Search results for "Absorption"
showing 10 items of 2701 documents
Optical properties and spectrometric performance of TlBr detector crystals
2006
Abstract It is shown that preliminary TlBr crystals optical parameters testing can be used for detector crystal selection. Absorption in fundamental spectral region was used for the band gap width definition and determination of homological impurities presence. The luminescence was applied for impurity and defects content study. Radionuclide spectra 241Am were measured using the ionizing radiation detectors with planar electrodes made from TlBr crystals. The detector energy resolution for TlBr detectors produced from different row materials was summarized and the results of detector testing parameters and results of optical investigation were compared.
Optical investigations of TlBr detector crystals
2004
Shift of fundamental absorption edge, the position of main luminescence bands, the luminescence decay and transient absorption spectra in three TlBr crystals were studied. The γ-quanta detector made from TlBr crystals with similar transient absorption and luminescence parameters shows similar detector properties. The iodine impurity in TlBr was detected by optical methods. The role of impurities and crystal defects in γ-quanta detectors manufactured is discussed.
Investigation of multiparticle final states in12C photoreactions
1998
The ${}^{12}\mathrm{C}(\ensuremath{\gamma},pn)$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},pp)$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},ppp)$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},pp{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},p{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})$ reactions have been studied using tagged photons of energy ${E}_{\ensuremath{\gamma}}=250$--600 MeV. A model which includes all major absorption mechanisms and final state interactions gives results that agree well with the shapes of missing energy spectra, but for some channels the predicted cross sections are too large.
Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions
1994
The total photofission cross section σγ,F for235U and238U has been measured in the energy range 50≤E γ≤800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4π arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section σγF , which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections σγ,F normalized to the atomic numberA for both isotopes coincide, and agree in theΔ-resonance region, within the systematic errors,…
Effects of weakly coupled channels on quasielastic barrier distributions
2009
Heavy-ion collisions often produce fusion barrier distributions with structures displaying a fingerprint of couplings to highly collective excitations. Similar distributions can be obtained from large-angle quasielastic scattering, although in this case, the role of the many weak direct-reaction channels is unclear. For $^{20}\mathrm{Ne}+^{90}\mathrm{Zr}$, we have observed the barrier structures expected for the highly deformed neon projectile; however, for $^{20}\mathrm{Ne}+^{92}\mathrm{Zr}$, we find significant extra absorption into a large number of noncollective inelastic channels. This leads to smearing of the barrier distribution and a consequent reduction in the ``resolving power'' o…
A new BeppoSAX observation of the Z Source GX 349+2
2004
Abstract We report on the results from two BeppoSAX observations of the Z source GX 349+2 performed in February 2001 and covering the broad energy range 0.12–200 keV. The average spectrum is well described by a soft blackbody (kTBB∼0.5 keV) and a Comptonized component having a seed-photon temperature of kT0∼1 keV, an electron temperature of kTe∼2.7 keV, and optical depth τ∼11. To well fit the energy spectrum three gaussian lines are needed at 1.2 keV, 2.6 keV, and 6.7 keV with corresponding equivalent widths of 13 eV, 10 eV, and 39 eV, probably associated to L-shell emission of Fe XXIV, Lyα S XVI, and Fe XXV, respectively. These lines may be produced at different distances from the neutron …
Photoemission of protons from4He in theΔ-resonance region
1996
High resolution proton energy spectra from the4He(γ,p) reaction have been measured with tagged photons in the range Eγ = 130−525 MeV using the large Mainz NaI(T1) spectrometer atΘplab=37.1°. Three separate reaction channels were identified, viz.4He(γ,p)t two-body breakup,4He photodisintegration via two-nucleon photon absorption processes and the quasifree pion production channel. Differential cross sections are presented for each of these channels as a function of photon energy. The sum of the two-nucleon photon absorption and the quasifree pion production differential cross sections, in the CM system, resembles that of the corresponding free-nucleon differential cross section when Fermi mo…
Determination of the total photo-absorption cross section of 197Au from () reaction cross sections
1984
Abstract Cross sections for the reactions 197Au ( γ, ℩ n ) (x ⩽ 12) have been measured for bremsstrahlung end-point energies in the range 60–340 MeV. From these dominant cross sections, the total photon absorption cross section is determined using a cascade-evaporation calculation to account for the missing reaction channels. The enhancement factor for the classical E1 sum rule is found to be 0.93 ± 0.10.
Total photofission cross section for 238U as a substitute for the photon absorption cross section in the energy range of the first baryon resonances
1992
Abstract The total photofission cross section σγ, F for 238U has been measured as a substitute for the total photon absorption cross section σtot in the energy range of the first baryon resonances (50⩽Eγ⩽800 MeV). The experiments were performed at the tagging facility of the new 855 MeV Mainz Microton MAMI B using monochromatic photons and a sophisticated 4π-arrangement of position sensitive fragment detectors. The measured cross section agrees in the Δ-resonance region with previous results and the so-called universal curve αtot/A. In the energy region of the D13-resonance near 710 MeV resonancelike structure could be observed as is seen for the free proton.
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.