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[en] Equations to extract the depth resolution from measured sputtering profiles of multilayer structures are presented. The range of application and the errors involved are discussed with respect to the ratio between depth resolution and layer thickness. (author)

[en] The beam characteristics of a dual physical wedge system, upper and lower, for Varian accelerators are studied over the energy range 6-18 MV. Wedge factors for both systems are measured in a water phantom as a function of field size, depth and source-to-wedge (SWD) distance. Our results indicate that apart from their physical differences, dosimetrically, the two wedge systems have <2% difference in central axis percentage depth dose beyond the build-up region. The lower wedge central axis percentage depth dose is consistently lower than that of the corresponding upper wedge, with the effect more pronounced for large field sizes. The wedge profiles are identical within 2% for all field sizes, depths and energies. The wedge factors for both wedge systems are also within 2% for all field sizes and depths for both 6 and 15 MV photons and slightly higher for the 18 MV beam and 45 deg. - 60 deg. wedge angle. The wedge factor variation with SWD reveals an interesting fact that thinner wedges (15 deg. and 30 deg. result in a higher surface dose in the central axis region than thicker wedges. As the SWD increases beyond 80 cm, the reverse is true, i.e. thicker wedges produce higher surface dose than thinner wedges. It is also verified that the wedge factor at any depth and for any field size can be calculated from the wedged and open field central axis percentage depth dose, and the wedge factor at d_max, resulting in nearly 44% reduction in water phantom scanning and 80% reduction in point measurements during commissioning

[en] In this paper, a theoretical approach was developed to determine the maximum depth of penetration of a impacting projectile on earth soil. The theory was formulated according to the dynamic spherical cavity expansion on a concentrically layered compressive media. The layer exhibit elasto-plastic response with non-linear strain hardening under shear stress and ideal locking compressibility under hydrostatic stress such that the transition from elastic to plastic state is accompanied by small but finite volumetric strain known as the locking strain. The projectile is assumed to be rigid and non-deformable throughout the penetration process. The theory predicts relatively well with the measured data for non-deformable projectiles and over predicts the penetration depth in the case of deformable projectile. (authors). 10 refs 7 figs., 2 tabs

[en] Multimedia mass balance models assume well-mixed homogeneous compartments. Particularly for soils, this does not correspond to reality, which results in potentially large uncertainties in estimates of transport fluxes from soils. A theoretically expected exponential decrease model of chemical concentrations with depth has been proposed, but hardly tested against empirical data. In this paper, we explored the correspondence between theoretically predicted soil concentration profiles and 84 field measured profiles. In most cases, chemical concentrations in soils appear to decline exponentially with depth, and values for the chemical specific soil penetration depth (d _p) are predicted within one order of magnitude. Over all, the reliability of multimedia models will improve when they account for depth-dependent soil concentrations, so we recommend to take into account the described theoretical exponential decrease model of chemical concentrations with depth in chemical fate studies. In this model the d _p-values should estimated be either based on local conditions or on a fixed d _p-value, which we recommend to be 10 cm for chemicals with a log K_ow > 3. - Multimedia mass model predictions will improve when taking into account depth dependent soil concentrations

[en] We are evaluating the application of stereoscopic imaging to digital mammography. In the current study, we investigated the effects of magnification and zooming on depth perception. A modular phantom was designed which contained six layers of 1-mm-thick Lexan plates, each spaced 1 mm apart. Eight to nine small, thin nylon fibrils were pasted on each plate in horizontal or vertical orientations such that they formed 25 crossing fibril pairs in a projected image. The depth separation between each fibril pair ranged from 2 to 10 mm. A change in the order of the Lexan plates changed the depth separation of the two fibrils in a pair. Stereoscopic image pairs of the phantom were acquired with a GE full-field digital mammography system. Three different phantom configurations were imaged. All images were obtained using a Rh target/Rh filter spectrum at 30 kVp tube potential and a ±3 degrees stereo shift angle. Images were acquired in both contact and 1.8X magnification geometry and an exposure range of 4 to 63 mAs was employed. The images were displayed on a Barco monitor driven by a Metheus stereo graphics board and viewed with LCD stereo glasses. Five observers participated in the study. Each observer visually judged whether the vertical fibril was in front of or behind the horizontal fibril in each fibril pair. It was found that the accuracy of depth discrimination increased with increasing fibril depth separation and x-ray exposure. The accuracy was not improved by electronic display zooming of the contact stereo images by 2X. Under conditions of high noise (low mAs) and small depth separation between the fibrils, the observers' depth discrimination ability was significantly better in stereo images acquired with geometric magnification than in images acquired with a contact technique and displayed with or without zooming. Under our experimental conditions, a 2 mm depth discrimination was achieved with over 60% accuracy on contact images with and without zooming, and with over 90% accuracy on magnification images. This study indicates that stereoscopic imaging, especially with magnification, may be useful for visualizing the spatial distribution of microcalcifications in a cluster and for differentiating overlapping tissues from masses on mammograms

[en] Beryllium is a kind of brittle metal, the large residual stress produced in processing must be eliminated before use, so the measurement of residual stress is important. X-ray stress analysis is a nondestructive test method based on the X-ray diffraction principle. Applied to beryllium, due to its lower density and little mass absorption coefficient for X-ray, the X-ray penetration depth is rather large. Therefore, the total average stress in the surface layer of beryllium can be measured by the X-ray method, but usually an uneven stress distribution in beryllium is existed, there would be some errors if the conventional X-ray stress analysis is adopted, moreover, the stress along depth distribution can't obtained. According to the X-ray penetration depth as a function of the inclination angles during X-ray stress analysis, a novel stress measurement method has been set up in this paper, which can measure the stress along depth distribution in the surface layer of beryllium. The feasibility of the method has been validated using the cantilever beam loading experiment of beryllium specimen. (author)

[en] Dose distributions of high-energy electrons were calculated using simple equations which were derived from experimental data. Equations are composed of functions of the percent depth dose, the field effect ratio and the off-axis ratio. The electron energy and field size are parameters for the calculation. Dose distributions were compared between experiments and calculations for different field sizes and energies. It is concluded that the equations can be applied clinically to calculate dose distributions for treatment planning. (orig.)

[en] In this paper, multiple regression analysis was performed on data gather red from the literature for derangement the maximum depth of penetration an impacting projectile of low and high velocities on earth soil. The data were divi deal into two groups. The first of which being related to the projectile characteristics including weight, frontal area, nose length and the impacting velocity. The second is being related to the soil properties including the unconfined compressive strength, bulk density, plasticity index, cohesion and the angle of friction. A total of 12 sets of equations were developed relating the penetration depth to various soil properties and projectile characteristics. The results of the regression showed that the equations provided relatively good predictive tools. The highest correlation ratio was found to be 0.975 while the lowest was 0.847. Most of the data fell within the 95% accuracy band. (author). 10 refs., 7 figs., 4 tabs

[en] In order to verify that the energies of electron beams used for external beam therapy remain constant, IPEM 81 recommends a constancy check based on the ratio of ionization chamber measurements at two depths along the central axis. Such measurements for a range of electron energies can be a time consuming process. The purpose of this study was to design a device that would use several ion chambers simultaneously to measure electron depth dose curves, and hence the electron energy. A design was developed for a device consisting of ten independent ionization chambers, shaped and arranged in a solid phantom like the steps of a spiral staircase, the axis of the staircase being coincident with the axis of the electron beam. Measurements were carried out to test the design of individual chambers and to optimize the radius of the spiral and both the depth intervals and the lateral spacing between adjacent chambers. For ranges of electron energy from 6-12 MeV and 12-20 MeV the radii of the spirals needed were found to be 36.5 mm and 30.9 mm, the angular separations between edges of the chambers were 52 deg. and 30 deg. and chamber depths were found to be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 mm and 20, 40, 45, 50, 55, 60, 65, 70, 75, 80 mm, respectively. (note)