Selenium

. The ingredient is also used in body lotions to treat Tinea versicolor due to infection by a different species of //Malassezia// fungus. Selenium has six naturally occurring isotopes, five of which are stable: 74Se, 76Se, 77Se, 78Se, and 80Se. The last three also occur as fission products, along with 79Se which has a half-life of 295,000 years, and 82Se which has a very long half-life (~1020 yr, decaying via double beta decay to 82Kr ) and for practical purposes can be considered to be stable. 23 other unstable isotopes have been characterized. //See also Selenium-79 // for more information on recent changes in the half-life of this fission product important for the dose calculations performed in the frame of the geological disposal of long-lived radioactive waste. The substance loosely called selenium sulfide, **SeS2**, actually selenium disulfide or selenium (IV) sulfide, is the active ingredient in some dandruff shampoos. The effect of the active ingredient is to kill the scalp fungus //Malassezia //which causes shedding of dry skin fragments

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34Proton 45Nurtron atomic number 34


 * Name:** Selenium
 * Symbol:** Se
 * Atomic Number:** 34
 * Atomic Mass:** 78.96 amu
 * Melting Point:** 217.0 °C (490.15 K, 422.6 °F)
 * Boiling Point:** 684.9 °C (958.05005 K, 1264.8201 °F)
 * Number of Protons/Electrons:** 34
 * Number of Neutrons:** 45
 * Classification:** Non-metal
 * Crystal Structure:** Hexagonal
 * Density @ 293 K:** 4.79 g/cm3
 * Color:** gray

**Date of Discovery:** 1817
 * Discoverer:** Jons Berzelius
 * Name Origin:** From the Greek word //Selênê// (Moon)
 * Uses:** photoelectric cells, TV cameras
 * Obtained From:** refining of lead, copper, nickel