Einsteinium (Es)

Isotopes of Einsteinium 

Isotope Atomic Mass Half-life Mode of Decay Nuclear Spin Nuclear Magnetic Moment
Es-249 249.07640 1.70 hours  EC to Cf-249;
α to Bk-245
 7/2 No data available 
Es-250 250.0787  8.60 hours   EC to Cf-250;
α to Bk-246
 6 No data available 
Es-251 251.07998  1.38 days  EC to Cf-251;
α to Bk-247
 3/2 No data available 
Es-252 252.082944  1.29 years   EC to Cf-252;
α to Bk-248;
ß- to Fm-252
 5 No data available 
Es-253 253.08482  20.47 days   α to Bk-249; SF  7/2 4.10
Es-254 254.08802  276 days   EC to Cf-254;
α to Bk-250;
ß- to Fm-254;
 7 No data available 
Es-255 255.09027  40 days   α to Bk-251;
ß- to Fm-255;
 7/2 No data available 


Einsteinium is a radioactive rare earth metal, discovered in 1952 by workers at Argonne and Los Alamos National Laboratories, along with the University of California - Berkeley, USA. It was identified by Albert Ghiorso and others in radioactive debris from the first large thermonuclear bomb explosion, which took place in the Pacific in November 1952. In 1961, a sufficient amount of einsteinium was produced to permit separation of a macroscopic amount of Einsteinium-253. It is named for Albert Einstein.

Einsteinium is a soft, silvery white, paramagnetic metal, believed to have a face-centered cubic structure. Einsteinium-253's conversion to berkelium and then californium at a rate of about 3% per day — along with its scarcity — makes it difficult to study einsteinium's properties; however, it shares many similarities with holmium in its physical and chemical properties. 

There is almost no use for any isotope of einsteinium outside of basic scientific research aiming at production of higher transuranic elements and transactinides; however, Einsteinium-254 was used as the calibration marker in the chemical analysis spectrometer of the Surveyor 5 lunar probe. All isotopes of einsteinium are extremely radioactive and are considered highly dangerous to health upon ingestion. 

Properties of Einsteinium

Name Einsteinium
Symbol Es
Atomic number 99
Atomic weight [252]
Standard state Solid at 298 °K
CAS Registry ID 7429-92-7
Group in periodic table N/A 
Group name Actinoid
Period in periodic table 7 (Actinoid)
Block in periodic table f-block
Color Unknown, but probably metallic and silvery white or grey in appearance
Classification Metallic
Melting point 1133 °K [or 860 °C or 1580 °F]
Boiling point No data available
Density of solid 13.50 g/cm3
Electron configuration [Rn]5f117s2


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