Einsteiniu

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Einsteinium (IPA: /ˌʌɪnˈstʌɪniəm/) is a synthetic element in the periodic table that has the symbol Es and atomic number 99. A metallic highly radioactive transuranic element (7th in the series) in the actinides, einsteinium is produced by bombarding plutonium with neutrons and was discovered in the debris of the first hydrogen bomb test. It was named after Albert Einstein and has no known uses. Tracer studies using the isotope ²⁵³Es show that einsteinium has chemical properties typical of a heavy trivalent, actinide element.

[modifică] Istoric

Einsteinium was first identified in December 1952 by Albert Ghiorso at the University of California, Berkeley and another team headed by G.R. Choppin at Los Alamos National Laboratory. Both were examining debris from the first hydrogen bomb test of November 1952 (see Operation Ivy). They discovered the isotope ²⁵³Es (half-life 20.5 days) that was made by the nuclear fusion of 15 neutrons with ²³⁸U (which then went through seven beta decays). These findings were kept secret until 1955 due to Cold War tensions, however.

In 1961, enough einsteinium was synthesized to prepare a macroscopic amount of ²⁵³Es. This sample weighed about 0.01 mg and was measured using a special balance. The material produced was used to produce mendelevium. Further einsteinium has been produced at the Oak Ridge National Laboratory's High Flux Isotope Reactor in Tennessee by bombarding ²³⁹Pu with neutrons. Around 3 mg was created over a four year program of irradiation and then chemical separation from a starting 1 kg of plutonium isotope.

[modifică] Izotopi

19 radioizotopi de einsteiniu au fost categorizaţi, cu cel mai stabil fiind ²⁵²Es cu o perioadă de înjumătăţire de 471,7 zile, ²⁵⁴Es cu o perioadă de înjumătăţire de 275,7 zile, ²⁵⁵Es cu o perioadă de înjumătăţire de 39,8 zile şi ²⁵³Es cu o perioadă de înjumătăţire de 20,47 zile. Toţi izotopii radioactivi rămaşi au perioade de înjumătăţire mai mici de 40 de ore, şi majoritatea acestora sunt mai mici de 30 de minute. Acest element are şi 3 stări meta, cea mai stabilă fiind ^254mEs (t_½ 39.3 ore). Izotopii de einsteiniu au masa atomică de la 240,069 u (²⁴⁰Es) până la 258.100 u (²⁵⁸Es).