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Neutrons have a magnetic moment that interacts with magnetic fields. This has been put to use to study magnetic materials. Polarised neutron imaging (PNI) is one such application that allows the observation of, for instance, magnetic domains and domain walls inside a sample. To facilitate a PNI experiment, the neutron beam from a neutron source needs to be polarised, meaning that the magnetic moments of all neutrons are aligned with an applied magnetic field. The device used to achieve this is called a “Polariser”. The focus of this thesis is the design of a polariser for the ODIN imaging instrument that is being constructed at the European Spallation Source (ESS). Among the different choices of polarisers, a “v-cavity” geometry will be used, which works on the principle of the polarisation-dependent reflection of neutrons from a surface structure called “polarising supermirror”. Here, Monte Carlo ray-tracing simulations are used to study the ODIN beam characteristics and subsequently to evaluate and optimise the polariser design. In addition, the design of a magnetic housing for the polariser is presented. This is needed, because the polarising supermirrors require a magnetic field to function. Using finite element method to compute the magnetic field, a magnetic housing is designed that would satisfy the field strength and field alignment requirements of the polariser., Neutrons can be used as a versatile tool to study material properties. Due to neutron having a magnetic moment, it is especially useful for studying magnetic materials. The magnetic moment is associated with an intrinsic property call “spin”. The spins of the neutrons need to be aligned in those studies. In this condition, the neutron beam is called “polarised”. One of the techniques that utilizes a polarised neutron beam is “polarised neutron imaging”. Using this technique, for instance, the magnetic domains inside a metallic sample can be directly seen and their behavior analyzed. At the European Spallation Source, a new large sale facility for the scientific use of neutrons, the imaging instrument ODIN is currently under construction. Polarised neutron imaging will be one of ODIN’s unique capabilities. The device to create a polarised beam is called “polariser”. It is based on a special magnetic layered structured called “polarising supermirrors” which reflects only neutrons with a selected spin-orientation, creating a spin-aligned neutron beam. This work focused on designing a polariser for ODIN by adapting conventional arrangement of polarising supermirrors for nonfocusing beam to a focusing polariser that will match ODIN’s strongly focused beam. A key design constraint is that ODIN will use neutrons in a wide energy range and reflection by supermirror is highly energy-dependent. Using “McStas”, a simulation tool for designing neutron instrument components, the performances over a range of polariser design parameters were analyzed. We succeeded in finding a geometry that satisfied all design requirements, primarily the degree of polarisation achieved for the full range of neutron energies to be used on ODIN. The polariser requires a magnetic field to function. Finite element calculations were done using COMSOL software to verify a magnetic housing design to have exceeded the design requirements.

In order to safely design accelerator-based research facilities, such as the European Spallation Source, shielding calculations are carried out using Monte-Carlo particle simulations. However, these calculations gain high uncertainty when large amounts of shielding are needed, due to decreasing particle statistics over distance and mass. To circumvent this issue, variance reduction methods are used to reduce errors in calculations. A possible method for this purpose is Kernel Density Estimation (KDE). In this thesis, KDE methods has been applied to shielding calculations done around the ESS linear accelerator. A model of the accelerator was constructed in which the calculations were run using a Monte Carlo particle transport code. It was found that using KDE can be used to reduce uncertainty in shielding calculations. However, the parameters of the bandwidth selection method, such as the property importance, needs to be worked with in order to get a good estimate of the distributions of the particle properties., Radiation shielding calculations are an important aspect when building a particle accelerator, such as the one at the European Spallation Source (ESS), a research facility located in the northern part of Lund. They are applied to determine how much shielding is needed to protect workers and the public from radiation during operation. However, these types of calculations can have high uncertainty when done for large amounts of shielding, due to the number of particles decreasing over distance from the accelerator from interactions in the shielding. To circumvent this issue, there are several different types of variance reduction techniques that can be applied to make the problem more tractable. As the name implies, they are used to decrease the uncertainty of calculations where needed. A possible variance reduction method for high-energy accelerator applications is Kernel Density Estimation (KDE). This is a method for estimating the probability distribution of a set of particles. Doing so allows the generation of new particles relative with said distribution. By creating a new source some distance away from the original source, the uncertainty beyond the new source term location can be decreased more efficiently. The goal of this project was to apply KDE techniques to shielding calculations done around the ESS accelerator. A computer model of the accelerator was constructed, in which the calculations were performed using Monte Carlo particle transport code. Properties of simulated particles crossing certain regions were recorded, and then used to create new source terms using KDE. The distributions of the properties from the different sources were compared to evaluate performance. The simulated dose rates were also compared to check the quality of the results.

The European Spallation Source ESS, under construction in Lund, Sweden, aims to produce high-brightness and intensity neutrons for a multitude of experiments upon completion. An efficient production of neutrons requires elaborate understanding of the moderation process which slows the neutrons from relativistic speed to a kinetic energy of meV. The moderator used at the ESS will be partially made of water and liquid para-hydrogen, which enables simultaneous production of thermal and cold neutrons. The interaction between neutrons and the moderator is best described by the total neutron scattering cross section which in turn is computationally derived from the scattering kernel. The liquid hydrogen kernel itself includes models of a self- and distinct scattering function which describe the interaction of individual molecules with neutrons as well as interference effects of scattered matter waves from neighboring molecules. Scattering kernels are commonly produced by a software called NJOY, however, an effort at ESS has been made to develop and transition to a new software called NCrystal. Its more flexible design allows for easier implementation of physics models beyond what is currently included in NJOY for more moderator materials. Thus far, NCrystal is primarily aimed at generating scattering kernels for poly-crystalline materials in solid phase, a capability which was now expanded to liquid water and liquid hydrogen. The resulting cross sections were bench-marked against proven software and show good agreement., The challenge of slowing down neutrons the right way The European Spallation Source ESS, which is currently under construction in Lund, Sweden, is a next-generation neutron research facility. Once completed, it will use neutrons to undertake a multitude of experiments, some of them carrying out fundamental research and others more practical in material science. The production of neutrons in a spallation source requires an energetic proton beam which is accelerated by a linear particle accelerator to velocities close the speed of light. This beam is impacted into a target made of solid metal. Here, the neutrons are produced by a phenomenon called spallation: the protons are so fast that they break apart the nuclei of the target into smaller nuclei and, crucially, several free and very energetic neutrons. For many applications these neutrons are too fast and thus have to be slowed down to appropriate speeds. But how can you brake particles that move close to speed of light and have no electric charge which you could grab them by? You send them through a moderator. A moderator is a material that acts like a sticky ”syrup” on neutrons and slows them down to the speed of sound before they can escape again and then be used for experiments. Moderators have been researched and used for decades in efforts to make nuclear energy a safe and reliable power source. Almost every nuclear power plant uses a very familiar moderator: water. However, even after passing through water, the neutrons, now called thermal neutrons, are still too energetic for a lot of material science applications. This is where current knowledge becomes sparser, since different, more rarely used moderators have to be employed, in case of the ESS liquid hydrogen. To design an efficient moderator, the slowing-down process is simulated with scattering software to obtain the scattering kernel, a quantity which describes how energy and momentum is deposited in the moderator when neutrons pass through it. So far

The European Spallation Source (ESS) is going to be the worlds most powerful spallation source once in full operation. The neutrons used by scientists and engineers are spallated from a rotating wheel of wolfram, being bombarded by accellerated protons. The wheel, also called the target, develops heat in the process, and is therefore cooled by a helium cooling system. The target primary cooling system, named system 1010, is modelled in the language Modelica but is not fully verified, nor has any practical testing been conducted. ETHEL is a test rig located at LTH, similar in function to that of system 1010. It can be used to conduct experiments, and the results can to some degree be extrapolated to system 1010. A model of ETHEL was constructed. The model was intended to both be faithful to the physical contraints of ETHEL, but also constructed similarly enough to the system 1010 model to allow for extrapolation of the conclusions made. Transient experiments were formulated, based on expected cases of failure for system 1010. The experiments were conducted on the ETHEL rig, the ETHEL model, and the system 1010 model. Based on the experiment results a model evaluation of the ETHEL model was conducted, both in regards to time-response behaviour, and in regard to data error. System identification on both the system 1010 model data, and the ETHEL data was conducted, with the purpose to identify significance of sensor location in the former case, and to determine the relative speed of the sensors in the latter case. Three sensor types were examined for their speed, however the analysis lacked the tools to evaluate their accuracy. The location analysis revealed that the exact location of the sensor in the system 1010 model did not significantly impact the time-response. The model evaluation showed that the ETHEL model performance was qualitatively good, demonstrating a good time-response compare to the real system, however significant quantitative errors were found. The re, The European Spallation Source (sv: Europeiska Spallationskällan) kommer att bli den mest kraftfulla spallationskällan i världen när den är i drift vid full kapacitet. Neutronerna som används av vetenskapsmän och ingenjörer är spallerade från ett roterande hjul av volfram, som blir bombarderat av accellererade protoner. Hjulet, även kallat målet, upplever värmeutveckling under spallationsprocessen, och är därför kyld av ett kylningssystem som använder helium. Målets primära kylsystem, även kallat system 1010, har blivit modellerat i programmeringsspråket Modelica, men är varken fullt verifierad eller praktiskt utvärderad. ETHEL är en test-rigg placerad vid LTH, och liknar system 1010 i funktion. Den kan användas för att utföra experiment, och resultaten kan till viss grad extrapoleras till system 1010. En modell av ETHEL var konstruerad. Modellen hade syftet att vara både trogen till de fysikaliska begränsningarna för ETHEL, och att konstrueras lika nog system 1010 modellen för att kunna extrapolera gjorda slutsatser. Transienta experiment formulerades, baserade på förväntade funktionsavbrott för system 1010. Experimenten utfördes på ETHEL-riggen, ETHEL-modellen, samt system 1010 modellen. Baserat på resultaten från experimenten utvärderades ETHEL modellen, både i avseende på tidssvar, samt avseende på dataavvikelse. Systemidentifiering på både system 1010 modelldatan och datan från ETHEL utfördes, med syftet att bedöma betydelsen av sensor-placering med den förstnämnda datan, samt att bedöma den relativa snabbheten med den sistnämnda. Tre sensortyper undersöktes i avseende av snabbhet, men analysen saknade verktygen att avgöra sensorns pricksäkerhet. Placeringsanalysen visade att sensors placering i system 1010 modellen inte signifikant påverkade tidssvaret. Modellutvärderingen visade att ETHEL-modellen presterad kvalitativt bra, den visade tidssvar som väl jämfördes med det riktiga datan, men att betydande kvantitativa fel upptäcktes. Resultaten extrapolerades til, The European Spallation Source (sv: Europeiska Spallationskällan) kommer att bli den mest kraftfulla spallationskällan i världen när den är i drift vid full kapacitet i 2027, med nästan samma effekt som 4000 mikrovågsugnar samtidigt. Spalleringen producerar neutroner som i sin tur används av vetenskapsmän och ingenjörer. Det sker genom att man bombarderar ett roterande hjul av tungsten med protoner. Hjulet värms upp under spallationsprocessen till väldigt höga temperaturer, och är därför kyld av ett kylningssystem. Målet med arbetet var att testa och utvärdera det primära kylsystemets matematiska modeller, så att ingenjörer som jobbar på ESS kan förutspå huruvida systemet kommer att fungera, redan innan det är byggt. Det var även tanken att man kan utvärdera vart man ska sätta temperatursensorer i kylsystemet, och av vilken typ dessa ska vara. Med hjälp till detta användes ETHEL, en testrigg placerad vid LTH, och liknar kylsystemet i funktion. Den kan användas för att utföra experiment, och från resultaten mellan ETHEL och sin modell, kan säga saker om förhållandet mellan kylsystemet och dess modell. Först var man tvungen att komma på bra experiment att utföra på modellerna och på ETHEL. Man kollade i riskanalyser för ESS, och såg några händelser som kunde uppstå, och återskapade dem för de alla systemen man skulle utföra experimenten på. Sedan kunde man, från resultaten av experimenten säga saker om modellen och sensorerna. Det viktigaste var att modellen betedde sig på samma sätt som systemet, bra! Tyvärr, kanske ganska fel i de exakta siffrorna, men tidsskalan stämde. Med grund i att tidsskalan för modellen stämmer kan man se hur lång tid sensorerna tar för att se en temperaturändring, då vi ändrar någonting annat i systemet, och vi kan lita på att det stämmer för det verkliga systemet. Det visade sig att det tunga tungstenshjulet absorberar en hel del energi, och därför tar ett bra tag innan man ser någon ändring alls från senorerna, och ännu längre tills de vis

To boost the science case of MIRACLES, the time-of-flight backscattering spectrometer at the European Spallation Source (ESS), an optimized neutron guide system, is proposed. This systematic study resulted in an enhancement in the transport of cold neutrons, compared with the previous conceptual design, with wavelengths ranging from lambda = 2 angstrom to 20 angstrom along the 162.5-m distance from source to sample. This maintained the undisturbed main focus of the instrument, viz, to carry out quasielastic and inelastic neutron scattering (QENS and INS) experiments on a large dynamic range and for both energy-gain and energy-loss sides. To improve the collection of cold neutrons from the source and direct them to the sample position, the vertical geometry was adjusted to an adapted version of a ballistic elliptical profile. Its horizontal geometry was conceived to: (i) keep the high-resolution performance of the instrument, and (ii) minimize the background originating from fast and thermal neutrons. To comply with the first requirement, a narrow guide section at the pulse shaping chopper position has been implemented. To fulfil the second, a curved guide segment has been chosen to suppress neutrons with wavelengths lambda < 2 angstrom. Subsequent tailoring of the phase space provided an efficient transport of cold neutrons along the beamline to reach a 3 x 3 cm(2) sample. Finally, additional calculations were performed to present a potential upgrade, with the exchange of the final segment, to focus on samples of approximately 1 x 1 cm(2); the proposal anticipates a flux increase of 70% in this 1 cm(2) sample area.

This report outlines the first stages of the development of the Neutron Activation Analysis station at the Lund Ion Beam Analysis Facility in the Division of Nuclear Physics, Lund University. The motivation for this project is to use the Neutron Activation Analysis detection technique for environmental monitoring around the European Spallation Source, soon to come into operation. In the event of an emergency scenario, some radiotoxic isotopes may be released into the environment from the Tungsten spallation target, including the difficult to detect lanthanide, 148Gd. In normal operation, a variety of radionuclides may also be released. In this initial stage, the aim was to build a measurement station which is able to measure very short-lived activation products, and to investigate if it is possible to trace gadolinium isotopes in environmental samples using neutron activation analysis. The measurement station was constructed over the span of one semester, and a selection of metal foils and environmental samples were activated and analysed. The samples were irradiated using a portable neutron generator with a maximum production rate of 4.71 ·10E8 n/s. Two methods of measurement were utilised: one which used irradiation- and measurement- times of longer than one hour, and another which used a fast pneumatic transport system with irradiation- and measurement-times of less than 1 minute. High Purity Germanium detectors were used to measure the γ-rays emitted from the activated samples. Results showed that with the selection of tested samples, it was possible to measure activation products with half-lives as short as two seconds using the fast pneumatic line. In the environmental samples, it was seen that amounts larger than several grams were needed in order to see activation and that longer irradiation time was more suitable. The results obtained show that the station has the potential to be developed for use with the Compact Accelerator-driven Neutron Source under dev, Scientists have been dating ancient pottery and other relics for decades, to uncover the stories of lost civilisations and forgotten traditions. Of the methods used, it turns out that it is a nuclear technique which best preserves these valuable pieces of history, while other techniques risk destroying them. The process, called ​Neutron Activation Analysis, (NAA), can not only find when and where a sample is from, but exactly what isotopes it is made up of. NAA involves ‘activating’ a chosen sample – an old pot, for example – by blasting it with billions of neutrons, until it becomes radioactive. The atoms in the pot absorb the neutrons, and their nuclei become unstable, quickly ejecting high energy electromagnetic waves called gamma rays, to reach stability again. The frequencies of the gamma rays are unique to each isotope and can be analysed to uncover it’s exact composition, and when and where it has been. The pot could remain radioactive for several days or weeks afterwards, but can eventually be safely returned to its owner. For example, a leading research scientist at Imperial College London, Judit Nagy, was able to use neutron activation analysis to date ancient Hungarian pottery to unearth the trade routes travelled by early European merchants. This technique is also used all the time in present day investigations too. Because NAA can reveal even minute traces of an isotope, materials such as bullet fragments, gunshot residue, DNA, and poison can be identified, rendering NAA particularly useful in forensic science and criminal investigations. In the wake of the climate crisis, a further important application of NAA is environmental monitoring. Samples such as soil, plants and sediment can be analysed to assess the health of a particular environment. From this, we can see where human activities are causing harmful effects on ecosystems and learn the origins of pollution. One issue that scientists run into with NAA, is that in order to get a high enough blast

The goal of this project is the design of the magnetic field of the neutron analyser for the European Spallation Source instrument DREAM (Diffraction Resolved by Energy and Angle Measurements). This instrument is a neutron diffractometer and its purpose is the determination of the magnetic and chemical structure of materials. Simulations have been performed over the span of a semester using the Finite Element Method (FEM) in a software called COMSOL Multiphysics. Three different setups, with different guide fields, have been investigated and compared in order to achieve the best results. This has required to study how to produce highly uniform magnetic fields with coils. The initial setup, where the guide was composed by four rectangular coils, was found not to meet the required field characteristics concerning adiabaticity and uniformity. The second setup, which comprised also four compensation coils, fulfilled the specifications. However, a third setup based on a Halbach four-coil exceeded the required field characteristics and thus allows for potential imperfections in the manufacturing of the coils. As part of this work, different aspects of neutron physics have been investigated, including, neutron scattering, spin-filtering and spin-transport, which are the main physics principles behind DREAM., European Spallation Source (ESS) is a world leading research facility and its main purpose is the production of neutrons. Someone might wonder what to do with all these neutrons. The answer is the following. Neutrons do have potentially a lot of useful applications. For example, if someone breaks their arm and needs to go to the hospital, their arms get scanned using X-rays. If the research that is being carried at ESS will succeed, then one day it might be possible to do it with neutrons instead. One advantage of that would be that neutrons can do a more precise imaging than X-rays. Another interesting aspect to consider is that X-ray can potentially damage a biological tissue, while neutrons cannot. This means that neutrons can allow us to carry out a much deeper study of how a medicine is perceived by the body for example. The principle behind the imaging is neutron diffraction. In other words we shoot neutrons against a sample, then by looking at what happens to them we figure out information about the sample, like its magnetic or chemical structure. My work is being carried in a particular instrument called DREAM. This machine works the following way. Once neutrons arrive, they are going to be filtered first, otherwise they cannot give us any interesting information. Neutrons are like the salad that you buy in the supermarket: you have to wash it before you eat it. Then the neutrons will do diffraction as already explained and finally they will be analysed. My project focuses on designing a Helium based analyser for the diffractometer DREAM instrument. This is made by essentially two components. First a tube in which the neutrons travel after they have hit the sample. Around this tube there is a magnetic field guide. Afterwards there is a coil structure containing a Helium gas that interacts with the neutrons. The main tasks I work on are the simulations and the design of the magnetic field. The simulations are being done with the help of the Finite Element Met

The violation of baryon number, , is an essential ingredient for the preferential creation of matter over antimatter needed to account for the observed baryon asymmetry in the Universe. However, such a process has yet to be experimentally observed. The HIBEAM/NNBAR program is a proposed two-stage experiment at the European Spallation Source to search for baryon number violation. The program will include high-sensitivity searches for processes that violate baryon number by one or two units: free neutron–antineutron oscillation () via mixing, neutron–antineutron oscillation via regeneration from a sterile neutron state (), and neutron disappearance (n → n'); the effective process of neutron regeneration () is also possible. The program can be used to discover and characterize mixing in the neutron, antineutron and sterile neutron sectors. The experiment addre

To control an accelerating proton beam that travels close to the speed of light, a large number of beam diagnostic instruments are needed. One of the instruments that will be used at the accelerator of the European Spallation Source is a Non-invasive Profile Monitor (NPM). Once installed, this system will measure the transverse beam profile by imaging the fluorescent gas induced by the accelerated proton beam. However, there are two problems that make this system more complex than just using a camera. In the Medium Energy Beam Transport (MEBT) section where this monitor is going to be placed, the light intensity will be very low. The NPM has to image the beam in a single photon counting mode. To achieve this, an image intensifier is used to amplify the number of photons. The second problem is the high level of radiation next to the beam. The camera has to be placed in a shielded area away from the beam, and the image is therefore transported via a 10-meter-long fiber bundle to the camera. The goal of this thesis is to understand the characteristics of the NPM and to demonstrate that single photon imaging is possible. The results show that these requirements are fulfilled if some suggested modifications are made. An additional model of the system was implemented in MATLAB, to understand its response when parameters of the system are varied. The work of this thesis, including the model, can be used when designing future systems similar to the NPM., How do you take a picture of an accelerating proton beam? Is it even possible? And why would you want to? To steer protons at close to the speed of light you need to see what you are doing. As it turns out, a good camera and a bit of fluorescent light makes this a possibility.

Understanding material behaviour has in the past enabled human development and will continue to characterize the various stages of our future development. The use of neutrons will greatly affect several research areas, such as sustainable energy production and cancer research, due to their interaction with nuclei. Neutrons will thus interact differently depending on the specific isotope, reveal information on crystal and magnetic structure and track dynamics of atoms. The European Spallation Source is currently under construction and can be compared to a giant powerful neutron microscope which is a huge step forward in everyday life science. To meet the need of each research area, numerous techniques and methodologies are required. To optimize performance, different energy spectra of the neutrons are needed depending on the research area. A neutron chopper is a type of mechanical neutron filter which filters out the wanted energy spectra. One of the most crucial components of the neutron chopper is the disc, made of carbon fibre reinforced epoxy, which will be in contact with the neutron beam. It is thus necessary to analyse the impact of radiation on the neutron chopper disc. To investigate whether the radiation damage is universal between different types of epoxy, two different epoxy resins were used. Each type of composite was then irradiated with 0, 3, 10 and 30 MGy. Using X-ray tomography in combination with a porosity analysis it was seen that the number of pores increased with radiation dose. However, this effect was only seen in one of the composites meaning that the radiation damage is not universal between different types of epoxy. It was seen that more elliptic medium sized pores are favourable. However, the mechanical properties, tested using three-point bending, showed no apparent change after exposures. Scanning electron microscopy revealed no evident changes of the fracture surfaces after irradiation. In totality, the results helped ESS to confidently, The European Spallation Source can be considered a giant powerful neutron microscope, enabling detailed material study. Depending on the research area, different energy spectra of the neutron beam are required. The neutron chopper disc is a mechanical filter selecting the wanted energy spectra. It is crucial to investigate the effect of radiation on this disc.