Development and performance of the anti-coincidence flow gas multi-wire proportional chamber

To achieve low-background alpha and beta ray measurements of trace radioactive nuclides in soil and scale deposits, we propose a scheme employing two flow gas multi-wire proportional chambers (MWPC) as anticoincidence detectors. The MWPCs exhibit high sensitivity, low background count, insensitivity to gamma rays, and the capability to cover a relatively large detection area. The MWPC has a sensitive area of 400 mm × 250 mm and adopts a structure of cathode layer-anode layer-cathode layer, with a layer spacing of 10 mm. MWPC1 is a traditional type of anode structure using 25 μm gold-plated tungsten wire, and wire spacing of 20 mm, and a cathode composed of a 12.5 μm thick double-sided aluminum-coated Mylar film; MWPC2 adds a 100 μm beryllium copper wire as a field wire in the middle of the anode wire. Test results indicate that the plateau region of MWPC1 is 1175 V–1550 V and the best energy resolution for 55 Fe is 15.95%; the plateau region of MWPC2 is 1250 V–1600 V and the best energy resolution for 55 Fe is 16.20%. After four consecutive days of cosmic ray measurements, the combined anticoincidence efficiency of the two is approximately 99.5%, while the anticoincidence efficiency of using either detector alone is approximately 94%. Further analysis reveals that the suppressed anticoincidence count rate is approximately two orders of magnitude lower than the original count rate in all energy regions; the overall anticoincidence efficiency exhibits an upward trend, with a minimum value of approximately 99.4% and a maximum value of approximately 99.8%.