LiZnNb4O11.5: A novel oxygen deficient compound in the Nb-rich part of the Li2O–ZnO–Nb2O5 system

A novel lithium zinc niobium oxide LiZnNb4O11.5 (LZNO) has been found in the Nb-rich part of Li2O–ZnO–Nb2O5 system. LZNO, with an original a-PbO2 related structure, has been synthesized by the routine ceramic technique and characterized by X-ray diffraction and transmission electron microscopy (TEM). Reflections belonging to the LZNO phase, observed in X-ray powder diffraction (XRPD) and electron diffraction, have been indexed as monoclinic with unit cell parameters a=17.8358(9) A˚ , b=15.2924(7) A˚ , c=5.0363(3)A˚ and g=96.607(5)1 or as a-PbO2-like with lattice constants a=4.72420(3) A˚ , b=5.72780(3) A˚ , c=5.03320(3) A˚ , g=90.048(16)1 and modulation vector q=0.3a*+1.1b* indicating a commensurately modulated a-PbO2 related structure. The monoclinic cell is a supercell related to the latter. Using synchrotron powder diffraction data, the structure has been solved and refined as a commensurate modulation (superspace group P1121/n(ab0)00) as well as a supercell (space group P21/b). The superspace description allows us to consider the LZNO structure as a member of the proposed a-PbO2-Z (3+1)D structure type, which unifies both incommensurately and commensurately modulated structures. HRTEM reveals several types of defects in LZNO and structural models for these defects are proposed. Two new phases in Li2O–ZnO–Nb2O5 system are predicted on the basis of this detailed HRTEM analysis

Increasing the production of the Mo-99 isotope by modernizing the design of targets irradiated in the experimental channels of the VVR-c reactor

There are various ways to obtain Mo-99. Some of them are widely used in industrial production, others are in the research stage with the aim of increasing the product yield. The main industrial method for obtaining Mo-99 using a nuclear reactor is the fragmentation method. This method provides for the presence of a uranium target and a nuclear reactor. The target is placed in the channel of the reactor core and irradiated with neutrons for the required time. After that, the target is removed from the channel to the “hot” chamber for the chemical separation of Mo-99. This is how Mo-99 is obtained practically all over the world. The paper considers the fragmentation method for producing Mo-99, which is implemented on the basis of the engineering and technological complex of the VVR-c research nuclear reactor. In order to increase the yield of Mo-99, a modernized model of the “tube-in-tube” target is proposed. The assessment of the production of Mo-99 and the cooling efficiency of the modernized target was carried out. The calculations were performed using the VisualBurnOut and Ansys CFX software packages. Computational studies have shown an increase in the energy release and the amount of the produced Mo-99 isotope in the target of the modernized design. In the most stressed zones, the target wall temperature exceeds the water saturation temperature. Surface boiling occurs in these zones. As a result, turbulization and mixing of the near-wall boundary water layer increases. This improves heat dissipation

Scientific program of DERICA — prospective accelerator and storage ring facility for radioactive ion beam research

Studies of radioactive ions (RIs) are the most thriving field of low-energy nuclear physics. In this paper, the concept and the scientific agenda of the prospective accelerator and storage ring facility for RI beam (RIB) research are proposed for a large-scale international project based at the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research. The motivation for the new facility is discussed and its characteristics are briefly presented and shown to be comparable to those of advanced world centers, the so-called "RIB factories". In the project, the emphasis is made on studies with short-lived RIBs in storage rings. Aunique feature of the project is the possibility of studying electron-RI interactions in a collider experiment to determine the fundamental properties of nuclear matter, in particular, electromagnetic form factors of exotic nuclei