Americium electrons

AH of the 15 plutonium isotopes Hsted in Table 3 are synthetic and radioactive (see Radioisotopes). The lighter isotopes decay mainly by K-electron capture, thereby forming neptunium isotopes. With the exception of mass numbers 237 [15411-93-5] 241 [14119-32-5] and 243, the nine intermediate isotopes, ie, 236—244, are transformed into uranium isotopes by a-decay. The heaviest plutonium isotopes tend to undergo P-decay, thereby forming americium. Detailed reviews of the nuclear properties have been pubUshed (18). 

Dacheux N, Aupiais J (1997) Determination of uranium, thorium, plutonium, americium, and curium ultratraces by photon electron rejecting alpha liquid scintillation. Anal Chem 69 2275-2282 Duan YX, Chamberlin EP, Olivares JA (1997) Development of a new high-efficiency thermal ionization source for mass spectrometry. Inti JMass Spectrom IonProcessesl61 27-39 Edwards RL, Chen JH, Wasserburg GJ (1987) systematics and the precise... 

Dacheux N, Aupiais J. 1997. Determination of uranium, thorium, plutonium, americium, and curium ultratraces by photon electron rejection a liquid scintillation. Anal Chem 69 2275-2282. 

Dacheux N, Aupiais J. 1998. Determination of low concentrations of americium and curium by photon/electron rejecting alpha liquid scintillation. Anal Chim Acta 363 279-294. 

Taya A, Hotz G, Seidel A. 1986. Biochemical and electron microscopic studies on binding and transport of americium and plutonium hydroxide polymers in bovine alveolar macrophages and rat lungs. J Aerosol Sci 17(3) 370-375. 

Periodic Table Americium, http //www.chemicalelements.com/elements/am.html (accessed September 6> 2005). Periodic Table Plutonium, http //www.chemicalelements.com/elements/pu.html (accessed September 6> 2005). Periodic Table Protactinium, http //www.chemicalelements.com/elements/pa.html (accessed September 6> 2005). Periodic Table Thorium (accessed September 6> 2005).Periodic Table Uranium (accessed September 6, 2005).Periodic Table Electron Configuration, http //www.chemicalelements.com/ show/electronconfig.html (accessed November... 

Whereas there are experimental evidences for the band behaviour of 5 f electrons up to plutonium (Z = 94) (see Table 3), the same criteria show that suddenly americium (Z = 95) behaves like a normal lanthanide having well localized 5f electrons ( and Chap. C) ... 

Table 3. Density of states at the Fenni level for actinide metals from band calculations (model) from the electronic contribution y to the specific heat from magnetic susceptibility measurements. The increasing values indicate a decreasing 5 f bandwidth pinned at Ep for americium metal (not shown) there is a sudden decrease in N(np)...

It can be stated that up to plutonium, 5 f electrons are in the conduction band and have no magnetic moment from americium on, 5f electrons are localized and carry a magnetic moment. 

The higher actinide metals americium, curium, berkelium and californium have - at normal pressure - again the common structure dhcp and are in this respect similar to some of the lanthanide metals. In fact, the theoretical calculations and certain experimental observations show that in these actinide metals, 5 f electrons are localized, as are the 4f electrons in the lanthanide metals. More detailed considerations on the possible correlations between electronic and crystal structure are found in. ... 

Fig. 8. Enthalpy vs. pressure curves for localized and itinerant 5 f electrons in americium metal (from )...

As a remark, it should be noted that a single electron ground state from a filled band (which would be the case of americium within a band description because the 5 f band is spin-orbit splitted into a filled 5/2 sub-band and an empty 7/2 sub-band) is equivalent to a localized state and thus a spin-polarized band description leads to the same conclusion as a simple Mott description. 

We have calculated the Radon core diamagnetism for actinide ions up to americium the results are reported in Table 6. These values are smaller than usually assumed in the literature. Diamagnetic contribution for localized 5f electrons are also given - From Table 6, we see that the core diamagnetism is large and has to be taken into account when a detailed analysis of the susceptibility is made. In the case of Th metal, for example, it amounts to 40% of the experimental susceptibility. 

It is apparent that Am3+ forms a stronger complex than Eu3+ with the same ligand. The main factors that may affect the stability of europium and americium complexes are ionic radii and the availability of the /-electrons. In the present case the /-electron participation of the 5/ orbital of Ams+ is possibly more important than the radius factor. If the radius factor was the more important one, Eu3+ with its smaller ionic size would be expected to form a stronger complex than Am3+. However, it is well-known that the 5/ orbitals are more polarizable than the wellshielded 4/ ones. 

Another isotope. Lr. hall-life about 45 seconds, was reported by the Soviet Union in 1965. It was produced by impact of oxygen atoms (l

alpha-particle emission and electron capture to form Fm See also Chemical Elements. 

A more satisfactory procedure involves a radioactive probe held a little above the water surface. The radioactive radiations ionise the air between the probe and the surface and ensure that they are at the same potential. The probe is connected to an electrometer having a very high input impedance which reads the surface potential. This procedure was pioneered by Guyot (70J and Frumkin [71J in the 1920s but has become much more convenient to use with the introduction of artificial radioactive isotopes and modern electronics. Americium 241 is particularly useful as the low energies of the a and y radiations produced only ionise the air in the immediate vicinity of the probe. 

Especially interesting in a discussion of radionuclide speciation is the behaviour of the transuranium elements neptunium, plutonium, americium and curium. These form part of the actinide series of elements which resemble the lanthanides in that electrons are progressively added to the 5f instead of the 4f orbital electron shell. The effective shielding of these 5f electrons is less than for the 4f electrons of the lanthanides and the differences in energy between adjacent shells is also smaller, with the result that the actinide elements tend to display more complex chemical properties than the lanthanides, especially in relation to their oxidation-reduction behaviour (Bagnall, 1972). The effect is especially noticeable in the case of uranium, neptunium and plutonium, the last of which has the unique feature that four oxidation states Pum, Pu, Puv and Pu are... 

Radioactive substances also have life-saving uses. A radioactive form of cobalt is extensively used in radiation therapy for cancer patients. The treatment was first developed by Harold Johns (1915—) in Canada, where he pioneered cobalt therapy units at the University of Saskatchewan. One of the artificially made elements, Americium (atomic number 95, i.e., with 95 protons in its atomic nucleus), is another life-saving radioactive element. As it decays, it emits alpha particles, which strip electrons from surrounding gas molecules ionized air conducts electricity much better than air containing smoke particles, and the reduction in conductivity produced by smoke is what triggers the alarm in smoke detectors. 



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