Polarity neutrons and

Deutsch M, Gillon B, Claiser N et al (2014) First spin-resolved electron distributions in crystals from combined polarized neutron and X-ray diffraction experiments. lUCrJ 1 194—199... 

In neutron reflectivity, neutrons strike the surface of a specimen at small angles and the percentage of neutrons reflected at the corresponding angle are measured. The an jular dependence of the reflectivity is related to the variation in concentration of a labeled component as a function of distance from the surface. Typically the component of interest is labeled with deuterium to provide mass contrast against hydrogen. Use of polarized neutrons permits the determination of the variation in the magnetic moment as a function of depth. In all cases the optical transform of the concentration profiles is obtained experimentally. 

For specimens where gradients in the ms etic moment are of interest, similar arguments apply. Here, however, two separate reflectivity experiments are performed in which the incident neutrons are polarized parallel and perpendicular to the surfiice of the specimen. Combining reflectivity measurements under these two polarization conditions in a manner similar to that for the unpolarized case permits the determination of the variation in the magnetic moments of components parallel and perpendicular to the film surface. This is discussed in detail by Felcher et al. and the interested reader is referred to the literature. 

CP-1 was assembled in an approximately spherical shape with the purest graphite in the center. About 6 tons of luanium metal fuel was used, in addition to approximately 40.5 tons of uranium oxide fuel. The lowest point of the reactor rested on the floor and the periphery was supported on a wooden structure. The whole pile was surrounded by a tent of mbberized balloon fabric so that neutron absorbing air could be evacuated. About 75 layers of 10.48-cm (4.125-in.) graphite bricks would have been required to complete the 790-cm diameter sphere. However, criticality was achieved at layer 56 without the need to evacuate the air, and assembly was discontinued at layer 57. The core then had an ellipsoidal cross section, with a polar radius of 209 cm and an equatorial radius of309 cm [20]. CP-1 was operated at low power (0.5 W) for several days. Fortuitously, it was found that the nuclear chain reaction could be controlled with cadmium strips which were inserted into the reactor to absorb neutrons and hence reduce the value of k to considerably less than 1. The pile was then disassembled and rebuilt at what is now the site of Argonne National Laboratory, U.S.A, with a concrete biological shield. Designated CP-2, the pile eventually reached a power level of 100 kW [22]. 

Papoular, R.J. and Gillon, B. (1990) Maximum entropy reconstruction of spin density maps in crystals from polarized neutron diffraction data, Europhys. Lett., 13(5), 429 134. 

As at room temperature Bragg reflections contain both nuclear and magnetic structure factors, the nuclear structure was refined from a combination of polarized and unpolarized neutron data. Contrary to the ideal structure where only three atomic sites are present, it has been shown [11, 12] that some Y atoms were substituted by pairs of cobalt. These pairs, parallel to the c-axis are responsible for a structure deformation which shrinks the cobalt hexagons surrounding the substitutions. The amount of these substituted Y was refined to be 0.046 0.008. Furthermore, the thermal vibration parameter of Coi site appeared to be very anisotropic. The nuclear structure factors Fn were calculated from this refined structure and were introduced in the polarized neutron data to get the magnetic structure factors Fu. 

Baron, V., Gillon, B., Plantevin, O. et al. (1996) Spin-density maps for an oxamido-bridged Mn(II)Cu(II) binuclear compound. Polarized neutron diffraction and theoretical studies, J. Am. Chem. Soc., 118, 11822-11830. 

Gillon, B. Schweizer, J. (1989) Study of chemical bonding in molecules the interest of polarized neutron diffraction, In Molecules in Physics, Chemistry and Biology, Maruani, Jean(Ed.), Kluwer, Dordrecht, The Netherlands, Vol. II, p. 111. 

It is a somewhat surprising fact that information about vibrational frequencies and bond lengths in very common and important ions is very sparse. Clearly, many more such determinations are necessary. Only this year, for example, have data become available which enable metal-ligand displacements on electron removal for the aquo Fe(II)/Fe(III) and Co(II)/Co(III) systems to be obtained. In view of the importance of these partially unpublished data, I have reproduced them in Table VI. The values of A for the Fe and Co systems are 0.128-0.137, and 0.208 8 respectively. The variability of the Fe results points to the fact that caution must be exercised in using data obtained in crystal lattices for a solution environment. Spin-polarized neutron diffraction studies on the structure of solu-... 

Monkenhusch M (1990) Nucl Inst and Methods A 287 465 Williams WG (1988) Polarized neutrons. Claredon, Oxford Golub R, Gahler R (1987) Phys Lett A 123 43... 

Ketonate complexes of Ru are reported in a number of papers. The parent complex [Ru(acac)3] has been subject to a polarized neutron diffraction study at 4.18 K, to powder neutron diffraction studies and to single-crystal structure determinations at 293 K, 92 K, and 10.5 K. The structure is disordered at all temperatures. Measurements of the magnetic susceptibilities (at 2.5 K and 300 K) have been made along different crystal axis directions, and the results analyzed. An investigation of the relationships between ionization potentials and half-wave potentials of a series of tris(/3-ketonate)Ru complexes has been reported, and the electrochemical properties of [Ru(acac)3] in chloroaluminate molten salt media have been reported. The reduced species [Ru(acac)3] can react with AICI4 reduction by bulk electrolysis of a small amount of [Ru-(acac)3] in the melt yields [RuClg]. ... 

The joint use of X-ray and neutron diffraction data is particularly expedient. Firstly, the interaction between the magnetic moments of neutrons and electrons is the basis for polarized-neutron diffraction, from which the unpaired spin density in a system can be derived. The diffraction of spin-polarized neutrons is an important technique, beyond the scope of this volume. Secondly, the interaction between neutrons and the atomic nuclei, which is the basis for structure determination by neutron diffraction, leads directly to information on the positions and mean-square vibrations of the nuclei. 

According to the neutron and X-ray diffraction measurements in KDP and DKDP, spontaneous polarization below Tc is produced by the shifts of the... 

Detailed studies - band structure calculations, de Haas-van Alphen effect and polarized neutron diffraction - have evidenced the strong hybridization of 5 f bands either with p anions bands (USi3, UGes, USns) or 4d bands (URhs, UIts). 

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