Zur Rückstreuung von Elektronen im Energiebereich von 10 bis 100 keV

Bachmann

The Journal of Cell Biology

1969

438

342

An analysis of grain distributions around a radioactive line source (consisting of polystyrene-1H) showed that the shape of the distribution was independent of the factors that influence resolution, i .en section and emulsion thickness, silver halide crystal, and developed grain size. These factors did effect the spread of the distribution, however, and thus the distance from the line source within which 50 % of the total developed grains fell . We called this distance "half distance" (HD) and determined it for a variety of specimens . When grain distributions were normalized in units of HD, one could plot universal grain distributions for specimens with radioactive sources of various shapes . The use of HD and the universal curves in interpreting radioautograms is discussed .

Section: B Use Of the Main Curvesmentioning

confidence: 84%

Resolution in Electron Microscope Radioautography

Bachmann

The Journal of Cell Biology

1969

438

342

“…Using inclined-scanning OC images the quartz inclusion microstructure is easily resolved. Experimental studies and numerical simulations (Kanter, 1957;Newbury et al, 1973;Bishop, 1974) show that the backscatter coefficient (the fraction of electrons scattered out of the sample) increases as the incident beam angle shallows from normal to the specimen surface but the ratio of backscatter coefficients of any two elements decreases. These data have been used to generate an approximate empirical relationship for pure elements (Goldstein et al, 1981), between specimen inclination and backscatter coefficient ( This relationship is shown graphically in Fig.…”

Section: The Response Of Forescatter Detectors To Compositional and Cmentioning

confidence: 99%

Orientation contrast imaging of microstructures in rocks using forescatter detectors in the scanning electron microscope

et al. 1996

We have developed a system using 'forescatter detectors' for backscattered imaging of specimen surfaces inclined at 50-80 ~ to the incident beam (inclined-scanning) in the SEM. These detectors comprise semiconductor chips placed below the tilted specimen. Forescatter detectors provide an orientation contrast (OC) image to complement quantitative crystallographic data from electron backscatter patterns (EBSP). Specimens were imaged using two detector geometries and these images were compared to those collected with the specimen surface normal to the incident beam (normal-scanning) using conventional backscattered electron detector geometries and also to an automated technique, orientation imaging microscopy (DIM). When normal-scanning, the component of the BSE signal relating to the mean atomic number (z) of the material is an order of magnitude greater than any OC component, making OC imaging in polyphase specimens almost impossible. Images formed in inclined-scanning, using forescatter detectors, have OC and z-contrast signals of similar magnitude, allowing OC imaging in polyphase specimens.OC imaging is purely qualitative, and by repeatedly imaging the same area using different specimen-beam geometries, we found that a single image picks out less than 60% of the total microstructural information and as many as 6 combined images are required to give the full data set. The DIM technique is limited by the EBSP resolution (1-2 ~ and subsequently misses a lot of microstructural information. The use of forescatter detectors is the most practical means of imaging OC in tilted specimens, but it is also a powerful tool in its own right for imaging microstructures in polyphase specimens, an essential asset for geological work.KEYWORDS: contrast images, scanning electron microscopy, backscattered electrons. Introductionpatterns (Alam et al., 1954;Venables and Harland, 1972;Dingley, 1981;; Dingley and Baba-Kishi, SELECTED area electron channelling patterns (Coates, 1990;Dingley and Randle, 1992;Randle, 1992; Day, 1967;Joy, 1974;Joy et al., 1982;Davidson, 1984; both provide quantitative data concerning Lloyd, 1985;1987;Schmidt and Olesen, 1989; Lloyd spatial variation of crystallographic orientations Lloyd, 1995) and electron backscatter minerals. In many problems relevant to geologists,

“…For the backscattered energy spectrum, the binning structure within CREEP was chosen to match that of Darlington [19], and the the agreement with those results is very close: the maximum deviation is approximately 0.2%, with CREEP being consistantly slightly higher than Darlingtion. The results from Kanter [34] show a similar overall shape, but a magnitude that is consistantly S-10% higher than CREEP or Darlington. The next distinctive feature of these curves is a gap of low amplitude following the peak.…”

Section: Backscatter Studiesmentioning

confidence: 69%

The macro response Monte Carlo method for electron transport

Svatos

1999

Med. Phys.

The main goal of this thesis was to prove the feasibility of basing electron depth dose calculations in a phantom on first-principles single scatter physics, in an amount of time that is equal to or better than current electron Monte Carlo mcthods.The Macro Response Monte Carlo (MRMC) method achieves run times that are on the order of conventional electron transport methods such as condensed history, with the potential to be much fa,ster. This is possible because MRMC is a Local-toGlobal method, meaning the problem is broken down into two separate transport calculations. The first stage is a local, in this case, single scatter calculation, which generates probability distribution functions (PDFs) to describe the electron's energy, position and trajectory after leaving the local geometry, a small sphere or "kugel" A number of local kugel calculations were run for calcium and carbon, creating a library of kugel data sets over a range of incident energies and sizes (0.025 cm to 0.1 cm in radius).The second transport stage is a global calculation, where steps that conform to the size of the kugels in the library are taken through the global geometry. For each step, the appropriate PDFs from the MRMC library are sampled to determine the electron's new energy, position and trajectory. The electron is immediately advanced to the end of the step and then chooses another kugel to sample, which continues until transport is completed.The MRMC global stepping code was benchmarked as a series of subroutines inside of the Peregrine Monte Carlo code. It was compared to Peregrine's class II condensed history electron transport package, EGS4, and MCNP for depth dose in i ii simple phantoms having density inhomogeneities. Since the kugels completed in the library were of relatively small size, the zoning of the phantoms was scaled down from a clinical size, so that the energy deposition algorithms for spreading dose across 5-10 zones per kugel could be tested. Most resulting depth dose calculations were within 2-3s of well-benchmarked codes, with one excursion to 4%.This thesis shows that the concept of using single scatter-based physics in clinical calculations would not only be possible, but would likely be more efficient than current methods, provided large kugels were generated.