Isotope of nobelium

The other actinides have been synthesized in the laboratory by nuclear reactions. Their stability decreases rapidly with increasing atomic number. The longest lived isotope of nobelium (102N0) has a half-life of about 3 minutes that is, in 3 minutes half of the sample decomposes. Nobelium and the preceding element, mendelevium (ioiMd), were identified in samples containing one to three atoms of No or Md. 

ISOTOPES There a total of 15 isotopes of nobelium, ranging from 0,25 milliseconds (No-250) to 58 minutes (No-59). None are found in nature all are unstable and are artificially produced In cyclotrons. 

In 1973, scientists at Oak Ridge National Laboratory and Lawrence Berkeley Laboratory, produced a relatively long-lived isotope of nobelium through the bombardment of 248C,m with 1 0 ions. A total half-title of 58-5 minutes was computed from the combined data of both laboratories, See also Chemical Elements... 

The first claim for the discovery of the element nobefium was made in Sweden in 1957. However, neither American nor Soviet researchers could du-phcate the original results, which are now known to have been interpreted incorrectly. The actual discovery of nobelium is credited to researchers in Berkeley, California, who in 1958 bombarded a curium target (95% " Cm and 4.5% Cm) plated on a nickel foil with 60 to 100 MeV ions, and detected both the 8.4 MeV a-particles created by the radioactive decay of No and the °Fm created from the a-decay of No. Known isotopes of nobelium possess 148 to 160 neutrons and 102 protons all are radioactive, with half-fives ranging between 2.5 milliseconds and 58 minutes, and decay by spontaneous fission, a-particle emission, or electron capture. No has the longest half-fife 58 minutes. 

In the example above in which isotopes of nobelium are produced by hot and cold fusion, the difference between the observed cross sections and the geometrical cross sections derive from two different effects. In the hot-fusion reaction, the compound nucleus is unlikely to survive the competition between fission and each of the four neutron-evaporation steps, leading to a small cross section. In the coldfusion reaction, the probability that the compound nucleus avoids the fission process is orders of magnitude higher than in the hot-fiision reaction, but the dynamical hindrance to complete fusion results in a lower probability for formation of that compound nucleus [227, 235-237]. It is a matter of some serendipity that the nobelium evaporation-residue cross sections for the two reaction types are approximately the same. 

The isotopes of nobelium, masses 251 through 259, have been produced (Table 13.4). The isotope No is the longest-lived, with a half-life of 58 min. However, the peak production rate via the Cm( 0, 3n) reaction is only about 1(X)... 

In 1957 workers in the United States, Britain, and Sweden announced the discovery of an isotope of element 102 with a 10-minute half-life at 8.5 MeV, as a result of bombarding 244Gm with 13G nuclei. On the basis of this experiment, the name nobelium was assigned and accepted by the Gommission on Atomic Weights of the International Union of Pure and Applied Ghemistry. 

Sixteen isotopes of fermium are known to exist. 257Fm, with a half-life of about 100.5 days, is the longest lived. 250Fm, with a half-life of 30 minutes, has been shown to be a decay product of element 254-102. Chemical identification of 250Fm confirmed the production of element 102 (nobelium). 

Three groups had roles in the discovery of nobelium. First, scientists at the Nobel Institute of Physics in Stockholm, Sweden, used a cyclotron to bombard Cu-244 with heavy carbon gC-13 (which is natural carbon-12 with one extra neutron). They reported that they produced an isotope of element 102 that had a half-life of 10 minutes. In 1958 the team at Lawrence Laboratory at Berkeley, which included Albert Ghiorso, Glenn Seaborg, John Walton, and Torbjorn Sikkeland, tried to duplicate this experiment and verify the results of the Nobel Institute but with no success. Instead, they used the Berkeley cyclotron to bombard cerium-... 

The element was discovered independently by several groups nearly simultaneously. In 1958, Ghiorso, Sikkeland, Walton, and Seaborg at Berkeley, California, synthesized an isotope of this new element by bombardment of a mixture of curium isotopes containing 95% Cm-244 and 4.5% Cm-246 with carbon-12 ions. This new element was named nobelium in honor of Alfred Nobel, discoverer of dynamite. 

T. Seaborg at the Lawrence Radiations Laboratory, University of California, was later judged to be the first verified production. The researchers created nobelium by bombarding curium with carbon ions. Only minute quantities of nobelium have been produced, and it is of scientific interest only. The longest lasting isotope has a half-life of three minutes. 

In 1961, the Ghiorso group at Berkeley bombarded 3 micrograms of californium 251 with "B ions and obtained element 103 with an apparent atomic mass of 257 and ti/, of 8 seconds (later corrected to mass 258, ti/ 3.9 seconds). In 1965, the Joint Institute for Nuclear Reactions 0INR) in Dubna reported an isotope of mass 256 with ti/, of 35 seconds. In 1968, Ghiorso s group demonstrated that element 103 is in the +3 oxidation state as predicted by Seaborg, unlike its predecessor nobelium (which favors +2) but consistent with most of the other actinides. The new element was eventually named lawrencium (Lr) after Ernest O. Lawrence (1901-58), the inventor of the cyclotron. The most stable isotope is now known to be Lr (ti/ 3.6 hrs). 

Elements with atomic numbers higher than that of uranium, 92, called transuranium elements, have been obtained artificially from 1940, and all are radioactive many isotopes of each are known. They are formed by bombarding ordinary uranium, or themselves, with neutrons, or high-energy helium ions He2+, and are called neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Mv), nobelium (No), and lawrencium, with atomic numbers from 93 to 103, respectively. Details must be sought elsewhere. ... 

In O Fig. 19.11 the partial fission half-lives of the doubly even isotopes of uranium and beyond are plotted on a logarithmic time scale versus the fissility parameter. In accordance with the expectation from the liquid drop model the dashed line labeled Bld, describing the fission half-life calculated with only the liquid drop barrier Bid, crosses the 2. line at nobeKum. The time Te. is needed for the formation of the electron shell of the atom, the lower time limit considered beyond which a chemical element cannot be formed (Barber et al. 1992). The experimental half-lives follow this general trend. They decrease from uranium to nobelium over more than 20 orders of magnitude, from the age of the solar system down to fractions of seconds. The structure of the isotopic chains of elements from curium to nobelium is caused by a subshell closure at M = 152. 

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