In situ measurement of transuranics using a calcium fluoride scintillation detection system

A prototype scintillation spectrometer capable of measuring low energy photons from transuranic elements in groundwater has been developed for in situ applications. The detector is a CaF₂ (Eu) crystal enclosed in a stainless steel casing with a 19 mg·cm^-2 stainless steel entrance window. Evaluation of the system was performed in the laboratory by submersing the probe into a number of aqueous solutions containing varying concentrations of ²⁴¹Am in a simulated well environment. Spectra obtained had easily discernible peaks associated with the low energy L X-rays and the 60 keV gamma-ray photopeak of ²⁴¹Am.     

First-principles DFT study of the structural, electronic and vibrational properties of azidopentazole

In this Letter we report a density functional all-electron calculation of the structural and electronic properties of the polynitrogen high-energy molecule, azidopentazole (N₈). We have also performed a vibrational analysis to determine the IR and Raman spectra. Our calculated geometrical properties and vibrational frequencies are in good agreement with previous ab initio and density functional calculations. The weaker IR modes show a different relative ordering than previously reported. We also report calculated Raman intensities for azidopentazole.     

Exact solution of two-species ballistic annihilation with general pair-reaction probability

The reaction processA + B → ∅ is modeled for ballistic reactants on an infinite line with particle velocitiesυ _A =c andυ _B = -c and initially segregated conditions, i.e., allA particles to the left and allB particles to the right of the origin. Previous models of ballistic annihilation have particles that always react on contact, i.e., pair-reaction probabilityp = 1. The evolutions of such systems are wholly determined by the initial distributions of particles and therefore do not have a stochastic dynamics. However, in this paper the generalization is made to p< 1, allowing particles to pass through each other without necessarily reacting. In this way, theA andB particle domains overlap to form a fluctuating, finitesized reaction zone where the product ∅ is created. Fluctuations are also included in the currents ofA andB particles entering the overlap region, thereby inducing a stochastic motion of the reaction zone as a whole. These two types of fluctuations, in the reactions and particle currents, are characterised by theintrinsic reaction rate, seen in a single system, and theextrinsic reaction rate, seen in an average over many systems. The intrinsic and extrinsic behaviors are examined and compared to the case of isotropically diffusing reactants     

Critical behavior in truncated quantum O(n) spin systems

We present a truncated O(n) quantum hamiltonian which in one spatial dimension exhibits a behavior quite similar to the standard untruncated versions of the model. We find using finite size scaling theory that the truncated O(2) model has a behavior reminiscent of the planar model (i.e., a critical line). For the O(3) and O(4) versions of the model we find no transition.     

Temperatures in differential scanning calorimetry

A recently described method is used to characterise thermal gradients in a DSC-2 and the results are compared with a conventional temperature calibration. Under certain circumstances the latter may be in error by several degrees with consequent adverse effects on calculated heat capacities. The errors are removed when allowance is made for variations in thermal lag from sample to sample.     

Thermodynamic properties of a hindered rotator

It is demonstrated that a finite dimensional representation of the hamiltonian of a hindered rotator can be used to get reasonably accurate values of thermodynamic properties, e.g., the specific heat of an assembly of such rotators. It is known that there is a large difference between the classical values and quantum statistical values when the height of the hindering potential is small.