals or three crystals are producing the signal then this organization geometry of crystals is called clover because it looks like clover of the flower leaf and there is another one which is called Europlaster and this is constructed from seven crystals one in the middle and six around it and this is called to be a composite detector a simple then since we cannot use infinitely large detectors then the gamma rays substantial amount of the time comtons scatters out from the crystal and we do not observe full energy peak the full energy peak is only characteristic to the elements or isotope which produced and not the comtons scattered peak so in order to be able to reduce such a signal in the measurement we usually use so called BGO guard detector the BGO guard detector has a hole in it and it has a taper shape like a cylinder then one can put the germanium detector inside this crystal then make a composite detector the composite detector in this case can be used to suppress the comton signals produced in the germanium detector so if we use it in anti coincidence mode we can decrease the comton events which would appear in the germanium detector spectrum and not only that it can also guard the detector from the ambient background coming from the outside the detector system so outside the radiation can come from this direction, not from the axial direction of the detector in fact this is a light shielding around the guard detector and when you put the germanium detector inside the guard detector then you can use it as a composite detector and the light shielding is still needed so it comes to irradiate directly the guard detector the guard detector has much higher efficiency than the internal detector so that is better to avoid otherwise we will see most of the time the guide detector signals so then you need such a shielding the detector inside is waiting on the order of 30-40 kilos made of bismuth germinate the bismuth has very high Z so it has a very high photopic efficiency so it can make up a nice system let's see that how it works so once we have a gamma ray hitting I repeat it once we have a gamma ray hitting the germanium detector then you see it in two projections then it showed a photo absorption so it was fully absorbed but we have possibility to come to scatter out then I repeat that one so then it goes to one of the segment of the guard detector then you can use the signal to stop the acquisition so then you get rid of the company then from the detector and this is the effect this was a prompt gamma ray spectrum on a PVC sample which contains chlorine see this is the so-called normal mode when we don't use the Compton suppression the detector is sitting in nice shielding but we do not switch on the Compton suppression then you have this spectrum then when you switch on the Compton suppression of the system then it reduces the background the peaks are completely normalized so that was one of the point that we measured up the area in fact not the height but the area of the signals so then at higher energy you can read here that you can have on the order of 20 suppression in the Compton background at lower energy this is a little bit less on the order of 5 substantially the background below the peaks which gives us a possibility to be more sensitive for the same amount of photo peaks now how does it go in life so you need a source here you can see the budapest research reactor then once it produced neutrons which in this case the neutrons are guided out here then you can see here some neutron guides how it looks in the real life so these are you can think of like a mirror but we are not using the mirror from the glass side but from the back so whatever is in the back of the mirror we use that to reflect neutrons so once you also learn from the scattering length and the nickel is one of the nucleus which has a very large elastic scattering length then we cover this glass mirror with nickel layer then the nickel serves as a reflection material for the neutrons it is able to produce a total reflection on the surface the incident angle must be below one degree so very low we are talking about very low angle then it can the neutron can totally reflect back from the surface without any loss so then this way if you make a long guide of it with a mirror surrounded hole then the neutrons will be bouncing over the guide and arrive to the experimental station these guides which you can see here has a 10 centimeter high and 2.5 centimeter width cross-section so that's 25 centimeter square is available for the neutrons to be guided then once then you have to also cover it with biological shielding it is not shown here because it was just at the production stage then the neutrons arriving to an experimental station which was shown before the neutrons are coming from this hole the guide ends about a meter from this wall and then we have only a flight tube so the flight tube is used for being able to make a vacuum in the system and of course the guide system is also under vacuum neutrons are flying in vacuum and do not interact with the ambient air here you can also produce vacuum in this system then there is a target chamber and there is the detector then the detector is observing the radiation from the excited nucleus and goes into some nuclear electronics then a multi-channel analyzer is used to collect the gamma spectrum then once you collected your gamma spectrum then you have to analyze it this shows this step then we will have a practice on that one and then you can produce a table using the library of the composition of the material you measured and if you have many of these compositions then people like to use statistical methods to make groups between the samples not always one needs to do that but in case of geology this is a practice that you measure hundreds of samples then makes groups or archeology is a typical example this table summarizes the main feature of the neutron activation analysis so this is as we learned nuclear analytical method, the energy corresponds to the element or isotope we always observe isotopes but I am talking about element and you will learn how you can make it from isotopes to elements then the intensity is proportional to the quantity of the element in the sample and as I told you this is non-destructive so then we can take whatever sample we can take the stick put it into the neutron beam and analyze it what is this made of and it is also a multi-analyzer technique so it is able to produce signals from all of the elements which is in the sample of course it has different sensitivity this is one of the methods which is able to observe for example hydrogen in samples which is very important in many applications so we try to use it and it is also valid for boron which is a high cross-section we can measure boron very well in a program activation analysis and in fact we can measure all the other light elements like oxygen, carbon which is important for biological samples later I will talk about what is the disadvantage with these light elements so in practice we do not need any preparation of the sample which is a big advantage so we can use the sample as it is then the method gives because the neutrons can penetrate deep in the material and the high energy gamma rays come out come out deep from the material it produces a so-called average composition of the irradiated volume then the method is exact for homogeneous samples that is always the case in all of the analytical methods it produces negligible activation of the sample most of the case the samples can be taken away just after the irradiation in some cases we have to wait a few days to decay out the fast components the long components will not be excited too much because of the the saturation for those takes much longer time, the flux is not sufficient to seculate them fast and in fact you activated them but you get very slowly back the irradiation so it is usually below all of the clearance levels if we have long lived it activated in the sample if we have a medium that can be shaky like silver is one of the bad example we cannot irradiate them very long in activation analysis because then it becomes just the right combination the lifetime and the activation we can make on this target is usually brings the sample above the clearance level in a few hours ok then it provides fast and instant result what does it mean so as long as we switch on the acquisition and the beam on the sample then in a few minutes it peaks so we can in a few minutes tell rough composition of the sample this is usually rather rare without any sample preparation we do not need so called external we do not need to measure a similar sample before or after the sample we are measuring we can produce so a wave which is called internal standardization so relative to each other or even in some cases absolute values can be given good for major components major components of the sample and some minor or trace components can be also measured hydrogen as I mentioned boron and some of the rarest nuclei can be measured which has very high cross-section on a trace level as you all know the cross-section from nuclear element to element is varying in a very large scale it is not similar to the other competing method there is the X-ray excitation the X-ray fluorescence where the sensitivity is increasing with the charge so the higher the charge the larger sensitivity for the element in this case this is very random so some element has very high cross-section some in the neighbor has very low cross-section but from this point of view the two methods complementer to each other how can we use the signal to determine the mass of the sample is summarized here this is very simple we measure the peak area actually we measure hundreds of them so we can select the biggest one many of them then use in this formula then the peak area is proportional to the mass of the irradiated area in the sample and this so called sensitivity and of course the time and in fact the precision of the mass if you reorganize this simple equation the precision of the mass can be increased with the measurement time in fact to infinitely but of course then we do not have usually that much of time now what is the sensitivity you can see here so the peak area is depends on the cross-section of the element or nucleus which is irradiated the so called gamma-ray production probability in one neutron capture that's what this measures and of course the mass of the certain element in the sample which is actually it is outside by but this one is put into the sensitivity and then the flux better the sensitivity the efficiency of the detector so then from this point of view yesterday you discussed that for high resolution it is better to have only one detector this is sometimes good but we would like to have more because then we can increase of course the efficiency but it depends also on the budget of the this if you use instead of one detector you use 20 detectors then you need to analyze 20 spectra so this is much more laborious so people are not tending to use many detectors for this kind of analysis and there are some problems also which is summarizing F this is a factor that takes into account the absorption of the neutrons within the target as the neutrons are passing through the target then the intensity is continuously changing decreasing and also the gamma rays can be absorbed by the sample the higher energy is less significantly than the lower energy lower energy can be very much absorbed in a centimeter size sample so then it's better not to use them ok so then how then one proceeds so once we have the peak areas analyzed in the spectrum then we can feed it into some program I will demonstrate that tomorrow how to do that but this summarizes how the program works so there is an input module which inputs basically the list of the energies and areas of the peaks which are found in the sample then it compares to a library which has other parameters used in the comparison so then there is a so called 25 line library list only up to the 25 most intense gamma rays which gives you already 1800 data then there is a 1% library which is used to calculate the interferences between gamma rays then we also need some other inputs both side like molecular rays observation number self absorption to be able to correct for these effects and then we need to subtract the background it is done with the equivalent mass how should I concept so we try to determine the equivalent mass which we need to put into the sample position to get the same amount of what we collect from the background which is not from the sample position it can be there because then as you see that the station is made up from material so then there is an aluminum cube which is a fly cube so then we ought to see some aluminum in the spectrum fly cube or the light shielding contains less so light will be there if we do not apply vacuum then the air will be seen in the spectrum so nitrogen is seen, oxygen is seen hydrogen is seen because that can also be in vapor in the spectrum so many things then you have to correct for the background correct for the system which is regularly taken once we change something on the detector system then we measure the efficiency so we already have hundreds of experiments on efficiency and they show us to be very stable for stable geometry but anyway we have a so called date range we use an efficiency for photo in a year then the program automatically selects the efficiency which corresponds to the acquisition time of the spectrum then there are other parameters which is needed, beam temperature, flux the density of the sample et cetera, sickness which has to be entered then there is a data evaluation model which then grinds all of this input and calculates the output then there is an output module which formats it in a readable format and it lets you change so in the afternoon we will see how you can change the program does something but if you are not satisfied with it then you can change it and it does it online if you click or type you can change the input basically which is used to calculate the output and then in this case then a trained person is needed with a lot of experience to be able to judge the quality of the result what it tells you what it should be ok, so this is done in an iterative way once you are satisfied with this iterative adjustment of the result then you arrive to the final result all of this is written in this reference this is how an output looks like from the program, you can see here a so called bioash so this is one of those green we were asked to measure the bioash composition one of those green electric power companies which burn bio material basically wood unfortunately most of the bio material is coming from wood then they were interested in finding out whether they can use the ash as a fertilizer of on field so in the agriculture so one of the major point was to measure the toxic component of the ash and this is the table we obtained for one of the sample which was on the order of gram and you can see here many things that we acquired for 40 seconds here is the neutron flux 1.5 to the times 8 so called thermal equivalent flux temperature of the beam then the background was used and then you can list the elements you see this is the so called measured mass then you can subtract the background from the measured mass then you get the net mass then finally you can express that in various different ways one of them is the atomic composition in percentage and ppm part problem Leon at the end there you can have elemental to elemental composition total element one element to total element composition then one element to oxide form of the element and also oxide to oxide this always gives different numbers but you don't need to calculate them from it's not that difficult to calculate of course but the program does it for us then whatever is required in the what people want to know that nuclear physicist like the atomic composition chemist or geologist like the oxide oxide composition chemist likes the elemental element composition so then we can give all of them a little bit more about the neutron source so then this is also the place where I am from so I am from Hungary Budapest and there is a research center which is run by the Hungarian Academy of Sciences situated in the hills this is here and this is an aerial view of the research center in Hungary we abbreviated as KFKI this is used to be the center for physics in Hungary and now it is it is not called anymore center of physics but this is nevertheless still a compass where research is going on right now there are two big centers one of it is the energy research center where I am from and the other one is the so-called Wigner physics center which is another center in the compass anyway the energy research center runs the Budapest research reactor and some history of the reactor can be seen here so it started up in 1959 with 2 megawatt power in 1967 and there was major reconstruction in this period after basically 30 years of operation then there was also an upgrade of the possible power and in 2000 we installed the so-called cold source then in 2012 we shifted to the 20% enriched uranium fuel from originally 36% enriched we used then we also have so-called Budapest neutron center which enables the researchers around the in the compass the utilization of the reactor so this coordinates the work between the energy research center and the Wigner research center to use the research reactor the PGA facility was commissioned in 1995 then we upgraded it into two experimental stations in 2001 then we did detector upgrades cabin upgrade radiograph system neutral radiograph system built into this station this is how the reactor surrounding look like the reactor building is here then offices are in the front then we have so-called neutron guide hall so the cold neutrons are coming into this hall and there are experimental stations around the cold neutron source in this hall and there are also experimental stations next to the reactor and this is situated in that building here you can see the main features of the reactor I don't go over it the most important thing to know that it has ten radio ten channels in about one meter high which leads out the neutrons for experimental purposes from the reactor eight of them are radio and two of them are tangentials so called tangentials and one of the tangentials has this cold source the cold source is very close to the reactor core and it is about half a liter liquid hydrogen which helps to cool down the neutrons to low temperature so long make the neutrons have longer wavelengths this is advantages for the neutron guide system because the total reflection depends on the wavelength longer the wavelength is the critical angle for the total reflection is larger so if we are cooling the neutrons then we can have a much better angle acceptance in the guide system this is the layout of the reactor hall so the reactor is here this is the reactor core you can see the cold source is here then we have three neutron guides which goes to the guide hall then we also have instruments around the reactor and I want to go over them there is no enough time to look all of them up this is neutron scattering research mainly they are in here at the guide hall and this one is a radiography tomography station at the reactor we also have a time of flight facility which is able to chop the neutron beam with the three chopper system and select and make a bunch of beam with well defined wavelengths what they can use also for scattering then in the guide hall we also have scattering instruments reflektometer, smaller neutron scattering triple axis spectro beta and then we also have the PGNU system at the end of the first guide and this is about 35 meters away from the reactor core now we go to the facility in a closer look this is a three dimensional drawing of the current status of the experimenter station the neutrons are coming from this direction then we have the flight cube and there are already two experimenter stations this is used for the PGA the other one is used for the so called PGAI this is a program activation imaging station here we can do the neutral radiography and tomography including a capability to measure elemental composition inside the material so not bulk but a special place and I will show you some examples at the end of the talk here you can see how we usually place from the gamma samples this is a powder sample wrapped in in a fat foil this is a fluid ethiopropylene foil bag which just keeps together the powder then it also relatively transparent for the neutrons it doesn't produce a lot of analytical signals so we are not interfere with the composition with the gamma rays coming from the real sample so you put it into the target chamber then you can put the whole system under vacuum and you can then switch on the neutron beam which in fact in the experimenter station we use two neutron beams the so called upper beam and lower beam this is made by diafragma and they are separated from each other about 6 cm so the upper beam goes to the PGA station and lower beam goes to the other station and at the same time independently from each other you can switch it on, switch it off when you want then another important parameter is the spectral distribution of the beam so the core neutrons has also you would expect Maxwell distribution of the beam energy profile and the way you can measure it in time of light technique here you can see that the neutron chopper which is just a blade and the other side of the blade is covered by a highly absorbent material I think in this case we use the lithium polymer and then we made a very narrow slit between the absorption you can see here then you can also make a very small hole from the beam with a lithium contained polymer so then the beam diameter was on the order of 2 mm then if you put together the system then you can chop the beam and then you can also place a position sensitive detector which is here this is a helium 3 field position sensitive wire cell produced by this company and it is filled up with 3 bar of helium 3 plus Cf4 2 bar then the spatial resolution of this system is in order of 1 mm but as you can see the sensitive area is 18 cm by 18 cm so it can read out about a thousand channel horizontally and vertically then you can also measure the time when the neutrons arrived how we measure the neutron energy distribution in the pinhole geometry so you have the guide in which the neutrons are bouncing around then arrive to the end of the guide then we use the collimator slit and the pinhole here then again collimated to the screen so everything will be upside down left and right will be turned around and things like that but still we can understand this figure so this shows the spatial and energy distribution of the beam if this hole collimator was put in the beam view then from the middle of the guide we put the beam hole to the right then this looks like this then if it is in the middle of the beam then it looks like that and if you go to the left then it looks differently so this is the radius beam from this point of view this other figure shows the composition of the beam spatial composition so this is a horizontal vertical direction and in this wavelength range from 0 to 1 angstrom 1 to 2 angstrom 3 to 4 and as you can see it is higher the wavelength then you have the larger beam but this is no wonder because then the guide is more efficient for the higher wavelengths so you get more and more beam as you go to the higher wavelength region so this is the end of the movie we can see here a four dimensional figure of the beam so two axes the x and y which is running here and there and z, z is the time the time of flight time relative to the trigger signal of the chopper and x and y is the distribution spatial distribution by the multivijer chamber and you can see here three different count range so if you only look for the maximum count rates then this looks like this and this is a nice system and you can turn around this, I am not prepared for demonstration of that but this is very nice, then you can cut actually you can cut at any direction and you can go into this 3D body what is this 3D body the intensity of neutrons at different places in two dimension and in time ok, now if you use all of the counts then you see that this is bigger than and this is from 0 to 300 counts now if you make projections what we just practiced in the case of cross section data then you can also project it to the time channel simply adding up all of the signals in the x and y direction and then I show this left, right and middle placement of the pinhole and as you can see the spectral composition of the beam did not change very much so we can see that horizontally at least the energy distribution of the beam is similar to each other we just have special differences in the beam then you can also see figure of all of the data or the middle data basically in the energy dimension and why does it look so ugly we would expect distribution would look like in this case like this but we have some more instruments in the beam and they are scattering out neutrons so then you can see the breakages so they are using scatterers which has breakages so then we actually observe something like this instead of having the whole beam so this was taken away by those guys and if you have many people around then you cannot do anything with that we need to live with this truncated spectral distribution of neutrons now there is another important thing in determining the composition is the detector efficiency you can see here high precision measurement for our detector system what you see here that this is an absolute efficiency so then the highest efficiency we have that system is 10 to minus 3 a little bit more than 10 to minus 3 then it is falling as the energy, gamma ray energy is increasing rapidly and at the end of at about 10mV we have two orders of magnitude less efficiency for the high energy gamma rays and up here you can see that the deviation from the curve of the measured point and as you can see this shows rather nice small deviation this is the way how you can calculate the efficiency from the measured quantities the R here is the rate of gamma peak so the area would be R times the measurement time this is just the speed how the peak is coming and then you have to divide with the activity of the source so the activity is here then you also need the transition probability for one decay which is P gamma then if you make this ratio then you can get the efficiency and then you can get more information from here then how the curve is actually done so you can get information there then the system is ideally linear in energy but it is not always and in the case of on PGA this is an important factor that the system is not completely linear and this is just a so called non-linearity curve the definition is here so what you see on this axis the y axis is measurements of many gamma peaks position were measured of radiative sources and some prompt gamma sources and then they actually measured from the actually fitted peak position in channel number we subtracted this quantity which is a transformation of the literature energy to channel number then the difference can be then figured out and it looks like that so then it means that in our case one channel is about one keebi so then since you can see that from this point here we have about two or three channel difference then it means that we can be off one, two, three channels and if we do not apply this correction from the the ideal energy then you can also get more information from here another theory so how can we get to the composition so this is in fact how you would calculate which is measured by the system this is the probability of the gamma ray if you capture one neutron then we have the detector efficiency which can depend on the which is depending on n and the place where the gamma is coming from then the number of nuclei if you have an inhomogeneous target then it also depends on the place then the correction factors for the absorption of neutrons and photons also has a special dependence then we have to integrate over the cross-section and flux now if we make all of these simplification so just a fast summary so we have one over v nuclei the sample is homogeneous then this means that it doesn't depend on air the space then we do not have any absorptions then the flux doesn't change in the sample and the flux doesn't change in time then for reactor this is always the case that you can simplify the whole equation and obtain this otherwise you need to make Monte Carlo calculation on the whole process and for ideal sample which is described here, what is that then you can use this very simple formulation and in here you can see that Ph, this is the so called thermal equivalent flux which gives the same rate as our neutron beam gives as gold so this is just a relative number now this is how we make the internal standardization of an experiment if you have two of these peak areas in the spectrum you have a comparator in the spectrum so if you want to make for example cross-section experiment you have to use a comparator which is a well known comparator together with the unknown basically unknown cross-section material then you can simply divide the two equations the two areas, peak areas then the nice thing is that the flux goes away for ideal samples then if everything is well mixed then you end up only with these quantities so the rest of it is gone from the sample then if you rearrange this then you can determine the concentration if you rearrange it another way then you need to know of course the number of atoms in the sample then you can determine the cross-section you can also determine for example if you know all the other things so this theory is very simple if everything is ideal now some problem which is not so well known for the efficiency do we have the efficiency ratio here in the equation and we use the same efficiency we measured it and this is the same now this means that it has correlation then this is just the formula which determines the uncertainty of this division then you can write it in this way and we have here since we fit for data with a polynomial then we have here a matrix which contains the power of the polynomial in this case this would be the logarithm of energy and v is the normal matrix which is used in the chi-square fit now the interesting thing here is that there is a subtraction here that can lower the uncertainty here I draw this ratio fixing the energy the energy 2 in this formula which is in denominator to 500 and also did the calculation with neglecting this term this is the red curve this fixed position basically the uncertainty goes to zero but that's what we expect so if you have something with the same energy then there shouldn't be any difference in the efficiency so the uncertainty which is coming from the efficiency is zero and this is just another example if I fix e2 to 2 MeV 5 MeV then you can see that it is a much bigger change here so if you choose it right then you can if you use here not the absolute value of the energy but the relative but the relative efficiency then you can have much more precision on this part and you can see the uncertainty in percentage and this is of course the efficiency curve in both cases and you can see that there is a huge difference in the uncorrelated and the correlated quantities now this is the way how we can then finally determine the cross section so this is just the rearrangement of the equation you have already seen and there are several ways you can determine cross section from our measurements this equation here is using decay gamma rays then here you need to know usually this P gamma which can be a problem then you can calculate all of the primary intensities here the problem is that we don't know gamma rays then you can also sum up all of the gamma rays which goes to the ground state using this formula then get the total cross section the problem here that this is also lacking all of the gamma rays which goes to the ground state however for this this is a more complicated method then it uses the level scheme basically so if you have a good level scheme then you can use this but this one which is equivalent to one which is the so called energy proportional detector what was explained yesterday by Carlo this here is the energy proportionality this is the some other people call it inverse Q value that's me but basically there used to be a Q value test in which you could determine how well your decay scheme was performing in the capture process but here you can also use this if you take the inverse to calculate the total cross section then as than the energy weighted gamma production cross sections and sum up for all of the gamma so this is simple, so you fit all of the peaks in your spectrum then you can calculate this then you get a cross section of course it's not always if you have a complicated nuclei then you have a zilience of the transitions this has to be more tricky then in this case one need to so called unfold the gamma ray spectra and to find all of the full energy peaks without the Compton background or the background continuum then you can apply this formula and calculate the cross section there are problems with one over V nucleide then this is just a figure of ratio here so we have the real cross section of X X is one of these nuclei then divided by the one over V formula and that's what you can see here except this one which is argon all of the others looks like almost straight line or at least fitted all with a second order polynomial so then you need to modify the calculation then the calculation what was shown before won't be so simple you have to put here the non one over V cross section and you see that we have not such a nice spectral distribution of the neutrons then you need to calculate the integral ok then if we express this F what I have just shown before then you can replace the cross section with the F and take out the one over V part then you can calculate this Y and then for example in the case of cadmium-1-13 you can fit this cadmium-1-13 is this one you can fit it with a second order polynomial with this one then if you plug it into this integral then you can perform numeric integration with our spectrum but this is a 0.87 as high as if it would be one over V function so this is actually smaller then you can proceed as before the library just very fast so there used to be two libraries and one of the most famous which was a compilation of MIT measured data however it had a lot of uncertainties so in summary then we decided that we have to, people tried to use this and at that time that was in the 90s people always measured their own values and they had no integrated library but most of them realized that the loan table is not sufficient for analysis then we decided to measure basically the whole periodic table at our instrument and we did it and with the thermal beam and always guided beam first time we didn't have cold beam, just a guided beam then we call it thermal guided beam but anyway then we measured all of the elements and we compared them to so called primary standards which is hydrogen, nitrogen, carbon and some secondary standards which is chlorine and sulfur to primary standard then we tried to use compounds in which one of these elements were present and we used the comparison equation to determine the partial gamma-ray cross-section which is basically in the formula so the partial gamma-ray this is the partial gamma-ray cross-section this is you have that for every peak in the spectrum so this was done then the analysis was done with this code you will see a demonstration in the afternoon how does it work and this code was basically written by this person who is this in the meanwhile and what we worked really quite a lot on this code then we made then we were in collaboration with Rick Firestone from Lawrence in the Berkeley laboratory he did the comparison of our data with the Abolated Nuclear Structure Data Library then we identified the isotopes to the peak which were measured and we ended up with the library of 32,000 gamma-ray data for which we measured gamma-ray energy this partial gamma-ray cross-section and other features we also measured that for decaying gamma-rays which were also in the spectrum the whole thing was summarized in this book if you can't get this book and still you are interested in that then just this is how the data is presented in the book so then you have a spectrum then it was analyzed then gives many information about the experiment then we also have tables tables in the book for all of the elements and it gives the first 100 peaks which is most intense peaks in the spectrum then we underline the highlighted ones we recommend for analysis but there is also another work which summarized basically the same data set this was done in this IAE CRP you can find that on the internet here is the reference and we were also working a lot on the collaborations how to improve the efficiency collaboration so then there is also some work in this book of IEA on these isotopes then you can also find the references here this is just a spectrum of one of the primary standard this is one of the primary standard for us at the nitrogen which we usually use in urea so we measure urea if it is possible we measure urea d they deteriorated urea so then the hydrogen line would not rule the spectrum this table summarizes the sensitivity so sensitivity is high if the cross section is high you can understand how then you can see here the detection limit which is also proportional to the sense of our corresponds to the sensitivity and this color table shows you that we are more sensitive for boron, cadmium, rearers, elements then sensitivity for hydrogen, scandium, cobalt et cetera and this figure to understand which are the most easy to observe elements now how all of this is validated this is always a good question am I right than us? validation is very important for IEA then all of this data can be validated through so called certified standards I don't go into the details I will show only one one of the standard is shown here for the major element and you can see here the fit value is not one it still has some problem here and there but this is very good and what you can see here the certified weight percentage of the elements in the geological sample and the measured one with PGA is on a straight line a 45 degree straight line and you can see that indeed the measurements are very well around this then on the next figure I will enlarge this part so then you can see that it is still not so bad, there are many elements here and there are some for which we didn't have data and there were some for the certified didn't have data so that's basically what I wanted to say and I invite you for the demonstration so do you have any questions?