User talk:Omar nusair

Large Area Neutron Detector
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Large Area Neutron Detector "LAND"
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This report presents the structure of the large area neutron detector. this detector is already installed and undrgone an experiment which aims to evaluate the cross section for astrophysics reactions such as 31_Cl(p,gamma)32_Ar, which is not easy to evaluate because of the small half life of 31_Cl, so the inverse of this reaction is solution.One of the probable outgoing particles is the neutron, so we will have 32_Ar(gamma,n)31_Ar, or 32_Ar(gamma,2n)30Ar, notice that our interesting reaction is 31_Cl(p,gamma)32_Ar. So we need a neutron detector to detect these neutrons,in order to study all the probabilities. This detector must be suitable for fast neutrons' detection, able to determine the position of the neutrons and their momenta.

== Neutron Detection ==

General Concepts in Neutron Detection

Neutrons are uncharged particles, so their interactions with matter are not as that of the charged particles, and its mass is not too large. so, the usual technique followed in case of charged particles' detection are not useful anymore; unless we convert the neutrons into either charged particles or gamma rays,which probably can be converted into charged particles depending on the efficiency of the detector. From here, if we want to detect neutrons, they have to be converted into Protons or alpha or gamma rays.

The conversion of neutrons into protons is our interest. In case of conversion the neutrons into heavy charged particles "fission fragments" happenes in nuclear fission reactors, where the fuel is induced by neutrons to undergo fission, which produces the fission fragments with high kinetic energy namely 200 MeV for both.in case of converting the neutrons into gamma rays, we depend on radiative capture reaction (n,gamma). Our interesting reaction is (n,p) reaction. Here we have to distinguish between two types of neutrons: In case of slow neutrons, we select the detector material that satisfies the following conditions: These detectors detect only the presence of neutrons. Where the previous 3 conditions still required with the demand to determine the initial energy which reaches an amount greater than 200 MeV, momentum of incident neutrons, and position if possible. This report will be only about the LAND as a fast neutron detector.  The discribtion of LAND The dependant reaction which converts neutrons into protons is $56_{Fe}$(n,p)$56_{Mn}$ where : Since the Q-value of this reaction is negative so only neutrons above the threshold energy will make the reeaction, which is guarnteed in our experiment since the neutrons have energy greater than 200 MeV. As we know the inverse reaction has +ve Q-value, so, for instance, the protons will directly make the inverse reaction, but it doesn't do, because the amount of $56_{Mn}$ is very small "the production rate is not enough to make the number of $56_{Mn}$ atoms reasonable for making the inverse reaction". but still there is a probability to have such a reaction, so the neutrons produced by the inverse reaction can again do an other reaction of the first type since they are emitted from iron-57, the compound nucleus, with high kinetic energy above the threshold energy of the reaction $56_{Fe}$(n,p)$56_{Mn}$. To go deep in details, LAND has front area of 2m x 2m and 1m in depth.It has a multilyer structure of passive convertor, the iron, and active scintillater material. The energy resolution delta T/T = 5.3% for a flight path of 15m and an overall detection effeciency epsilon 1 is anticipated with neutrons' energy T=1 GeV. The paddle structure The paddle structure has the advantage that the scintillater stripes serve as efficient light guides. they focus the scintilation light along the directions perpendicular to the neutron incidence direction.Position information can be obtained from the time difference between the light pulses arriving at the two paddle ends. The paddle thickness has to be chosen in accordance with both the accuracy envisaged for position measurement and that required for TOF measurement.So, LAND is subdivided into 200 paddles of 200 cm x 10 cm area and 10 cm depth. Each paddle contains 11 sheets of iron (the two outer ones are 2.5 mm thick, the others are 5 mm), notice that if we increase this thickness more than this amount we will probably lose some of these protons because of the energy loss,and 10 sheets of 5 mm thick scintillaters, mounted in an iron-sheet box which has a wall thickness of 1 mm. This sandwich structure in order to increase the efficiency. 20 paddles are arranged in one layer; subsequent layers are mounted with the paddles perpendicular to each other. Light produced in a paddle is collected by means of stripe light guides on both ends of the scintillater sheets and is directed to the photomultiplyers. In front of LAND there is a Veto detector for charged particles is installed. It consists of two crossed layers, each with 20 scintillaters' stripes. Their size of 200 cm x 10 cm x 0.5 cm matches the neutron paddle size. The reason of having such a detector is to avoid counting the external protons com from the background, by the using of anti-coencidence principle, where the protons will hit the Veto first then the first scintillater coencidently, so we can ignore this count registered in the data acquzition system. '''
 * Slow "thermal neutrons".
 * Fast Neutrons.
 * High Q-value.
 * High cross section in slow neutron energy region.
 * Abundant material.
 * The Q-value is -2.91312 MeV.
 * It has a high cross section of $56_{Fe}$(n,p)$56_{Mn}$ in fast neutron regionit is about hundreds of millibarns.
 * The Iron-56 is the most stable isotope, abundant and cheap.

== Application of the LAND =='''

The experiment is categorized in Nuclear-Astrophysics field,to evaluate the cross section of some kind of reactions happened in the stars "p-process" in specific nuclie, like Cl-31(P,gamma)Ar-32; it is easy to study the cross section for such a reaction by using "4-Pi" Gamma detectors if the nucleus of clorine-31 is stable, but it is not, and has a very short half life time, even if we accelerate the ions of clorine and have a time dilation it is not enough to reach the target alive, so here they thougt about inversing the reaction, by applying suitable Gamma rays to Ar-32 to become Cl-31 and detect the protons, but also the aArgon 32 is not stable, so what to do now, the idea is to accelerate the most stable argon isotope namley Ar-36", by using "SIS" the synchrotron, then smash it by any target to have many fragments, one of these is the Ar-32, and by using the "FRS" fragment seperator, we will have a pure beam of Ar-32, which will be drived to the experimental area, short distance, and inside the vaccumed ball, the target, there will be a high Z-material namely natural Pb, to have a source of energy to make the inverse reaction mintioned before Ar-32(gamma,P)Cl-31. There are three sources for having protons in this experiment and we have to distinguish between them because we need only that one of Gamma rays, the three sources are : all what we need to know, what is the probability of having Ar-32(gamma,P)Cl-31 exactly, so we first do the experiment but with C-12 target to have the pure excitation comes from the nuclear collisions, and this is useful since C-12 is not a high-z material and well sheilded to avoid any one of the other two excitation methods, then the calculation of this cross section will give an indication about that for the Pb, by using the extrapolation of the excitation function and making a corriction for it because the radius of Pb is Lager than that of C-12. Now to test the other excitation method namely the background radiation we do the experiment without a target and then we can evaluate the cross section. The experiment with Pb target produced the products: protons. Neutrons, because of that we use the LAND. Survived Argons and othe ions produced by the smashing or the interaction of the Ar-32. Now by using the "ALADIN", A LArge DIpole magNet, to seperate the products, the neutron will keep going in zero angle, the protons and the ions will be scatterd with different angles related to thier charges. The LAND was installed at the front side of the beam "zero angle". There are of course a TOF wall detector, GFI, RULO, and crystal ball, each one has a special purpose.
 * The virtual photons, compressed because of the relativistic motion, do the same work of Gamma Rays in exciting the Argon-32 to emitt proton.
 * The nuclear interactions between Pb and Ar-32 which can excite these Argons, the excitation guarentees the seperation of proton.
 * The background radiation "Cosmic rays" and Gammas.