 So, in this lecture, we will discuss about the protons in cotton, it is a class of protons in cotton, which is used for the spellation neutron sources. So, first of all, when we are talking about the spellation neutron source means, this accelerator is used for getting the neutrons. So, what are the other neutron sources? So, very small scale neutron sources consists of some natural radioactive isotopes and some artificially created radioactive isotopes naturally was used by the rather forward in his experiment. Now, for getting higher and higher flux, some artificially created radioisotopes are used and mainly californium 252 is used as a neutron source and it gives the 10 to 9 neutrons per second type of flux. And this californium is obtained through nuclear reactors. Other small scale neutron sources are sealed tubes and some small accelerators. In this kind of you can have 2.5 mm proton from a very small linaque and impinges those protons on the lithium target. So, a decent flux can be obtained using this kind of isotope neutron sources. A very large facility which can give a very large neutron flux is basically the fission reactor, nuclear reactor in which uranium 235 or plutonium 239 are filled as the fuel. And by capturing the neutron, these emit the 2 or 3 neutrons as well as some fragments. So, a nuclear reaction takes place and schematically this is shown here. So, this is the neutron, it impinges on the target, target may be the uranium 235 or plutonium 239 nucleus and after this reaction, there are some fragments, some small nucleus can be created and neutrons are generated. So, 2 to 3 neutrons are generated per reaction. And so on an average, we can say that 2.5 neutrons are generated in one nuclear reaction. And out of these 2.5, one neutron is used for sustaining the chain reaction and you can say that 0.5 neutrons roughly lost in the absorption. So, one neutron per fission is available to the user. The flux from these kind of reactors, neutron flux which we get is 10 to 15 per second or 10 to 2 like that. This is the nuclear reaction which is shown here and on each nuclear fission, we get roughly 200 mab thermal energy. When a high particle impinges on a nucleus, the nucleus disintegrates in nucleons and light nuclear particles. So, what is the expalation and how it is different from the fission we see now. This is a very, very high energy particle. In case of fission, the energy of these particles will low, either it is a thermal neutron or the fast neutron. In this case, it may be one GV proton and it impinges on the target nucleus. Target nucleus may be a high Z material, even it can be a uranium 238 and a large number of neutrons and protons are ejected through this nucleus and some light nuclei can be ejected as fragments and some other particles are also ejected. So, the basic difference from the fission is that in fission, large fragments are there. In this case, small fragments are there and a large number of nucleons are ejected. So, if a target is suitably built, one GV proton can eject 20 to 30 neutrons. So, we can get a high flux of neutrons by this kind of sources. So, how these sources are made using the accelerator? We see now. First of all, we have some proton sources, then a linear accelerator which accelerates the protons up to highest energy or up to some desired energy level. And then after acceleration, these protons, it is the target. There may be two kind of espalation source based on the accelerator. One is long pulse espalation neutron source and the other one is the short pulse espalation neutron source. In long pulse espalation neutron source, protons hit the target directly from the linac. While in the short pulse espalation source, after linac, there is a ring. This ring may be a synchrotron or an accumulator ring and after that, these protons ejected from this ring and then these protons hit the target. So, how these are different? We see now. From ion source or linac, we can accelerate a long pulse of protons. However, the current is not so high. We can say this is the number of protons. This is not so high. So, a small current or low peak current, but a longer pulse. This pulse has the pulse length of Tp. This may be 1 to 2 millisecond long. This pulse can be accelerated. Very high peak current or high peak high pulse current cannot be obtained directly by the ion source or if it is available, then it cannot be accelerated in the linac. Because of the low energy part, there is a severe problem of a space charge. We will see again this kind of problem a little bit in this lecture. What is the space charge problem? Already, you might have learned about some space charge problem in the linac in your linear accelerator modules. So, very high current cannot be obtained at lower energies. So, a lower current and longer pulse is accelerated and then via multi-turn injection scheme. What is that scheme? Means, suppose we have an accelerator in which these protons or ions will be injected through a line. You can say H negative ion or proton and now after injection, these will revolve in the ring. So, say this is the T-revolution is the revolution type. Now if T-revolution is much, much smaller than T-pil, then how the pulse will be injected? Means pulse head will be injected first and it will keep revolving and it will make many revolutions until the tail will be injected. So, in this fashion, the complete pulse will be injected in many turns. So, if suppose T-revolution is near the T-p by 1000 or 2000 means 1000 or 2000 turns injection will be there. Means head will be injected first and when tail will be injected, the head will revolve around 1000 or 2000 turns. So in this fashion, finally the pulse of particles will be of only T-revolution type. Means this pulse time has been reduced to T-revolution but has become very intense. So, by multi-turn injection scheme, we can get very short but high peak neutron pulses. And when this high peak neutron pulses impinges on the target, it generates a very high flux of neutrons. So, we can say that accelerator-based dispensation neutron source are pulsed neutron source and it generates a very high peak flux of the neutrons while the reactor-based system generates a continuous flux of neutrons. So, if a user wants very high peak flux of neutrons in the pulsed mode, then accelerator-based dispensation source is the choice and if user wants a continuous flux of neutrons, high flux of neutrons, then reactor is the choice. It means reactor and dispensation sources are complementary to each other in case of the neutron sources. Now in case of synchrotron radiation sources, the main goal was to increase the brightness of the emitted radiation. Means we want to lower down the beam emittance as much as possible. Means reducing the beam emittance was the goal for the accelerator designer. Here, instead of emittance, the main thing is the beam power as much as you can. If we have higher beam power, higher beam power means it will eject large number of neutrons from the target. So, we want to increase the yield of the neutrons from the target, so we have to have very high beam power in the accelerators. Now, how this high beam power can be achieved and what is the beam power actually, how it is defined? We see this. We know that if charged particles are passing through a point, it constitutes a current. So, suppose n number of charged particles has passed in time t, then i average is n cuban. So, this is known as average beam current of an accelerator, that how many charge has been passed through a point in one circuit. This is the similar to the electrical point definition. Now, if we multiply this average beam current with energy of the beam, here pay attention to the units. Energy should be in EV, while current should be in the ampere, so we will get the average beam power involved. Now, how current and energy gives you power? We can see here that suppose there are n number of particles, so how much energy it contains? It contains n into E into, this energy is contained into the beam. If what is the current now, or what is the power, we want to calculate the power, so this is the energy contained in the beam. So, if energy contained is divided by time, that how much time is taking to cross these n particles at a point, then it will give you the power. Now, instead of joule, if we convert this E joule into the electron volt, we will get n cube E electron volt upon t. This n cube t is the average beam current, and this EEV is the energy, so power becomes all average into EEV. By a simple calculation, we can see what is the required beam power in a special source. Let the required neutrons per second from source is tenders to 17, this is the flux of the neutrons per second, that is tenders to 17 neutrons per second, we want. This is a typical number because from the reactor, we get almost in the order of tenders to 14 to 15 neutrons per second, so in the peak flux we want 1 to 2 order more neutrons than the reactor, so we take a simple number of tenders to 70. Now consider a 1GV proton, 1GV proton when it impinges on the target and if the target is well built, then it can easily eject out 20 neutrons. So how many protons will be required for so many neutrons, we calculate it, tenders to 17 by 20. So number of protons required to generate tenders to 17 neutrons will be tenders to 17 upon 20 because 1 proton ejects 20 neutrons, so number of protons will be 20 times less than the neutrons. So this gives you 5 into tenders to 15 protons, now what is the average current due to this number of protons, so average number of current will be number of proton multiplied by the charge, charge on the proton is 1.6 into tenders to minus 19 coulomb and we have seen that if this proton, number of proton is for 1 second, then we have divided this number by 1 second to get the current, this gives you 800 micro ampere, means an accelerator having 1GV proton energy, if it operates with 800 micro ampere of average beam current, it can generate tenders to 17 neutrons per second with a suitably designed target. So what is the power of beam, just current this is 800 micro ampere, so I have converted into the ampere, so 800 into tenders to minus 6 and 1GV, I have converted into the EV that is 1 into tenders to 9 and it gives you 800 kilowatt. So 800 kilowatt of beam power is required to eject so many neutrons.