Superheavy elements synthesis

Unfortunately, the neutron-rich isotopes that are preferred as projectiles in superheavy element synthesis experiments are almost invariably minor components in the natural isotopic mixture of the element (" Ar is a notable exception). As a result, extraction of the desired ions from the ion source can be maximized through the use of enriched isotopic mixtures as feed stock. As an example, early uses of " Ca involved the profligate consumption of the input material in sputter or... 

When not constrained to the stable nuclei, beams of particles with neutron numbers out to the neutron-drip line can be considered as possible reactants. Though the lack of suitable accelerator facilities makes this a hypothetical exercise, there are practical concerns governing production of the radioactive species for acceleration as the secondary beam. Continuous production of large quantities of these nuclides is required for the generation of a radioactive beam that is sufficiently intense for a superheavy element synthesis experiment. This limits our discussions to radioactive species close to the line of stability, because of both primary production rate and half-life. To confine the following discussion, only radioactive ions within four mass numbers of the heaviest stable isotope of each element will be considered as projectiles unless there is a stable isotope of a nearby element at higher neutron number (e.g., " Ar, at the same neutron number as Ca). 

Meldner, H.W. Superheavy element synthesis. Phys. Rev. Lett. 28, 975—978 (1972)... 

Since the radioactive half-lives of the known transuranium elements and their resistance to spontaneous fission decrease with increase in atomic number, the outlook for the synthesis of further elements might appear increasingly bleak. However, theoretical calculations of nuclear stabilities, based on the concept of closed nucleon shells (p. 13) suggest the existence of an island of stability around Z= 114 and N= 184. Attention has therefore been directed towards the synthesis of element 114 (a congenor of Pb in Group 14 and adjacent superheavy elements, by bombardment of heavy nuclides with a wide range of heavy ions, but so far without success. 

The experimental work of the last two decades has shown that cross sections for the synthesis of the heaviest elements decrease almost continuously. However, recent data on the synthesis of element 114 and 116 in Dubna using hot fusion seem to break this trend when the region of spherical superheavy elements is reached. Therefore a confirmation is urgently needed that the region of spherical SHEs has finally been reached and that the exploration of the island has started and can be performed even on a relatively high cross section level. 

The 48Ca+248Cm reaction was generally considered to be most promising for the synthesis of superheavy elements because the compound nucleus Z=1 16, A=180 provides at a moderate overshooting of the proton shell a relatively close approach to the neutron shell. Also, the decay chain after evaporation of four neutrons was expected [12] to be suitable for detection. It should start at 292116)76 by a-decay with a few seconds half-life, followed within several minutes by two electron captures in 288114i74 and 2881 13 75 and ends at 288112i76 by spontaneous fission with a 50 min half-life. 

The main fields of application of heavy ions are synthesis of new elements (superheavy elements), production of nuclides far away from the line of ji stability (exotic nuclides), investigation of nuclear matter at high densities, production of small holes of certain diameters in thin foils and irradiation of tumours in medicine. 

The general aspects of the synthesis of superheavy elements can be summarized as follows ... 

There is general agreement that theoretical predictions of nuclear stability, which we discuss briefly in the next paragraph, define a range of superheavy elements with sufficiently long half-fives to allow their study, provided they can be S3mthesized. What cannot be predicted is whether there exist nuclear reactions for such synthesis in detectable amounts on earth. 

The expectation that superheavy elements will be detected by chemical and other identification procedures, even with these very small-cross sections, is now shifting to the heavy-ion accelerator laboratory (GSI) in Germany. There is the hope that the use of other heavy ions (including ions up to uranium) and greater beam intensities will lead to the synthesis and identification of superheavy elements. There are also several groups associated with GSI presently developing setups to detect superheavy elements using chemical separation methods similar to those described above as well as phase separations. 

Chemists will synthesize millions of new compounds tailored for a wide spectrum of practical uses. Nuclear chemists will be involved in the synthesis of additional chemical elements, hopefully in the region of the superheavy elements predicted to exist in the island of stability. ... 

Oganessian, Yuri Ts., Vladimir K. Utyonkov, and Kenton J. Moody. Voyage to Superheavy Island. Scientific American 282 (January 2000) 63-67. This is a highly accessible discussion of the synthesis of superheavy elements using both cold fusion and hot fusion techniques. 

In recent years, the number of elements has increased well beyond 100 as the result of the synthesis of artificial elements. At the time of writing, conclusive evidence has been reported for element 111. Such elements are typically very unstable, and only a few atoms are produced at any time. However, ingenious chemical techniques have been devised that permit the chemical properties of these so-called superheavy elements to be examined and allow one to check whether extrapolations of chemical properties are maintained for such highly massive atoms. On a more philosophical note, the production of these elements allows us to examine whether the periodic law is an exceptionless law, of the same kind as Newton s law of gravitation, or whether deviations to the expected recurrences in chemical properties might take place once a sufficiently high atomic number is reached. No surprises have been found so far, but the question of whether some of these superheavy elements have the expected chemical properties is far from being fully resolved. One important complication that arises in... 

In spite of worldly distractions, Glenn Seaborg has never wavered in his life-long commitment to science. He continues his research into the chemistry and nuclear systematics of the actinide elements. Recently, he has focused his attention on the possible existence of still another family of superheavy elements at the end of the Periodic Table, and the development of new methods for the synthesis of superheavy elements. The dedication of these volumes to Glenn Seaborg is not only a testimonial to his scientific achievements, it is also an appreciation of the example that he continues to set. 

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