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The magnetic cross-section for photons is small and difficult to observe; however, when the X-ray energy is tuned to certain absorption edges an enormous enhancement of the magnetic scattering cross-section is observed. This process is now understood in terms of atomic resonances. By chance, the largest enhancements, the most convenient for diffraction experiments, occur at the M edges (3.5 - 4.5 keV) in the actinides. Recent work at the NSLS, Brookhaven National Laboratory has been on small single crystals of NpAs. The higher resolution available with X-ray synchrotron beams, compared to that at neutron sources, has made it possible to determine new features in both the magnetic structure and the critical fluctuations just above T(N). Because of the high-absorption of the X-rays, the technique is extremely sensitive to the near-surface region, and the results often show significant differences from those determined by neutron diffraction, which examines the bulk of the material. Thus the two techniques are complementary. Very small samples are all that is required for the synchrotron experiments, since the beam illuminates no more than 1 micro-g of NpAs, so that studies of the magnetic properties of transcurium materials become possible for the first time.

Additional information

Authors: LANDER G H, JRC Karlsruhe (DE);STIRLING W G, Keele University, Department of Physics (GB);LANGRIDGE S, Keele University, Department of Physics (GB);TANG C C, Keele University, Department of Physics (GB);GIBBS D, Brookhaven National Laboratory, Department of Physics, Long Island (US)
Bibliographic Reference: Paper presented: International Conference Actinides '93, Santa Fe (US), September 19-24, 1993
Availability: Available from (1) as Paper EN 37474 ORA
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