FUNDAMENTALS OF X-RAY FLUORESCENCE - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 53

Figure1.29. The incident, the reflected, and the refracted beam at the interface of media 1 and 2.
On the left, medium 2 is optically denser than medium 1 ( n 2 > n 1 ); on the right, it is vice versa
( n 1 > n 2 ). The latter is usually the case for X-rays though it is exaggerated here. Figure from Ref. [8],
reproduced with permission. Copyright1996, John Wiley and Sons.

1.5DEFLECTIONOFX-RAYS

In a homogeneous medium, the X-ray beam just behaves like a light beam and
follows a straight path on which the photons travel. But if the beam hits the
boundary surface of a second medium, the incident X-ray beam will be
deflected from its original direction. It can even be split, that is, partly reflected
into the first medium and partly refracted into the second medium.

1.5.1ReflectionandRefraction

In accord with Figure 1.29, the following rules are valid:

• The incident, the reflected, and the refracted beam span a plane that is
normal to the boundary plane.
• The glancing angles 2

of the incident and the reflected beam are equal:

α * 1

α 1 (1.50)

• The glancing angles of the incident and the refracted beam follow Snell's
law (also called Snellius'law):

υ 2 cos α 1 υ 1 cos α 2 (1.51)

2 Glancing angles are considered in X-ray optics. They are complements of the angles of incidence
conventionally used in light optics.