 In this lecture, I will be discussing various components of neutron scattering beams, components of neutron scattering facilities, which means the tailoring of the beam and the transportation of the beam. We will start with tailoring and then we will talk about transportation. So, regarding this, I must say that I will be discussing about reactor configuration, then various sources that we use in the reactor, then beam lines for neutron transportation and also guides which can transport neutron beams very far. There are components like in-pile collimators, filters to reduce the unwanted fast neutrons and unwanted gamma in the beam, because they also come out in a reactor or in a sparation neutron target. There are solid collimators in the beam which retains the beam size but improves the resolution at the same time. How they do it? I will discuss. I will discuss the monochromators that are put in the beam to get a beam of one energy in case of reactors and then a beam collimated, that means direction decided an energy proper incident on the sample that we are going to study and up to this point I will narrate briefly how we reach. Neutron detectors are extremely important component in a neutron scattering experiment. Then I will spend some time on describing to you the role of neutron detectors and the various detectors that you have got to improve the quality of data and time we need to collect data. So, in a research facility either a reactor or a target in a spallation source one provides penetrations to bring neutrons to the spectrometer. In case of reactor the penetrations reach to the core and from the core the beam comes out the neutrons flows, neutrons flow to the beam mouth. In case of spallation neutron sources the target is surrounded by a few moderators because the target produces fast neutrons in spallation. These neutrons they go in various directions which are captured in the moderators kept nearby and after that again we have large beam paths to take this moderated neutrons away from the target and to the experimental stations. Here I am talking about either research reactors or spallation neutron sources I am not considering the other neutron sources like radium, alpha, beryllium sources or californium sources which are used for many other purposes but they are of very low intensity they are actually typically these sources are 10 to the power 5 to 10 to the power 9 neutrons per second not per centimeter square per second per second. This is too low a flux for utilization in a neutron scattering experiments. We talk about sources neutron nuclear reactors where the flux varies between 10 to the power 13 to the power 15 neutrons per centimeter square per second. In case of pulse neutron sources like spallation neutron sources we have for example Rutherford Appleton Laboratory in UK the source ICS the average flux is possibly so much lower but because of the pulse nature of the source where 50 pulses come every second and we use something called TOF spectroscopy. We can this source can compete with the 10 to the power 16 neutrons per centimeter square per second reactor source because of the kind of spectroscopy and at the moment spallation neutron sources are the most sought after neutron sources for experimental purposes. So before I discuss the source tailoring let me show you how the complete setup looks like it's a schematic of ILL granable reactor the white circle at the center here is the core of the reactor which is very small because it is swimming pool type reactor with highly enriched uranium core the core may be 10 to 13 to 40 centimeter wide or maybe of that order and then surrounding it there is a large quantity of reflector that helps to have a reasonably isotropic flux in the reactor in the reflector sorry and various kinds of facilities to tailor the beam and also various beam lines you can see some of the beam lines have ended in the reflector itself and not going up to the core because the flux is fairly isotropic and almost same compared to the core maybe better from the core the thermal neutron flux and that's why it is okay to have beam lines ending in that and then there are certain advantages which I will discuss later. So typically this is how it looks like the core the beam lines and the long guides that you can see the beam lines are there and then here after the beam lines you have got the neutron guides which go to the guide hall and you can carry the neutrons away from the core and inside this reflector region around the core you can see this is something called hot neutrons there are thermal neutrons there are cold neutrons so why this these are you can say a hot neutron source or a cold neutron source is a facility to tailor the neutron energies to our requirement and how it is done and discuss now I also show you the reactor core in Dhruva in BRC Trombay here also you can see there are beam lines some of them are radial some of they are tangential why they are so I'll come to it and these penetrations they bring the neutron beams out and then we have two long neutron guides I'll discuss how the guides transport neutron in this talk and explain to you the role of guides being played in accommodating more number of experiments. So in almost all the targets all the cores you can see these beam lines the core and the tailoring facilities now thermal neutron sources what are they so the core is here again the same schematic for Dhruva reactor and similarly the spallation neutron source at ISIS this is the target and surround the target you have all the beam lines and surround the target you also have the beam tailoring facilities what I mean by beam tailoring facilities are the moderators these moderators are important in case of neutron the moderator the thermal moderator thermal moderator like D2O H2O they are right in the core in case of target stations they surround the target in a spallation neutron source and from there the beams are transported to the required experimental sites so as I told you in a reactor core the fuel and the moderators are present and neutrons of around 2.5 neutrons per fusion are born in a spallation neutron source the neutrons are around 15 to 30 per spallation and the moderators are outside the target and the reactor flux is typically around 10 to the power 13 to 10 to the power 15 neutrons per centimeter square per second in Dhruva we have 1.8 into 14 neutrons per centimeter square per second I like to show you the spectrum here you can see that the spectrum peaks in the thermal energy region around 30 millilectron volt energies but there are regions which are called cold region typically neutrons energy less than 5 millilectron volts or typically you can say 100 to 500 millilectron volt and more they are called the epithymal neutrons they are hot and the Maxwell Goldman distribution is given here which is plotted shown here in the plot so but for some experiments we need low energy neutrons typically energies less than 5 millilectron volt now we can't increase the reactor power so that the entire Maxwellian the integrated flux goes up and the cold flux also goes up that is desirable but we can't do that can't even cool the entire reactor reactor core because in reactor design will not allow that so now the thing is that we can shift the Maxwellian to lower energies if we keep some cold moderators at some specific location to shift the spectrum of the room temperature thermal neutrons to lower temperature the cryogenic moderator is a cold neutron source and the principle of a cold neutron source is to re-thermalize so you can see I have just plotted some Maxwellians at various energies now you can see if I look at this orange line in this orange line this orange line is a Maxwellian at a higher temperature compared to the green line and the other red line so what is done is this I have got a beam line I have got a beam line at the end of which either the thimble which is inserted vertically or we can even insert some cryogenic moderator from here when they say some cryogenic moderator is a tall technology order technological capability but for the time being to explain the principle some cold moderators placed inside a location in the reactor core the reactor core is huge and you don't try to cool the entire core or raise the power but at one location we keep some cold moderator and either it is if it is inserted vertically there is new cold neutrons this beam looks at this cold moderator maybe there will be one more beam which is looking at the cold moderator and they see more number of cold neutrons coming out and not thermal neutrons so the thermal neutrons come from the rest of the reactor go inside it undergo collision undergo collisions undergo collisions this is a fiki and diffusion and collision and in this process they here their temperature is t is much much lower than the t of the moderator of the reactor and this is a maximum at lower temperature and as I shown in the drawing shown in the drawing that this moderated spectrum has large number of cold neutrons and that way I can enhance the number of cold neutrons so a cold neutron source is primarily not a source but a spectrum shifter it shift the spectrum can shift the spectrum to lower energy and we can get gain as large as 10 to 15 if we design everything properly so the mostly the moderators used the liquid hydrogen at around 20 Kelvin liquid deuterium at around 20 Kelvin or liquid methane at around 110 Kelvin at one point of time solid d2 ice was also used and solid methane was used in some ipns argon these are all attempts to shift the spectrum of the neutron now the issue is that why do you liquid deuterium when liquid hydrogen is good enough it is because deuterium has a much smaller absorption cross section for thermal neutrons and when we use 20 k hydrogen then it absorbs neutrons and the flux goes down slightly liquid deuterium can give much higher flux because it doesn't absorb any neutron and that's why liquid deuterium is used but the other fact is that liquid hydrogen has a much large scattering cross section deuterium has a much smaller liquid scattering cross section so when we use hydrogen around 500 cc of hydrogen is good enough for hydrogen but for liquid deuterium around the same temperature 20 k you need around 20 liters of deuterium because it has got a smaller scattering cross section because why you need so much because you need to thermalize the neutron it has to undergo collision and if the scattering cross section is low then you need larger volume to do the same thing so so to maintain half a liter of hydrogen at 20 k is a much lesser cryogenic load than to maintain 20 liters of deuterium at the same temperature and that's why to maintain 20 liters of deuterium is a tall order cryogenically but it gives gains I am just trying to show you the energy spectrum for water at room temperature compared to ice at 20 k and 70 k it's just a demonstration I show you the circle then you can use a log scale so there is a gain at some energy let us say 10 to the power minus 2 e v or 10 to the power minus 3 e v the gain is very large or somewhere around say 4 or 5 mega electron volt the gain can be 10 to the power 6 10 to the power 7 so gains can be as large as 10 nyc has a liquid I mean liquid hydrogen cold source you can see this is the beam line in which it is inserted and you can see the gain nyc cold source the gain is as large as you can see at the energy of let us say this is 1 millilektron volts and the gain is you can see 10 to the power 3 to say 10 to the power 5 there is a huge gain here over here at 1 millilektron volt again is almost 100 here so it's such high gains allows us to use cold neutrons for experiments where they are required I will come to it later in which kind of experiments we need cold neutrons so in Dhruva also we have got a recess to use cold neutrons for our experimental purposes but still that has to be done we have to install a cold neutron in the beam hole CS3003 I give the list of some of the cold sources ILL Grenoble France they have a 20k liquid deuterium so large volume FRM2 in Germany they have got 20k liquid deuterium Opal Australia has 20k liquid deuterium Kyrie has got liquid hydrogen nyc liquid hydrogen rather for Dappleton laboratory they have got methane as well as liquid hydrogen hydrogen Oak Ridge SNS has got 20k liquid hydrogen these are just a representative list so most of the major neutron sources have liquid hydrogen using the same principle of cold neutron so we also need hot neutrons or high energy neutrons for some experiments and we can always improve the hot neutrons by shifting the spectrum from thermal energy to higher energies and then at the cost of low energies we have gains at the higher energies if it is 100 MeV then this is the place where I get gain that is gain in hot neutrons hot neutrons and such sources are also used in various places where you put a piece usually it's a piece of graph graphite block at around 2000 degree centigrade it is heated we don't get any separate heating it can be heated using the gamma rays from the reactor itself ILL Grenoble and FRM2 at Munich have hot sources but not too many neutron sources these days have hot neutron sources because the spallation neutron sources can provide lots of hot neutrons and stop here