Results 1 - 10 of 15092
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[en] We demonstrate the possibility to extract nuclear state femtosecond lifetimes from two-step γ ray cascades measured with a Ge-detector array. The technique is based on measuring the Doppler shift of a γ ray, caused by the recoil of a preceding γ ray emission. Since the two γ rays are populating/de-populating the same state they form a start/stop signal, the delay of which is compared to the slowing down motion of the nucleus within the target material. A multi-detector array combined with digital acquisition electronics in list mode, allows to measure several angular combinations and two-step cascades efficiently and simultaneously within one single experiment. The concept was demonstrated with the FIPPS array for the Cl(n,γ)Cl reaction, where we obtained good agreement with literature values showing the validity of the method.
[en] The first Nigeria Research Reactor (NIRR-I), which is a Miniature Neutron Source Reactor (MNSR) type, is operated using the reactor Control console or the Computer controlled interface. The latter having the advantage of data logging over the former. Each control scheme has a distinct set of transducers/sensors it uses for data acquisition and control. Under normal condition, results obtained using either of the control scheme should be the same. Problem arises when results obtained using one scheme does not tally with corresponding results recorded on the other. This brings about constraint in ascertaining which of the two sets of results to be accepted. This paper presents a conceptual design of a Data acquisition system that could be used to identify the malfunctioning sensor set in the event of disagreement between the two corresponding results obtained from the operation of the reactor. The system, which is PIC 16F877A microcontroller based, focuses on temperature measurement, considering its critical role in the safe operation of the reactor. It processes the signal from a pair of thermocouples that measure the reactor core water inlet and outlet temperatures and display the results in degree Celsius (°C). The results obtained from the developed system fall within ±5.2% error margin. (author)
[en] Neutron-induced fission reactions play a crucial role in a variety of fields of fundamental and applied nuclear science. In basic nuclear physics they provide important information on properties of nuclear matter, while in nuclear technology they are at the basis of present and future reactor designs. Finally, there is a renewed interest in fission reactions in nuclear astrophysics due to the multi-messenger observation of neutron star mergers and the important role played by fission recycling in r-process nucleosynthesis. Although studied for several decades, many fundamental questions still remain on fission reactions, while modern applications and the development of more reliable nuclear models require high-accuracy and consistent experimental data on fission cross sections and other fission observables. To address these needs, an extensive fission research programme has been carried out at the n_TOF neutron time-of-flight facility at CERN during the last 18 years, taking advantage of the high energy resolution, high luminosity and wide energy range of the neutron beam, as well as of the detection and data acquisition systems designed for this purpose. While long-lived isotopes are studied on the 185 m long flight-path, the recent construction of a second experimental area at a distance of about 19 m has opened the way to challenging measurements of short-lived actinides. This article provides an overview of the n_TOF experimental programme on neutron-induced fission reactions along with the main characteristics of the facility, the various detection systems and data analysis techniques used. The most important results on several major and minor actinides obtained so far and the future perspectives of fission measurements at n_TOF are presented and discussed.
[en] The BGOOD experiment at the ELSA facility in Bonn has been commissioned within the framework of an international collaboration. The experiment pursues a systematic investigation of non-strange and strange meson photoproduction, in particular t-channel processes at low momentum transfer. The setup uniquely combines a central almost 4π acceptance BGO crystal calorimeter with a large aperture forward magnetic spectrometer providing excellent detection of both neutral and charged particles, complementary to other setups such as Crystal Barrel, Crystal Ball, LEPS and CLAS.
[en] The Budapest Neutron Centre (BNC) is the research organisation enabling open access utilization in science and technology development of the 10 MW Budapest Research Reactor (BRR) facilities. The reactor has 10 horizontal beam tubes and a liquid hydrogen cold source with three neutron guides. On the super-mirror guide system both thermal and/or cold spectra are available. BNC operates 15 experimental stations: diffraction, small angle scattering, inelastic scattering, radiography or irradiation, in-beam gamma capture and in-pile irradiation facilities are available. Instrument development has been always in the focus of BNC research. Detectors are essential part of the instrumentation, thus a thorough programme on the development of 2D/area detectors was started in 2000. Multiwire counters have been chosen and they are likely to remain a reliable and cost-efficient option for a large class of instruments. Delay-line position encoding is widely used in multiwire position sensitive particle detectors. Improvement of several detector parameters is a continuous demand, such as count rate, position resolution, and energy resolution. Besides detector chambers, digitized/analogue signal acquisition systems have been also developed. In co-operation with spin-off companies at the reactor campus a standard detector family was produced with 20 cm × 20 cm active area, based on 3He gas as neutron converter. Six of the BNC experimental stations are equipped with this type of detector. This activity of developing 3He counters has remained in the scope of our detector programme by constructing prototypes of detectors with larger area and faster data acquisition system. Following the worldwide 3He crisis, however, we have turned our interest also towards systems based on solid boron converters. Typically, a convertor can be created as a thin layer on a substrate by a sputtering process using pure 10B, or more practically, boron carbide (B4C). In particular, the construction of a multiwire chamber with multiple boron layer converters is described here. The detector team also takes advantage of the flexibility of the BNC instruments to perform various kind of test measurements to probe and qualify detectors of new developments. Several beamlines/devices are available for test experiments to be used cold, thermal, as well as white or monochromatic neutron beams. (author)
[en] Beam Parameter Stabilization for the P2 Experiment at MESA At the new electron accelerator Mainz Energy-recovering Superconducting Accelerator (MESA) in the Institute of Nuclear Physics in Mainz the P2 experiment will measure the weak mixing angle sinθ with extreme precision of 0.14% via elastic electron-proton-scattering with longitudinally polarized electrons. The weak mixing angle is a parameter of the electroweak interaction and can be measured by means of the parity violating asymmetry, which derives from the asymmetry of the cross sections for electrons with positive and negative helicity in electron-proton-scattering: A = The small electron energy of 140 MeV, which was chosen to suppress the contributions of box graphs with two-boson exchange, leads to a tiny difference of the cross sections - and an expected measured asymmetry of 30-40 ppb. This is more than ten times less than the smallest asymmetry ever measured before. This demands for extreme precise measurement of all false asymmetries coming from helicity correlated fluctuations of the beam parameters position, angle, energy and current. The P2-experimenters demands embrace a maximum of few ppb total false asymmetry with an uncertainty of 0.1 ppb after ten thousand hours of measurement time. Consequently the result of the P2 experiment is highly dependent on the beam quality delivered by the accelerator. In this thesis, a feedback system, including a digital control and data acquisition system, is introduced. This system is capable of measuring and stabilizing the beam parameters position and angle in a way that the demanded precision can be met. The developed system was tested successfully with a 180 MeV-beam at MAMI. The second part of the thesis describes the development of a resonator cavity as a minimal-invasive beam position monitor for MESA based on a design used in MAMI for several years. Successful functional tests of a prototype monitor took place at the MESA Low-energy Beam Apparatus (MELBA).
[de]Am neuen Elektronenbeschleuniger Mainz Energy-recovering Superconducting Accelerator (MESA) am Institut für Kernphysik in Mainz soll mit dem P2-Experiment der elektroschwache Mischungswinkel sinθ, auch Weinbergwinkel genannt, mit extremer Präzision von 0,14% anhand elastischer Elektron-Proton-Streuung mit longitudinal polarisierten Elektronen bestimmt werden. Der Weinbergwinkel ist ein Parameter der elektroschwachen Wechselwirkung und kann anhand der paritätsverletzenden Asymmetrie gemessen werden. Diese ergibt sich aus den unterschiedlichen Wirkungsquerschnitten für Elektronen positiver und negativer Helizität. A = Die Elektronenenergie wurde mit 140 MeV so gewählt, dass der Untergrund aus Boxgraphen mit dem Austausch jeweils zweier Bosonen unterdrückt wird. Allerdings ist aufgrund der geringen Strahlenergie die Differenz der Wirkungsquerschnitte - extrem klein und die erwartete Asymmetrie von 30-40 ppb etwa eine Größenordnung kleiner als die kleinste jemals gemessene Asymmetrie bei polarisierter Elektron-Proton-Streuung. Die kleinen zu messenden Asymmetrien haben zur Folge, dass jede nicht- physikalische Asymmetrie, die von helizitätskorrelierten Schwankungen der Strahlparameter stammen, extrem präzise gemessen und stabilisiert werden muss. Eine präzise Messung der Parameterschwankungen und deren Stabilisierung hin zu einer gesamten apparativen Asymmetrie von wenigen ppb mit einer Unsicherheit von 0,1 ppb nach 10.000 Stunden Messzeit ist die Forderung der P2-Experimentatoren. Die Ergebnisse des P2-Experiments hängen damit maßgeblich von der Qualität des erzeugten Strahls ab. In dieser Arbeit wird ein Feedbacksystem vorgestellt, das in der Lage ist, mithilfe geeigneter Messinstrumente sowie digitaler Datenerfassung und Regelung, die Strahlpa- rameter Lage und Winkel so zu messen und zu stabilisieren, dass die geforderte Genauigkeit erreicht werden kann. Die erfolgreich verlaufenen Testmessungen hierfür wurden am Mainzer Mikrotron (MAMI) mit einer Elektronenenergie von 180 MeV durchgeführt. Lage und Winkel des Strahls werden bei MESA genau wie bei MAMI mit einem minimal-invasiven Hohlraumresonator gemessen. Für MESA wird im zweiten Teil dieser Arbeit ein neues Design eines solchen Monitors vorgestellt und die Funktion eines Prototyps bei Messungen am MESA-Testaufbau MESA Low-energy Beam Apparatus (MELBA) überprüft.
[en] The variety of research being conducted at the instruments on the external beams of the IBR-2 pulsed research reactor in Frank Laboratory of Neutron Physics of Joint Institute for Nuclear Research (FLNP JINR) leads to a variety of requirements for detectors. This leads to the necessity of developing a variety of detectors in the Laboratory (gaseous 3Hebased detectors: 1D and 2D multi-wire proportional chambers (MWPC), ‘ring’ detectors; 6Li-scintillator-based detectors with wavelength shifting fibers, detectors and monitors with solid 10B converters etc.). This article describes the neutron detection systems developed and used at the instruments, as well as the current status and projects carried out at FLNP on the development of detectors and data acquisition systems. (author)
[en] The CMS detector at the LHC is foreseen to experience a major upgrade in order to cope with increased radiation flux due to the high-luminosity operation phase of the accelerator. The CMS tracker will be replaced completely, introducing a new module concept in the outer part of the subsystem, which will exploit the strong magnetic field inside the CMS detector to select high transverse momentum particles locally and send the corresponding information to the triggering system thus enhancing the efficiency of the latter.In order to allow for module prototyping and production testing, an intermediate DAQ system, referred to as μDTC, was developed in the scope of this thesis. The system allows for prototype configuration, control, monitoring and read-out, and provides all the necessary infrastructure for the module qualification. This thesis describes the upgrade project with a focus on the existing module prototypes and the structure of the FPGA firmware developed for the μDTC. A sequence of test beam measurement campaigns was carried out using the aforementioned DAQ system, and the results obtained from two of them are described in detail in the text.