Samarium

Samarium is a chemical element with the symbol Sm and atomic number 62. Like other rare earth elements, is contained in many minerals. Mischmetal containing about 1% of samarium has long been used, but it was not until recent years that relatively pure samarium has been isolated through ion exchange processes, solvent extraction techniques, and electrochemical deposition. The metal is often prepared by electrolysis of a molten mixture of samarium(III) chloride with sodium chloride or calcium chloride. Samarium can also be obtained by reducing its oxide with lanthanum.

Characteristics

Samarium is a rare earth metal, with a bright silver luster. Three crystal modifications of the metal also exist, with transformations at 734 and 922 °C, making it polymorphic. Individual samarium atoms can be isolated by encapsulating them into fullerene molecules. Samarium oxidizes in air and ignites at 150 °C. Even with long-term storage under mineral oil, samarium is gradually oxidized, with a greyish-yellow powder of the oxide-hydroxide being formed. The metallic appearance of a sample can be preserved by sealing it under an inert gas such as argon; it is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form samarium hydroxide: Samarium dissolves readily in dilute sulphuric acid to form solutions containing the pale green Sm(III) ions, which exist as a [Sm(OH2)9]3+ complexes. The most common oxidation state of samarium is +3, but +2 compounds are known too, such as SmI2. Naturally occurring samarium is composed of four stable isotopes, 144Sm, 150Sm, 152Sm and 154Sm, and three extremely long-lived radioisotopes, 147Sm (1.06 × 1011y), 148Sm (7 × 1015y) and 149Sm (>2 × 1015y), with 152Sm being the most abundant (26.75% natural abundance). 151Sm has a halflife of 90 years, and 145Sm has a halflife of 340 days. All of the remaining radioisotopes have half-lives that are less than 2 days, and the majority of these have half-lives that are less than 48 seconds. This element also has 5 meta states with the most stable being 141mSm (t½ 22.6 minutes), 143m1Sm (t½ 66 seconds) and 139mSm (t½ 10.7 seconds). The long lived isotopes, 146Sm, 147Sm, and 148Sm primarily decay by alpha decay to isotopes of neodymium. Lighter unstable isotopes of samarium primarily decay by electron capture to isotopes of promethium, while heavier ones decay by beta minus decay to isotopes of europium

Natural Samarium has an activity of 128 Bq/g.

Value

The base value of each unit of ranges between 5 and 50Ð per unit, with up to 2 units being found at any one time.

Presence on Mars: Very Rare