SummaryThe efficiency of two argon-bromine counters is determined for Mo-K~, Cu-K= and Cr-K~ quanta as a function of the overvoltage and as a function of the distance from the axis where the quanta are absorbed. The efficiency drops sharply at greater distances from the wire. This effect is partially ametiorated at higher overvoltages. The .more energetic X-ray quanta show a higher relative efficiency in the outer regions. The explanation is to be found in the electronegativity of the halogens. § 1. Introduction. The efficiency of halogen-quenched geiger-counters for X-rays has been measured as a function of the distance between the axis of the counter and the place where the X-ray quantum is absorbed, and as a function of the overvoltage.Halogens are strongly electronegative 1).The electrons are attached so firmly, that usually F/p (where F is the fieldstrength, p the total pressure) in a halogen-quenched geiger-counter around the wire is not strong enough to detach the electron from a negative halogen ion. For this'reason no pulse will result when all primary electrons formed inside the counter by the particle or quantum to be counted are caught by halogen molecules. § 2. Method o! measurement. A stabilized diffraction tube is used as X-ray source. The emission is kept constant at 5 or 8 mA. The anode potential is taken 1 or 2 kV higher than the K-excitation level of the anode material. With the aid of a crystal monochromator the K-radiation is separated. After having passed through a lead diaphragm with a hole 0.6 mm in diameter at a distance of 40 cm from the crystal, the X-ray beam is directed through a mica window
SummaryHalogen-quenched counters may be divided into two groups I and II, comprising counters in which the ionization potential of the halogen molecules lies respectively above and below the metastable level of the rare gas atoms. In counters of group II the ionization of halogen molecules by metastably excited rare gas atoms and by reso'nance photons of the rare gas is supposed to play an important part in the nmltiplication. The resonance photons are absorbed and re-emitted many times before an excited rare gas atom ionizes a halogen molecule. Experiments with two counters in one glass envelope, one with a cylinder as cathode and one with a helically wound wire as cathode, show that the photo-effect at the cathode does not play a part in the multiplication process. When one of two identical counting systems in the same bent glass envelope discharges, the other is nearly ahvays ignited by resonance photons of the first discharge, with a delay of the order of some microseconds. The propagation of the discharge parallel to the wire in most cases appears to be faster than the lateral spread of the discharge, The region below the starting potential has been explored with an a-particle source, An ionization chamber region and a proportional region have been found. § t. Introduction. Halogen-quenched counters may be divided into two groups, each group having a different gas discharge mechanism.Group I contains counters in which the ionization energy of the halogen molecules is greater than the energy of the lowest metastable state of the rare gas atoms. An example of this type of counter is one filled with argon and chlorine or one filled with krypton and bromine.
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