Beam-smiling in bent-Laue monochromators
- Medical Department, Brookhaven National Laboratory (BNL), Upton, New York11973 (United States)
- Center for Synchrotron Radiation Research and Instrumentation (CSRRI), Illinois Institute of Technology, Chicago, Illinois60616
- National Synchrotron Light Source, BNL, Upton, New York11973 (United States)
When a wide fan-shaped x-ray beam is diffracted by a bent crystal in the Laue geometry, the profile of the diffracted beam generally does not appear as a straight line, but as a line with its ends curved up or curved down. This effect, referred to as {open_quotes}beam-smiling{close_quotes}, has been a major obstacle in developing bent-Laue crystal monochromators for medical applications of synchrotron x-ray. We modeled a cylindrically bent crystal using the Finite Element Analysis (FEA) method, and we carried out experiments at the National Synchrotron Light Source and Cornell High Energy Synchrotron Source. Our studies show that, while beam-smiling exists in most of the crystal{close_quote}s area because of anticlastic bending effects, there is a region parallel to the bending axis of the crystal where the diffracted beam is {open_quotes}smile-free{close_quotes}. By applying asymmetrical bending, this smile-free region can be shifted vertically away from the geometric center of the crystal, as desired. This leads to a novel method of compensating for beam-smiling. We will discuss the method of {open_quotes}differential bending{close_quotes} for smile removal, beam-smiling in the Cauchios and the polychromatic geometry, and the implications of the method on developing single- and double-bent Laue monochromators. The experimental results will be discussed, concentrating on specific beam-smiling observation and removal as applied to the new monochromator of the Multiple Energy Computed Tomography [MECT] project of the Medical Department, Brookhaven National Laboratory. {copyright} {ital 1997 American Institute of Physics.}
- Research Organization:
- Brookhaven National Laboratory
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 678718
- Report Number(s):
- CONF-9706157--
- Journal Information:
- AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 417; ISSN APCPCS; ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
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