[en] Controlling the ferroelectric polarization at macroscopic or microscopic levels is crucial in the framework of the development of ferroelectric materials used in yet challenging photo-electrochemical (PEC) cells and spintronic applications. We report here on polarization methods allowing to electrically polarize prototypical samples of BaTiO_3 (001) films. Epitaxial single crystalline layers were grown up to a thickness of 25 nm by atomic oxygen assisted molecular beam epitaxy on 1 at.% Nb doped SrTiO_3 (001) single crystals. The samples were both microscopically and macroscopically polarized using Piezoresponse Force Microscopy and electrochemical poling in an electrolyte respectively. In addition we demonstrate the possibility to retrieve a quasi-native mixed ferroelectric polarization state after annealing. These polarization methods may be applied to many other ferroelectric thin films. - Highlights: • Ferroelectricity of BaTiO_3 layers can be micro- and macroscopically controlled. • Microscopic ferroelectric domains are defined with piezoresponse force microscopy. • Poling in a LiClO_4 electrolyte is a macroscopic poling method. • Air annealing above the Curie temperature “resets” the polarization state.

[en] Magnetisation reversal by precession has been observed for a micron-sized (4 μmx8 μm) spin-valve element in response to 250 ps field pulses. Due to the dispersion of the magnetisation orientation at remanence, the magnetisation of only a small fraction of the sample is aligned perpendicular to the excitation field and can undergo precessional reversal. Although this leads to an overall reduced magneto-resistance ratio, two well-defined signal levels can be established

[en] Superconducting a-Nb_xSi_1-x thin films experience a lowering of the T_c until the superconductivity disappears through a Superconductor-Insulator Transition (SIT). We here present transport measurements on 2D a-Nb_xSi_1-x films, close to the SIT, for different compositions and thicknesses. We investigate the lowering of the T_c in light of existing theories, especially the one developed by Finkel'stein.

[en] The X-ray diffraction studies, IR absorption spectra, NMR and thermal analysis on V₂O₅ - MoO₃ system are presented. The existence of solid solution (α phase) range, and that of the variable composition compound: Vsub(2+x)Mosub(1+x)Osub((5,5x+8) - delta)(β-phase) is determined. The lattice distortion of α phase is studied as function of the concentration and thermal treatment. Structural properties are correlated with the catalytic activity, emphasizing the part played by the lattice distortions. (author)

[en] This is an exclusive product designed for applied nuclear research at RIKEN Institute Japan. The granular structure detection system has been designed for fast neutron detection in ¹¹ Li fusion process on silicon targets. It has the following physical characteristics and performances: - active area : 36x36 cm²; - structure of active area: 81 detector elements of plastic scintillator BC-400 type and XP2972 Philips photomultipliers; - dimension of scintillator (granular dimension): 4x4x12 cm³; - height of the active area centre to the beam position: 1.8 m; - the distance from target for time of flight measurements: 1.5 m; - detection efficiency for the neutrons with E_n = 13 MeV: 35%; - time resolution: 0.9 - 1.4 ns; - rise time: 1.8 ns; -crosstalk between the neighbouring elements: 3.3%. (authors)

[en] We have investigated the growth of BaTiO₃ thin films deposited on pure and 1% Nb-doped SrTiO₃(001) single crystals using atomic oxygen assisted molecular beam epitaxy and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO₃ layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at ∼10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for well crystallized layers. We show that the Ba oxide rich top layer can be removed by chemical etching. The present work stresses the importance of stoichiometry and surface composition of BaTiO₃ layers, especially in view of their integration in devices.

[en] It was predicted that in a fusion experiment induced by ¹¹ Li on light targets, due to the very large dimension of ¹¹ Li, the valence neutrons will not be absorbed together with the ⁹ Li core, but will be emitted in the early stage of the reaction process. The experiment aiming to check this expectation was performed at the RIKEN-RIPS facility. It was found from neutron energy spectra measurements that an important number of fusion events, about 40 %, are preceded by the pre-emission of 1 or 2 neutrons. In the position spectra measurements, a very narrow neutron component has been found. The recent results of time-position coincidence measurements show that within the narrow component, the neutrons are pre-emitted predominantly as neutron pairs. The Program Advisory Committee of RIKEN has approved a new experiment at the RIKEN Ring Cyclotron aiming the investigation of neutron-neutron coincidences by using a new neutron array detector. This detector has been recently achieved within the collaboration existing between IFIN-HH, Romania and RIKEN-Japan. It consists of 81 plastic scintillation crystals, 4 x 4 x 12 cm³, each being viewed by a Philips XP2972 photomultiplier. At IFIN-HH, Bucharest the scintillation BC400 crystal quality, the time characteristics of the detector, the response to γ rays and to neutrons, have been tested with good results. It is expected that up to ∼ 900 n-n coincidences could be investigated with the new array detector, within the approved beam time. (authors)

[en] This study analyses the efficiency of the justification of individual computed tomography (CT) procedures using the good practice guide. The conformity of the CT scans with guide's recommendations was retrospectively analysed in a paediatric emergency hospital in Romania. The involved patient doses were estimated. The results show that around one-third of the examinations were not prescribed in conformity with the guide's recommendations, but these results are affected by unclear guide provisions, discussed here. The implications of the provisions of the revised International Atomic Energy Agency's Basic Safety Standards and of the Council Directive 2013/59/EURATOM were analysed. The education and training courses for medical doctors disseminating the provisions of the good practice guide should be considered as the main support for the justification of the CT scans at the individual level. (authors)

[en] Evidence for neutron pair pre-emission in the fusion of ¹¹ Li halo nuclei with Si targets was reported by us for the first time in 1996. For further testing of this effect, an array detector covering (36x36) cm², has been built. To have also good position resolution a 4 x 4 cm² area of a single scintillation element was chosen. As concerns the thickness of the scintillation element, a compromise between efficiency, cross-talk between adjacent detectors and cost was established. For example, for 6 cm thickness of the plastic crystal, the detection efficiency for 13 MeV neutrons is only 20% and the cross-talk 1.7%. For 12 cm thickness the detection efficiency significantly raises to 35% and the cross-talk becomes 2.8%. For larger thickness the efficiency only slightly increases. For 18 cm thickness the efficiency is expected to be 41%, and the cross-talk 3.3%. Therefore, by choosing the 12 cm thickness, one expects good efficiency with a reasonable increase of the cross-talk. The above mentioned efficiency and cross-talk values were obtained by Monte-Carlo calculations. The 81 BC400 plastic scintillation elements were cut from two 1000 x 300 x 40 mm³ pieces. After polishing, the quality of the surfaces was tested by optical methods. The BC400 crystal detects charged particles, γ rays, and neutrons. The γ-ray and neutron separation will be done at RIKEN by the time of flight technique. The Philips XP2972 photomultiplier was selected for building the array detector. This selection was based on the following considerations: 1.the diameter is suited to the granularity of the detector; 2. the phototube sensitivity matches the plastic crystal emission; 3. the output pulse has very good characteristics (pulse height close to 1 volt and a rise time of 2.1 ns). The voltage divider has been designed for large multiplication and stability, in conditions of counting rates up to 104 pulses/s. The total resistance is 2.6 MΩ. The following testings on the new array detector have been performed: 1. testing of scintillation crystal quality; 2. testing of time characteristics of the detector; 3. testing of response to β and γ rays; 4. testing of response to neutrons. A detailed description of these testings and of the obtained results, will be published elsewhere. (authors)

[en] An array detector consisting of 81 elements 4x3x12 cm³, has been built. This detector will be used for n-n coincidence measurements on neutrons pre-emitted in fusion induced by ¹¹ Li halo nuclei. A detection efficiency equal to 34% for 13 MeV neutrons was estimated for adjacent two detectors and equal to about 1% for two separated by one detector. The detector was designed to heave a 36x36 cm² area, witch at ≅ 150 cm from target, will cover almost entirely the narrow neutron spot, according to requirements of the new experiment. To heave also good position resolution the area of a single scintillation element was chosen 4x4cm². As concerns the thickness of the scintillation element, one has considered a compromise between the efficiency, the cross-talk between the adjacent detectors and cost. For example, for 6 cm thickness of the plastic crystal, the detection efficiency for 13 MeV neutrons is only ≅ 1.7%. For 12 cm thickness the detection efficiency significantly raises at ∼ 35% and the cross-talk becomes 2.8%. For larger thickness the efficiency is expected ≅ 41%, and the cross-talk ≅ 3.3%. Therefore, by choosing the 12 cm thickness, one expects good efficiency with a reasonable increase of the cross-talk. The above mentioned efficiency and cross-talk values were obtained by Monte Carlo calculations. (authors)