Gamma ray computed tomography for fast rotating objects

Recently, we have developed a high resolution gamma ray computed tomography system to analyze processes at hydro dynamic and multi phase flow facilities non-invasively. Typically, the measurement system consisting of a collimated isotopic source and a gamma ray detector is rotated around the object of investigation to record projections from different angle positions in one plane. In our case we use Cs137 with an activity of about 165 GBq. For fast rotating objects our developed measurement system is arranged in a fixed position and the stir of the object is used. By cyclically read-out of the measurement system’s electronic the number of projections per revolution can be determined. A trigger signal that is also included in the data transfer indicates a full revolution. That information is important for the later data processing if the object is rotating non-uniformly and thus the number of projections per revolution differs. After the recording the data of one projection can be resorted in a matrix – called sinogram - to the corresponding angle position column. Typical applications areas are the behaviour analysis of hydro dynamic couplings and the determination of gas fraction in a stirrer vessel reactor. Therefore we developed a new electronic that is compatible to the existing digital unit and realizes a periodical read-out of our 320 single detector arc every 40 µs. That means for an object that is rotating with 1500 rpm 1000 projections can be recorded per revolution.