The main activities of the group on Radiation Sensor Systems concern pixellated detectors for ionizing radiation including both particles and photons. A significant part of the work is based on the MEDIPIX family of readout electronics and the collaboration within the MEDIPIX consortium.

Understanding the performance of the sensor elements and the readout electronics is essential in order to predict the image quality for a certain imaging system. X-ray imaging requires high-Z sensor materials in order to get sufficient quantum efficiency. Unfortunately these materials typically include high concentrations of defects which affect the charge transport. Extensive work is going on in order to determine the effects of charge transport, trapping and fluorescence in pixellated CdTe sensors. Significant results have been obtained from the measurements with a monoenergetic mircobeam done at DIAMOND.

 

Light Separates fibers and coating

Imaging of light materials is of high interest for the forest industry. One interesting application concerns separation of fibers and coating in a sheet of paper. This could be done either by spectroscopic imaging, taking advantage of the absorption edge of Ca when CaCO3 is used as the coating material or by using phase contrast imaging. The phase contrast effect is generally larger than the effects of attenuation for light materials. So far we have been able to separate different layers using spectroscopic imaging. A setup for phase contrast imaging is currently being built.

Monitor efficient radon reduction

Radon is a problem in many buildings. It has health effects since the decay chain of radon contains charged ions which stick to the lungs where further decays can cause lung cancer. A project to develop an electronic radon monitor is going on in collaboration with one of the spin-off companies. The unit is fast enough to monitor the weather induced variations in the radon levels in a building and to control radon reduction equipment. By using this kind of sensor the radon levels can be kept below the limits with minimal use of energy.

Semiconductor detectors for neutron imaging

Neutron imaging is a growing field. The construction of the European Spallation Source in Lund will further increase the demand for efficient neutron detectors. So far most of the neutron imaging has been done using gas detectors (3He) and large scintillators. However semiconductor detectors for neutron imaging are gaining growing interest. Main reasons are the lack of 3He and that semiconductor detectors provide higher spatial resolution and better timing than the current detectors. Options for developing high efficiency neutron detectors based on the MEDIPIX technology are studied in collaboration with ESS and the Institute of Experimental and Applied Physics in Prague.

The research group is active in national and international collaborations to define roadmaps for further detector development and to launch collaborative projects in this field. The most important of these collaborations is the Detector Network of the European Synchrotrons. On the national level we participate in a project funded by the Swedish Research Council and coordinated by Uppsala University for form a detector development network in Sweden.

International collaborations

The research group has a strong and continuing collaboration with the partners in the MEDIPIX consortium. An agreement has been made to send one of our PhD-students to CERN to address stability issues in the TIMEPIX readout chip within the MEDIPIX family.

A specific collaboration has been formed with University of Glasgow and the synchrotron DIAMOND in England. The purpose is to investigate the behavior of pixellated CdTe sensors under X-ray illumination. Experiments have been done at DIAMOND using a monoenergetic microbeam. Results show effects of depth of interaction, charge transport and fluorescence.

New x-ray characterization lab

At STC the group has access to a class 1000 cleanroom specifically equipped for sensor fabrication. During this year an X-ray characterization lab has been built. The room is about 4 meters long and fully shielded with lead. A nanofocus X-ray tube together with slits and an extensive set of sample holders is mounted on an optical table. This setup is suitable for X-ray microscopy as well as phase contrast imaging.