Double volume reflection of a proton beam by a sequence of two bent crystals

The doubling of the angle of beam deflection due to volume reflection of protons by a sequence of two bent silicon crystals was experimentally observed at the 400 GeV proton beam of the CERN SPS. A similar sequence of short bent crystals can be used as an efficient primary collimator for the Large Hadron Collider

NMR and NQR investigation of the lattice dynamics in (CH₃)₂CHNH₃CdBr₃

The temperatures dependences of the Br⁷⁹ quadrupole resonance, Br⁷⁹ and proton spinlattice relaxation times have been studied in the perovskite layer structure compounds (CH₃)₂CHNH₃CdBr₃. It is shown that anomalies in the temperature behaviours of NQR frequencies and quadrupole relaxation of Br⁷⁹ and related to the reorientation of NH₃ groups. The main mechanisms of Br⁷⁹ and proton spin relaxation as well as their correlations with motion nature of the methylammonium groups and their fragments are discussed.Приведены результаты исследований температурных зависимостей частот ядерного квадрупольного резонанса Br⁷⁹, квадрупольной спин-решеточной релаксации ядер Br⁷⁹ и протонной ЯМР релаксации в кристалле (CH₃)₂CHNH₃CdBr₃ с перовскито-подобной структурой. Показано, что аномальное температурное поведение частот ЯКР и квадрупольной релаксации ядер брома обусловлено реориентацией NH₃ групп и динамикой водородной связи N-H... Br. Обсуждаются механизмы релаксации протонов и ядер брома, а также их связь с характером движения метиламмонийных групп и их фрагментов

Evidence for Indirect Action of Ionizing Radiation in 18-Crown-6 Complexes with Halogenous Salts of Strontium: Simulation of Radiation-Induced Transformations in Ionic Liquid/Crown Ether Compositions

Ionic liquid/crown ether compositions are an attractive alternative to traditional extractants in the processes for spent nuclear fuel and liquid radioactive wastes reprocessing. These compositions are exposed to ionizing radiation, and their radiation stability, especially in the presence of metal salts, is a crucial issue. In the present study, the macrocyclic 18C6·Sr(BF4)2 and 18C6·Sr(PF6)2 complexes simulating the components of metal loaded ionic liquid/crown ether extractants were synthesized and their structures were characterized by FTIR spectroscopy and single-crystal X-ray diffraction analysis. Inclusion of Sr2+ cation into the 18C6 cavity resulted in more symmetric D3d conformations of the macrocycle. The structural transformations of the crown ether were accompanied by an elongation of polyether C - O bonds that could increase the possibility of radiolytic cleavage of the macrocycle. However, EPR study of the synthesized compounds subjected to X-ray irradiation revealed predominant formation of macrocyclic -CH2-ĊH-O- radicals. This result demonstrated an evidence for indirect action of ionizing radiation on individual components of the complexes and was reasonably described by a positive "hole" transfer from primary macrocyclic radical cation to fluorous anion at the primary stages of radiolysis and a subsequent interaction of fluorine atom with 18C6 macrocycle in secondary radical reactions. The observed effects may be partially responsible for enhanced sensitivity of the ionic liquid/crown ether extractants to ionizing radiation due to chemical blocking of the crown ether with radiolytic HF, radiation-chemical degradation of the 18C6, and precipitation of a low-soluble SrF2. © 2018 American Chemical Society

Evidence for Indirect Action of Ionizing Radiation in 18-Crown-6 Complexes with Halogenous Salts of Strontium: Simulation of Radiation-Induced Transformations in Ionic Liquid/Crown Ether Compositions

Ionic liquid/crown ether compositions are an attractive alternative to traditional extractants in the processes for spent nuclear fuel and liquid radioactive wastes reprocessing. These compositions are exposed to ionizing radiation, and their radiation stability, especially in the presence of metal salts, is a crucial issue. In the present study, the macrocyclic 18C6·Sr(BF4)2 and 18C6·Sr(PF6)2 complexes simulating the components of metal loaded ionic liquid/crown ether extractants were synthesized and their structures were characterized by FTIR spectroscopy and single-crystal X-ray diffraction analysis. Inclusion of Sr2+ cation into the 18C6 cavity resulted in more symmetric D3d conformations of the macrocycle. The structural transformations of the crown ether were accompanied by an elongation of polyether C - O bonds that could increase the possibility of radiolytic cleavage of the macrocycle. However, EPR study of the synthesized compounds subjected to X-ray irradiation revealed predominant formation of macrocyclic -CH2-ĊH-O- radicals. This result demonstrated an evidence for indirect action of ionizing radiation on individual components of the complexes and was reasonably described by a positive "hole" transfer from primary macrocyclic radical cation to fluorous anion at the primary stages of radiolysis and a subsequent interaction of fluorine atom with 18C6 macrocycle in secondary radical reactions. The observed effects may be partially responsible for enhanced sensitivity of the ionic liquid/crown ether extractants to ionizing radiation due to chemical blocking of the crown ether with radiolytic HF, radiation-chemical degradation of the 18C6, and precipitation of a low-soluble SrF2. © 2018 American Chemical Society