Structural parameters for the ferrimagnetic and paramagnetic phases of magnetite have been refined from neutron multiple diffraction data. Experimental neutron multiple diffraction patterns were obtained by measuring the 111 primary reflection of a natural single crystal of this compound. Measurements were made at room temperature for the ferrimagnetic phase and at 976 K for the paramagnetic phase. The corresponding simulated patterns have been calculated by MULTI, a computer program for the simulation of neutron multiple diffraction patterns. A step‐by‐step process was used in the refinements according to the parameter‐shift method. Both isotropic and anisotropic thermal parameters were assumed for the temperature factor. Isotropic thermal parameters were considered in two different ways: an overall parameter for all ions in the structure and three different parameters for the three special positions occupied by them in the structure. The best results were found in the refinements with anisotropic thermal parameters. In this case, the values of the profile R factor found for these refinements were 3.00 and 3.32%, respectively, for the ferrimagnetic and paramagnetic phases.
This work reports on calculations of the deformation energy of a nucleus for nonlinear deformations. The working hypothesis is that, beyond the usual linear approximation, the nonlinear analysis yields soliton solutions moving on its surface. The potential barrier against the emission of a soliton is calculated within the macroscopic-microscopic method. The outer turning point of the barrier determines limitations on the geometrical and kinematical parameters for the formation of a surface soliton. For large asymmetry, the two-centre shell model is used to assign a structure to the soliton. Calculations for 248 No with the emission of a 40 Ca soliton are reported; likewise for 224 Th with the emission of 16 O. Except for necked shapes at the very first stages of soliton formation, the greatest portion of the deformation path displays rather compact configurations with large neck radii. These shape sequences correspond to allowable soliton velocities. Close to and just beyond the touching point configuration, where the shape becomes concave, the width and the velocity of the soliton approaches zero. The calculations suggest that the emission of a 40 Ca structure is quite probable due to a low potential barrier, whereas the emission of an 16 O-type soliton is rather unlikely due to the higher penetration barrier.
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