| 摘要 |
<p>An imaging optical system having a Rowland geometry can be used in a spectrometer for X-ray fluorescence. For the focusing of the X-ray beam emanating from the specimen to be analyzed, use is made of a curved analyzer crystal (28) whose radius of curvature may be variable, as in the case of a crystal surface (29) in the form of a logarithmic spiral (40). If such an analyzer crystal is to be made sufficiently large so as to achieve adequate intensity in the X-ray detector, a part of the crystal would have to be given a radius of curvature which is smaller than permissible so as to avoid fracturing of the crystal. In accordance with the invention, a first part (40) of the reflective surface (29) has a radius of curvature which is dependent on the location on the crystal whereas another part (42) of the reflective surface has a constant radius of curvature (44). A crystal part having a constant radius of curvature exhibits angular deviations, but for as long as these angular deviations are smaller than a given (not very low) limit value, they can be ignored in relation to other, larger deviations of the log spiral part. Such larger deviations occur notably when a multilayer mirror is chosen for the analyzer crystal (28).</p> |
