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Neutron-induced cross sections represent the main nuclear input to models of stellar and Big-Bang nucleosynthesis. While (n,γ) reactions are relevant for the formation of elements heavier than iron, (n,p) and (n,α) reactions can play an important role in specific cases. The time-of-flight method is routinely used at n_TOF to experimentally determine the cross section data. In addition, recent upgrades of the facility will allow the use of activation techniques as well, possibly opening the way to a systematic study of neutron interaction with radioactive isotopes. In the last 20 years n_TOF has provided a large amount of experimental data for Nuclear Astrophysics. Our plan is to carry on challenging measurements and produce nuclear data in the next decades as well.

During the second long shutdown period of the CERN accelerator complex (LS2, 2019-2021), several upgrade activities took place at the n_TOF facility. The most important have been the replacement of the spallation target with a next generation nitrogen-cooled lead target. Additionally, a new experimental area, at a very short distance from the target assembly (the NEAR Station) was established. In this paper, the core commissioning actions of the new installations are described. The improvement in the n_TOF infrastructure was accompanied by several detector development projects. All these upgrade actions are discussed, focusing mostly on the future perspectives of the n_TOF facility. Furthermore, some indicative current and future measurements are briefly reported.

The n_TOF neutron time-of-flight facility at CERN is used for nuclear data measurements. The n_TOF Collaboration works closely with the Nuclear Reaction Data Centres (NRDC) network to disseminate the experimental data through the international EXFOR library. In addition, the Collaboration helps integrate the results in the evaluated library projects. The present contribution describes the dissemination status of n_TOF results, their impact on evaluated libraries and ongoing efforts to provide n_TOF resonance parameters in ENDF-6 format for further use by evaluation projects.

We present uniformly reprocessed and re-calibrated data from the RoboPol programme of optopolarimetric monitoring of active galactic nuclei (AGNs), covering observations between 2013, when the instrument was commissioned, and 2017. In total, the data set presented in this paper includes 5068 observations of 222 AGN with Dec. > -25a -. We describe the current version of the RoboPol pipeline that was used to process and calibrate the entire data set, and we make the data publicly available for use by the astronomical community. Average quantities summarizing optopolarimetric behaviour (average degree of polarization, polarization variability index) are also provided for each source we have observed and for the time interval we have followed it. © 2020 The Author(s).

We report the highly efficient catalytic activity of a transition metal selenide-based coordination complex, [Ni{(SePi Pr2 )2 N}2 ], (1) for oxygen evolution and hydrogen evolution reactions (OER and HER, respectively) in alkaline solution. Very low overpotentials of 200 mV and 310 mV were required to achieve 10 mA cm-2 for OER and HER, respectively. The overpotential for OER is one of the lowest that has been reported up to now, making this one of the best OER electrocatalysts. In addition, this molecular complex exhibits an exceptionally high mass activity (111.02 A g-1 ) and a much higher TOF value (0.26 s-1 ) at a overpotential of 300 mV. This bifunctional electrocatalyst enables water electrolysis in alkaline solutions at a cell voltage of 1.54 V. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The synthesis of the M[(OPPh2)(SePPh2)N]2, M = Co (1), Ni (2) complexes was accomplished by metathetical reactions between the corresponding M(ii) salts and the deprotonated form of the dichalcogenated imidodiphosphinato ligand [(OPPh2)(SePPh2)N]-. X-Ray crystallography revealed a pseudo-tetrahedral MO2Se2 coordination sphere, owing to the asymmetric (O,Se) nature of the chelating ligand. Slow diffusion of the coordinating solvent dimethylformamide into dichloromethane solutions of Ni[(OPPh2)(SPPh2)N] 2 or 2, afforded the pseudo-octahedral trans-[Ni(OPPh 2)(EPPh2)N2(dmf)2], E = S (3), Se (4) complexes, respectively. UV-vis spectra provided evidence that, in solution, complexes 3 and 4 revert to the corresponding pseudo-tetrahedral complexes, most likely due to the removal of the dmf molecules from the coordination sphere. The IR spectra of all complexes reflect the structural features observed by X-ray crystallography. The magnetic properties of the S = 3/2 complex 1, as well as the S = 1 complexes 2, 3 and 4, were extensively studied, and the magnitude of their g and zero-field splitting D parameters was estimated. The reported structures establish a structural transformation of tetrahedral to octahedral geometry of Ni(ii) complexes bearing asymmetric imidodiphosphinate ligands, upon recrystallization from coordinating solvents. The structural correlations between the Ni(ii) coordination spheres are aided by DFT and ab initio multi-configuration MCSCF calculations, which investigate the corresponding interconversion pathways. In addition, the calculations provide descriptions of the bonding interactions in the octahedral Ni(ii) complexes, as well as predictions of their D values. © 2011 The Royal Society of Chemistry.

Sulfur-containing mono-or bidentate types of ligands, usually form square planar Ni(II)S4 complexes. However, it has already been established that the bidentate L- dithioimidodiphosphinato ligands, [R2P(S)NP(S)R′2]-, R, andR′ = aryl or alkyl, can afford both tetrahedral and square planar, NiS4- containing, homoleptic NiR,R′L2 complexes, owing to an apparent structural flexibility, which has not, so far, been probed. In this work, the literature tetrahedral Ni[R2P(S)NP(S)R2] 2 complexes, R = Ph (NiPh,PhL2, 1Td) and R = iPr (NiiPr,iPrL2, 2) as well as the newly synthesized Ni[iPr2P(S)NP(S)Ph2] 2 complex (NiiPr,PhL2, 3), have been studied by UV-vis, IR, and 31P NMR spectroscopy. Complex 3 was shown by X-ray crystallography to be square planar, and magnetic studies confirmed that it is diamagnetic in the solid state. However, it becomes paramagnetic in solution, as it shows a similar UV-vis spectrum to one of the tetrahedral 1Td and 2 complexes. The crystal structure of the potassium salt of the asymmetric ligand, [iPr2P(S)NP(S)Ph2]K, has also been determined and compared to those of the protonated iPr 2P(S)NHP(S)Ph2 ligand and complex 3. All three, 1 Td, 2, and3, NiR,R′L2 complexes show strong paramagnetic effects in their solution 31P NMRspectra. Themagnetic properties of paramagnetic complexes 1 and 2 in the solid state were investigated on oriented crystals, and their analysis afforded remarkably small values of the spin-orbit coupling constant (λ) and orbital reduction factor (k) parameters, implying significant delocalization of unpaired electronic density toward the ligands. The above experimental findings are combined with data from standard density functional theory and correlated multiconfiguration ab initio theoretical methods, in an effort to investigate the interplay between the square planar and tetrahedral geometries of the NiS4 core, the mechanistic pathway for the spin-state interconversion, the degree of covalency of the Ni-S bonds, and the distribution of the spin density in this type of system. The analysis provides justification for the structural flexibility of such ligands, affording Ni R,R′L2 complexes with variable metallacycle conformation and NiS4 core geometries. Of particular importance are the large zero-field splitting values estimated by both experimental and theoretical means, which have not, as yet, been verified by direct methods, such as electron paramagnetic resonance spectroscopy. The findings of our work confirm earlier observations on the feasibility of synthesizing either tetrahedral or square planar NiS4 complexes containing the same type of ligands. They can also form the basis of investigating structure-properties relationships in other NiS4-containing systems. © 2010 American Chemical Society.

The reaction between Co(II) and the deprotonated tetraphenylimidodiphosphinic acid, [(OPPh2)2N]-, afforded a binuclear [Co2{(OPPh2)2N}4] complex, as revealed by X-ray crystallography. The structure contains two monometallic biconnective [(OPPh2)2N]- ligands, with an averaged Co-O bond length of 2.008 Å. The other two [(OPPh2)2N]- act as bimetallic triconnective ligands, forming two oxygen atom bridges, with the four Co-O(bridging) distances averaged at 2.155 Å, and the two Co-O(non-bridging) distances at 1.973 Å. The two approximately trigonal bipyramidal Co(II) ions are at a Co⋯Co distance of 3.301 Å. The analysis of the magnetic properties of [Co2{(OPPh2)2N}4] is consistent with an unusual ferromagnetic interaction, in a binuclear Co(II) system, between the two S = 3/2 Co(II) ions. © 2009 Elsevier B.V. All rights reserved.

The S/Se-containing bidentate ligands LH of the type R2P(E) NHP(E)R′2, E = S, Se and R, R′ = Ph or iPr have been employed to synthesize ML2 (M = Mn, Co) complexes which contain the biologically important MS4 core. Theoretical calculations on the LH and L- forms of the ligands probe the geometric and electronic changes induced by the deprotonation of the LH form, which are correlated with structural data from X-ray crystallography. These results reflect the flexibility of the ligands, which enables them to be rather versatile with respect to the formation of ML2 complexes with varied geometries and MEPNPE metallacycle conformations. A series of old and new ML2 complexes have been synthesized and their structural, spectroscopic and magnetic properties characterized in detail. The nephelauxetic ratio β of the CoL2 complexes provides evidence of covalent interactions, whereas the EPR properties of the MnL2 complexes are interpreted on the basis of predominant ionic interactions, between the metal center and the ligands, respectively. Additional evidence for the existence of covalent interactions in the CoL2 complexes (R = Ph, iPr, or mixed Ph/iPr), is offered by comparisons between their 31P NMR. The aforementioned notations are supported by extensive theoretical calculations on the ML2 (E = S, R = Me) modelled structures, which probe the covalent and ionic character of the M-S bonds when M = Co or Mn. Wider implications of the findings of the present study on the M-S covalency and its importance in the active sites of various metalloenzymes are also discussed. © The Royal Society of Chemistry 2006.

The thermally stimulated depolarization current (TSDC) method was used to study relaxation phenomena of low symmetry complexes in CaF2:Gd3+ crystals. During successive TSDC scans under exactly the same experimental conditions the shape of certain peaks was observed to change in a manner indicating conversions of tetragonal (type I) to trigonal (type II) Gd3+-Fi- complexes. In a first attempt to interpret the phenomenon, the transformation of type I to type II dipoles, which are considered as two distinctive configurations of the Gd3+-Fi- structure, is tentatively ascribed to the influence of the applied external electric field in the relaxation processes involved. © 1992.

LiF doped with 10(-2) mole fraction of Ba2+ impurity concentration was studied using two experimental techniques, namely thermally stimulated depolarization currents and depolarization currents at constant temperature. Both methods gave compatible results indicating the existence of three relaxation mechanisms. The activation enthalpies of reorientation, h(m), and the preexponential factors tau-0 were determined. The estimated parameters h(m) = 0.24 eV, and tau-0 = 6.59 X 10(-5) sec and h(m) = 0.50 eV and tau-0 = 1.78 X 10(-11) sec may be attributed, respectively, to reorientation of ion-vacancy dipoles by means of nearest-neighbor –> next-nearest-neighbor and nearest-neighbor –> nearest-neighbor jumps. A third mechanism with energy parameters h(m) = 0.81 eV and tau-0 = 4.93 X 10(-20) sec is attributed to a cluster.