Improved detector response characterization method in ISOCS and LabSOCS

The In-Situ Object Calibration Software (ISOCS) and the Laboratory Sourceless Calibration Software (LabSOCS) developed and patented by Canberra Industries have found widespread use in the gamma-spectrometry community. Using the ISOCS methodology, one can determine the full energy peak efficiencies of a germanium detector in the 45 keV-7 MeV energy range, for practically any source matrix and geometry. The underlying mathematical techniques used in ISOCS (and LabSOCS) have undergone significant improvements and enhancements since their first release in 1996. One of these improvements is  a spatial response characterization technique that is capable of handling the large variations in efficiency that occurs within a small region. The technique has been in use in ISOCS and LabSOCS releases since 1999, and has significantly improved the overall quality of the close-in and off-axis response characterization for HPGe detectors, especially for Canberra’s Broad Energy Germanium (BEGe) detectors. In this method, the detector response is characterized by creating a set of fine spatial efficiency grids at 15 energies in the 45 keV-7 MeV range. The spatial grids are created in (r,⊝) space about the detector, with the radius r varying from 0 to 500 meters, and the angle ⊝ varying from 0 to π. The reference efficiencies for creating the spatial grids are determined from MCNP calculations using a validated detector model. Once the efficiency grids are created, the detector response can be determined at any arbitrary point within a sphere of 500-meter radius, and at any arbitrary energy within the specified range. Results are presented highlighting the improved performance achieved using the gridding methodology.     

Virtual state scattering with cold electrons: para-xylene and para-difluorobenzene

The scattering of electrons with kinetic energies down to a few meV by para-xylene and para-difluorobenzene has been observed experimentally with an electron beam energy resolution of 0.95 to 1.5 meV (full width half maximum). At low electron energies the collisions can be considered as cold scattering events because the de Broglie wavelength of the electron is considerably larger than the target dimensions. The scattering cross sections measured rise rapidly at low energy due to virtual state scattering. The nature of this scattering process is discussed using s- and p-wave phase shifts derived from the experimental data. Scattering lengths are derived of, respectively, -9.5+/-0.5 and -8.0+/-0.5 a.u. for para-xylene and para-difluorobenzene. The virtual state effect is interpreted in terms of nuclear diabatic and partially adiabatic models, involving the electronic and vibronic symmetries of the unoccupied orbitals in the target species. The concept of direct and indirect virtual state scattering is introduced, through which the present species, in common with carbon dioxide and benzene, scatter through an indirect virtual state process, whereas other species, such as perfluorobenzene, scatter through a direct process.     

Intensity Measurements and Collision-Broadening Coefficients for the Oxygen A Band Measured by Intracavity Laser Absorption Spectroscopy

High-sensitivity, high-resolution intracavity laser absorption spectroscopy (ICLAS) has been used to measure line intensities, nitrogen-broadening coefficients, and self-broadening coefficients in the A band (b(1)Sigma(+)(g) <-- X(3)Sigma(-)(g)) of oxygen. Both linear cavity and ring cavity ICLAS configurations were used for these measurements, and the results were intercompared. The results were compared to values measured using long-path multiple-reflection cells by K. D. Ritter and T. D. Wilkinson [J. Mol. Spectrosc. 121, 1-19 (1987)] and L. Brown and C. Plymate, [J. Mol. Spectrosc. 199, 166-179 (2000)]. New results are included for weakly absorbing transitions, not observed in the earlier measurements, such as high rotational states (up to J = 39), hot-band transitions (v' = 1 <-- v" = 1), and isotopically substituted species ((18)O(2) and (16)O(18)O). Isotopic variants ((16)O(2), (18)O(2), and (16)O(18)O) have similar broadening coefficients for corresponding rotational levels, but the self-broadening coefficients are larger in the hot band (v' = v" = 1) as compared with v' = v" = 0 transitions. An ECS-EP scaling analysis of the v' = v" = 0 self-broadening data accurately represents the available data, with the exception of the N = 0 and N = 1 levels. Copyright 2000 Academic Press.     

Laser excited fluorescence of CS2

Resonance fluorescence excited by ultraviolet lines of argon and krypton ion lasers has been observed from carbon disulfide. The strongest excitations are to single rotational levels within bands of Kleman's R system having K = 0 and 1. Fluorescence in each instance forms a long progression in the ground-state bending vibration, ν″₂. Vibrational levels as high as (1,28°,0) have been identified.     

Analysis of perturbations in the A2Π-X2Σ+ “Red” system of CN

Deperturbed vibration-rotation constants of the A²Π(v′ = 0 to 12) and X²Σ⁺(v″ = 0 to 8) states of CN are obtained. Specroscopic data from several sources are combined using a weighted, nonlinear least-squares fitting routine. The diagonalized effective Hamiltonian matrix contains as many as two ²Π and four ²Σ⁺ mutually interacting vibronic levels. Perturbations of A²Π by both X²Σ⁺ and B²Σ⁺ are treated simultaneously. The deperturbed constants and interaction matrix elements obtained provide a significantly more accurate representation of all perturbed and unperturbed observed lines than the previously reported values. The electronic factors of the spin-orbit and rotation-electronic perturbation matrix elements for the A ～ X and A ～ B interactions are determined and several previously unreported perturbations are detected and analyzed. Merged constants and Dunham coefficients are calculated; a detailed statistical treatment of the parameters and error estimates has also been carried out.