Alpha spectrometric evaluation of SRM-995 as a potential uranium/thorium double tracer system for age-dating uranium materials

Uranium-233 (t _1/2 ~ 1.59E5 years) is an artificial, fissile isotope of uranium that has significant importance in nuclear forensics. The isotope provides a unique signature in determining the origin and provenance of uranium-bearing materials and is valuable as a mass spectrometric tracer. Alpha spectrometry was employed in the critical evaluation of a ²³³U standard reference material (SRM-995) as a dual tracer system based on the in-growth of ²²⁹Th (t _1/2 ~ 7.34E3 years) for ~35 years following radiochemical purification. Preliminary investigations focused on the isotopic analysis of standards and unmodified fractions of SRM-995; all samples were separated and purified using a multi-column anion-exchange scheme. The ²²⁹Th/²³³U atom ratio for SRM-995 was found to be 1.598E?4 (±4.50 %) using recovery-corrected radiochemical methods. Using the Bateman equations and relevant half-lives, this ratio reflects a material that was purified ~36.8 years prior to this analysis. The calculated age is discussed in contrast with both the date of certification and the recorded date of last purification.     

A brief introduction to analytical methods in nuclear forensics

Nuclear forensic (NF) techniques are critical in responding to both environmental releases of nuclear materials and illicit trafficking activities involving both nuclear and counterfeit materials. Despite rising need, however, significant barriers exist to the future success of such research. This subset of analytical chemistry contains unique concerns (e.g. chronometry and impurity signatures), a wide variety of preparatory/instrumental approaches, and is in need of innovative solutions to current problems both in and out of the lab. The present work introduces existing NF research, development challenges and notes potential areas for advancement by highlighting several key analytical approaches. Examples of concerns and techniques discussed in this review include: chronometry, reference materials, separations, counting spectrometry, mass spectrometry and more.     

Migration of Silicon from Oxygen to Carbon in O-Trialkylsilyl Ketene Acetals

The migration of silicon from oxygen to carbon for 1 and 3 is intramolecular. The half—life of migration is not influenced by the presence of t-BuMe₂SiCI or triethyIbenzylammonium chloride.     

Active centre structure and the stereoregulation process in anionic polymerization

The mechanism of stereoregulation in the anionic polymerization of butadiene and isoprene is discussed in terms of what is known about the structure of the active centres. This includes the effect of the presence of cis and trans isomers and the dynamics of their interconversion and in the isoprene case, the effect of two distinct types having 1,4 and 4,1 structures.     

On the equilibrium configurations of an elastically constrained rotating disk: An analytical approach

According to the linear theory of vibration for spinning disks, the backward traveling waves of some of the modes may have zero natural frequency at what are called the critical speeds. At these speeds, the linear equations of motion cannot properly predict the amplitude response of the spinning disk, and nonlinear equations of motion must be used. In this paper, geometrical nonlinear equations of motion based on Von Karman plate theory are employed to study the dynamics of an elastically constrained disk near its critical speeds. A one-mode approximation is used to examine the effect of elastic constraint on the amplitude response. Presenting the equations in a space-fixed coordinate system, this study aims to find closed-form solutions for some of the equilibrium configurations of an elastically constrained spinning disk. Also, the stability of these configurations is studied using analytical techniques. It is shown that below the critical speed, one neutrally stable equilibrium solution exists, while above it, a bifurcation occurs. In this situation, two more branches of equilibrium configurations emerge, one of which is neutrally stable and the other unstable. Closed-form expressions for the bifurcation points are obtained. Due to the effect of an elastic constraint, a bifurcation occurs and the previously neutrally stable equilibrium configuration turns unstable. Also at this bifurcation point, two more branches of equilibrium solutions emerge.