Parallax error severely limits the use of gas detectors for neutron and X-ray single-crystal diffractometry. This is particularly the case in Neutron Macromolecule Crystallography (NMC), where a large solid angle is needed. High-resolution cylindrical detectors based on Neutron Image Plates provide a large angular coverage but they are gamma sensitive and do not allow time-resolved measurements. We describe the principle of a gas counter, the multi-blade Microstrip Gas Chamber (MSGC), which has the potential to design parallax-free cylindrical detectors. It contains radial MSGC plates, providing a partitioning of the gas volume and a segmentation of the signal readout. The axial coordinate is measured by reading out the charge signal on the anodes and the trans-axial coordinate is deduced from the electron drift distance measured optically using the time difference between the primary and the avalanche light. Expected characteristics are a sub-millimeter position resolution, a sub-microsecond time resolution, and a global counting rate greater than 10 7 s - 1 .
