Geigcr-Mueller Counter for X-Rays

A test counter with its circuit especially aimed for the detection of blow holes or cracks in metallic specimens has been constructed. This counter method has been applied to the test of a specimen of Kelmet metal and found to be more convenient and speedy in detecting, interior defects than the. usual radiographic methods. The photoelectric quantum efficiencies of a brass counter containig one part of alcohol and five parts of argon at 60mm, Hg for several wave lengths have been determined in two cases: 1) the x-ray beam passing through the gas filling only, 2) the beam passing through the gas and striking the cathode metal. The quantum efficiencies. Qp. are 1.56-1.64% for Fe-Kα, 0.63-0.85% for Cu-Kα and 0.21-0.25% for Mo-Kα in the former case and 5.9-6.0% for Fe-Kα, 2.8-3.0% for Cu-Kα and 0.45-0.49% for Mo-Kα in the latter case. The resolving time necessary for the measurement of x-rays is given in the cases of the scale-of-2 or scale-of-16 circuit, and also that for the detection of feeble x-rays. The calculation shows the number of impulses arriving randomly within intervals less than the resolving time not counted due to doubles, triples, etc.