Search results for "electromagnetic [radiation]"
showing 10 items of 873 documents
Observation of scattering and absorption centers in lead fluoride crystals
2006
For the first time, lead fluoride is used as a fast and compact material in electromagnetic calorimetry. Excellent optical and mechanical properties of the pure Cherenkov crystals are necessary for the A4 collaboration to perform a measurement of the nucleon's strange form factors. Visible scattering and absorption centers as well as surface damages have been investigated to characterize the quality of more than one thousand crystals. Besides, transmittance measurements have been performed on all crystals to reveal absorption bands produced by intrinsic or impurity related point-structure defects. As a consequence, 89 crystals had to be replaced by the Chinese manufacturer SICCAS.
Many-body approach to low-energy pion-nucleus scattering
1993
Abstract We have extrapolated for low-energy pions ( T π = 0–50 MeV) the results for the pion-nucleus optical potential previously developed for pionic atoms. The evaluation is done using microscopic many-body techniques which allow us to separate the different contributions to the imaginary part of the potential and relate them to the different reaction channels: quasielastic and absorption. Elastic differential, reaction, absorption and quasielastic cross sections are evaluated for different nuclei and energies and contrasted with experiments. The agreement with data for the different channels, energies and nuclei is rather good with some isolated discrepancies.
Dependency of Energy-, Position- and Depth of Interaction Resolution on Scintillation Crystal Coating and Geometry
2008
Options for optimizing the energy and spatial resolution of gamma-ray imaging detectors based on thick, monolithic crystals shaped like flat-topped pyramids were studied. Monte Carlo simulations were made of the scintillation light transport for evaluating the effect of four parameters on the energy resolution, the spatial resolutions, and the depth of interaction (DOI) resolution of the gamma-ray imaging detector. These four parameters are: the reflectivity of the surface coating; the scatter mean free path; the absorption mean free path of the scintillation light; and the angle that defines the inclination of the sides of the pyramidal frustum. In real detectors, the values for the mean f…
Duality relation between radiation thermodynamics and cosmic string loop thermodynamics
2011
We discuss thermodynamics of electromagnetic radiation, with p=(1/3){rho} and S{proportional_to}T{sup 3}V, and of cosmic string loops, with p=-(1/3){rho} and S{proportional_to}T{sup -3}V, where p stands for pressure, T temperature, {rho} energy density, S entropy, and V volume. We write the thermodynamic formalisms under a common framework that illustrates their formal relationship and allows us to go from one to the other through a smooth transformation. From a microscopic perspective, these relations arise from the energy relations u({lambda})=hc/{lambda} for the photons of electromagnetic radiation, and u(l)=(c{sup 4}/a{sup 2}G)l for cosmic string loops, a being a numerical (dimensionles…
Radiation resistance and optical properties of lead fluoride Cherenkov crystals
1998
Abstract Optical properties of large size lead fluoride (PbF 2 ) crystals of three different manufacturers and their degradation caused by 60 Co γ-radiation have been investigated. Transmission losses have been systematically studied at absorbed energy doses between 0.1 and 7 kGy. Several radiation induced absorption bands have been observed. Optical bleaching with light of wavelengths ≳365 nm has been found very effective to restore the original characteristics even after repeated irradiations. This observation together with the high density and the ultraviolet extended transmission make PbF 2 an excellent choice for high rate and high resolution e.m. calorimetry.
Luminescent detectors of ionising radiation
2003
Abstract At present in slow neutron imaging an active layer of an imaging plate IP contains a mixture of storage phosphors, usually BaFBr:Eu 2+ used for imaging of X-rays, and a neutron converter material, usually Gd 2 O 3 , LiF. A novel Li-containing luminescent material perspective for a direct neutron conversion and storage is discussed. Irradiation of LiBaF 3 crystals results in generation of Frenkel defect pairs and creation of F-type centres responsible for three absorption bands in UV-and visible spectral region. Because photo-stimulation in each of these absorption bands leads to bleaching of induced absorption, the F-type colour centres are convenient for storage of radiation dose.…
Determination of helium number densities in high-frequency electrodeless plasma
2010
Abstract The number densities of He first excited states 2 3 S 1 , 2 1 S 0 , 2 3 P 0,1,2 , and 2 1 P 0 were measured by absorption and self-absorption methods. The emission lines in the range 290–730 nm were used to determine the number densities of He metastable and resonant states of inductively coupled high-frequency electrodeless lamps filled with helium at pressure 0.1 Torr. The obtained number densities of helium metastable levels 2 3 S 1 and 2 1 S 0 are 2×10 12 and 3×10 11 cm −3 , respectively. For the 2 3 P 0,1,2 and 2 1 P 0 levels the determined number densities are ten times smaller than that of the metastable levels. Values of number densities from measurements using both method…
Resonant Nuclear Fusion Processes and the Gamma Rays of SS 433
1984
Gamma-ray spectral lines have recently been reported coming from the celestial object SS 433, which is known to emit high-speed jets in opposite directions. The proposed identification of the lines as coming from fusion reactions on nitrogen nuclei as part of the carbon-nitrogen-oxygen cycle operating in the jets has now received observational support. Predictions of strengths and widths of additional lines which, if seen, would provide valuable new information about conditions giving rise to the jets are presented.
TAS measurements for reactor physics and nuclear structure
2011
In this contribution we will present recent total absorption measurements of the beta decay of neutron‐rich nuclei performed at the IGISOL facility of the Univ. of Jyvaskyla. In the measurements the JYFL Penning Trap was used as a high resolution isobaric separator. The total absorption technique will be described and the impact of recent results in the fields of reactor physics (decay heat calculations) and nuclear structure will be discussed.
Results from the Real Photon Programme at MAMI
1995
The accelerator MAMI (Mainzer Mikrotron) with its excellent beam properties and its duty factor of 100% allows to apply coincidence techniques in intermediate energy nuclear physics, which has led to a variety of results with high precision. The real photon collaboration (A2) uses energy tagged bremsstrahlung photons with energies up to 800 MeV. We have results on total photon absorption (proton, deuteron, 3He and U), on Compton scattering (proton, 4He and 12C) and on meson production, especially on π°- and η-photoproduction. Double pion production on the proton and the deuteron was measured. The two and three body breakup of 3He was investigated as well as the reactions (γ,NN) and (γ, π ± …