A practical method to determine the spatial resolution of GEM detector

A new method to determine the spatial resolution of a one-dimensional gaseous electron multiplication (GEM) prototype is demonstrated via an experimental test using an Fe-55 source with an adjustable slit. In this method, the total variance of the incident position σtot2, contributed by the GEM spatial resolution and the geometrical acceptance of the slit, is presented as a function of the event rate n under the full energy peak, with the latter being employed to calibrate the square of the slit width. Using a linear fit to the experimental data, a spatial resolution of σg=56±15μm(1σ) is measured. Compared to the existing methods, the novel method presented here is robust considering the inaccuracy in the direct measurements of the slit widths, and hence greatly circumvents machining difficulties.