Elements stability

As seen from Table 2 and Fig. 1, many main-group elements act as stabilizers, e.g., Li, Mg, Al, Zn, Ga, Ge, with a constantly decreasing content, when the group number is increased . A rather similar behavior applies for the electropositive transition metals. The similarity is demonstrated by exchange of comparable main-group and transition-element stabilizers (Table 2) . 

Das Promethium konnte als ungeradzahliges Element stabile Isotope mit der Masse 145 und 147 besitzen, die jedoch auf Grund der Mattauch-schen Isobarenregel auBer Frage stehen, so daB alle Promethium-Isotope instabil sind. Es besteht jedoch die Moglichkeit, daB noch unent-deckte Promethium-Isotope existieren, die eine langere Halbwertszeit als Pm 147 aufweisen. Hierfiir kommen hauptsachlich das Pm 145 und... 

The M-ferrihydrite coprecipitate contains M-O/OH-Fe and M-O/OH-M as well as Fe-O/OH-Fe linkages. The transition elements stabilize ferrihydrite in the order, Mn < Ni < Co < Cu < Zn (Cornell, 1988 Giovanoli Cornell, 1992). This order does not correspond with that of the electronegativities or the crystal field stabilization energies (CFSE) of these elements, nor does it match the order of binding constants for the M-surface complexes. If Zn is omitted from the series, however, there is a reasonable cor-... 

Enium Ions of Other Group 16 Elements. Furukawaetal.316,320 have obtained enium ions of the heavier chalcogen elements stabilized by intramolecular complexation with dimethylamino groups (322). Resonances of the benzylic and methyl protons in the 1H NMR spectrum of cation 322a are shifted downfield... 

The negative charge on an electronegative element stabilizes the conjugate base... 

Redox Properties of Oxo Bridged Di- and Tri-nuclear Complexes of Heavy Transition Elements Stability of Mixed Valence State. 

Figure 31.39. Transferrin-receptor mRNA. This mRNA has a set of ironresponse elements (IREs) in its 3 untranslated region. The binding of the IRE-binding protein to these elements stabilizes the mRNA but does not interfere with translation.

The cations Sr and Ba concentrate in the vertebrate skeleton, and the amounts of these elements vary as a function of mineral stmcture. In vivo, strontium has been found to accumulate in bone by exchange onto crystal surfaces, and is rapidly washed out after exogenous strontium is withdrawn (Dahl et al. 2001). Incorporation of strontium into the crystal lattice as a substitute of calcium occurs at a low level in vivo, in contrast to the extensive lattice substitution of strontium for calcium in fossil bone. Strontium is not easily washed out of subfossil bone (Tuross et al. 1989), and the uptake of strontium into biological apatite was once proposed as a potentially useful chronometer analogous to fluorine uptake (Turekian and Kulp 1956). The combined uptake of strontium and fluorine into vertebrate calcified tissue may in no small part account for the existence of a fossil record. Both of these elements stabilize biological apatite, and add substantially to the crystal stability of apatite under acidic conditions (Curzon 1988). 

If a graph is made (Fig. 3.1) of the relation of the number of neutrons to the number of protons in the known stable nuclei, we find that in the light elements stability is achieved when the number of neutrons and protons are approximately equal (N = Z). However, with increasing atomic number of the element (i.e. along the Z-line), the ratio of neutrons to protons, the NIZ ratio, for nuclear stability increases from unity to iqiproximately l.S at bismuth. Thus pairing of the nucleons is not a sufficient criterion for stability a certain ratio NIZ must also exist. However, even this does not suffice for stability, because at high Z-values, a new mode of radioactive decay, a-emission, appears. Above bismuth the nuclides are all unstable to radioactive decay by a-particle emission, while some are unstable also to / -decay. 

Metallurgical aspects of alloyed steel. The alloying of the different modifications of iron with other metals leads to a shear infinite number of materials all with different corrosion properties. The alloying element stabilizes one or the other modification of steel. In a rough scheme one can distinguish the following main routes ... 

A carrier-free tracer in a solution is sometimes adsorbed on the surface of the vessel or on colloid particles of dust in the solution, or may react specifically with a minute impurity species in the solution. Moreover, the behavior of a carrier-free tracer can be different from that of the same species in ordinary macro chemistry (Guillaumont et al. 1989 Choppin et al. 2002). Therefore, it is desirable in general to add a carrier to the tracer in an amount not disturbing the experiment. The carrier added must be in the same chemical form as, and thoroughly mixed with the tracer. In case of elements stabilized in two or more oxidation states, such as Fe, As, Se, Sb, and I, it is recommended to perform the so-called oxidation-reduction sweep, that is, oxidation of the tracer with the carrier to the highest possible oxidation state followed by reduction down to the lowest possible state preferably in repetition. 

Radiochemical purity. The radiochemical purity is the fraction of the stated radioactive nuclide present in the stated chemical form. For tracers of elements stabilized in two or more oxidation states, it is necessary to check their oxidation state by their chemical behavior, ion exchange for example, preferably just before the experiment. In organic compounds labeled with a radioactive nuclide, it is desirable that the number and position of labeling of the radioactive nuclide are unique. However, when the number and position of the nuclide in a compound do not essentially affect its chemical behavior as is often the case in tritium-labeled ones, use of a mixture of a compound labeled with different number of the stated nuclide or labeled at different positions is acceptable. The purity of some labeled compounds decreases gradually due to oxidation, self- or radiolytic decomposition during long storage. Such a labeled compound should be assayed and purified, if necessary, before use. 

Rare-earth elements stabilize different layered structures involving thallium, lead, and mercury, owing to their large size and also to their trivalent character allowing more oxygen to be incorporated. 

Dilution of the copper oxide by the barium oxide and melting the fluxes with a higher Ba Cu ratio (0.3, 0.4, 0.6, 0.8) results (fig. 17b) in a pronounced shift of the copper absorption edge to the higher energy direction (1050"C). This probably means that the alkaline-earth element stabilizes the higher copper valence. 

It is noteworthy that, in these two structures, the coordination of the rare earth is always 6. This value, unusual for the first lanthanides in their chal-cogenides, explains the absence of the MRX2 compounds for the light lanthanides from La to Nd in the case of M = Tl, and for La and Ce in the case of M = Li. But the very weak electronegativity of the other lA elements stabilizes this low coordination (as does the very strong electronegative character of the anions of the fluorine compounds). 

Fuel pin and fuel element stability tests have been conducted both In alr/water and freon loops, in the latter case under nucleate boiling conditions. These tests have all shown the fuel pins to be inherently very stable in the reference design, but have revealed some cluster vibration at about 7 c/s which is initiated by flow around the neutron scatter plug. An early type of twisted strip scatter plug was rejected because it set up torsional oscillations in the fuel the current torpedo shaped plug can be stabilized by a device already developed, but this will not be applied to reactor fuel unless the instability proves to be damaging to fuel or pressure tubes. 

Table I -1. Limiting NIZ values for element stability (source Geary, 1986).

Some more recent calculations [28], based on careful consideration of the effect of mass asymmetry on the fission barrier and a reduced spin-orbit coupling strength, have indicated that the Z = 114 shell effect is not very large. These calculations do confirm the existence of a shell atN = 184, but also suggest less stability for species with N < 184 that is, the island of stability has a cliff with a sharp drop-off for N < 184. If these considerations are correct, it would become considerably more difficult to synthesize and detect the superheavy elements (defined as those elements stabilized by spherical closed-nucleon shells). A premium would be placed on produdng a nucleus with N = 184 or, very close to this, N = 183, in order that it might have a half-life sufficiently long to make it detectable. 

Several out-of-pile tests were executed to evaluate susceptibility to FCCI of ODS steels [84—86]. In the high-temperature oxidation test at 700°C, 9Cr-ODS steel was shown to have substantial oxidation resistance equivalent to type 316 stainless steel in spite of its low Cr concentration [84]. This can be presumably ascribed to two major mechanisms fine grain size of 9Cr-ODS steels enhancing Cr supply to surface oxide layer throughout the accelerated grain boundary diffusion, and effect of Y as a rare earth element stabilizing surface oxide layer. Out-of-pile corrosion tests using... 

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