Fermium atomic properties

The transeinsteinium actinides, fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr), are not available in weighable (> ng) quantities, so these elements are unknown in the condensed bulk phase and only a few studies of their physicochemical behavior have been reported. Neutral atoms of Fm have been studied by atomic beam magnetic resonance 47). Thermochromatography on titanium and molybdenum columns has been employed to characterize some metallic state properties of Fm and Md 61). This article will not deal with the preparation of these transeinsteinium metals. 

Laboratory. The isotope produced was the 20-hour Fm. During 1953 and early 1954, while discovery of elements 99 and 100 was withheld from publication for security reasons, a group from the Nobel Institute of Physics in Stockholm bombarded with O ions, and isolated a 30-min a-emitter, which they ascribed to 100, without claiming discovery of the element. This isotope has since been identified positively, and the 30-min half-life confirmed. The chemical properties of fermium have been studied solely with tracer amounts, and in normal aqueous media only the (III) oxidation state appears to exist. The isotope and heavier isotopes can be produced by intense neutron irradiation of lower elements such as plutonium by a process of successive neutron capture interspersed with beta decays until these mass numbers and atomic numbers are reached. Twenty isotopes and isomers of fermium are known to exist. Fm, with a half-life of about 100.5 days, is the longest lived. °Fm, with a half-life of 30 min, has been shown to be a product of decay of Element 102. It was by chemical identification of Fm that production of Element 102 (nobelium) was confirmed. Fermium would probably have chemical properties resembling erbium. 

As researchers performed experiments that advanced them along the row of actinide elements on the Periodic Table, the general trends with increasing atomic number were smaller production probabilities expressed as cross sections (a consequence of the diminishing fission barrier and higher fission probabilities), an increased probability of decay by a-particle emission (a consequence of increasing a-decay Q values) and shorter half-lives. For the elements below fermium, spontaneous fission is not an important decay mode. Experimental work was dominated by radiochemical techniques in which atomic number was determined by chemical properties and atomic mass was determined by mass spectrometry and the connections of nuclei to one another by the processes of radioactive decay. The physical separation and detection methods that were used in later work were developed in the 1960s. 

Photoionization detection in a buffer gas has also been used to study the properties of superheavy (transuranium) elements with charge numbers Z > 92. Isotopes of such elements can only be produced by fission reactions in heavy-ion collisions or by transfer reactions using radioactive targets. The elements produced can be placed in an optical buffer-gas cell for the purpose of laser resonance photoionization spectroscopy. This was successfully demonstrated with atoms of such radioactive elements as americium (Z = 95) (Backe et al. 2000), einsteinium (Z = 99) (Kohler et al. 1997), and fermium (Z = 100) (Sewtz et al. 2003). 

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