Hisatoyo Kato

Elastic cross sections for electron scattering from GeF4: Predominance of atomic-F in the high-energy collision dynamics

We report absolute differential cross sections (DCSs) for elastic electron scattering from GeF(4). The incident electron energy range was 3-200 eV, while the scattered electron angular range was typically 15°-150°. In addition, corresponding independent atom model (IAM) calculations, within the screened additivity rule (SCAR) formulation, were also performed. Those results, particularly for electron energies above about 10 eV, were found to be in good quantitative agreement with the present experimental data. Furthermore, we compare our GeF(4) elastic DCSs to similar data for scattering from CF(4) and SiF(4). All these three species possess T(d) symmetry, and at each specific energy considered above about 50 eV their DCSs are observed to be almost identical. These indistinguishable features suggest that high-energy elastic scattering from these targets is virtually dominated by the atomic-F species of the molecules. Finally, estimates for the measured GeF(4) elastic integral cross sections are derived and compared to our IAM-SCAR computations and with independent total cross section values.

Development Of A New Digital Radiographic Image Processing System

A new digital radiographic image processing system has been developed. The important capabilities of this system include a large image format, high image quality, on-line operation for reading, processing, and writing, and a software package for various types of image processing. A non-linear filtering technique is introduced which improves contrast of radiographic image structure while maintaining low noise in low-density areas. Preliminary clinical results demonstrate the improvements in diagnostic image quality.

A study of electron interactions with silicon tetrafluoride: elastic scattering and vibrational excitation cross sections

We report absolute differential cross sections for elastic electron scattering from SiF4. The incident electron energy range is 1.5–200 eV, while the scattered electron angular range was from 15° to 150°. The absolute scale of the differential cross sections was set using the relative flow technique with helium as the reference species. Corresponding integral elastic and momentum transfer data have been derived from our differential measurements. As a part of this study, independent atom model calculations were also performed. Those computations were found to be in generally quite good accord with the experimental results at both the differential and integral levels. In addition, excitation function measurements at a scattering angle of 60° and in the energy range 1–14 eV for the ν3 (d-stretch) and ν4 (d-deformation) fundamental vibrational modes are reported. Finally, differential cross sections for all four fundamental modes (ν1, ν2, ν3, ν4) at the single electron energy of 7 eV are given. These vibrational excitation measurements, when coupled with the elastic angular distributions in the 5–8 eV energy range, demonstrate the presence of a t2-symmetry shape resonance.

Elastic cross sections for electron collisions with molecules relevant to plasma processing

Absolute electron-impact cross sections for molecular targets, including their radicals, are important in developing plasma reactors and testing various plasma processing gases. Low-energy electron collision data for these gases are sparse and only the limited cross section data are available. In this report, elastic cross sections for electron-polyatomic molecule collisions are compiled and reviewed for 17 molecules relevant to plasma processing. Elastic cross sections are essential for the absolute scale conversion of inelastic cross sections, as well as for testing computational methods. Data are collected and reviewed for elastic differential, integral, and momentum transfer cross sections and, for each molecule, the recommended values of the cross section are presented. The literature has been surveyed through early 2010.

Single-exposure dual-energy chest images with computed radiography. Evaluation with simulated pulmonary nodules.

RATIONALE AND OBJECTIVES Dual-energy subtraction radiography using computed radiography (CR) can aid in the detection of pulmonary abnormalities such as nodules, but the subtracted image requires higher x-ray exposure than usual to reduce quantum mottle. To reduce quantum mottle without increasing x-ray exposure, a new dual-energy subtraction algorithm was investigated that included an edge-adaptive smoothing process and a subtraction process. The signal-to-noise ratio and the image quality of this new subtracted image was significantly superior to that of conventional subtracted images. METHODS Observer performance of the subtracted digital radiography in detecting simulated pulmonary nodules was compared with original CR images and conventional subtracted digital radiography of 50 patients. RESULTS A combination of an original CR image and a new subtracted CR image was significantly superior to a single original CR image or a combination of an original CR image and a conventional subtracted CR image (P < .01). DISCUSSION The single-exposure dual-energy subtraction method is superior to the conventional subtraction method in the detection of pulmonary nodules.

Cross sections for electron impact excitation of the C Π1 and D Σ1+ electronic states in N2O

Differential and integral cross sections for electron-impact excitation of the dipole-allowed C (1)Pi and D (1)Sigma(+) electronic states of nitrous oxide have been measured. The differential cross sections were determined by analysis of normalized energy-loss spectra obtained using a crossed-beam apparatus at six electron energies in the range 15-200 eV. Integral cross sections were subsequently derived from these data. The present work was undertaken in order to check both the validity of the only other comprehensive experimental study into these excitation processes [Marinkovic et al., J. Phys. B 32, 1949 (1998)] and to extend the energy range of those data. Agreement with the earlier data, particularly at the lower common energies, was typically found to be fair. In addition, the BEf-scaling approach [Kim, J. Chem. Phys. 126, 064305 (2007)] is used to calculate integral cross sections for the C (1)Pi and D (1)Sigma(+) states, from their respective thresholds to 5000 eV. In general, good agreement is found between the experimental integral cross sections and those calculated within the BEf-scaling paradigm, the only exception being at the lowest energies of this study. Finally, optical oscillator strengths, also determined as a part of the present investigations, were found to be in fair accordance with previous corresponding determinations.

Computerized detection of pulmonary nodules by single-exposure dual-energy computed radiography of the chest (part 1)

OBJECTIVE To clarify the usefulness of computerized detection of pulmonary nodules (PNs) in single-exposure dual-energy subtraction computed radiography (CR) images of the chest. METHODS AND MATERIAL Our scheme uses bone-subtracted CR (BS-CR) images, and consists of a contrast-adaptive filter for detection of the candidates for PNs and a vessel-enhancing filter for elimination of vessel opacities in the candidates for PNs. For the evaluation, 12 clinical cases with multiple PNs were used, and four radiologists participated in this study. RESULTS The detectability of our computer-aided diagnosis (CAD) was compared with detectabilities of radiologists. The mean true-positive (TP) number of four radiologists was 1.60+/-1.03, and that of the CAD was 1.83+/-1.34. There was no significant difference in the nodule detectabilities between the radiologists and CAD (P=0.18). However, the false-positive (FP) rate of the CAD was 9.42+/-2.54 per image, whereas the mean FP rate of the radiologists was 1.40+/-0.64 per image. CONCLUSION Computerized detection of PNs is considered to be useful in the determination of radiological diagnoses. However, reducing the number of FP findings remains an important problem to be solved.

Quantitative analysis of imaging performance for computed radiography systems

The computed radiography (CR) system consists of three processes: reading, image processing, and display. Image noise from the reading process consists of quantum noise and fixed noise. Quantum noise is dependent on exposure but fixed noise is independent of it. Quantum noise can be divided into light photon noise and x-ray photon noise. The former is inversely proportional to the light detection efficiency and the latter is independent of it. We separated the noise components of the Fuji computed radiography (FCR) 7000 system. At a spatial frequency of 1 cycle/mm, the ratio of x ray photon noise to light photon noise to fixed noise was about 8:1:1 at 1 mR(2.58 X 10-7 C/kg). In the new CR system (FCR9000), we decreased x-ray photon noise and fixed noise. As a result, the FCR9000 system yields DQE of approximately 1.4 times higher at a spatial frequency of 0.5 cycle/mm and approximately 1.2 times higher at 1.0 cycles/mm at 1 mR (2.58 X 10-7 C/kg).

Improvement of detection in computed radiography by new single-exposure dual-energy subtraction.

It is reported that the use of the dual-energy subtraction method enhances the abnormal shadow detection capability. However, because the subtracted image is significantly inferior to the original in signal-to-noise ratio (SNR), the x-ray dosage normally used for chest x-rays has not yielded subtracted images with adequate SNRs. Under these circumstances, we focus on the fact that there is a correlation between the noise contents of bone-and soft-tissue-subtracted images although there is no correlation between the signal that improves SNRs of subtraction images by reducing the noise only.

Integral cross sections for electron impact excitation of the 1Σ+u and 1Πu electronic states in CO2

We apply the method of Kim (2007 J. Chem. Phys. 126 064305) in order to derive integral cross sections for the 1 � + u and 1 � u states of CO2, from our corresponding earlier differential cross section measurements (Green et al 2002 J. Phys. B: At. Mol. Opt. Phys. 35 567). The energy range of this work is 20‐200 eV. In addition, the BEf -scaling approach is used to calculate integral cross sections for these same states, from their respective thresholds to 5000 eV. In general, good agreement is found between the experimental integral cross sections and those calculated within the BEf -scaling paradigm, over the entire common energy range. Finally, we employ our calculated integral cross sections to determine the electron energy transfer rates for these states, for a thermal electron energy distribution. Such transfer rates are in principle important for understanding the phenomena in atmospheres where CO2 is a dominant constituent, such as on Mars and Venus. (Some figures in this article are in colour only in the electronic version)