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Die Protonentherapie zeichnet sich durch steile Dosisgradienten und damit einen gut lokalisierbaren Energieübertrag aus. Um dieses Potential voll ausschöpfen zu können, werden weltweit Möglichkeiten erforscht, die Dosisdeposition und insbesondere die Reichweite der Protonen im Patienten zu verifizieren. Eine vielversprechende, erst im letzten Jahrzehnt entdeckte Methode ist das Prompt Gamma-Ray Timing (PGT), das auf der Abhängigkeit der detektierten Flugzeitverteilung prompter Gammastrahlung von der Transitzeit der Protonen im Patienten beruht. In dieser Arbeit wird eine Geant4-Simulation zur Vorhersage der PGT-Spektren bei Bestrahlung eines PMMA-Phantoms entwickelt und durch den Vergleich mit experimentellen Daten validiert. Sowohl die Emissionsausbeute prompter Gammastrahlung im Phantom als auch die Detektionsrate werden abhängig von der Protonenenergie analysiert. Zur Vergleichbarkeit mit den gemessenen Spektren wird eine mehrschrittige Prozessierung der Simulationsergebnisse vorgestellt. Schließlich wird die Simulation genutzt, um die Sensitivität der PGT-Methode auf Reichweitenänderungen zu demonstrieren. Dafür können in das Phantom Cavitäten unterschiedlicher Dicke und verschiedenen Materials eingefügt werden. Für geeignet gewählte Verteilungsparameter der simulierten PGT-Spektren wird deren detektierte Änderung mit der bekannten induzierten Reichweitenänderung ins Verhältnis gesetzt. Die so bestimmte Sensitivität ist mit früheren Ergebnissen für gemessene Spektren im Rahmen der Unsicherheiten in Übereinstimmung.:1 Einleitung und Motivation 1 2 Theoretische Grundlagen 5 2.1 Wechselwirkung von Protonen mit Materie 5 2.1.1 Bethe-Bloch-Gleichung 6 2.1.2 Reichweite im CSDA-Modell 9 2.1.3 Tiefendosiskurve und Bragg-Peak 10 2.2 Prompt Gamma-Ray Timing 11 2.2.1 Emission prompter Gammastrahlung 11 2.2.2 Korrelation zur Protonen-Reichweite und Dosisdeposition 11 2.2.3 Idee des Prompt Gamma-Ray Timings 14 3 Material und Methoden 17 3.1 Dresdner IBA-Protonentherapie 17 3.1.1 Beschleunigungsprinzip des Isochronzyklotrons 17 3.1.2 Zeitliche Struktur der Protonen-Pakete 18 3.2 Teilchentransportrechnungen mit Geant4 20 3.3 PLD-Format für Pencil-Beam-Scanning-Pläne 21 3.3.1 Geometrische Definition der Spots 21 3.3.2 Dosimetrische Definition der Spots 23 3.3.3 Verwendete Bestrahlungspläne 24 3.4 Messaufbau zur experimentellen Validierung 26 3.4.1 Target – PMMA-Phantom mit verschiedenen Cavitäten 27 3.4.2 Detektoren – CeBr3-Szintillatoren mit Photomultipliern 27 4 Ergebnisse und Diskussion 29 4.1 Simulierte Emission prompter Gammastrahlung 29 4.1.1 Simulierte Emissionsspektren 29 4.1.2 Simulierte Emissionsprofile 30 4.1.3 Totale Emissionsausbeute 31 4.2 Simulierte Detektion prompter Gammastrahlung 33 4.2.1 Detektionsrate und Raumwinkeleffekt 33 4.2.2 Simulierte PGT-Spektren 35 4.2.3 Simulierte Energiespektren 37 4.3 Vergleich simulierter und gemessener Spektren 39 4.3.1 Nachverarbeitung der Simulationsergebnisse 40 4.3.2 Auswahl des Energiefensters 45 4.3.3 Empirisches Modell zur Beschreibung der Zeitspektren 47 4.3.4 Diskussion systematischer Abweichungen 49 4.4 Sensitivität der Simulation gegenüber induzierten Reichweitenänderungen 51 5 Zusammenfassung und Ausblick 59 Anhang 61 A Parameter des Messaufbaus 61 B Angepasste Modellparameter aus Abbildung 4.12 62 C Sensitivität auf Reichweitenänderung bei 162 MeV 63 Literaturverzeichnis 69 / Proton therapy is characterized by steep dose gradients and thus a well-localizable energy transfer. To fully harness this potential, possibilities are being explored worldwide to verify the dose deposition and especially the range of protons in the patient. A promising method discovered only in the last decade is prompt gamma-ray timing (PGT), which relies on the dependence of the detected time-of-flight distribution of prompt gamma radiation on the transit time of protons in the patient. In this study, a Geant4 simulation is developed to predict PGT spectra during irradiation of a PMMA phantom and validated by comparison with experimental data. Both the emission yield of prompt gamma radiation in the phantom and the detection rate are analyzed depending on the proton energy. For comparability with the measured spectra, a multi-step processing of the simulated results is presented. Finally, the simulation is used to demonstrate the sensitivity of the PGT method to changes in range. For this purpose, cavities of different thicknesses and materials can be inserted into the phantom. For appropriately chosen distribution parameters of the simulated PGT spectra, their detected change is compared to the known induced change in range. The sensitivity determined in this way is consistent with previous results for measured spectra within the uncertainties.:1 Einleitung und Motivation 1 2 Theoretische Grundlagen 5 2.1 Wechselwirkung von Protonen mit Materie 5 2.1.1 Bethe-Bloch-Gleichung 6 2.1.2 Reichweite im CSDA-Modell 9 2.1.3 Tiefendosiskurve und Bragg-Peak 10 2.2 Prompt Gamma-Ray Timing 11 2.2.1 Emission prompter Gammastrahlung 11 2.2.2 Korrelation zur Protonen-Reichweite und Dosisdeposition 11 2.2.3 Idee des Prompt Gamma-Ray Timings 14 3 Material und Methoden 17 3.1 Dresdner IBA-Protonentherapie 17 3.1.1 Beschleunigungsprinzip des Isochronzyklotrons 17 3.1.2 Zeitliche Struktur der Protonen-Pakete 18 3.2 Teilchentransportrechnungen mit Geant4 20 3.3 PLD-Format für Pencil-Beam-Scanning-Pläne 21 3.3.1 Geometrische Definition der Spots 21 3.3.2 Dosimetrische Definition der Spots 23 3.3.3 Verwendete Bestrahlungspläne 24 3.4 Messaufbau zur experimentellen Validierung 26 3.4.1 Target – PMMA-Phantom mit verschiedenen Cavitäten 27 3.4.2 Detektoren – CeBr3-Szintillatoren mit Photomultipliern 27 4 Ergebnisse und Diskussion 29 4.1 Simulierte Emission prompter Gammastrahlung 29 4.1.1 Simulierte Emissionsspektren 29 4.1.2 Simulierte Emissionsprofile 30 4.1.3 Totale Emissionsausbeute 31 4.2 Simulierte Detektion prompter Gammastrahlung 33 4.2.1 Detektionsrate und Raumwinkeleffekt 33 4.2.2 Simulierte PGT-Spektren 35 4.2.3 Simulierte Energiespektren 37 4.3 Vergleich simulierter und gemessener Spektren 39 4.3.1 Nachverarbeitung der Simulationsergebnisse 40 4.3.2 Auswahl des Energiefensters 45 4.3.3 Empirisches Modell zur Beschreibung der Zeitspektren 47 4.3.4 Diskussion systematischer Abweichungen 49 4.4 Sensitivität der Simulation gegenüber induzierten Reichweitenänderungen 51 5 Zusammenfassung und Ausblick 59 Anhang 61 A Parameter des Messaufbaus 61 B Angepasste Modellparameter aus Abbildung 4.12 62 C Sensitivität auf Reichweitenänderung bei 162 MeV 63 Literaturverzeichnis 69

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Douglas S. McGregor / Cadmium Zinc Telluride (CdZnTe) has been used for many applications, such as medical imaging and astrophysics, since its first demonstration as a room temperature operating gamma-ray detector in 1992. The wide band gap, high effective Z-number and high resistivity of CdZnTe make it a good candidate for use as a room temperature operated detector with good absorption efficiency, while maintaining a low bulk leakage current at high electric fields. Nevertheless, the low mobility lifetime products mu tau of holes in CdZnTe makes detectors position sensitive, unless advanced detector designs are employed. Among those designs is the Frisch collar technology which turns the detector into a single carrier device by negating the degrading effects of hole trapping and low mobility. The superiority of the Frisch collar technology over other methods include its inexpensive associated electronics and straight forward fabrication process. The main objective of this research study is to develop a large volume gamma-ray detector with an array of individual CdZnTe Frisch collar gamma-ray spectrometers while still using a single readout. Several goals were to be accomplished prior to the main objective. One goal is to develop a reliable low cost method to fabricate bulk CdZnTe crystals into Frisch collar detectors. Another goal was to investigate the limitations of crystal geometry and the crystal electrical properties to obtain the best spectroscopic performance from CdZnTe Frisch collar detectors. Still another goal was to study all other external parameters such as the collar length, anode to cathode ratio, the insulator thickness and applied voltage on performance of CdZnTe Frisch collar detectors. The final goal was to construct the CdZnTe Frisch collar devices into an array and to show its feasibility of being used for large volume detector.

published_or_final_version / abstract / Physics / Master / Master of Philosophy

We present axisymmetric hydrodynamical simulations of the long-term accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto the central compact object, which we take to be a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in two spatial dimensions and with an explicit shear viscosity. The evolution of the central accretion rate exhibits phases reminiscent of the long GRB [gamma]-ray and X-ray light curve, which lends support to the proposal by Kumar et al. (2008a,b) that the luminosity is modulated by the central accretion rate. In the first "prompt" phase, the black hole acquires most of its final mass through supersonic quasiradial accretion occurring at a steady rate of [scientific symbols]. After a few tens of seconds, an accretion shock sweeps outward through the star. The formation and outward expansion of the accretion shock is accompanied with a sudden and rapid power-law decline in the central accretion rate Ṁ [proportional to] t⁻²̇⁸, which resembles the L[subscript x] [proportional to] t⁻³ decline observed in the X-ray light curves. The collapsed, shock-heated stellar envelope settles into a thick, low-mass equatorial disk embedded within a massive, pressure-supported atmosphere. After a few hundred seconds, the inflow of low-angular-momentum material in the axial funnel reverses into an outflow from the thick disk. Meanwhile, the rapid decline of the accretion rate slows down, which is potentially suggestive of the "plateau" phase in the X-ray light curve. We complement our adiabatic simulations with an analytical model that takes into account the cooling by neutrino emission and estimate that the duration of the prompt phase can be ~ 20 s. The model suggests that the steep decline in GRB X-ray light curves is triggered by the circularization of the infalling stellar envelope at radii where the virial temperature is below 10¹⁰ K, such that neutrino cooling is inefficient and an outward expansion of the accretion shock becomes imminent; GRBs with longer prompt [gamma]-ray emission should have more slowly rotating envelopes. / text

In this study, two methods of analysing activity concentrations of natural radionuclides (U, Th and K) in soil are critically compared. These are the Window Analysis (WA) and Full Spectrum Analysis (FSA). In the usual WA method, the activity concentrations are determined from the net counts of the windows set around individual &gamma / -ray peaks associated with the decay of U, Th and K. In the FSA method, the full energy spectrum is considered and the measured spectrum is described as the sum of the three standard spectra (associated with U, Th and K, respectively), each multiplied by an unknown concentration. The concentrations are determined from the FSA and correspond to the activity concentrations of U, Th and K in the soil. The standard spectra derived from separate calibration measurements using the HPGe detector, represents the response of the HPGe to a Marinelli sample beaker containing an activity concentration of 1 Bq/kg.

The importance of gamma-ray spectroscopy – the science of determining the distribution of energy in a gamma field – can rarely be overstated. High performance scintillators for gamma-ray spectroscopy in Nuclear Nonproliferation applications and homeland security require excellent energy resolution to distinguish neighboring element and isotope lines while minimizing the time and exposure to do so. Semiconductor detectors operate by converting incident photons directly into electrical pulses, but often have problems of high costs due to constituent segregation and surface states as is the case for Cadmium Zinc Telluride. The ideal scintillator material for gamma spectrometer will therefore requires high light yield, excellent proportionality between light yield and gamma photon energy, and material uniformity. A scintillator should possess the following properties; it should convert the kinetic energy of the generated charged particles (typically K-shell electrons) into detectable visible light. This conversion should be linear-the light yield should be proportional to deposited energy over as wide a range as possible. For good light collection, the medium should be transparent to the wavelength of its own emission. The decay time of the induced luminescence should be short so that fast signal pulses can be generated. The medium should be of good optical quality and subject to manufacture in sizes large enough to be of interest as a practical detector. Its index of refraction should be near that of glass (~1.5) to permit efficient coupling of scintillation light to a photomultiplier tube or other photo-sensor. In the past decade, inorganic scintillator research has focused less on improving the characteristics of known scintillators, but rather on the search for new hosts capable of fast response and high energy resolution. Extensive searches have been made for hosts doped with lanthanide activators utilizing the allowed 5d-4f transition. These 5d-4f transitions are dipole-allowed and thus are about 106 times stronger than the more frequently observed 4f-4f transition in the trivalent rare earth ions. Ce3+, Nd3+ and Pr3+ have been investigated for fast response applications while Ce3+, Eu2+ and Yb2+ stand out as the most promising activators offering high light yield, and high energy resolution. Using a modified Bridgman growth technique we have grown crystals with a low energy resolution of 2.6% at 662 keV, which is lower than the previous 2.8% reported for SrI2:Eu2+. The modified technique (called so for its vertical crystal growth orientation) is necessary due to the anisotropic thermal expansion coefficient of Strontium Iodide. The problem plaguing the growth of the crystal is spontaneous cracking, which usually appear during cooling in the bulk. With the use of a zone separating shield, one can achieve more control of the temperature gradient between the two zones without compromising the actual temperature of the two zones. Additionally the use of codopants, in particular divalent magnesium improved the crystalline quality by acting as a gathering for iodine ions, which led to reduction of defect density.

Gamma-ray bursts (GRBs) are one of the phenomena that still puzzle the astrophysi- cists. Due to their extreme luminosities, they are visible in cosmological distances. They could provide a tool for understanding the early Universe. This thesis focuses on the estimation of the total energy released by the GRBs, their luminosities and how these quantities depend on the redshift. For a sample of 28 long GRBs with known redshifts, a dependence of their total energies and luminosities on the redshift is found. The thesis further studied if this dependence is either an observational bias or a real astrophysical phenomenon. Firstly, proper use of k-correction revealed that it has lit- tle effect on the redshift dependence of these quantities. Secondly, a new approach has been proposed to investigate the redshift dependence of the luminosity function. Thirdly, selection effect has been found, when investigating the sample of bursts with known redshifts, implying a caution when combining data from different sources. All these efforts show that the observational bias can still explain the redshift dependence.

Les expériences d’astroparticules n’ont cessé de fleurir ces dix dernières années dans le but de connaître l’origine des rayons cosmiques et les procédés mis en œuvre dans leur accélération à des ultra-hautes énergies. Les télescopes Cherenkov tels que ANTARES détectent la lumière Cherenkov issue des muons se propageant dans l’eau de mer méditerranée. Les muons sont les produits d’interaction de neutrinos cosmiques (signal) ou atmosphériques (bruit) avec les noyaux de la terre. Pour offrir les meilleures conditions de détection de la lumière Cherenkov, et par conséquent bien reconstruire les traces des muons détectés, les détecteurs de lumière i.e les photomultiplicateurs doivent satisfaire plusieurs conditions. Le premier volet de cette thèse porte sur le développement de photomultiplicateurs utilisant le cristal comme préamplificateur de signal optique. L’avantage d’un tel procédé est la possibilité de séparer plusieurs pics photo-électrons et d’améliorer la résolution tem- porelle grâce à un fort champ électrique. La conception d’un tel prototype et la possibilité de son industrialisation à grande échelle sont développés pour la première fois dans cette thèse. Le deuxième volet s’inscrit dans la nouvelle thématique multi-messagers d’ANTARES.Un suivi avec six télescopes optiques répartis sur chaque hémisphère est déclenché lorsque ANTARES détecte un neutrino de haute énergie ou un ensemble de neutrinos coïncidents en temps et en direction. Un tel système permet d’augmenter la sensibilité de détection de neutrinos provenant de sources transitoires tels que les sursauts gamma et les Supernovæ à effondrement de cœur. Un système d’alertes neutrino est maintenant implémenté et fonctionne continument et de manière autonome sur ANTARES. Le système offre de bonnes performances; le suivi optique se déclenche dans la minute suivant la détection neutrino et l’incertitude sur la reconstruction de la trajectoire du neutrino est de 0.4◦ (valeur médiane). Une fois l’alerte reu çe par un des télescopes, celui-ci se repositionne sur la direction du neutrino et entame une série d’observations réparties sur le mois suivant l’alerte. Cette thèse a porté dans un premier temps sur l’aspect neutrino en développant le filtre sélectionnant les évènements haute énergie et multi-neutrinos. Des outils d’analyse d’images optiques ont ensuite été implémentés pour la recherche de sources transitoires. Les premiers résultats de recherche de contreparties optiques de sursauts gamma en corrélation avec un signal neutrino sont présentés. / Astroparticle experiments are being developed with the aim of resolving the mystery of cosmic rays. Questions like from where cosmic rays originate or how do they get accelerated up to ultra high energies are still unresolved. Cherenkov telescopes like ANTARES detect the Cherenkov light emitted by muons propagating in the sea water. Muons are produced by the interaction of cosmic neutrinos (signal) or atmospheric neutrinos (noise) with the Earth nuclei.In order to offer the best detection conditions of Cherenkov light, and subsequently ensure a good reconstruction quality of the muons trajectory, the light sensors i.e the photomultipliers must satisfy various conditions.The first part of this thesis focuses on the development of photomultipliers using crystals as a preamplifier of the light signal. The advantage of such a method is the possibility to separate individual photo-electrons and to enhance the temporal resolution by applying a high electric field.The design and conception as well as the possibility to produce such devices at large industrial scales is for the first time developed in this thesis.The second part of the thesis is inspired from the new multi-messenger approach in ANTARES. An optical follow-up with six telescopes spread over the two hemispheres is triggered by the detection of a high energy neutrino or a set of neutrinos coincident in time and direction. Such a system enhances the sensitivity to transient sources such as Gamma Rays Bursts (GRB) or Core Collapse Supernovae. The neutrino alert system is now fully operational. The system offers good performances; the optical follow-up starts within one minute from the neutrino detection and the median angular accuracy of the reconstructed neutrinos is 0.4$^circ$.Upon the reception of an alert, the telescopes point at the neutrino direction and start the acquisition of image series almost each night of the month following the neutrino alert. Image analysis tools have been implemented to search for optical transients; First results on the search of GRB optical counterparts correlated with a neutrino signal are presented.