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Title:The Mossbauer effect in iron under very high pressure
Author(s):Pipkorn, David Nieman
Doctoral Committee Chair(s):Frauenfelder, Hans
Department / Program:Physics
Subject(s):Mossbauer effect
internal magnetic field
s electron density
Abstract:The Mossbauer spectrum of Fe57 in iron metal has been measured at pressures up to 240 kilobars at room temperature. Below 133 kilobars the spectrum consists of the normal six lines characteristic of ferromagnetic, body-centered cubic iron. The internal magnetic field at the nucleus H decreases linearly with pressure; ~ = -1.6 x 10-4 kilobar-l , o where H is the field at atmospheric pressure. The center of gravity of o the spectrum shifts with pressure indicating an increase in s electron density at the nucleus. The initial variation, -8 .3 x 10 -5 cm sec -1 kilobar -1 , is consistent with scaling the 4s wavefunction with volume while at higher pressures the variation is slower. Above 133 kilobars a seventh line appears near the center of the spectrum due to the transformation of part of the iron source to the hexagonal-close-packed high pressure phase. With increasing pressure this line becomes more intense and the split spectrum disappears although the transformation is sluggish. From the absence of splitting and from the observed linewidth we conclude that the internal field in the hexagonal phase is (0 ~ 3) kilogauss. There may be a small broadening due to electric quadrupole interactions in the hexagonal lattice. The isomer shift of the hexagonal phase relative to the cubic phase is -0.017 cm/sec (s electron density greater in hexagonal phase). The pressure dependence of the shift in the hexagonal phase is very slight and is not consistent with scaling the 4s wavefunction with volume. Apparatus and experimental techniques that were developed for measuring the Mossbauer spectra of sources under pressure are described.
Issue Date:1964
Genre:Dissertation / Thesis
Rights Information:1964 David Nieman Pipkorn
Date Available in IDEALS:2011-05-19
Identifier in Online Catalog:6144509

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