GENERATION AND DETECTION OF THE POLARIZATION OF MULTI-GEV PHOTONS BY USE OF TWO DIAMOND CRYSTALS

Abstract Presented are experimental results for the difference in pair production probability (the asymmetry) for 5–150 GeV photons polarized parallel and perpendicular to a (110) plane in a 1.5 mm thick diamond 〈100〉 crystal. The photons are produced by interaction of 150 GeV electrons with an aligned diamond 〈100〉 crystal of 0.5 mm thickness. A significant asymmetry is found over the whole energy range, which corresponds to a high degree of linear polarization of the photons as well as a difference in the refractive index. This proof-of-principle result gives the possibility of producing high energy photons with circular polarization by use of a crystal. This might open for several opportunities in high energy physics like for instance the investigation of the contribution of the gluons to the spin of the nucleon

Energy migration processes in phosphate nanocrystals: size and dimensionality dependence

Peculiarities of electronic excitation energy migration in phosphate nanocrystals with three-dimensional (EuPO₄) and one-dimensional (EuP₃O₉) arrangement of regular ions under variation of concentration of both energy traps (Nd³⁺ ions) and scattering centres (La³⁺ ions) are discussed in the paper. Processes of energy migration in both EuPO₄ and EuP₃O₉ nanocrystals are phonon-assisted ones due to absence of resonance between energy levels of adjacent Eu³⁺ ions. The distance of energy migration for both EuPO₄ and EuP₃O₉ nanocrystalswas found to be equal to tens of nanometres, however, for EuPO₄ nanocrystals energy migration leads to stronger quenching of Eu³⁺ luminescence. For 10 nm EuPO₄ nanocrystals sufficient hampering of energy migration isobserved due to the depletion of the low-energy phonon spectrum as a result of the phonon confinement effect

Features of energy transport in EuMgB₅O₁₀ and EuP₃O₉ quasi-one-dimensional lattices

Processes of excitation energy migration in EuMgB₅O₁₀ and EuP₃O₉ quasi-one-dimensional matrices have been investigated by means of steady-state and time-resolved luminescence spectroscopy. It was shown that the patterns of energy migration in these materials are sufficiently different - while for EuMgB₅O₁₀ the most effective energy transport takes place at room temperature via ⁵D₀ →⁷F₁ transitions of Eu³⁺ ion, for EuP₃O₉ energy transfer is more effective at low temperatures and mediated by Eu³⁺-O²⁻ charge transfer states. The difference in energy transport processes can be explained taking into account the peculiarities of phonon subsystem for borate and phosphate matrices

Energy transport in EuAl₂.₀₇(B₄O₁₀)O₀.₆ nanocrystals with two-dimensional Eu³⁺ sublattice

Energy transport processes in EuAl₂.₀₇(B₄O₁₀)O₀.₆ nanocrystals with two-dimensional arrangement of Eu³⁺ subsystem were investigated using the methods of stationary and time-resolved spectroscopy. Sufficient difference in Eu³⁺- Eu³⁺ distances inside and between (001) planes (4.58 A vis 9.28 A, respectively) leads to two-dimensional character of energy migration. Comparison of energy transport processes in aluminium borate nanocrystals with two-dimensional (EuAl₂.₀₇(B₄O₁₀)O₀.₆) and three-dimensional (EuAl₃(BO₃)₄) arrangement of Eu³⁺ ions have shown that despite higher Eu³⁺-Eu³⁺ shortest distances (5.9 A), energy migration in EuAl₃(BO₃)₄ leads to stronger quenching of Eu³⁺ luminescence

Spectroscopically detected segregation of Pr³⁺ ions in YPO₄:Pr³⁺ nanocrystals

Segregation of Pr³⁺ ions in YPO₄:Pr³⁺nanocrystals was revealed by means of spectroscopic techniques. Increase of doped ions concentration in the near-surface layer of YPO₄:Pr³⁺ nanocrystals was confirmed by modification of luminescence spectra and decay curves depending on the heat treatment temperature. Relaxation of excess elastic stresses created by Pr³⁺ ion with volume greater than volume of regular Y³⁺ ion was determined to be the main cause of observed effects. Theoretical estimations obtained are in a good agreement with the experimental data

Aging of ZnS:Mn thin - film electroluminescent devices grown by two different atomic-layer epitaxial processes

Electroluminescent characteristics and the photodepolarization spectra of ZnS:Mn thin-film electroluminescent devices made with two different atomic-layer epitaxy processes based on chlorine and metalorganic precursors have been studied during initial stage of accelerated aging. Essential differences have been revealed. They are explained in assumption that different impurity centers exist in the ZnS:Mn films grown by using chlorine and metalorganic precursors, namely, MnCl₂, Cli⁻, Cls⁺ and isovalent oxygen traps, respectively. The mechanism of aging in both types of devices is discussed

Measuring the linear polarization of γ\gammas in 20-170 GeV range

The NA59 collaboration aims to measure the linear polarization of its photon beam in the 20-170 GeV range, using an aligned thin crystal. The tracks of $e^-/e^+$ pairs created in two different crystal targets, germanium and diamond, are reconstructed to obtain the photon spectrum. Using the polarization dependence of the pair production cross section in an aligned crystal, photon polarization is obtained to be 55% at the vicinity of 70 GeV.The Na59 collaboration aims to measure the linear polarization of its photon beam in the 20-170 GeV range, using an aligned thin crystal. The tracks of $e^-/e^+$ pairs created in two different crystal targets, germanium and diamond, are reconstructed to obtain the photon spectrum. Using the polarization dependence of the pair production cross section in an aligned crystal, photon polarization is obtained to be 55% at the vicinity of 70 GeV.The Na59 collaboration aims to measure the linear polarization of its photon beam in the 20–170 GeV range, using an aligned thin crystal. The tracks of e − / e + pairs created in two different crystal targets, germanium and diamond, are reconstructed to obtain the photon spectrum. Using the polarization dependence of the pair production cross section in an aligned crystal, photon polarization is obtained to be 55% at the vicinity of 70 GeV

Measurement of Coherent Emission and Linear Polarization of Photons by Electrons in the Strong Fields of Aligned Crystals

We present new results regarding the features of high energy photon emission by an electron beam of 178 GeV penetrating a 1.5 cm thick single Si crystal aligned at the Strings-Of-Strings (SOS) orientation. This concerns a special case of coherent bremsstrahlung where the electron interacts with the strong fields of successive atomic strings in a plane and for which the largest enhancement of the highest energy photons is expected. The polarization of the resulting photon beam was measured by the asymmetry of electron-positron pair production in an aligned diamond crystal analyzer. By the selection of a single pair the energy and the polarization of individual photons could be measured in an the environment of multiple photons produced in the radiator crystal. Photons in the high energy region show less than 20% linear polarization at the 90% confidence level