|Limits Of Artificial Production Of New Elements|
What are the limits of artificial production of new atomic species?
"Early in the 1960s it seemed that it was only a question of time when this limit would be achieved. The heavy transuranium elements became ever more unstable in relation to spontaneous fission, their half-lives being now measured in seconds and fractions of a second. Extrapolations of the data led one to conclude that Zcr beyond which there could be no synthesis lies within the range 108-110. But, as so often in science, a brilliant insight gave things an unexpected turn: it was the hypothesis of the so-called stability islands (SI) for nuclei in the regions of some of the magic values of Z and N that lie well beyond the frontiers of the science. Islands were assigned to Z = 110, 114, 126 and even 164 and N = 184 and 196. It was assumed that the corresponding nuclei must exhibit heightened stability to spontaneous fission. This gave grounds for optimism that some of these 'superelements'; could be synthesized or found in nature.
"But the coming of the SI hypothesis at the same time introduced a measure of uncertainty into the estimates of Zcr and the modern understanding of the periodicity. Should the hypothesis be proved, the value of Zcr will, generally speaking, be dependent on one of the two factors. It might be determined by a certain boundary of nuclear instability. But where does this magic boundary lie (beyond Z = 114, 126 or 164)? On the other hand, for example, although a nucleus with Z = 164 is allowed and it would be relatively long-lived, the corresponding atom would be unable to exist, forbidden for another reason (the interaction of electron configuration with nucleus); this reason, as mentioned above, has been held in question. Therefore, the artificial upper boundary (in Z) for atomic structures of matter remains an enigma of modern atomistics.
"Since all attempts at breakthroughs in the region of 'islands'; failed, the synthesis of transuranium elements (quit slack now) follows the well-trodden path: increasing Z by one in succession. There is no saying now how long will it yield results. But there is one consideration to take into account: even if a nucleus with a given Z is synthesized successfully, will it imply that the result is an atom of a new element? For an atom-like structure to form the synthesized nucleus must acquire a certain electron configuration. This requires a time of the order of 0.00000001 to 0.000000001 s. If the nucleus's lifetime is shorter, it makes no sense speaking about synthesis of a new atom, about any chemism of the resultant nuclide.
"Let us now turn to another sequel of the SI hypothesis. Clearly, our understanding of the laws governing a phenomenon is the more profound the larger the number of objects covered by them. As long as the periodic system terminated at uranium, the treatment of the periodicity appeared quite rigorous and consistent. But already a detailed study of the properties of the so-called actinides (their synthesis greatly increased the number of known chemical elements, and thereby the scope of the periodicity) showed that in this region of Z the periodic variation of properties becomes more complicated in nature. When synthesizing transactinides researchers had to deal with their isolated atoms, therefore even a rough estimate of the chemism of an elements appeared to be a challenging and delicate work, and the experimental results obtained cannot be viewed as final. It is quite obvious that when the issue of 'island superelements' came to the fore, the scarcity of new atoms was not to be overlooked. Accordingly, it was quite desirable to predict the electron configurations of these atoms and the most important properties of the corresponding elements. The predictions were made on a computer for Z = 104-172. It was found that for the given interval of Z one was to expect a further complication of the phenomenon of periodicity, which would in essence destroy the current conceptions of the laws governing the periodic system. Whether these predictions come true or not we cannot judge so far. A successful synthesis of at least one 'superelement' would provide exceedingly important fuel for discussions." D. N. Trifonov, Origins and Development of Modern Atomistics, PHYSICS OF THE 20TH CENTURY: HISTORY AND OUTLOOK, translated from the Russian by Alexander Repyev, 1st printing, pages 136-138, Mir Publishers, 1987.
|Two Different Extensions For The Periodic Table|
|End Of The Periodic Table|