Indium

Indium is a chemical element with symbol In and atomic number 49. It is a post-transition metallic element that is rare in Earth's crust. The metal is very soft, malleable and easily fusible, with a melting point higher than sodium, but lower than lithium or tin. Chemically, indium is similar to gallium and thallium, and it is largely intermediate between the two in terms of its properties. It has no obvious role in biological processes and common compounds are not toxic. It is most notably used in low melting point metal alloys such as solders, soft metal high vacuum seals, and in the production of transparent conductive coatings of indium tin oxide (ITO) on glass.

Properties

Indium is a very soft, silvery-white, highly ductile, relatively rare post-transition metal with a bright luster. It is so soft (Mohs hardness 1.2) that the metal can be cut with a knife, as can sodium. It also leaves a visible line on paper. Like tin, when it is bent indium emits a high-pitched "cry". Like gallium, indium is able to wet glass. Like both, indium has a low melting point, 156.60 °C (313.88 °F); higher than its lighter homologue, gallium, but lower than its heavier homologue, thallium, and lower than tin. Only mercury, gallium, and most of the alkali metals have lower melting points. Its boiling point is 2072 °C (3762 °F), higher than that of thallium, but lower than that of gallium, showing opposition to the melting points' trend. Indium thus has a very large liquid range of around 2000 °C. The density of indium, 7.31 g·cm⁻³, is also higher than that of gallium, but lower than that of thallium. Below its critical temperature of 3.41 K, indium becomes a superconductor. At standard temperature and pressure, indium crystallizes in the tetragonal crystal system in the space group I4/mmm (lattice parameters: a = 325 pm, c = 495 pm).

Isotopes of indium

Indium (In) consists of two primordial nuclides, with the most common (~ 95.7%) nuclide (¹¹⁵In) being measurably though weakly radioactive. Its spin-forbidden decay has a half life of 441 trillion years.

The stable isotope ¹¹³In is only 4.3% of naturally occurring indium. Among elements with a known stable isotope, only tellurium and rhenium similarly occur with a stable isotope in lower abundance than the long-lived radioactive isotope. Other than ¹¹⁵In, the longest-lived radioisotope is ¹¹¹In, with a half-life of 2.8047 days. All other radioisotopes have half-lives less than a day. This element also has 47 isomers, the longest-lived being ^114m1In, with a half-life of 49.51 days. All other meta-states have half-lives less than a day, most less than an hour, and many measured in milliseconds or less.

Indium-111 is used medically in nuclear imaging, as a radiotracer nuclide tag for gamma camera localization of protein radiopharmaceuticals, such as In-111-labeled octreotide, which binds to receptors on certain endocrine tumors (Octreoscan). Indium-111 is also used in indium white blood cell scans, which use nuclear medical techniques to search for hidden infections.

Indium-111

Indium-111 is an isotope of indium with a radioactive half-life of 2.80 days, making it useful as a radioactive tracer. It is made for this use by the Nordion(Canada) Inc. unit of Nordion, Inc. as indium-111 chloride solution, and shipped to several firms which sterilize the pure solution, combine it with carrier compounds if needed, and repackage it for medical and industrial uses.

Among the medical applications of indium-111 are specialized diagnostic uses: