 Οπότε τι γίνεται με γαμαραίες, μερικές εξαιρετικές εξαιρετικές. Τότε θα μιλήσουμε για τα πιο σημαντικά εξαιρετικές εξαιρετικές που βρίσκουμε με σέμπικοντακτος. Αυτό θα βλέπεις ότι αυτή είναι around 80% of the detectors we are using in Ion BIM analysis. Τις πράγματις για συντηλίες. Θα χρησιμοποιήσουμε συντηλίες mainly for gamma ray analysis, for Pige. Τότε θα μιλήσουμε για κάποιες γασουλίες και τελειώσεις. Αυτές οι δυο πιο σημαντικές εξαιρετικές που βρίσκονται mainly in Toferda. Δεν πιο σημαντικά. Οι δυνατότητες είναι όλοι μπορούν να βοηθούν να δημιουργήσουν τη δυνατότητα. Αυτό είναι το δυνατότητα. Βέβαια, αν έχεις ένα δυνατότητα που μπορεί να δημιουργήσει μια εξαιρετική εξαιρετική, για παράδειγμα, να δημιουργήσεις τη δυνατότητα ή να δημιουργήσεις τη δυνατότητα, αυτό είναι called a detector. Βέβαια από το δυνατότητα και τη συγχωρή της εξαιρετικής, θα υπάρχει κάποιες εξαιρετικές, like the efficiency of the detector, the efficiency of the resolution. Βέβαια, να μην πω ότι εδώ, εγώ λέω τα υποχή της δυνατότητας, δεν τα υποχή της εξαιρετικής. Όταν έχεις δυνατότητας, αυτή η ευσυκταία παράδει. Τι είναι οι πιο χρήματα δυνατότητα για υλαχθαλωνία ενάνθρωπες εξαιρετικών της ρόλας της εξαιρετικής. Βέβαια, έτσι όταν θέλεις να ενώ models μεms Ridge Particle, 99% θα χρησιμοποιούν υποχή για δυνατότητα. Αυτό είναι χρήματο, πιο χρήτου, δημιουργήσει να μην υπάρχει πόνο 5-6000 ευρώς, όχι περιכול, γιανητοφίσω θα πλήξεις τα νέα δυνατότητα ή τα αρχές χρησιμολφορές δυνατότητα. Για Πίγε, έχετε άλλο από τα τελευταία, τα τελευταία Γερμανίου λύθμου διτεκτος. Αυτό είναι ακριβώς χρησιμοποιημένος, αλλά όπως βλέπετε, έχετε κάποιες προβλήματα χρησιμοποιώντας. Οι πιο σημαντικές προβλήματα είναι να τους κοιμήσουν αλλιώς, όχι να χρησιμοποιηθούν. Προβλήματος Γερμανίου, αυτά είναι χρησιμοποιημένος διτεκτος. Και φυσικά, έχουμε σωδημαϊκό σιντυλαίτες. Για τοφέρδα, πρέπει να χρησιμοποιήσουμε σωδημαϊκό σιντυλαίτες για να έχουμε κάποιο σωδημαϊκό σιντυλαίτες. Και για την ενέργεια, πρέπει να χρησιμοποιήσουμε σωδημαϊκό σιντυλαίτες, όπως στην περίπτωση του ΡΜΑ, αλλά υπάρχουν also ionization chambers. Το καλύτερο thing with ionization chambers is that they live longer than surface barrier detectors. As you will see, surface barrier detectors and all silicon detectors, after using them, they have a certain lifetime. If you use surface barrier detectors for RBS and NRA, they can last for 10 years with no problem. But if you use them for TOFERDA, as the number of elements, the number of ions entering the surface barrier is much greater than in RBS and NRA, these will last for one or two years, depending always on the use of the system. On the other hand, if you use GIC, a gas ionization chamber, you don't have the problem of surface barrier detectors, you have less resolution, but they will live forever, you don't have to change them. So, let's begin with the interaction of the matter. Depending on the kind of radiation, you have different effects. So, I have split that in two. I'll talk about interaction with matter for charged particles and then I'll go to gamma rays. What does it mean? I have an interaction with the matter. When you have a charged particle entering in your medium, here I put, as an example, some ions entering, if I remember well, aluminum. You will have loss of energy, what we said, energy loss, and the deflection from the initial trajectory. As you can see here, as your ions entering the matter, they change also course, they change their destination. What are the process of energy loss? The main process is in elastic collisions with atoms, with electrons. There is also some elastic scattering from nuclei, what we call nuclear stopping power. And then you can have also Terenkov radiation, nuclear reaction with nuclei and the Brems-Tranlung. The three last give you something like 1% or less than the energy loss. So, I won't do anything about that. I'll just talk about elastic collisions with atoms and nuclei. Again, between these two, there is at least one order of magnitude difference. So, in elastic collisions, this is something easy to understand. When you have a charged particle entering your matter, your detector, they will find some electrons, and through the Coulombian interaction, they can either excite the atom or they can ionize the atom, depending on how close the interaction is taking place between the charged particle and the atom and the electron, and of course on the energy of the charged particle. But while you will excite or ionize an atom, this means that your charged particle will lose energy. How much energy will it lose? In the maximum, after one collision, it will lose something like 4 times m, the kinetic energy of your particle. If you want the 500, 1 over 500% of its initial energy. This is something very little, as you understand. So, in order for my nucleus, for my ion to lose the whole energy, it means that it has to do multiple interactions with electrons. So, whenever your ion enters the matter, it finds an electron, loses some energy, finds another electron, loses some energy, some, some, some, and continues like that, and after multiple interactions, you end up with no energy in your particle. Because these collisions are purely statistical and it's very difficult to see what's happening in any collision, we have defined what we call stopping power, which is the average energy loss per unit path length. What it means that it's statistical that if you have two ions entering your sample with the same energy, the exact same ions, it doesn't mean that they will lose the same energy. Okay, there is some difference in the energy, but as I can't see what every ion does, I take an average between a big number of ions. The good thing with inelastic collisions is that I have a perfect solution in order to find these DDX. If you go to the classical approach, the first guy who did the calculation was Bohr, and we have the Bohr's calculations, but if you go then to quantum mechanics, you use the better block formula. These are the two formulas. This is Bohr, and this is for a better block. The main thing that I want you to keep into mind about this formula is that the heavier is your element, the more energy it loses, and the lighter it is, it loses less energy. If you look here, I'm proportional to the velocity of my ion. This means that if I have a fast ion, it will lose less energy than a slow ion. You can also see over here, so here as a mean, as a matter, I use just air, plain air, nothing else, and this is the particle energy. So, for example, if you look protons, you see that slow protons lose much energy in air. As I go into higher energies, I lose less and less and less energy, so quick moving protons lose less energy than slower ones. And if you look at alpha particles, you will see that alpha particles lose much more energy from protons in the same energy. Okay, for example, if you go here at 1 MeV, you will see that this is the stopping power of protons and neutrons, almost the same, into air, while alphas lose much more energy. So alphas and heavier elements are interacting more with the matter because of the club interaction, and they are losing faster energy. These are some additional quantities that you may find in your work with interaction with matter. For example, what is a black chair? It's how my stopping power increases as I go deeper into my sample. And why is that? This is because here you have a lot of energy. As you move into your sample, you go into lower energies. The stopping power goes up. This means you have more interactions, more interactions. You reach up a peak and after that you have very low energy and your ions start, instead of ionizing the matter, they start collecting electrons from the matter and they slow down. And this is the famous black curve and this is what we call the black peak. So here you have, if you want, the maximum number of ions interacting with the medium. This is very useful in some cases, especially for medical situations, when you have, for example, therapy of a cancer and you are using protons, you want to use maximum interaction of particles with the tumor, so you adjust the energy in order to have the black peak into the tumor and not before that or after that. Another thing that is good to know which energy is struggling, so when you have a distribution of ions with, let's say, a very narrow distribution of energies like that and you are entering matter, as the interactions are statistical, this means that some of the particles will lose more energy, some of them will lose less energy than that and as you go deeper into your sample, this Gaussian distribution goes bigger, bigger, bigger, bigger, bigger. This is a good thing to know that as you go into matter the knowledge of the energy gets worse and worse and worse and worse. Sorry. Range is how deep your particles can reach into a material. To be honest, to be precise, for the range, if you want to really define the range, the range is not where your beam stops, it's where your beam, your particles, drop to one half of their initial intensity. This is what we call range. But in ion beam analysis and in everyday physics when we say range, we are referring to the extrapolated range where this is where your particles stop. Where your particles, if you throw, for example, 100 particles into your matter, in which depth they will arrive. So if you look here, this RM is what we call range. This is the real thing of the range. But in everyday life we use extrapolated range. This means over here where my particles really stop. This is very good to know because this will also give you an idea of the thickness of the detector that you are going to use. When you use a detector in particle physics, in most of the cases you want your particles to stop into your detector. So you must know the range of the ions into this detector. If your detector is thinner, this means that your particles will go outside the detector, they will not deposit all their energy into the detector, and this may cause you problems when you are measuring. Now, of course, today we are not solving Bethes formula or Bethe-Bloch formula in order to see what is the energy loss in something, in some material, in some detector. And also we want to see the struggling, the energy struggling, or the angular struggling, or the range, how deep we go. We have SRIM. SRIM is a tool. It's not the only tool, but it's widespread used. Where you can put here the ion that you are interested for. You can put the energy of the ion. You find here the thickness of your target or your detector. The material of your detector, you run it and it gives you the depth of your energy loss and the depth of your ions. For example, here I used ions of α, α-particles of 3MeV. You can see it over here that I have α-particles of 3MeV and they are perpendicular into silicon. And you can see that this is 30 μμ. You need around 15 μμ in order to really stop all the α into your detector. Things are easier when you have the interaction of photons with matter. You have only three effects. So you have the photoelectric absorption. This means simply ionization. This is the energy of the photoelectron that you are using. This means you have an atom. You have the photon. The photon interacts with the electron. The electron goes out of your atom. This is the probability. Here the good thing to see is that it's proportional to the atomic number of the matter that you will find your gamma. And it's inverse proportional with the energy of your gamma. Now, n is not exactly known between 4 and 5 depending on the energy of the gammas that you are going to use. After the photoelectric absorption you have the copton scattering. This is also something easy to understand. You have a gamma ray. It finds an electron and both of them scatters. Because they scatter, they lose energy. They have some of the energy of the photon is taken by the electron. And this is how you can find the energy of the new electron. So you can understand that if I have photon entering the matter it can do multiple scatterings and lose all its energy. And at the end we have pair production. This is when your gammas are above one MeV. You need to be close to the Coulomb potential of a nucleus. And close to that your gamma may break up giving birth to one electron and one positron. But as the mass of these things is 511 kV this happens only for high energy gammas. If you want to see how these three effects, how these three phenomena are used for your interaction with matter this is the probabilities. So here you have the Z of the absorber and here you have the energy of your gamma ray. So for low gammas you see that the photoelectric effect is dominant. For one MeV you have the Compton effect dominant and if you go above 10 MeV then you have the pair production dominant. But using this scheme over here, this figure over here you see how your gammas are losing energy depending on their energy or their initial energy. Again now for gamma rays things that you may use is what we call linear attenuation coefficient that is defined just as the sum of the probabilities of having the photoelectric, the Compton and the pair production. This is how the intensity of your gamma ray beam is decreasing according to the linear attenuation coefficient. So this can show you how gammas are getting less and less as they are propagating into your matter. And another thing that we can define here is what we call mean free path. This means how much, what is the average length that a photon can travel into your matter before having an interaction and this as you can see here is inverse proportional to the linear attenuation coefficient. Okay, having said that let's pass to detectors. First thing that you are interested about detectors is what we call energy resolution. What is energy resolution is very simple. If I have two events with closed energies how much be, how big this difference must be in order to see these two events as two different events. This is what we call energy resolution. For particle detectors, for surface barrier detectors the energy resolution is between 13 and 15 kV for alpha particles. Have in mind that for particle detectors the energy resolution has to do also with the kind of the particle you are detected. The heavier the particle, the worse the resolution gets. So it may be 13 or 14 kV for alpha particles but if you use the surface barrier in order to detect oxygen this will go up to 40 or 45 kV. If you go to heavier elements these go worse and worse and worse. For gamma detectors the things are a little more complicated because now the resolution depends also on the energy of the gamma. So if you have higher gammas then you have worse resolution. Most of the time for gamma detectors as the resolution depends on the energy when you are talking about resolution you must also give the energy of the gamma. In most of the cases when you are talking about germanium detectors they will tell you that they have a resolution of for example 2.6 kV but they have also to tell you at what energy. Many times especially for scintillators instead of giving an absolute number you give the percentage but again you have to tell at which energy. So for example for sodium iodide detectors a typical resolution is something like 7% at 661 kV and here is just a figure to show you that the resolution changes as your energy goes higher. The second thing that we are interested about Can you tell me what is the reason for the first one that the energy gets worse when the particle gets energy resolution from the piece of the particle. It has mainly to do with the struggling the energy struggling. As here you have heavier particles they stay okay you need thinner detector but then the distribution gets really worse in the beginning. You mean with the optical detector There is also this plasma effect and deficit because when you introduce in silicon so huge amount of charges then the electric field drops locally and as it drops locally the combination probability increases and you lose some and this is why and it is also statistic. The second thing you have to know about your detector is detection efficiency. This means easily that I throw 1000 particles into my detector. How many of them are going to be detected? All of them, half of them, what does it mean? For particle detectors in most of the cases we assume a 100% efficiency. You throw 10 particles it will see 10 particles. You throw 100 particles it will see 100 particles. This is absolutely true for surface barrier detectors except if your detector has a problem. If you don't see 100% efficiency this means that you have a problem. Sorry? Yes but you don't take that into the efficiency because if the energy is too low it will never enter your detector. If it will never enter your detector it will be never detected. So it's outside let's say of the definition of efficiency. Efficiency means that I throw some particles they enter the detector do they interact with the detector and I can see them? Yes or no? If they stop for example in the dead layer of the detector Maybe they can stop inside the detector but generate a signal close to the noise or something like that. Ok but this is again it doesn't have to do with your detector it has to do let's say with the electronics. When we are talking here about efficiency of the particle detectors it means that it can enter your detector but you can see that but can you see all of them? Yes or no? In what we are talking it's entering the detector it gives you the signal but you can't see the signal if you can't see the signal either because you have much noise from your detector or you have much noise from your electronics you can't say that your detector is deficient I would call it inappropriate. Ok I would say that for example you have 5kV of protons they will be never detected but I wouldn't say that my detector is inefficient I would say that it's inappropriate for what you want to do. Ok For gamma detectors efficiency is slightly different because now the efficiency depends on the energy of the gamma and the bigger the energy the less the efficiency. In most applications when we are talking about efficiency for gamma detectors we incorporate into the calculation also the solid angle and this is easy to understand it's very difficult for a gamma detector to find its intrinsic efficiency because you should have the crystal surrounding your source this is not possible in most of the cases so you have your source here You mean like a form? Like a well you will see you have your source here you have your detector here so you measure the efficiency but this has it's not only the efficiency of the detector how good your detector can see the gammas how it can detect it it has also incorporated the solid angle that you are covering between your source and your detector. Most of the times when we are talking about gamma detectors we give a relative efficiency we don't talk about numbers like my efficiency at this energy 0.00 and this is because of the solid angle in most of the time you talk about relative efficiency with respect to a sodium iodide detector for example if you try if you go to buy a germanium detector you will ask for germanium detector of 50% efficiency this means that your detector has half the efficiency of a sodium iodine 3 inches time 3 inches placed at 12 cm ok so it's just a way of comparing detectors most of the detectors that you can buy germanium detectors have a relative efficiency of 40-50% if you go higher the price goes much much higher in our days we can have also germanium detectors with efficiencies higher than sodium iodide so you may find germanium detectors with 110% efficiency this means that they are 10% more efficient than sodium iodides but this is this costs very much so let's see now how the detectors are working 90% of the detectors that you are using in ion beam analysis it's based on semiconductors what is a semiconductor ok this is a conductor this means that I have a valence band and the conduction band and the one enters the other so this means that in the conduction band I have free electrons also in room temperature so here I have free electrons going back and forth this is a conductor the insulator means that here I have a band a gap between the conduction band and valence band this is almost 6 to 7 EVs and in room temperature or if you apply external voltage you don't have the migration of electrons from the valence band to the conduction band so you don't have any signal or any current in the conduction band while semiconductors are in between these two so you have again the valence band and the conduction band but the gap between them is not 0 but it's not also 6 EVs so for semiconductors we are talking mostly about silicon and germanium the gap here as you can see is for germanium 0.66 EVs for silicon 1.12 EVs this means that in room temperature or if you apply here an external voltage you have some free electrons jabbing from the valence band and the conduction band now if you want to use a detector to make a detector what you need you need something that when your ionization your radiation enters that it will produce a pair of electrons and holes it will ionize your your detector but you must find a way to collect these electrons or holes and distinguish them from free electrons you can't use a conductor because you always have free electrons so in free electrons you will produce also a small number of new electrons you will never be able to distinguish between them here you will produce nothing so you have to stick onto semiconductors so types of semiconductors as I told you we have intrinsic or purely you want semiconductors so you have this band gap for silicon is 1.1 EVs you have radiation the radiation goes into the valence band it finds an electron the electron is excited over here and you have the production of an electron over here and a hole over here in normal situation the number of electrons is equal to the number of holes if you have just a pure semiconductor you must find a way of increasing either the number of electrons or the number of holes and how you can do that you can do that by doping by substituting some silicon atoms with other atoms if you substitute a silicon atom with a phosphorus atom phosphorus have 5 electrons while silicon has 4 electrons you have an extra electron for the lattice of the silicon this is the first effect the second effect is that phosphorus have some intruder states as we call them some states that entering between the conduction band of the semiconductor and the valence band this means that it makes it easier for electrons to reach the conduction band because they have let's say a step as they can pass through this intermediate state for phosphorus the gap between the intruder state and the conduction band is about 0.04 eVs so the first thing you can do is to add donors add electrons so from an intrinsic you go to n type keep in mind negative type so we have surplus of protons or you can add acceptors or you can add holes how you add holes into a semiconductor you put something with less electrons than silicon so you put something that has 3 electrons for example boron so instead of putting phosphorus you put a boron here it has again an intruder state but this intruder state it's closer to the valence band and here you add up holes so instead of n type you have now a p type let's say semiconductor now how I'm going to use this trick in order to make a detector the easiest thing the first thing I could think to do is ok I have a semiconductor when radiation pass I produce electrons and holes if I just put two plates, two ohmic plates in the semiconductor I can collect the electrons or the holes I can integrate and I have a detector, perfect life is perfect the problem with just putting ohmic plates is that if you close the circuit over here you will start having electrons from the plate under the semiconductor and holes or positive carriers if you want from the other plate entering in order to keep the equilibrium of charges so if you have like that a system like that and if you apply let's say 500 volts to these two ohmic plates you will have a current, what we call a leakage current through the your detector of the order of 0.1 amps when radiation come and produces this pair of holes and electrons it will give you this is 10 to the 5 sorry, it's not 105 it's 10 to the 5 carriers this means that you will add up at 100 microns 1 micron you will never be able to distinguish a difference of 1 micron sitting on 100 microns, this means that if you are going to use that you will never succeed to use a semiconductor using ohmic plates as a detector you have to do if you want to use it as a semiconductor somehow you have to prevent electrons from the ohmic plates to enter your semiconductor or holes from the other side or if you want you have to build you have to do what we call non-injective or blocking or blocking electrons here you should put something to block the electrons or the holes under your semiconductor and mess with your signal ok how I can do that if you use the DOP surfaces this kind of thing and type in P-type detectors here you can block them and how I can use that with different ways and this is the different semiconductor detectors I have I have other diffused junction detectors surface barrier detectors that I mainly use PIN detectors and high purity detectors let's now see how we realize each thing before talking about that we are going to talk about PN junction what is a PN junction you have a P-type semiconductor and an N-type semiconductor and you bring them to contact one with another to be honest you can't do that you bring them in contact but let's say that you just press one over the other what it will happen the P-type has holes the N-type has electrons as you bring them into contact what is going to happen electrons will jump to the P-type will go over there and holes will go on the other side so you will have you start have diffusion of electrons through the P-type and holes to the N-type as an electron goes here and fills the hole here you will start having a surplus of negative charge also when an electron leaves here your semiconductor it will leave behind positive charge so by doing this diffusion of holes from here what you build you build here a zone where you have negative charge because of the electrons that jumped over here and positive charge here either because of the holes that migrated here or from the holes that the electrons left as they jumped over here in this case you will continue having this migration of holes and electrons until when they will stop somehow stop or it will continue doing that they will stop eventually why because as you have here negative and positive you start building there an electric force you have building you start building a potential and when the potential is big enough that will will embed electrons from jamming to this area or proton or holes jamming to this area this procedure will stop so I put the two they start jamming jamming my electric field starts building building building building and I'll arrive in one position that will prevent electrons from going there and then the procedure stops is what we say that we are reach an equilibrium this region over here the depletion layer of my semiconductor and this is the area that I'm going to use in order to detect my radiation keep in mind that here I still have holes and here outside the depletion layer I still have surplus of electrons now I have this nice semiconductor this nice junction and I'm going to put some voltage between them so this is unbiased this is the normal let's say situation now what it happens if I put a forward bias so if I push if I put voltage and push more electrons over here this means that my potential here is going to lower instead of being like that it will lower and this means that more electrons will jump here more holes will jump here and this means that I will have a bigger movement until I reach again equilibrium if you put an inverse biasing this means that you attract electrons over here and holes over here you are going to make your depletion layer bigger and bigger and this is what we normally use we bias inverse biasing our semiconductors in order to make the depletion layer bigger bigger depletion layer means thicker detector means more able to stop gammas or alphas so how I make this junction to semiconductors there are various ways of doing that but the first one they are not used so much in our days is what we call diffusion junction so when you begin with a p-type semiconductor and then either by implantation or using vapors of n-type donors you start implanting n-type things n-type donors into your p-type semiconductor if you do that you can reach a depletion layer of 15nm if you are using implantation up to 2 micrometers if you are using diffusion if you do this procedure you will end up with this thing over here so now you have your semiconductor here the p-type here you have an n-plus and here you have a p-plus semiconductor n-plus and p-plus the plus sign means that it is very doped so n-plus it means that I have a surplus a big surplus of electrons and here I have a surplus of holes the good thing with this detector is that if you apply now your inverse biasing these two p-plus and n-plus layers are acting as blocking electrons but they don't permit to have a big leakage current between that they drop your leakage current down to less than one microamp and then you can really see the holes, the pairs of holes and electrons that your radiation is producing nowadays most of the time we are using surface barrier detectors what you are going to end up is the same thing but it's the different thing how you produce them you begin with an n-type semiconductor and here you build a very thin electrode of gold while on the other side you build a very thin layer of aluminum now if you have a conductor or an n-type here in the junction between them you again produce something like the p-enjunction is another effect it's called the Sotki junction but let's say that it's much alike the p-enjunction so with this procedure you also end up here now what is the difference between the two and why we prefer using surface barrier detectors instead of diffusion junction detectors the problem is the thickness of the entrance window here you have this n-plus with the diffusion this is big enough this means as you ask me that if you have let's say an alpha particle of low energy this is thick enough it may stop the alpha particle into the electron never it's my semiconductor never to be seen if you are using a surface barrier using metallization you can make very thin layers of gold so you have again a dead layer but this dead layer is much much thinner than this one over here this means that surface barrier is able to detect heavier elements or if you want light elements of lower energy they can pass through the window the bad thing with surface barrier detectors almost the bad thing they are sensitive to light they can see light if you have a surface barrier detector into the air you will see your oscilloscope the 50 Hz light if you have a 50 Hz light and this is because of the thin entrance window on the other hand you don't much care because if you are going to use surface barrier detector you can put it under vacuum when you put it under vacuum you put it in chamber but it's closed with no light so you really don't care should it be here ok let's say it should be here these are some positions as detectors normally you will never use that in ion beam analysis techniques these are constructed let's say in the same way as these ones but now you have for example in these double phase strips dopped p-type or dopped n-type so you have let's say different detectors in the same paths in the same detector this means that if radiation pass over here you have the energy of the particle but you can also find the position of the particle do I care about that 95% of the cases no in similar ion beam analysis techniques no I don't care I just care about the energy as we saw in the RBS but if you are using some devices like what we saw before the high resolution RBS there you just don't need just the energy of the particle you need also the position so there you have to use some of these positions where my particle has hit the detector PIN detectors so here you have a p-type detector sorry semiconductor typically dopped with boron and here you have some lithium that is diffused in your semiconductor as lithium enters the semiconductor and it diffuses it's let's say anilates boron and it makes what we call a compensation region this is a region with no free carriers it's like the depletion layer of the previous detectors so when radiation passes over here it will again ionize give you holes and electrons you gather holes and electrons and again you have your signal you can see your radiation typical detectors was the jelly and silicon so you had a p-type germanium semiconductor diffused with lithium the problem the good thing with this detector was that the depletion layers could go up to millimeters so you could really make big thick detectors which were ideal for gamma ray detection for x-ray detection we use germanium for gamma rays because of its high Z why we use silicon silicon detectors for x-ray detection because of the lower Z what was the problem with them as you can see here they had as we said in the beginning lower efficiency than scintillators but better resolution what was the problem with these detectors the problem is lithium as lithium diffuses here and finds goes up to an equilibrium it's okay but lithium must stick there mustn't move and lithium likes to move has a great mobility so in order to make lithium stick into there you need to keep it in low temperature so you have to cool them with liquid nitrogen the problem is that you have to cool them down even if you don't use them so when you have a jelly or a silly detector they must be always always cooled with liquid nitrogen if you forget to put some nitrogen and leave them warm up what will be done lithium will drift further into the into the semiconductor or go to the surface you will destroy the commensation region and if you destroy the commensation region you don't have a detector that's why these are going slowly out of the market these were replaced with high purity germanium detectors just a comment jelly has to be cooled all the time it doesn't but again I have seen problems with silly not the cool I do the same thing I have two or three dead jelly detectors I have some silly detectors that are still working but I have seen deterioration in their resolution I thought that it was a problem of lithium drifting in germanium for example to gamma radiation after some but the problems with cool detectors come much earlier but even in any case detecting x-rays or detecting gamma rays that is intrinsically damaging yes but let's say that the life of a detector of a gamma detector if you are using normally in a normal use it's 15 or 20 years it's not something that will happen in five I don't know three or five years the biggest problem with germanium detectors is neutrons you have much problems much bigger problems if they are in an environment of neutrons not because they are detecting gamma rays surface barrier detectors are much sensitive if you want into radiation their life expectation is much less because of the damage let's say the radiation damage done by the particles that you are detecting I have killed surface barrier detectors because I put them too close to the beam so they saw 100nm of protons for five seconds not more than that and from a spin conductor it began a real conductor but there I had something like 10 to 15 protons in two seconds or three seconds if you are not planning to do that they can live for six to seven years easily germanium detectors much much more I have germanium detectors since the 80s and they are still working nicely with no problems so the solution for these two was what we call the high purity germanium detectors when you have a semiconductor by itself have some impurities so you can't use it like that but if you find a way of purifying the crystal then you can produce a same region like the one you produced with lithium but you have to do it very carefully so germanium is a crystal is a material that is used very often and they have found ways of purifying it with multiple purification process so what they do is that they take the crystal they heat it up they use some melting material on top of that to take out the impurities they cool it they heat it up again they make it liquid they purify it again and again and they can now reach something down to 10 to 9 impurities per centimeter square this work like the jelly the good thing with them is that as you don't have now lithium you don't care about drifting so you don't care to have liquid nitrogen when you don't use them when you use it of course you always use liquid nitrogen because of the small gap you have in a semiconductor you may have noise because of the thermal movement of electrons so you have to stop them you have somehow to depress the kinetic energy but you use liquid nitrogen in order to stop the thermal movement and the noise now with high purity germanic detectors also for jelly detectors you can have multiple geometries depending on what you are going to do this is a well formation so here you have the n type and this is your crystal you don't use that for ion beam analysis but at the time you use that if you want to do some environmental samples because your sample enters this hole over here and you have almost a 4 pi geometry in most of the cases when you are doing pige you are using either planar with p and 10 over here as we show there or coaxial so here you have again a detector the peak contact is in the middle and it's in contact this is better as you see the crystal is big so you have better efficiency instead of a planar but you can use both of them for pige analysis before the semiconductors everything started with scintillators what are scintillators? scintillators first of all can be organic and inorganic in most of the cases we are not using any organic scintillators for example there are organic scintillators liquid organic scintillators these are using nuclear physics not in ion beam analysis mostly for detection of neutrons you can use organic scintillators for neutrons because they have inside hydrogen but in our cases in ion beam analysis most of the time you are using inorganic the most known of that it's sodium iodide but also there are new crystals new scintillators like lanthanum bromide or chromium bromide lanthanum bromide has almost the same efficiency as sodium iodide but it has a better resolution how scintillators work? scintillators work in the principle that when you have an ionization an ionization radiation again you take an electron from the valence band you throw it up to the conduction band and here you have electrons and you leave back holes as the electron will de-excite most of the cases it will give you photons if you have just a crystal like sodium iodide the problem is that the photon that you will produce here is not in the visible range ok it is it is photon but it's not light it's not visible light in order to solve this problem sometimes you use what we call activators for sodium iodide in most of the cases you use thallium so thallium has this property that introducing some levels like the donors or the acceptors in the semiconductors between the conduction band and the valence band of the scintillator now how this help me into detecting radiation again you have radiation you produce a hole and an electron the whole propagation to the crystal it may find an activator it will find an activator it will excite the activator so it will excite the activator here you will miss an electron from the activator the electron that you produced from the radiation will find this hole and will go inside to fill it up and then it will de-excite into the activator levels but now as you can see here the distance between the levels is much less than the distance between the conduction band and the valence band of the crystal and this will give you light but this time this will give you visible light it will give you light if you see the light things are easier because you take the light you use a photomultiplier so you couple your scintillator with a photomultiplier which will see the light it will produce electrons then the electrons will be multiplied through the dinotes and will give me the signal in the anode the problem with the scintillators is while they are highly efficient much more efficient than the normal high purity germanium they don't need external cooling that's cool if you don't have to pay for liquid nitrogen the problem is first of all that most of them are hydroscopic this means that if they take some moisture they start being destroyed that's why they are always closed in aluminum cases the bad thing is that they have a very bad resolution and this is taken from Ortec just to see that here this is the spectrum that I see when I have a high purity germanium detector you can see the resolution I have in every peak if you use a sodium iodide then you look at the red line much worse here you can see that this line became like that forget all these lines you will never see that forget all these lines this line became like that if you use a cadmium cadmium efficiency cadmium zinc tellulite detector you have very poor efficiency and if you use a plastic scintillator you will see that has higher efficiency but no resolution you can't see anything so in most of the cases when you are talking about PGE you are obliged to use either a germanium detector or if you can't afford the germanium detector you can use a sodium iodide detector but have in mind that the resolution of the sodium iodide will be much worse you can do some job over here but I have seen papers from various groups but it's not let's say used for every case sorry and let's go let's finish with some very specific detectors gas detectors hide the work it's very easily most of the time gas detectors as I told you the beginning are used in TOFERDA instead of a surface buried detector at the end as an energy detector so you have here a cylinder you have inside a gas your radiation produces again protons and ions you have a voltage difference between them you collect to the end of the electrons you measure the electrons and that's all how many protons and holes and sorry ions you are going to create depends first of all to the gas that you are going to use so by changing the gas over here you have different number of pairs of ions and electrons the second thing you are interested of is the proportionality of this thing what does it mean proportionality is the number of pairs that I'm producing here proportional to the energy of the radiation yes or no if you look at this sorry, diagram over here this is the different regions of operation of a gas detector depending on the voltage that you are going to apply here as you can see you are proportional in the number of ions and the energy that you are going to produce and this is the region that we are using for ion chamber regions here the proportionality is lost is what you are using for proportional counting detectors and here over here you already are saturated so here you have no proportionality and here the only thing that you care is if something arrived or not and this is why this region is used for Geiger Geiger Miller detectors here the only information you have if something arrived something didn't arrive nothing else so we care about this region over here and this is how a gas ion chamber looks like so here you have your gas you have a nano and a cathode your radiation pass produces ions and electrons the electrons are drifted towards the anode ions are drifted towards the cathode now the signal that you are going to measure depends on the position of the radiation where your radiation passed it passed over here because it depends on X as you understand this is a problem because if I have a particle an alpha particle let's say of 3 MeV going here and an alpha particle of 3 MeV again but if they give me a different signal how I'm going to distinguish the two how can I know where it entered for this reason just keep in mind that here the signal you have it's not only produced by the collection of electrons but also it's produced by the use current on the anode by the electrons and by the movement of the ions so the solution is to use this freeze grid this freeze grid is kept in a voltage between the anode and the cathode and what it does it shields the anode from the movement on electrons and ions so your anode doesn't see anything as the electrons move and the ions move until the ions, sorry until the electrons pass through the grid when they pass the grid then they are visible from the anode and then the anode starts measuring and this is good because like that you don't care where they are produced if they are produced here and they move nothing happens when they pass the freeze grid then you start measuring and it's the same if they are produced here or here or here this is the reason we are using a freeze grid when you are using a freeze grid then you must be very precise when you construct that because you want to have a big shielding from the electrons on the other hand you want it to be transparent to the electrons and the last detectors that we are going to talk it's again used in TOFERDA is timing detectors so the trick here is the following you have here the ions entering your chamber or whatever you have over here and here you have a carbon foil as the ions pass through the carbon foil they will start emitting electrons ok they ionize if you want the carbon foil they extract electrons between the carbon foil and what we call here an electrostatic mirror you have a voltage difference so electrons are accelerated towards the grid this mirror bends the electrons towards a multichannel plate over here and electrons are detected this is not good detector if you want to use it for energy measurements because it doesn't give you any information about the energy of the ion that pass the carbon foil on the other hand it's very quick and you can use it as a timing signal it can tell you just something passed in TOFERDA measurement this is what I need I need something very quick to tell me something passed this is a start or a stop signal and then I have at the end either a gas ionization chamber or TOFERDA or a surface barrier detector that they measure the energy of the ion so that was all do I left you time?