09436 IUPAC Gold Book - beam footprint 10.1351/goldbook.09436 09436 current 1 Area on the specimen irradiated by X-rays in X-ray reflectrometry. In typical commercial equipment, the beam width is \(\pu{200 \upmu m}\), so at \(\pu{0.3\!^{\circ}}\) incident angle, the beam footprint is \(\pu{38 mm}\) long; at \(\pu{1\!^{\circ}}\), it is \(\pu{11.5 mm}\) and at zero incidence angle it is infinite. For \(\pu{100 \upmu m}\) incident beam width, these values are halved. The beam footprint along the beam direction can be reduced by the use of a suitable knife-edge diaphragm mounted in a plane that is normal to the sample surface and whose normal, in turn, aligns with the beam azimuth. The knife-edge is parallel to, and adjusted to be close to, the surface at the point where the X-ray beam centre strikes the sample surface. This closeness limits the footprint size but also reduces the measured signal intensity. X-ray reflectrometry https://goldbook.iupac.org//terms/view/09214 PAC, 2020, 92, 1781. 'Glossary of methods and terms used in surface chemical analysis (IUPAC Recommendations 2020)' on page 1847 (https://doi.org/10.1515/pac-2019-0404) https://goldbook.iupac.org/terms/view/09436/html https://goldbook.iupac.org/terms/view/09436/json https://goldbook.iupac.org/terms/view/09436/plain Citation: 'beam footprint' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.09436 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-06-07T12:45:48+00:00