Sensitive Geiger-Muller Counters for Detection of Gamma Rays

The various factors determining the efficiency of a gamma ray counter and its applicability as a detector of gamma radiation are evaluated. As theory to the construction of an ultra-sensitive counter, such a counter has been built and tested. The results verify the theory and prove that gamma ray counters may be constructed with much greater sensitivity than the simple Geiger-Muller tube counter. In estimating the ultimate range of counters for detection of radium, criteria for detection are discussed. For rapid detection, i.e., for measurements covering about one second, it is shown that the above test counter can reliably detect 50 milligrams of radium at 250 feet in air and at almost 6 feet under water.