Suppression of Surface Effect by Using Bent-Perfect-Crystal Monochromator in Residual Strain Scanning

Abstract:

Using our long experience in Bragg diffraction optics we successfully used focusing principles for substantial increasing both luminosity and resolution of the strain scanners with respect to the conventional devices. Monochromatic neutrons are selected by the cylindrically bent monochromator from the reactor spectrum. There is a strong correlation between divergences of incoming and outgoing beams with respect to the polycrystalline sample, which can be easily manipulated by changing the monochromator bending radius. By setting a proper value of the radius, a narrow, quasiparallel and highly luminous output beam can by adjusted. The strong correlation between wavelength and direction of incoming and outgoing beams depending on the monochromator bending radius can be as well used for suppression of surface effect in residual strain scanning. In scanning near a sample surface aberration peak shifts arise due to the fact that the gauge volume defined by input and output slits is partially out of the sample and its value can be of the same order as the residual strain effects. In this work we demonstrate that by changing of the bending radius of monochromator, this surface effect can be suppressed to values smaller then experimental errors in residual strain scanning.

• Periodical: Materials Science Forum (Volumes 490-491)
• Pages: 234-238
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.490-491.234
• Online since: July 2005
• Authors: Miroslav Vrána, Pavol Mikula
• Keywords: Bent Monochromator, Neutron Diffraction, Residual Strain Scanning

References

[1] I. C. Noyan and J. B. Cohen, Residual Stress - Measurement by Diffraction and Interpretation Springer-Verlag, New York, (1987).

[2] A. D. Krawitz, Introduction to Diffraction in Materials Science and Engineering, John Wiley & Sons, (2001).

[3] P. Mikula et al., Nucl. Instrum. and Methods A 338 (1994) 18.

[4] P. Mikula et al., Journal de Physique IV, Coll. C7, 3 (1993) 2183.

[5] M. Vrána et al., Nucl. Instrum. and Methods A338 (1994) 125.

[6] P. Mikula et al., Physica B 213&214 (1995) 922.

[7] J. Kulda, J. Šaroun, Nucl. Instrum. and Methods A379 (1996) 155.

[8] P. Mikula, P. Lukáš and M. Vrána, Physica B, 234-236 (1997) 1058.