rutherfordium

rutherfordium (Rf), an artificially produced radioactive transuranium element in Group IVb of the periodic table, atomic number 104. Soviet scientists at the Joint Institute for Nuclear Research at Dubna, Russia, U.S.S.R., announced in 1964 the discovery of element 104, which they named kurchatovium, symbol Ku (for Igor Kurchatov, a Soviet nuclear physicist). In 1969, a group of American researchers at the Lawrence Radiation Laboratory of the University of California at Berkeley announced that they had identified isotopes of the element, different from the one identified by the Soviets; the Americans then proposed the name rutherfordium, in honour of the British physicist Ernest Rutherford.

In their experiment, the Soviets bombarded plutonium-242 with ions of neon-22, claiming to have obtained an isotope of element 104 that had a mass number of 260 and a half-life of 0.3 second. The Soviets then performed a series of chemical experiments with the isotope to demonstrate that it behaved in a manner that had been predicted for the element. When the workers at Dubna later used a more refined measuring technique, however, they found that the half-life of the isotope was 0.1 second, not 0.3 second as originally reported. This finding cast doubt on the chemical experiments with the element, because the results of those experiments could not have been obtained with atoms having a half-life of 0.1 second.

The American investigators did not follow the same procedure as the Dubna group, because the American equipment could not accelerate neon-22 ions to the necessary energies. Instead, they bombarded a target of californium-249 with ions of carbon-12 and carbon-13. Although unable to obtain the same isotope as the Soviet scientists, the Berkeley team did report positive identification of two, possibly three, isotopes of element 104. The bombardment of californium-249 with carbon-12 produced an isotope with a mass number of 257 and a half-life of 4–5 seconds; the carbon-13 bombardment produced an isotope with a mass number of 259 and a half-life of three to four seconds. The investigators at Berkeley subsequently, by bombarding curium-248 with oxygen-18, synthesized an isotope of element 104 that has a mass number of 261 and a half-life of 70 seconds.

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Although the Soviets could make only a few atoms of their mass-260 isotope, the Berkeley group obtained thousands of the atoms having mass numbers of 257 and 259. Moreover, because the latter isotopes have longer half-lives, the Berkeley team was able to measure the energies of their emissions (alpha particles) and to detect their decay products (nobelium isotopes), thereby providing more extensive evidence of their discovery. The International Union of Pure and Applied Chemistry eventually ruled that element 104 be named rutherfordium.