Indium is a soft, silvery metal that is widely used in optics, microelectronics, and high-performance solar cells. It is available in a variety of stable metallic isotopes, including indium-111 and indium-113m.
Indium-111 is a nuclear imaging agent and is commonly labeled with diethylenetriaminepentaacetic acid to form a chelate for intracranial cisternography. It is also used in white blood cell scanners, which use nuclear medical techniques to search for hidden infections.
Radioactive indium-113 is produced by irradiation of a tin compound with neutrons. It decays to indium 113m with a half-life of 118 days. indium 113m has a high stability and is useful for nuclear imaging applications such as the localization of protein radiopharmaceuticals using gamma cameras.
Alternatively, indium 113m can be produced by irradiating a tin containing material with an atomic radiation source such as a cyclotron. This method has the advantage of producing radioactive indium-113m with a relatively short half-life, but it can be expensive and time-consuming to produce large quantities.
Another alternative is to dissolve a tin containing material in concentrated hydrochloric acid. This has the benefit of providing a relatively high concentration of tin to a relatively small volume, but it can be difficult to obtain in sufficient quantity to satisfy industrial requirements.
Fortunately, it has recently been discovered that indium-113m can be selectively extracted from a dissolved tin compound by contacting the diluted tin solution with silica gel. The process operates at an elution rate of over percent, which provides a very high efficiency and is simple to operate.