D.J. O'Connor

Science Communication: A Contemporary Definition:

Science communication is a growing area of practice and research. During the past two decades, the number of activities, courses, and practitioners has steadily increased. But what actually is science communication? In what ways is it different to public awareness of science, public understanding of science, scientific culture, and scientific literacy? The authors review the literature to draw together a comprehensive set of definitions for these related terms. A unifying structure is presented and a contemporary definition of science communication positioned within this framework. Science communication (SciCom) is defined as the use of appropriate skills, media, activities, and dialogue to produce one or more of the following personal responses to science (the AEIOU vowel analogy): Awareness, Enjoyment, Interest, Opinion-forming, and Understanding. The definition provides an outcomes-type view of science communication, and provides the foundations for further research and evaluation.

Comparison of theoretical and empirical interatomic potentials

Abstract Despite a wealth of theoretical and experimental research on interatomic potentials, there has been only limited guidance on how well each compares to all others. In this report, many popular theoretical potentials are compared to a large range of experimental potentials to gauge the accuracy of the various theoretical models. From this comparison it is found that the “ Universal Potential” of Biersack and Ziegler agrees best with the available measurements. Correction factors are derived which give similar agreement for the other potentials, but some systematic deviations still persist at the low or high energy end for most other potentials, as demonstrated for the Moliere potential.

Empirical formulae for energy loss straggling of ions in matter

Abstract A detailed survey of the currently available data for the energy loss straggling of hydrogen, helium and heavy ions in matter has been undertaken. An empirical formula based on Chus calculation has been obtained for the energy loss straggling of hydrogen ions. Using this formula with the effective charge and the scaling of straggling, similar to the scaling of stopping powers, good estimates have been made for He and heavy ions. The empirical formulae represent the available data accurately and permit reliable estimates for combinations of projectile and target where currently no data is available.

Surface analysis methods in materials science

I Introduction.- 1 Solid Surfaces, Their Structure and Composition.- 2 UHV Basics.- II Techniques.- 3 Electron Microscope Techniques for Surface Characterization.- 4 Sputter Depth Profiling.- 5 SIMS - Secondary Ion Mass Spectrometry.- 6 Auger Electron Spectroscopy and Microscopy - Techniques and Applications.- 7 X-Ray Photoelectron Spectroscopy.- 8 Vibrational Spectroscopy of Surfaces.- 9 Rutherford Backscattering Spectrometry and Nuclear Reaction Analysis.- 10 Materials Characterization by Scanned Probe Analysis.- 11 Low Energy Ion Scattering.- 12 Reflection High Energy Electron Diffraction.- 13 Low Energy Electron Diffraction.- 14 Ultraviolet Photoelectron Spectroscopy of Solids.- 15 EXAFS.- III Processes and Applications.- 16 Minerals, Ceramics and Glasses.- 17 Characterization of Catalysts by Surface Analysis.- 18 Application to Semiconductor Devices.- 19 Characterisation of Oxidised Surfaces.- 20 Coated Steel.- 21 Thin Film Analysis.- 22 Identification of Adsorbed Species.- 23 Surface Analysis of Polymers.- 24 Glow Discharge Optical Emission Spectrometry.- IV Appendix.- Acronyms Used in Surface and Thin Film Analysis.- Surface Science Bibliography.

Melting of al surfaces

The thermal disordering of Al(110) and Al(111) surfaces was studied up to temperatures of 0.5 and 1.2 K below the bulk melting point Tm, respectively. With the use of medium energy ion scattering it was found that surface melting is present on the (110) face but not on the (111) face. The (110) disordered layer thickness increases with temperature as ln[Tm(T>m − T)]. The result in terms of a thermodynamic model that was presented earlier to explain the melting of Pb surfaces.

Measurement and modeling of the effect of support arm backscatter on dosimetry with a varian EPID.

PURPOSE Amorphous silicon EPIDs have been used for planar dose verification in IMRT treatments for many years. The support arm used to attach some types of EPIDs to linear accelerators can introduce inaccuracies to dosimetry measurements due to the presence of metallic parts in their structures. It is demonstrated that this uncertainty may be as large as approximately 6% of maximum image signal for large fields. In this study, a method has been described to quantify, model and correct for the effect of backscattered radiation from the EPID support arm (E-Arm type, Varian Medical Systems). METHODS Measurements of a support arm backscatter kernel were made using several 1 x 1 cm2 6 MV pencil beam irradiations at a sample of positions over the sensitive area of the EPID in standard clinical setup and repeated with the EPID removed from the support arm but at the same positions. A curve-fit to the subtraction of EPID response obtained on and off the arm was used to define the backscatter kernel. The measured kernel was compared with a backscatter kernel obtained by Monte Carlo simulations with EGS/BEAM code. A backscatter dose prediction using the measured backscatter kernel was added to an existing EPID dose prediction model. The improvement in the agreement of the modified model predictions with EPID measurements for a number of open fields and IMRT beams were investigated by comparison to the original model results. RESULTS Considering all functions tested to find the best functional fit to the data points, a broad Gaussian curve proved to be the optimum fit to the backscatter data. The best fit through the Monte Carlo simulated backscatter kernel was also found to be a Gaussian curve. The maximum decrease in normalized root mean squared deviation of the measured and modeled EPID image profiles for open fields was 13.7% for a 15 x 15 cm2 field with no decrease observed for a 3 x 3 cm2 (the smallest) field as it was not affected by the arm backscatter. Gamma evaluation (2%, 2 mm criteria) showed the improvement in agreement between the model and measurement results when the backscatter was incorporated. The average increase in Gamma pass rate was 2% for head and neck and 1.3% for prostate IMRT fields investigated in this study. CONCLUSIONS The application of the backscatter kernel determined in this study improved the accuracy of dosimetry using a Varian EPID with E-arm for open fields of different sizes: Eight head and neck and seven prostate IMRT fields. Further improvement in the agreement between the model predictions and EPID measurements requires more sophisticated modeling of the backscatter.

Studies of surface composition and structure of Cu3Pt(111) by low energy alkali ion scattering

Abstract The composition and structure of the Cu 3 Pt(111) surface have been investigated by low energy alkali ion scattering. The surface composition of the top two layers was determined by Li + ion scattering using selective scattering geometries with calibration measurements on reference samples of Cu(111) and Pt(111). Under thermal equilibrium conditions, these results consistently showed a surface composition of 80%Cu20%Pt in the first layer, while the second layer was 69%Cu31%Pt. The surface structure was probed by measuring the intensity of Li + ion scattering as a function of incident angle along the main azimuthal directions. The interpretation of experimental data was based on a chain model simulation. The results showed that the Pt atoms were coplanar with the Cu atoms in the first layer. A clustering effect of Pt has also been tested using 1 keV K + ion scattering. The results revealed that the Pt atoms in the first layer were not clustered by lack of the PtPt pair double scattering peak along the two long azimuthal directions.

A STM study of the effects of the ion incident angle and energy on surface damage induced by Ar+ bombardment of HOPG

Abstract Scanning tunnelling microscopy has been used to study the surface damage induced by ion bombardment of highly ordered pyrolytic graphite (HOPG). Ar ions with energies in the range from 0.5 to 3 keV were used to bombard HOPG surfaces at different angles of incidence. A low fluence ( 12 ions cm 2 ) was used to enable characterisation of single ion impacts on surfaces. It is shown that each ion impact creates a small protrusion on the HOPG surface whose average volume increases as the ion energy and the incident angle to the surface decreases in the range investigated. Statistical distributions of protrusion diameter and height are given for comparison, as well as the average diameter and height. The origin of these features on the surfaces is discussed. It is suggested that thermal spikes created by the ion in the near surface region may play a very important role in producing this surface damage.

Neutralisation of He+ and Ne+ scattered from Ag

Abstract The neutralisation of low energy He + and Ne + ions scattered from Ag has been studied by measuring the angular distribution of ions scattered into the plane normal to that containing the incident beam and the normal to the surface of the solid. Assuming that the probability of the ion surviving in a charged state is given by P =exp(− V c /V ⊥ ), the energy dependence of V c has been measured. This is the survival coefficient appropriate to the incoming and outgoing trajectories but the experiment studies changes only in the outgoing trajectory. A strong energy dependence has been observed, as well as features consistent with some recent theoretical models of the neutralisation event.

Detection and correction for EPID and gantry sag during arc delivery using cine EPID imaging

PURPOSE Electronic portal imaging devices (EPIDs) have been studied and used for pretreatment and in-vivo dosimetry applications for many years. The application of EPIDs for dosimetry in arc treatments requires accurate characterization of the mechanical sag of the EPID and gantry during rotation. Several studies have investigated the effects of gravity on the sag of these systems but each have limitations. In this study, an easy experiment setup and accurate algorithm have been introduced to characterize and correct for the effect of EPID and gantry sag during arc delivery. METHODS Three metallic ball bearings were used as markers in the beam: two of them fixed to the gantry head and the third positioned at the isocenter. EPID images were acquired during a 360° gantry rotation in cine imaging mode. The markers were tracked in EPID images and a robust in-house developed MATLAB code was used to analyse the images and find the EPID sag in three directions as well as the EPID + gantry sag by comparison to the reference gantry zero image. The algorithm results were then tested against independent methods. The method was applied to compare the effect in clockwise and counter clockwise gantry rotations and different source-to-detector distances (SDDs). The results were monitored for one linear accelerator over a course of 15 months and six other linear-accelerators from two treatment centers were also investigated using this method. The generalized shift patterns were derived from the data and used in an image registration algorithm to correct for the effect of the mechanical sag in the system. The Gamma evaluation (3%, 3 mm) technique was used to investigate the improvement in alignment of cine EPID images of a fixed field, by comparing both individual images and the sum of images in a series with the reference gantry zero image. RESULTS The mechanical sag during gantry rotation was dependent on the gantry angle and was larger in the in-plane direction, although the patterns were not identical for various linear-accelerators. The reproducibility of measurements was within 0.2 mm over a period of 15 months. The direction of gantry rotation and SDD did not affect the results by more than 0.3 mm. Results of independent tests agreed with the algorithm within the accuracy of the measurement tools. When comparing summed images, the percentage of points with Gamma index <1 increased from 85.4% to 94.1% after correcting for the EPID sag, and to 99.3% after correction for gantry + EPID sag. CONCLUSIONS The measurement method and algorithms introduced in this study use cine-images, are highly accurate, simple, fast, and reproducible. It tests all gantry angles and provides a suitable automatic analysis and correction tool to improve EPID dosimetry and perform comprehensive linac QA for arc treatments.