A Low Background Organic Type G.M. Tube

A low background organic type small G.M. tube with a short tungsten wire anode of 1 cm length and a cylindrical steel cathode is constructed. Reduction in the background caused by cosmic rays and contamination is achieved by using small G.M. tube with short length. At the same time, the problem of the low counting efficiency caused by the tube short length is overcome. The drop in the field values near the ends of the short cylindrical G.M. tube below the values required to produce Geiger action; which in turn causes the decrease in the counter efficiency, is corrected using two metallic balls connected to the both ends of the tungsten wire anode. The optimum size of these metallic balls corresponding to the minimum capacitance of the counter is determined using simulation technique. Plateau curves of tubes with different metallic balls' size are reported. Then, plateau curve of the tube with optimum ball size is compared with that of ordinary cylindrical G.M. tube having the same dimensions to evaluate the effect of using wire anode with two metallic balls at the ends in improving counter performance and efficiency.