Naturally-occuring actinides

Planet pluto) Plutonium was the second transuranium element of the actinide series to be discovered. The isotope 238pu was produced in 1940 by Seaborg, McMillan, Kennedy, and Wahl by deuteron bombardment of uranium in the 60-inch cyclotron at Berkeley, California. Plutonium also exists in trace quantities in naturally occurring uranium ores. It is formed in much the same manner as neptunium, by irradiation of natural uranium with the neutrons which are present. 

Thorium [7440-29-1], a naturally occurring radioactive element, atomic number 90, atomic mass 232.0381, is the second element of the actinide ( f) series (see Actinides AND transactinides Radioisotopes). Discovered in 1828 in a Norwegian mineral, thorium was first isolated in its oxide form. For the light actinide elements in the first half of the. series, there is a small energy difference between and 5/ 6d7 electronic configurations. Atomic spectra... 

Prior to 1940 only the naturally occurring actinides (thorium, protactinium and uranium) were known the remainder have been produced artificially since then. The transactinides are still being synthesized and so far the nine elements with atomic numbers 104-112 have been reliably established. Indeed, the 20 manmade transuranium elements together with technetium and promethium now constitute one-fifth of all the known chemical elements. 

Americium (pronounced,, am-8- ris(h)-e-8m) is a man-made, radioactive, actinide element with an atomic number of 95. It was discovered in 1945. Actinides are the 15 elements, all of whose isotopes are radioactive starting with actinium (atomic number 89), and extending to lawrencium (atomic number 103). When not combined with other elements, americium is a silvery metal. Americium has no naturally occurring or stable isotopes. There are two important isotopes of... 

Most of the naturally occurring chelating agents are substituted hydroxamates which are produced by a variety of protista so that iron(III) subsequently becomes available for biochemical processes. Neilands (73) has suggested that the hydroxamates facilitate the transport of iron across cell membranes. The distribution of hydroxamates in the biosphere appears limited. However, if there was a wider distribution of hydroxamates in the environment then the management of actinide wastes could become a problem of horrifying dimensions if these chelators facilitated the transport of actinides across cell membranes. 

Choppin, G. R. Allard, B. Complexes of actinides with naturally occurring organic compounds, Handbook on the Physies and Chemistry of the Aetinides Eds. Freeman, A. J. Keller, C. North-Holland Amsterdam, 1985, pp. 407-429. 

Symbol Th atomic number 90 atomic weight 232.04 an actinide series radioactive element electron configuration XRn]6d27s2 valence state +4 atomic radius 1.80 A ionic radius, Th4+ 1.05 A for coordination number 8 standard electrode potential, E° for Th4+ -1- 4e Th is -1.899V all isotopes are radioactive the only naturally-occurring isotope, Th-232, ti/2 1.4xl0i° year twenty-six isotopes are known in the mass range 212-237. 

Symbol U atomic number 92 atomic weight 238.029 an actinide series radioactive element heaviest naturally-occurring element electron configuration J Rn]5/36(ii7s2 valence states +2, -i-3, +4, -i-5, -1-6 ionic radii 1J3+ l.OSA, IJ4+ O.89A, 0.76A, for coordination number 6 and U 0.45 A and 0.81 A... 

Actinides, the chemical elements with atomic numbers ranging from 89 to 103, form the heaviest complete series in the Periodic Table. They are radioelements, either naturally occurring or synthesized by nuclear reactions. Their predominant practical application depends on the nuclear properties of their isotopes decay, spontaneous or induced fission. Their chemical and physical properties reflect a very complex electronic structure, and their study and understanding are a challenge to experimentalists and theoreticians. 

Hart, K. P., Lumpkin, G. R., Giere, R., Williams, C. T., McGlinn, P. J. Payne, T. E. 1996. Naturally occurring zirconolites - analogues for the long-term encapsulation of actinides in Synroc. Radiochimica Acta, 74, 309-312. 

The purpose of this paper is to compare the biogeochemical behavior of the actinides which are important constituents of nuclear fuel cycles. To the extent possible, the environmental behavior of the essentially man-made elements Pu, Am, Cm and Np will be compared to Th and U, which are ubiquitous in the environment. By comparing the man-made actinides to naturally occurring actinides, a generic perspective of the potential hazard of the synthetic actinides to people is obtainable. 

Data bases for the naturally-occurring actinides, Ra and 2 U, are more fragmentary. Thus, one has to make some assumptions in order to attempt a meaningful comparison between the... 

From the calculated bone/soil ratios in man for the naturally-occurring actinides as well as the laboratory and field studies on small mammals, the availability of Pu, Am, and Cm relative to U and Th can be deduced. First, the field studies indicate a similar degree of uptake by mammals for Pu and Th (Fig. 4, Table VI) which are both characterized by the tetravalent state in the terrestrial environment (20). Second, the trivalent actinides. Am and Cm, tend to exhibit similar (Fig. 3) or slightly greater (Fig. 4) uptake by mammals than Pu. Last, U exhibits consistently greater uptake in mammals than Th or Pu (Fig. 4, Table VI). On the basis of available data, the following rank order of bone ash/soil ratios for... 

Olofsson, U. Allard, B. "Complexes of Actinides with Naturally Occurring Organic Substances - Literature Survey, KBS Technical Report 8309, Stockholm, Sweden, 1983. 

Uranyl carbonato complexes are important and much studied since they occur in Nature and are of environmental concern this is also the case for other actinide carbonate complexes.40 The C03 ion is exceptionally strongly bound to UO + and similar actinide ions. There are several naturally occurring minerals such as U02C03 while the anion [U02(C03)3]4 has importance in the extraction of U from ores and is responsible for the migration of U02+ in ground waters. Interaction of the 4-ion with HC104 proceeds as follows ... 

G. R. Choppin, B. Allard, Complexes of Actinides with Naturally Occurring Organic Compounds, in Handbook on the Physics and Chemistry of the Actinides, Vol. 3 (Eds. A. J. Freeman, C. Keller), Elsevier, Amsterdam, 1985... 

The aim of this chapter is to review the observations of uranium series nuclide studies on mid-ocean ridge basalts (MORBs) and discuss their implications for melt transport processes. We note that a recent review by Lundstrom (2003) has a similar remit and makes a useful companion contribution. We initially recap the fundamental behavior of the naturally occurring actinide decay chains, and outline the analytical challenges of... 

A third naturally occurring actinide decay chain is headed by Th and decays to The intermediate nuclides in this chain have not been used to elucidate melting processes beneath ocean ridges, and here we only concern ourselves with the behavior of the Th parent, h is the overwhelmingly dominant Th nuclide, and is important as a reference nuclide for the shortlived °Th nuclide in the chain. Although the decay of and Th support... 

To understand the behavior of U-series nuclides, we start by discussing closed systems. These models form the basis for more complicated open-system models discussed later. Here we discuss the behavior of generic radioactive decay chains that apply to all the naturally occurring actinide chains. 

The major decay paths for the naturally occurring isotopes of uranium and thorium are shown in Table 1. Other actinides of environmental importance include Np, Pu, Pu, and " Am. These have decay series similar to and overlapping those of uranium and thorium. Neptunium-237 (fy2 = 2.14 X 10 yr, a) decays to ° Bi through a chain of intermediates, emitting seven a- and four j3 "-particles. Plutonium-238 (h/2 = 86 yr, a) decays into an intermediate daughter on the decay series. 

Radioactive materials have been present in the environment since the accretion of the Earth. The decay of radionuclides provides an important source of heat that drives many large-scale planetary processes. The most abundant naturally occurring radionuclides are Th, and and The bulk of the natural global inventory of actinide radioactivity in the upper 100 m of the... 

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