The planispherical chamber: A parallax-free gaseous X-ray detector for imaging applications

Six Concepts in Search of an Author

“…The position of the conversion can be recorded with a projective strip electronic readout [16], or with a simpler albeit rate-limited optical recording, as described for example in [17]. Promising results have been reported with a prototype device [18]; see the inserted recorded patterns in the figure. The operation of the concept relies on two basic assumptions: -A GEM-like structure could hold in vacuum the required potential difference to generate X-rays of therapeutic interest-ten to fifteen kV; -A thin wire can generate a sufficient electron current by spontaneous field emission, without heating-possible, but a significant complication to the design.…”

“…The position of the conversion can be recorded with a projective strip electronic readout [16], or with a simpler albeit rate-limited optical recording, as described for example in [17]. Promising results have been reported with a prototype device [18]; see the inserted recorded patterns in the figure. .…”

“…Schematics and field lines in the planispherical detector; the GEM electrode is patterned with rings powered at appropriate potentials to create a quasi-radial field. In the insert, the image of a square reticle placed in front of the detector with planar (a) and spherical field (b) demonstrate the correction of the parallax error [18]. The black rings correspond to the separations between the various rings.…”

Radiation imaging with optically read out GEM-based detectors

“…Drift field lines radially focused on a point-like radiation source can be used to minimise the parallax error. While previous designs employing spherical GEMs [13] to achieve radially focused drift fields were not ideally suited for optical readout, segmented cathode and GEM electrodes biased at different potentials can be used to maintain a flat detector geometry while achieving radially focused drift field lines [14]. Such a planispherical GEM detector is well suited for X-ray fluorescence and crystallography and enables the preservation of the high position resolution in applications requiring thick drift regions for increased radiation detection efficiency.…”