Actinide electrical resistivity

For solids in which IN([Xf) is very near to 1, often, although no magnetic order occurs, long-range fluctuations of coupled spins may take place, giving particular form to properties such as the (Stoner enhanced) magnetic susceptibility x, the electrical resistivity, and the specific heat of the solid. Spin fluctuations have been observed in actinides, and will be discussed in more detail in Chap. D. 

However, the intra-atomic Coulomb interaction Uf.f affects the dynamics of f spin and f charge in different ways while the spin fluctuation propagator x(q, co) is enhanced by a factor (1 - U fX°(q, co)) which may exhibit a phase transition as Uy is increased, the charge fluctuation propagator C(q, co) is depressed by a factor (1 -H UffC°(q, co)) In the case of light actinide materials no evidence of charge fluctuation has been found. Most of the theoretical effort for the concentrated case (by opposition to the dilute one-impurity limit) has been done within the Fermi hquid theory Main practical results are a T term in electrical resistivity, scaled to order T/T f where T f is the characteristic spin fluctuation temperature (which is of the order - Tp/S where S is the Stoner enhancement factor (S = 1/1 — IN((iF)) and Tp A/ks is the Fermi temperature of the narrow band). 

Many light actinide alloys which are not magnetic have a T dependence of the resistivity at low temperature as well as a large electronic specific heat coefficient y (Table 4). However, the archetype of a spin fluctuation system is UAI2. The electrical resistivity is proportional to T with a very large coefficient a = 0.15 qQcm/K up to 5... 

We now give a simple application of the present method to Plutonium which is a good test case. Pu lies between light actinides with itinerant 5/ electrons and heavy actinides with localized 5/ electrons. The competition between these two electronic regimes in Pu is responsible for a lot of unusual properties as large values of the linear term in the specific heat coefficient and of the electrical resistivity or a very complex phase diagram. 

The used resin from each column may contain a small amount of actinides that failed to elute. The amount is estimated by counting fast neutrons from 2 2Cf with the in-cell neutron probe. The 252Cf content of the resin, usually <100 pg of 252Cf, can be recovered by leaching with strong HNC. After acid leaching several batches of resin have been calcined in an electric resistance furnace and the ashes leached with HNO3 however, very little additional 2 2cf was recovered. 

Additional requirements to high level and actinide waste forms are due to transportation to repository and long-term storage. From this point of view such properties as density, porosity, thermal and temperature conductivity, tensile, flexural and compressive strength. Young s and bulk modules, and microhardness are measured [24]. For the waste forms whose production via melting is suggested some properties of their melts (viscosity, electric resistivity, surface tension) are also important. 

The electrical resistivities of most of the lighter actinide metals - due to their f electron participation in bonding -differ remarkably from those of "normal" metals. The resistivities start to increase along the actinide series after Pa, and reach a maximum at Pu, before localization of 5f electrons sets in. (Figure 2). 

Spectroscopy. The application of optical and photoelectron spectroscopy to elucidate electron energy states of pure actinide metals is still in the initial stages (46). Reflectivity measurements on Th samples (mechanically polished, electropolished, or as grown from the vapour phase) demonstrate the importance of sample and surface preparation (47), and explain reasons for discrepancies in published results (48, 49). Preliminary measurements of the optical reflectivity of Am films evaporated on different window materials (50) seem to indicate that the 5f levels are lying more than about 6 eV below the FERMI level, thus supporting the interpretation of the electrical resistivity results... 

In this section we describe how the specific heat, magnetic susceptibility and electrical resistivity of anomalous lanthanide and actinide intermetallics respond to applied pressure. Generally each subsection is organized by material type first Ce-based compounds, then those based on Yb and finally U-based systems. Only in the last subsection on semiconductors are these systematics broken. Although on occasions we digress into a brief discussion of the experimental observations, ihe bulk of critical discussion related to data presented here and in sect. 3 is reserved for sect. 4. 

Electrical resistivity has been a popular means of studying the pressure response of anomalous lanthanide and actinide compounds, both because of the relative simplicity of the measurement and because techniques are readily available for extending the measurements to pressures substantially higher than achievable with specific heat or susceptibility. Consequently, there is a rather large body of p T,P) data that can be chosen... 

We have focused on two issues (1) the degree to which the pressure response of the electrical resistivity, magnetic susceptibility and specific heat is similar in a given material or class of materials and how this pressure dependence is related to the Griineisen parameter obtained from ambient pressure measurements and (2) the extent to which this comparison holds in both anomalous lanthanide and actinide compounds. 

Fig. 15. The electrical resistivity of the light actinide metals from thorium to curium (from Fournier and Troc 1985).

In the next chapter (115), J.M. Fournier and E. Gratz have reviewed the transport properties of lanthanide/actinide compounds. These include the electrical resistivity, thermal conductivity, thermoelectric power, magnetoresistance and the Hall effect. As expected, most of this review deals with the electrical resistivity because of the preponderance of data oa this property, relative to the other four. Throughout this chapter the authors attempt to use the available information on the transport properties to help improve our understanding of the differences and similarities of... 

A number of the properties covered in this chapter are also given elsewhere in this volume. In this presentation, the properties of the actinide elements are taken as a whole and attempts are made to compare them with the properties of metallic elements occurring in other parts of the periodic table. The actinide metals are often thought to be exotic, because they tend to have properties that are difficult to explain by simple theoretical approaches that have been useful for simple metals. The properties of the actinide metals do in fact represent a severe test to the theoretical solid-state scientist, as do the other transition-metal series. But, like other metals, they are lustrous and may be malleable they have, among their several crystalline structures, some simple atomic arrangements and they have relatively low electrical resistivities and high thermal conductivities. 

The GFR system is top ranked in sustainability because of its closed fuel cycle and excellent performance in actinide management. It is rated good in safety, economics, and in proliferation resistance and physical protection. It is primarily envisioned for missions in electricity... 

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