Nobelium-260

Main isotopes of nobelium

Isotope			Decay
	abundance	half-life (t_1/2)	mode	product
²⁵³No	syn	1.6 min	80% α	²⁴⁹Fm
²⁵³No	syn	1.6 min	20% β⁺	²⁵³Md
²⁵⁴No	syn	51 s	90% α	²⁵⁰Fm
²⁵⁴No	syn	51 s	10% β⁺	²⁵⁴Md
²⁵⁵No	syn	3.1 min	61% α	²⁵¹Fm
²⁵⁵No	syn	3.1 min	39% β⁺	²⁵⁵Md
²⁵⁷No	syn	25 s	99% α	²⁵³Fm
²⁵⁷No	syn	25 s	1% β⁺	²⁵⁷Md
²⁵⁹No	syn	58 min	75% α	²⁵⁵Fm
			25% ε	²⁵⁹Md
			<10% SF

Nobelium (₁₀₂No) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized (and correctly identified) was ²⁵⁴No in 1966. There are 12 known radioisotopes, which are ²⁵⁰No to ²⁶⁰No and ²⁶²No, and 3 isomers, ^251mNo, ^253mNo, and ^254mNo. The longest-lived isotope is ²⁵⁹No with a half-life of 58 minutes. The longest-lived isomer is ^251mNo with a half-life of 1.7 seconds.

This cold fusion reaction was first studied in 1979 at the FLNR. Further work in 1988 at the GSI measured EC and SF branchings in ²⁵⁴No. In 1989, the FLNR used the reaction to measure SF decay characteristics for the two isomers of ²⁵⁴No. The measurement of the 2n excitation function was reported in 2001 by Yuri Oganessian at the FLNR.

Patin et al. at the LBNL reported in 2002 the synthesis of ^255–251No in the 1-4n exit channels and measured further decay data for these isotopes.

The reaction has recently been used at the Jyvaskylan Yliopisto Fysiikan Laitos (JYFL) using the RITU set-up to study K-isomerism in ²⁵⁴No. The scientists were able to measure two K-isomers with half-lives of 275 ms and 198 s, respectively. They were assigned to 8⁻ and 16⁺ K-isomeric levels.

The reaction was used in 2004–5 at the FLNR to study the spectroscopy of ^255–253No. The team were able to confirm an isomeric level in ²⁵³No with a half-life of 43.5 s.

This reaction was studied in 2003 at the FLNR in a study of the spectroscopy of ²⁵⁰No.

The measurement of the 2n excitation function for this reaction was reported in 2001 by Yuri Oganessian and co-workers at the FLNR. The reaction was used in 2004–5 to study the spectroscopy of ²⁵³No.

The measurement of the 1-4n excitation functions for this reaction were reported in 2001 by Yuri Oganessian and co-workers at the FLNR. The 2n channel was further studied by the GSI to provide a spectroscopic determination of K-isomerism in ²⁵²No. A K-isomer with spin and parity 8⁻ was detected with a half-life of 110 ms.

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