The response of a 5 cm (diameter) by 5 cm cylindrical NE213 liquid scintillator to neutrons has been measured as a function of neutron energy in the range 15-63 Me V, using time-of-flight to select neutron energy. The response function at each neutron energy was separated into components associated with the emission of different charged particles, identified by pulse · shape dissimilation to be protons, deuterons, and alphas, respectively. The response (light output) of NE213 to protons, deuterons and alphas was measured as a function of energy. Furthermore, total cross sections for neutron-induced proton, deuteron, and alpha production from 12C were determined from the charged particle yields. The simultaneous presence of n-p elastic scattering in the scintillator provided a reference for establishing an absolute cross section scale for the measurements. The results give information about reaction mechanisms and provide an improved basis for determining the neutron detection efficiency of the scintillator as a function of energy over this range.

<p>The PAMELA space experiment is scheduled for launch towards the end of 2004 on-board a Russian Resurs DK1 satellite, orbiting Earth at an altitude of 300– 600 km. The main scientific goal is a study of the antimatter component of the cosmic radiation. The semipolar orbit (70.4◦) allows PAMELA to investigate a wide range of energies for antiprotons (80 MeV–190 GeV) and positrons (50 MeV– 270 GeV). Three years of data taking will provide unprecedented statistics in this energy range and will set the upper limit for the ratio He/He below 10−7. PAMELA is built around a permanent magnet silicon spectrometer, surrounded by a plastic scintillator anticoincidence shield built at KTH. The anticounter scintillators are used to aid in the rejection of background from particles not cleanly entering the acceptance of the tracker. Information from the anticounter system will be included as a veto in a second level trigger, to exclude the acquisition of events generated by false triggers.</p><p>An LED-based monitoring system has been developed for the anticounter system. The LEDs mimic the light signal produced in the scintillator by an ionising particle. This allows the functionality of the AC system to be verified in-orbit. The development and testing of the monitoring system are presented and comparisons have been made with independent radioactive source-based calibration methods. The anticounter system has also been extensively tested with cosmic rays and particle beams. Most of these tests have been performed with the anticounters integrated with the other PAMELA subdetectors in a flight-like configuration.</p>

The PAMELA space experiment is scheduled for launch towards the end of 2004 on-board a Russian Resurs DK1 satellite, orbiting Earth at an altitude of 300– 600 km. The main scientific goal is a study of the antimatter component of the cosmic radiation. The semipolar orbit (70.4◦) allows PAMELA to investigate a wide range of energies for antiprotons (80 MeV–190 GeV) and positrons (50 MeV– 270 GeV). Three years of data taking will provide unprecedented statistics in this energy range and will set the upper limit for the ratio He/He below 10−7. PAMELA is built around a permanent magnet silicon spectrometer, surrounded by a plastic scintillator anticoincidence shield built at KTH. The anticounter scintillators are used to aid in the rejection of background from particles not cleanly entering the acceptance of the tracker. Information from the anticounter system will be included as a veto in a second level trigger, to exclude the acquisition of events generated by false triggers. An LED-based monitoring system has been developed for the anticounter system. The LEDs mimic the light signal produced in the scintillator by an ionising particle. This allows the functionality of the AC system to be verified in-orbit. The development and testing of the monitoring system are presented and comparisons have been made with independent radioactive source-based calibration methods. The anticounter system has also been extensively tested with cosmic rays and particle beams. Most of these tests have been performed with the anticounters integrated with the other PAMELA subdetectors in a flight-like configuration.

PAMELA is a satellite-borne experiment designed to study the charged component of the cosmic radiation of galactic, solar and trapped nature. The main scientific objective is the study of the antimatter component of cosmic rays over a wide range of energies (antiprotons: 80 MeV–190 GeV, positrons: 50 MeV–270 GeV). PAMELA is also searching for antinuclei with a precision ~10^−7 in anti-He/He measurements. PAMELA is mounted on the Resurs DK1 satellite that was launched on June 15th 2006 from the Baikonur cosmodrome and is now on a semipolar (69.9°) elliptical (350 × 600 km) orbit. The experiment has been acquiring data since July 11th 2006 and has a foreseen lifetime of at least 3 years. The PAMELA apparatus consists of a permanent magnet silicon spectrometer, an electromagnetic imaging calorimeter, a time of flight system, a scintillator-based anticoincidence (AC) system, a tail catcher scintillator and a neutron detector. The AC system can be used to reject particles not cleanly entering the PAMELA acceptance. Tests of the PAMELA instrument in its final flight configuration involved long duration acquisition runs with cosmic particles (mainly muons) on ground. A study of the functionality of the AC system during these runs is presented here with a set of selected muons. Studies of activity in the AC detectors as function of the rigidity of the muons and in correlation with the activity in the spectrometer and in the calorimeter are presented. A study of the AC system functionality during in-flight operations provides a map of the particle flux in orbit, and shows the anisotropy in the arrival direction of trapped particles in the Van Allen radiation belts. The singles rates indicate that the AC system saturates in the South Atlantic anomaly (SAA). Information from the AC system in the SAA is therefore not reliable for physics analysis. The timing and multiplicity of AC activity correlated to particle triggers has been studied. A dependence on orbital position was observed. An LED (Light Emitting Diode) based monitoring system was designed to determine the in-orbit behaviour of the AC system independently of the radiation environment and to compare it to the pre-launch behaviour. The LED system shows that the properties of the AC system are stable during flight and that no significant changes in performance occurred as a result of the launch. / QC 20100811

Es werden die Entdeckung der organischen Szintillatoren durch Hartmut Kallmann und seine anderen Arbeiten, insbesondere die Entwicklung der flüssigen Szillitatoren beschrieben. / The discovery of organic scintillators by Hartmut Kallmann and his further work, especially the development of liquid scintillators are described.

The use of organic scintillators is an established method for the measurement of neutron spectra above several hundred keV. Fast neutrons are detected largely by proton recoils in the scintillator resulting from neutron elastic scattering with hydrogen. This leads to a smeared rectangular pulse-height distribution for monoenergetic neutrons. The recoil proton distribution ranges in energy from zero to the incident neutron energy. In addition, the pulse-height distribution is further complicated by structure due to energy deposition from alpha particle recoils from interactions with carbon as well as carbon recoils themselves. In order to reconstruct the incident neutron spectrum, the pulse-height spectrum has to be deconvoluted (unfolded) using the computed or measured response of the scintillator to monoenergetic neutrons. In addition gamma rays, which are always present when neutrons are present, lead to Compton electron recoils in the scintillator. Fortunately, for certain organic scintillators, the electron recoil events can be separated from the heavier particle recoil events in turn to distinguish gamma-ray induced events from neutron-induced events. This is accomplished by using the risetime of the pulse from the organic scintillator seen in the photomultiplier tube as a decay of light. In this work, an organic scintillator detection system was assembled which includes neutron-gamma separation capabilities to store the neutron-induced and gamma-induced recoil spectra separately. An unfolding code was implemented to deconvolute the spectra into neutron and gamma energy spectra. In order to verify the performance of the system, a measurement of two reference neutron fields will be performed with the system, unmoderated Cf-252 and heavy-water moderated Cf-252. After the detection system has been verified, measurements will be made with an AmBe neutron source.

Ce travail de thèse porte sur le développement de techniques de spectroscopie neutronique dans les champs de rayonnement mixte pour des applications liées aux réacteurs de recherche à neutrons rapides, en particulier l’installation MASURCA.La première partie est consacrée à l'étude des configurations expérimentales spéciales de MASURCA dans lesquelles un canal radial est construit pour extraire un faisceau continu de neutrons d'énergie intermédiaires et rapides, adaptable à différents besoins. Exploiter MASURCA en tant qu'installation de faisceau de neutrons ouvrirait de nouvelles possibilités d'expériences telles que des expériences de protection et de transport de neutrons rapides, la production de champs neutroniques standards (de référence), le développement et étalonnage de systèmes de détection des neutrons rapides, etc.La deuxième partie de la thèse est dédiée au développement d’une capacité de spectrométrie neutronique rapide pour la caractérisation en ligne de la distribution d'énergie neutronique. Différents types de détecteurs sont comparés. Le meilleur compromis pour ce spectromètre est un système combinant des compteurs proportionnels et des scintillateurs organiques. Ce système est capable de couvrir le domaine énergétique entre 10 keV et 10 MeV. Le scintillateur organique sélectionné est un monocristal de stilbène obtenu par un procédé “solution-grown” développé récemment. Au bilan, on conclut qu'un spectromètre à neutrons basé sur le stilbène de type “solution-grown” serait adapté à une utilisation dans MASURCA et dans d'autres champs de rayonnement mixte et qu'il serait plus performant que les systèmes de détection traditionnels. / This doctoral thesis work is focused on the development of neutron spectroscopy techniques in mixed radiations fields for fast research reactor applications, especially for the MASURCA facility.The first part of the thesis is dedicated to the study of special MASURCA configurations in which a radial channel is built to extract a continuous beam of intermediate-to-fast energy neutrons, tailorable to meet different needs. Operating MASURCA as a neutron beam facility would open up new possibilities of experiments, such as fast neutron attenuation and shielding experiments; measurements in standard (reference) fast neutron fields, development and calibration of fast neutron detection systems etc.The second part of the thesis is dedicated to the development of fast neutron spectrometric capabilities for the on-line characterization of the neutron energy distribution. Different candidate detector systems are compared. A “best compromise” spectrometer is shown to be a system combining proportional counters and organic scintillators. Such a system would be able to cover the neutron energy domain between 10 keV and 10 MeV. The selected organic scintillator is a stilbene single crystal obtained by a recently developed solution-grown process. Overall, it is concluded that a neutron spectrometer based on a solution-grown stilbene detector would be suitable for use in MASURCA and in other mixed radiations fields, and would perform better than traditional detector systems.

Es werden die Entdeckung der organischen Szintillatoren durch Hartmut Kallmann und seine anderen Arbeiten, insbesondere die Entwicklung der flüssigen Szillitatoren beschrieben. / The discovery of organic scintillators by Hartmut Kallmann and his further work, especially the development of liquid scintillators are described.

In dieser Arbeit wird die Signalanalyse eines Ortsdosisleistungsmessgerät mit organischem Szintillatoren der Arbeitsgruppe Strahlungsphysik optimiert, damit die Signalanalyse die Anforderungen der PTB im Hinblick auf eine Baumusterprüfung erfüllt. Dafür wird der Mittellungszeitraum der Dosisleistung dynamisch an die Zählrate angepasst, um einen Kompromiss zwischen schneller Ansprechzeit und geringer statistischer Messunsicherheit der gemessenen Dosisleistungen zu erreichen. Bei hohen Zählraten wird die Datenmenge begrenzt, damit die CPU nicht mit der Auswertung der Einzelereignisse überlastet wird. Weiterhin wird für 2 Prototypen des Dosimeters eine Energiekalibrierung und Wichtung gefunden. Als zusätzliches Feature ist eine Fourier-Transformation implementiert, mit der die Frequenz von gepulster Strahlung bestimmt wird.:Inhaltsverzeichnis 1 Motivation 1 2 Physikalischer Hintergrund 3 2.1 Dosis 3 2.2 Kernreaktionen 3 2.3 Wechselwirkung zwischen Strahlung und Materie 4 2.4 Detektoren 6 3 Material und Methoden 9 3.1 Aufbau und Funktionsweise 9 3.2 Funktionsprüfung 13 3.3 Kalibrierung 15 3.4 Anforderungen der PTB 18 3.5 Überlastungsschutz 19 3.6 Fourier-Transformation 20 4 Messungen 23 4.1 Messung mit dem Pulsgenerator 23 4.2 Messungen mit dem NaI-Szintillator 25 4.3 Messungen mit organischem Szintillator 27 5 Zusammenfassung 41 6 Anhang 43 6.1 Beobachtete Röntgen und γ-Linien 43 6.2 Pulsladungshistogramme 44 Abbildungsverzeichnis 53 Tabellenverzeichnis 55 Literatur 57 / In this thesis, the signal analysis of a local dose rate measurement device is improved for a type examination at the PTB. For this the averaging time of the dose rate measurement is dynamically optimized to archive a trade-off between a short reaction time and low statistical uncertainty of the measured dose rate in order to fulfil the expectations of the PTB and an overload protection is added to ensure a swift analysis of the incoming events even at high count rates. Furthermore, an energy calibration and weight is determined for two prototypes of the dose rate measurement device. As an additional feature a Fourier transformation is implemented to determine the frequency of pulsed radiation fields.:Inhaltsverzeichnis 1 Motivation 1 2 Physikalischer Hintergrund 3 2.1 Dosis 3 2.2 Kernreaktionen 3 2.3 Wechselwirkung zwischen Strahlung und Materie 4 2.4 Detektoren 6 3 Material und Methoden 9 3.1 Aufbau und Funktionsweise 9 3.2 Funktionsprüfung 13 3.3 Kalibrierung 15 3.4 Anforderungen der PTB 18 3.5 Überlastungsschutz 19 3.6 Fourier-Transformation 20 4 Messungen 23 4.1 Messung mit dem Pulsgenerator 23 4.2 Messungen mit dem NaI-Szintillator 25 4.3 Messungen mit organischem Szintillator 27 5 Zusammenfassung 41 6 Anhang 43 6.1 Beobachtete Röntgen und γ-Linien 43 6.2 Pulsladungshistogramme 44 Abbildungsverzeichnis 53 Tabellenverzeichnis 55 Literatur 57