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This paper describes and discusses how isotope measurements of low content uranium materials can be optimized using a multi-ion counting system consisting of five discrete dynode electron multiplier (EM) detectors.

A primary tool for detecting undeclared nuclear activities is the analysis of uranium-bearing particles collected on cotton swipes. For many years, secondary ion mass spectrometry (SIMS) has been used as one of the mainstay techniques for particle analysis of nuclear safeguards samples. SIMS is unique in that it is the only technique that can both localize the particles of interest and also provide the isotopic composition of single particles. This paper presents data obtained on standard uranium particle samples using large geometry (LG)-SIMS instruments equipped with the newly developed, automated particle measurement screening software. Both sample screening measurements and microbeam analyses on individual particles are presented. The enhanced performance of the SIMS method for nuclear safeguards applications using LG-SIMS instruments equipped with automated screening capabilities is also discussed. Figure 7. Microbeam measurements, (a) 234 U versus 235 U and (b) 236 U versus 235 U on particles selected from the screening measurement. Intersection of dotted lines indicates the nominal values for 234 U, 235 U, or 236 U atom % for SRM U005a and U010. Error bars correspond to AE 2s.Nuclear safeguards applications using LG-SIMS

SUMMARYThis paper treats the mathematical derivation of a novel formulation of the Navier-Stokes equation for general non-orthogonal curvilinear co-ordinates. The covariant velocity components are solved in this FVM formulation, which leads to the pressure-velocity coupling becoming relatively easy to handle at the expense of a more complicated expression of the convective and diffusive fluxes. When a velocity component is solved at a point P, the neighbouring velocities are projected in the direction of the velocity component at the point P. Thus the base vectors are changed at the neighbouring points. This renders a simpler expression for the covariant derivatives. Neither the Cristoffel symbol nor its derivatives need be computed. This contributes to the accuracy of the formulation. The procedure of changing the base vectors affects only the convected velocity. The convecting term (dot product of velocity and area) is calculated without any change of the base vectors. The same is true for the operator on the covariant velocity in the diffusion term.It is shown that when using upwind differencing the use of projected velocities gives better results than when curvature effects are included in the source term. The discretized equations are written in a form which enables the use of the tridiagonal matrix algorithm (TDMA). The equations can be solved using either the SIMPLEC or the PIS0 procedure.Two examples of laminar flows are given.