Einsteinium longest lived isotope

Like einsteinium, this unstable element was discovered in the fallout from the first hydrogen bomb. To date, only fragments in microgram amounts can be isolated. 258Fm ends the series of transuranium elements that can be produced in a reactor by neutron bombardment. The longest-lived isotope decays with a half-life of 100 days... 

Radioactive, short-lived element. The longest-lived isotope (256Md) has a half-life of 55 days. To date, only a few atoms have been prepared by a nuclear reaction between einsteinium and helium nuclei in a particle accelerator. 

When these isotopes become available, chemical studies will be greatly simplified, and the complications introduced by the radioactivity of the actinide elements will be substantially minimized. The longest-lived isotopes of berkelium, californium, and einsteinium are still fairly short-lived substances, and macroscopic amounts have a tremendous associated radioactivity. Nevertheless, it should eventually be possible to prepare and study the solid halides of the actinide elements through the element einsteinium using weighable amounts of reactants. This remains for the future, however. The special experimental problems associated with highly radioactive substances are considered below. 

The original einsteinium isotope discovered in Enewetak fallout was Es with a half-life of 20 days. Eventually other einsteinium isotopes were created under controlled conditions. The longest-lived is Es, ty, = 275 days. The longest-lived isotope of fermium is Fm, ti/, = 100.5 days. Chemically speaking, einsteinium and fermium are... 

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