XRTG4 is an X-ray tracer based on the Geant4 toolkit developed by cosine. The XRTG4 ray-tracer was originally developed to support the development of Silicon Pore Optics, but it can now be used to simulate any X-ray system.

Developing X-ray optics

The importance of detailed ray-tracing simulations in the development, construction, testing, and operation of X-ray optics has long been recognized. To a large extent X-ray imaging systems can be treated as any other optical system, and their properties in terms of aberrations and focusing capabilities can be examined with the standard tools of optics. However, when detailed performance predictions of the effective area and the point spread function are required, specific ray-tracing tools are needed in order to take into account the change of the reflectivity with the angle of incidence, and the scattering caused by the details of the surface finish. To the best of our knowledge, and certainly within the domain of X-ray optics for astrophysical missions, this problem has always been solved with ad hoc tools built to address issues related to the particular design under consideration.

Extending the Geant4 toolkit

At cosine we have developed a set of extensions for the Geant4 toolkit that allows one to trace X-ray optics of arbitrary complexity, as long as the geometrical model of the system can be described by the geometry library available in Geant4. The core component of these extensions consists of a Geant4-compatible implementation of the reflection of X-ray photons on a surface. Additionally, by making use of the available Geant4 functionality, we have created a framework that allows one to introduce a microscopic description of the properties of the surfaces of the optics. Through this framework it becomes possible to model the effects that these microscopic properties have on the scattering of the photons.

Working with the space sector

Besides introducing the notion of a generic tracer for X-ray optics, this development has the potential to ease the interaction of scientists and engineers during the study phase of X-ray space missions. Geant4-based models are in fact already widely used to study the effect of cosmic radiation on the spacecraft structures and instruments. By making use of the same tools in order to model both the spacecraft and the telescope, the study of a mission can be carried out on the basis of a shared understanding of its mechanical and optical properties.

Commercial support

If you are interested in acquiring the complete XRTG4 package, or wish to have us study the performance of a particular X-ray optical system or develop a Geant4 model or extension, get in touch with us: the details are available at the contact page.

Free download

We make part of our extensions available for free, under an open source licence. With it Geant4 is augmented with a new physical process, implementing the grazing angle scattering of X-ray photons. The only thing you need to do is define the geometry of your system. With the free download you also obtain an example program demonstrating its use.