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The Large Hadron Collider, LHC, at CERN is capable of producing proton-proton collisions at a total energy of 14 TeV. Four principal detectors are installed in the LHC to detect the various particles created in the collisions. In one of these detectors, the CMS, scintillating crystals of lead tungstate are utilized to convert the energy of electromagnetic particles to visible light. Due to the high amount of radiation in the detector, the performance of the crystals may degrade during the lifetime of the detector. In this work, crystals such as the ones used in the CMS detector are irradiated with gamma radiation and protons to estimate the transmission loss in the crystals. The spontaneous recovery at room temperature is studied over a period of several weeks. Induced diffusion is also studied. In addition, techniques for reversing crystal damage are presented and studied. The techniques used are thermal bleaching, restoration by  heating the crystals, and optical bleaching, restoration by exposing the crystals to light of a specified wavelength.The light yield, the amount of light extracted per unit of deposited energy, for different crystals and different types of sources has also been compared. The sources used have been gamma, alpha and neutron sources. The induced absorption of standard PWO endcaps at 422 nm after being exposed to 1 kGy gammas was measured to be in the range of 0.6 to 0.7 m-1For mo-doped crystals the corresponding value was measured in the range of 0.2 to 0.3 m .-1 When increasing the dose to 100 kGy the induced .absorption at 422 nm was found in the range of 1.17 to 1.32 m-1for standard crystals and 3.02 to 4.43 m-1for molybdenum doped crystals. The transmission could be completely recovered using thermal bleaching for both gamma and proton induced damage, while optical bleaching has so far only been shown to perform a limited recovery. Proton irradiated samples demonstrated an induced diffusion, which could be eliminated using thermal bleaching.The light yield of the measured crystals was shown to be consistently lower for alpha particles and neutrons than for gamma particles. The rates varied in the range of 5% to 27% when comparing the light yield for alpha particles to gamma particles, and in the range of 5% to 70% when comparing neutrons to gammas / LHC, “Large Hadron Collider”, är  en partikelaccelerator vid CERN med en förmåga att producera kollisioner mellan protoner och protoner vid 14 TeV total energi. Fyra huvuddetektorer är installerade i LHC för att detektera de partiklar som skapas vid kollisionerna. I en av dessa detektorer, CMS, används scintillationskristaller av bly-wolfram-oxid för att omvandla energin från elektromagnetiska partiklar till synligt ljus. På grund av den stora mängden strålning i detektorn kan dessa kristallers egenskaper försämras över tiden.I detta arbete har kristaller av den typ som används i CMS-detektorn bestrålats med gammapartiklar och protoner för att uppskatta förlusten av transmission i kristallerna. Den spontana återhämtningen av transmission har studerats över en period av flera veckor. Inducerad diffusion från protoner har också studerats. Tekniker för att återfå kristallernas egenskaper presenteras och deras effektivitet studeras. Teknikerna som används är termisk blekning, återhämtning genom uppvärmning av kristallerna, och optisk blekning, återhämtning genom att belysa kristallerna med ljus av en specifik våglängd.Mängden ljus en kristall producerar per enhet av deponerad energi för olika kristaller och typer av källor har studerats. De använda källorna har varit gamma-, alfa- och neutronkällor.Den  inducerade absorptionen hos standard  endcap-kristaller vid 422 nm efter 1 kGy gammastrålning uppmättes mellan 0,6 och 0,7 m-1 För molybdenium-dopade kristaller var det motsvarande värdet .mellan 0,2 och 0,3 m-1 Efter en dos av 100 kGy uppmättes den inducerade absorptionen mellan 1,17 .och 1,32 m-1för standardkristaller och mellan 3,02 och 4,43 m-1för molybdenium-dopade kristaller. Transmissionen kunde  helt återfås medelst termisk blekning för både gamma- och protoninducerad skada, medan optisk blekning hittills endast uppvisat delvis återhämtning. Protonbestrålade prov visade en inducerad diffusion, som kunde elimineras med termisk blekning.Mängden ljus de studerade kristallerna producerar visades vara konsekvent lägre för alfapartiklar och neutroner än för gammapartiklar. Kvoten mellan mängden ljus producerat av alfapartiklar och gammapartiklar varierade mellan  5 % och  27 % för de olika kristallerna. Motsvarande kvot för  ljus producerat av neutroner och gammapartiklar varierade mellan 5 % och 70 %.

There is high industrial demand for materials with a high piezoelectrical response which are stable at high temperatures. A recent study on ScAlN has explained the microscopic origin of the increased piezoelectric response in the alloy and its effect on the energy landscape. Y is a promising candidate to observe the same phenomena. The ab initio DFT-GGA calculations for Y0.375Al0.625N, using a 128 atom SQS model, show a less pronounced increase of the piezoelectric response. The Y0.375Al0.625N energy landscape shows a flattening due to competition between the parent wurtzite phase of AlN and the hexagonal phase of YN. The flattening causes softening of the C33 elastic constant, while the piezoelectric constant e33 is only slightly increased. This slight increase can be explained by the quite stable local tetrahedral environment in Y0.375Al0.625N, which is related to the big volume mismatch between the parent YN and AlN. In summary we conclude the importance of the volume matching to obtain high piezoelectric response via phase competition.

Utgångspunkten i detta arbete är vårt intresse för hur elever uppnår förståelse i fysik och om/hur de ser kopplingar till verkligheten/vardagen. Anser gymnasieelever att det är viktigt med denna koppling? I vårt arbete har vi valt att dela in fysikundervisningen i fyra moment, genomgång, problemlösning, demonstration samt laboration, här har vi skrivit momenten i ordningen, från det mest abstrakta till det mest konkreta. Vårt syfte är att redogöra för de fyra momentens betydelse i undervisningen när det gäller att alla elever ska kunna uppnå förståelse. Vi har valt att utforma en elevenkät med ett antal frågor kring fysikundervisning och bl.a. frågat vilket moment som i första hand ger en elev förståelse samt om det är någon speciell ordning som eleverna föredrar. Dessutom har ett antal elever intervjuats kring dessa frågor. Fysikelever från tre gymnasieskolor i Växjö kommun, två kommunala och en friskola har svarat på enkäten. Resultatet från enkäten blev att de fyra momenten värderades lika viktiga för förståelsen.

<p>Observations of gamma-rays have been made from objects such as active galaxies and supernova remnants and also as diffuse emission from the Galactic ridge. The study of gamma-rays can provide information about production mechanisms and tell us about cosmic ray acceleration. In the high energy regime, the dominant mechanism for gamma-ray production is the decay of neutral pions produced in interactions of accelerated cosmic ray nuclei and interstellar matter. Having an accurate model for this is an integral part in the study of gamma-rays and the sources in which they are produced.</p><p>We present here a parametric model for calculations of inclusive cross sections for stable secondary particles (gamma-rays, electrons, positrons, nue, anti nue, numu and anti numu) produced in proton-proton interactions. The model is based on the up-to-date proton-proton interaction model by Kamae et al., which includes the diffraction dissociation process, violation of the Feynman scaling law and the logarithmically rising inelastic proton-proton cross section. To improve fidelity to experimental data for lower energies, two baryon resonance excitation processes were added to the model: one representing the Δ(1232) and the other multiple resonances with masses around 1600 MeV/c^2. The parametric model predicts the spectra for all secondary particles to be harder by about 0.05 in power-law index than that of the incident proton and their inclusive cross sections to be larger than those predicted by previous models based on Feynman scaling. The transverse momentum distributions for gamma-rays have also been calculated from the described proton-proton interaction model, showing the potential of also having a parametric model for the transverse momentum distributions.</p>

No description available.

<p>Atomic nuclei are complex many-body systems and exhibit an interplay between single-particle and collective degrees of freedom. In order to describe and predict the “behavior” of nucleons inside the nuclei a variety of theoretical models have been created, each applicable to their own domain of nuclear phenomena. Experimental information is needed in order to test and improve the various theoretical models with the ultimate goal of creating unified theory of nuclear structure. In-beam -ray spectroscopy is one way of probing the inner structure of nuclei and it is the subject of this thesis, which describes the first identification of excited states in the extremely neutron deficient nuclei ¹⁰⁶Te and ¹⁰⁷Te. The experiments were performed at the Accelerator Laboratory of the University of Jyväskylä, Finland, using the recoil-decay tagging technique. Prompt  rays emitted following fusion evaporation reactions were detected by the Jurogam detector array and the selection of the  rays of interest was based on the recoil identification provided by the RITU gas-filled recoil separator and the GREAT focal plane spectrometer. The production cross sections were estimated to be 25nb and 1 b for¹⁰⁶Te and ¹⁰⁷Te, respectively. In case of the nucleus ¹⁰⁶Te, several  rays have been observed. A vibrational-like yrast band has been suggested. For¹⁰⁷Te a number of  rays have been assigned and a tentative partial level scheme has been suggested. The experimental data have been compared to shell model calculations.</p>

<p>This thesis describes separate studies of high-energy Rydberg and ion-pair states in small molecules using resonant multi-photon ionisation spectroscopy.</p><p>* OODR/REMPI study of ungerade Rydberg states in O₂</p><p>The energy region between 75000 and 99900 cm^-1 of O₂ has been studied using optical-optical double resonance (OODR) with resonance enhanced multi-photon ionisation (REMPI). Three-photon excitation via single rotational levels of the b(¹Σ⁺_g ) valence state was used to study <i>n</i>p (<i>n</i>=3–10) and <i>nf </i>(<i>n</i>=4–9) Rydberg states converging on O₂⁺X(²Π_1/2,g) and X(²Π_3/2,g). The excitation pathway picks out non-predissociated states that are singlet in the (Λ,S) coupling scheme – suitable for np states for n ≥8, or are linear combinations of equal weight of singlet and triplet-spin states in the (Ω,ω) coupling scheme which was found to be suitable for nf states for all values of n.</p><p>* OTR/RI study of Rydberg and ion-pair states in I₂</p><p>Optical triple resonance (OTR) together with resonance ionisation (RI) has been used to study the ungerade manifold of molecular iodine between 57000 and 73000 cm^-1 via the E 0_g⁺(³P₂) ion-pair state. Two 6s Rydberg states with 0 +u symmetry based on excited states of the ion core have been observed.</p><p>During this study we also observed electric-field-induced mixing of nearly isoenergetic rovibrational levels of the E0_gP⁺(³P₂) and D0<i>u</i><i>+</i>(³P₂) ion-pair states. Detectable mixing with an applied field of 1kV/cm occurs over a range of energy level separations of ≤0.3 cm^-1.</p><p>* (2+1)and (3+1) REMPI study of pyrrole (C₄H₅N) The two- and three-photon REMPI spectra of Rydberg states of pyrrole (C₄H₅N) have been recorded using circularly and linearly polarised light. The spectra were compared to the single-photon absorption spectrum of pyrrole and a similar study of furan (C₄H₄O). Although the ionisation spectra of pyrrole were considerably weaker than corresponding furan spectra, a strong propensity for excitation of d series with two photons and p and f series with three photons was observed for both molecules. The totally symmetric nd-Rydberg series associated with the first ionisation energy, [A₂<i>]n</i>d;A₁, was identified from <i>n</i>=3 to <i>n</i>=15 and extrapolated to obtain IE1.</p>

<p>This thesis summarises the experimental results on molecular spectroscopy of gas phase molecules using synchrotron radiation in the UV- VUV and soft-X rays regions. The results of applying Photon Induced Fluorescence Spectroscopy (PIFS) to <em>D</em><em>2,</em><em> H</em><em>2</em><em>S, H</em><em>2</em><em>O</em> and pyrimidine are presented and discussed. Both inner and outer shell excitations of free molecules lead to different relaxation processes. However, a common result is that when the molecule breaks and the resulting neutral fragments are left in an excited state, they might fluoresce in the UV- Vis range. PIFS technique has two main advantages, it permits to detect neutral fragments and to identify the fluorescing species. From this fact, we can infer dissociation channels and trace back the electronic processes that led to the fluorescence. For these molecules we have analysed and interpreted both dispersed and undispersed fluorescence. What motivates our work is the lack of fluorescence studies and in a more general sense, to contribute to the knowledge of important molecules for life such as water and pyrimidine.</p>

No description available.