Photoionization of the valence shells of the neutral tungsten atom

Results from large-scale theoretical cross section calculations for the total photoionization of the 4f, 5s, 5p and 6s orbitals of the neutral tungsten atom using the Dirac Coulomb R-matrix approximation (DARC: Dirac-Atomic R-matrix codes) are presented. Comparisons are made with previous theoretical methods and prior experimental measurements. In previous experiments a time-resolved dual laser approach was employed for the photo-absorption of metal vapours and photo-absorption measurements on tungsten in a solid, using synchrotron radiation. The lowest ground state level of neutral tungsten is $\rm 5p^6 5d^4 6s^2 \; {^5}D_{\it J}$, with $\it J$=0, and requires only a single dipole matrix for photoionization. To make a meaningful comparison with existing experimental measurements, we statistically average the large-scale theoretical PI cross sections from the levels associated with the ground state $\rm 5p^6 5d^4 6s^2 \; {^5}D_{\it J}[{\it J}=0,1,2,3,4]$ levels and the \rm 5d^56s \; ^7S_3 excited metastable level. As the experiments have a self-evident metastable component in their ground state measurement, averaging over the initial levels allows for a more consistent and realistic comparison to be made. In the wider context, the absence of many detailed electron-impact excitation (EIE) experiments for tungsten and its multi-charged ion stages allows current photoionization measurements and theory to provide a road-map for future electron-impact excitation, ionization and di-electronic cross section calculations by identifying the dominant resonance structure and features across an energy range of hundreds of eV.Comment: 10 pages, 3 figures, accepted for publication in J Phys B: At. Mol. Opt. Phy

Experiment and theory

Photoionization of neutral atomic sulfur in the ground and metastable states was studied experimentally at a photon energy resolution of 44 meV (full width at half maximum). Relative cross section measurements were recorded by using tunable vacuum ultraviolet radiation in the energy range 9–30 eV obtained from a laser-produced plasma and the atomic species were generated by photolysis of molecular precursors. Photoionization of this atom is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. A wealth of resonance features observed in the experimental spectra are spectroscopically assigned and their energies and quantum defects tabulated. The cross section measurements are compared with state-of-the-art theoretical cross section calculations obtained from the Dirac Coulomb R-matrix method. Resonance series in the spectra are identified and compared, indicating similar features in both the theoretical and experimental spectra

Investigation of optical coherence micro-elastography as a method to visualize micro-architecture in human axillary lymph nodes

This project is supported with funding from the Australian Research Council; and Cancer Council WA, which allowed us to develop the technology; Department of Health of Western Australia, National Breast Cancer Foundation (Australia); and the National Health and Medical Research Council, Australia, which allowed us to design and implement the clinical protocol, and to perform the clinical measurements.Background : Evaluation of lymph node involvement is an important factor in detecting metastasis and deciding whether to perform axillary lymph node dissection (ALND) in breast cancer surgery. As ALND is associated with potentially severe long term morbidity, the accuracy of lymph node assessment is imperative in avoiding unnecessary ALND. The mechanical properties of malignant lymph nodes are often distinct from those of normal nodes. A method to image the micro-scale mechanical properties of lymph nodes could, thus, provide diagnostic information to aid in the assessment of lymph node involvement in metastatic cancer. In this study, we scan axillary lymph nodes, freshly excised from breast cancer patients, with optical coherence micro-elastography (OCME), a method of imaging micro-scale mechanical strain, to assess its potential for the intraoperative assessment of lymph node involvement. Methods : Twenty-six fresh, unstained lymph nodes were imaged from 15 patients undergoing mastectomy or breast-conserving surgery with axillary clearance. Lymph node specimens were bisected to allow imaging of the internal face of each node. Co-located OCME and optical coherence tomography (OCT) scans were taken of each sample, and the results compared to standard post-operative hematoxylin-and-eosin-stained histology. Results : The optical backscattering signal provided by OCT alone may not provide reliable differentiation by inspection between benign and malignant lymphoid tissue. Alternatively, OCME highlights local changes in tissue strain that correspond to malignancy and are distinct from strain patterns in benign lymphoid tissue. The mechanical contrast provided by OCME complements the optical contrast provided by OCT and aids in the differentiation of malignant tumor from uninvolved lymphoid tissue. Conclusion : The combination of OCME and OCT images represents a promising method for the identification of malignant lymphoid tissue. This method shows potential to provide intraoperative assessment of lymph node involvement, thus, preventing unnecessary removal of uninvolved tissues and improving patient outcomes.Publisher PDFPeer reviewe

Interstellar X-Ray Absorption Spectroscopy of Oxygen, Neon, and Iron with the Chandra LETGS Spectrum of X0614+091

We find resolved interstellar O K, Ne K, and Fe L absorption spectra in the Chandra X-Ray Observatory Low-Energy Transmission Grating Spectrometer (LETGS) spectrum of the low-mass X-ray binary X0614+091. We measure the column densities in O and Ne and find direct spectroscopic constraints on the chemical state of the interstellar O. These measurements probably probe a low-density line of sight through the Galaxy, and we discuss the results in the context of our knowledge of the properties of interstellar matter in regions between the spiral arms