The Production of X-Rays by Swiftly Moving Mercury Ions

A study has been made of the production of soft x-rays (4 to 9A) by mercury ions having energies up to 2.38 million electron volts. The ions were accelerated by the method of Sloan and Lawrence. It has been shown conclusively that the x-rays are actually produced by the ions and not by electrons. Through absorption measurements in aluminum and in air the wave-length of the radiation has been determined for the following targets: aluminum, sulfur, bromine, molybdenum, silver, tin and lead. No radiation could be detected from lithium, boron, carbon, oxygen, sodium, nickel or copper. The wave-lengths were characteristic of the target in the case of aluminum, sulfur, bromine, lead and probably molybdenum. The radiations from tin and silver were not characteristic either of the target or of mercury. The variation in x-ray intensity as a function of the energy of the ions has been studied for targets of lead, bromine, molybdenum, silver and aluminum. The x-ray intensity is found to increase very rapidly with the energy of the ions. No radiation could be detected from bromine, molybdenum, or aluminum when the ions had energies less than 700 kv, nor from lead or silver when the ions had energies less than 400 kv. It is found that at least one in every 2000 mercury ions produces an x-ray quantum when silver is bombarded. The ions in this case had 2.38 million electron volts and produced 2600 volt quanta. A theory is proposed to explain the excitation of x-rays by positive ions, wherein it is assumed that the ion and the target atom temporarily form a quasi-molecule. Loss of some of the inner electrons by one of the atoms as the molecule breaks up necessitates refilling of the empty levels and consequent radiation. Support for this theory is afforded by the agreement between the calculated and the experimental values for the minimum energy necessary for excitation.