Modeling and measurement of the scattering properties of the source pinhole in the BEaTriX facility

Abstract

The purpose of this brief technical note is to provide an assessment of the performance of the tungsten pinhole placed in front of the microfocus Incoatec X-ray source with Titanium anode in the BEaTriX X-ray facility. The pinhole is a part of the collimator kit by Amptek purchased years ago to collimate a solid-state detector, and consists of a small (1/2 inch) tungsten disk with a 2.2 mm thickness and a 450 μm diameter. The pinhole is placed at a 20 mm distance from the source and limits the beam along the short arm of the facility, avoiding so the X-ray incidence on the tube walls which might cause unwanted X-ray reflection/scattering or diffuse background. At the same time, the pinhole located near the X-ray source provides visual reference for the parabolic mirror alignment. Pinholes are crucial optical components, as they have to diaphragm an X-ray beam without degrading it. Due to the closeness of the lateral walls of the pinhole to the X-rays, the surface has to be properly ruggedized in order to avoid unwanted reflections or diffuse scattering when X-rays impinge on it in grazing incidence conditions. Should this condition not be fulfilled, the pinhole would cause a broadening of the X- ray source and a consequent worsening of the finally collimated X-ray beam in BEaTriX. In this short note, we will show measurements of the X-ray beam in the BEaTriX facility aiming at ascertaining the scattering properties of the pinhole surface. The conclusion is that the amount of scattered/reflected radiation off the pinhole is hardly detectable and that the pinhole appears perfectly suitable for the collimation of the X-ray beam in the short arm of BEaTriX.