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To investigate the relationship between ultrasonic backscatter and trabecular microstructure, ultrasonic backscatter measurements were performed on cylindrical bovine cancellous bone samples in vitro. The backscatter signals from different specimen angles were obtained by rotating the specimen at various central frequencies. The backscatter signal varied a lot as the specimen angle changed. The main trabecular alignment (MTA) orientation was estimated by the maximum of signal energy and integrated reflection coefficient, or the minor axis of fitted ellipse for apparent integrated backscatter and the backscattered spectrum centroid frequency versus specimen angle. The degree of anisotropy (DA) was estimated by the eccentricity of the fitted ellipse with highly significant correlations. The MTA orientation and DA value estimation method proposed in this study is useful for ultrasonic cancellous bone assessment. [ABSTRACT FROM AUTHOR]

This article extends new materialist theorizing on the constructive role played by the physical stuff of the world. Specifically, it draws on Kenneth Burke's writings on recalcitrance to theorize the materialities of rhetorical invention. It takes X-rays as a case study in recalcitrance-driven invention, focusing on two particular applications, traditional medical X-rays, a pervasive category of contemporary technical communication, and backscatter X-ray airport security scans, a controversial and short-lived one. Its analysis shows how recalcitrance (1) is harnessed as means of technical invention and (2) is key to invention's bidirectionality, by which our material interventions, in turn, work upon us. [ABSTRACT FROM AUTHOR]

A great deal of interest concerns the study of vigilance performance, and trust in automation, due to their implications for public safety. This work provides an experimental resource for scholars in need of a vigilance style task. The dataset includes 150 X-ray images of luggage, and participants indicate whether or not they believe each image contains a dangerous item (simulating airport security screening). Using a sample of 991 adults recruited via MTurk, we normed these items in terms of difficulty. These stimuli can be used to study vigilance performance, trust in an automated decision aid, and other areas. [ABSTRACT FROM AUTHOR]

To achieve good quality of service level such as throughput, power control is of great importance to passive quadrature amplitude modulation (QAM) multisensor backscatter communication systems. First, we established the RF energy harvesting model and gave the energy condition. In order to minimize the interference of subcarriers and increase the spectral efficiency, then, the colocated passive QAM backscatter communication signal model is presented and the nonlinear optimization problems of power control are solved for passive QAM backscatter communication systems. Solutions include maximum and minimum access interval, the maximum and minimum duty cycle, and the minimal RF-harvested energy under the energy condition for node operating. Using the solutions above, the maximum throughput of passive QAM backscatter communication systems is analyzed and numerical calculation is made finally. Numerical calculation shows that the maximal throughput decreases with the consumed power and the number of sensors, and the maximum throughput is decreased quickly with the increase of the number of sensors. Especially, for a given consumed power of sensor, it can be seen that the throughput decreases with the duty cycle and the number of sensors has little effect on the throughput. [ABSTRACT FROM AUTHOR]

The Brillouin backscattered wave was examined in a short-length single-mode fiber at different ambient temperatures using a 1553-nm wavelength laser source. To obtain Brillouin scattering depending on the temperature change in a 95-m long single-mode fiber cable, the Brillouin optical time domain reectometry (BOTDR) technique was used. In this technique, a 1553 nm wavelength signal was sent from one side of the test fiber. The FC/APC connector was attached to the other end of the test fiber. The temperature parameters of the single-mode fiber cables of different brands and types can be obtained using Brillouin scattering. The Brillouin frequency shift is found 0.93 MHz/ ° C. Measured linear change demonstrated its use as the temperature sensor of Brillouin Scattering. [ABSTRACT FROM AUTHOR]

Changes in the bone mineral density distribution (BMDD), due to disease or drugs, can alter whole bone mechanical properties such as strength, stiffness and toughness. The methods currently available for assessing BMDD are destructive and two-dimensional. Micro-computed tomography (μCT) has been used extensively to quantify the three-dimensional geometry of bone and to measure the mean degree of mineralization, commonly called the tissue mineral density (TMD). The TMD measurement has been validated to ash density; however parameters describing the frequency distribution of TMD have not yet been validated. In the current study we tested the ability of μCT to estimate six BMDD parameters: mean, heterogeneity (assessed by the full-width-at-half-maximum (FWHM) and the coefficient of variation (CoV)), the upper and lower 5% cutoffs of the frequency distribution, and peak mineralization) in rat sized femoral cortical bone samples. We used backscatter scanning electron microscopy (bSEM) as the standard. Aluminum and hydroxyapatite phantoms were used to identify optimal scanner settings (70 kVp, and 57 μA, with a 1500 ms integration time). When using hydroxyapatite samples that spanned a broad range of mineralization levels, high correlations were found between μCT and bSEM for all BMDD parameters (R 2 ≥ 0.92, p < 0.010). When using cortical bone samples from rats and various species machined to mimic rat cortical bone geometry, significant correlations between μCT and bSEM were found for mean mineralization (R 2 = 0.65, p < 0.001), peak mineralization (R 2 = 0.61, p < 0.001) the lower 5% cutoff (R 2 = 0.62, p < 0.001) and the upper 5% cutoff (R 2 = 0.33, p = 0.021), but not for heterogeneity, measured by FWHM (R 2 = 0.05, p = 0.412) and CoV (R 2 = 0.04, p = 0.469). Thus, while mean mineralization and most parameters used to characterize the BMDD can be assessed with μCT in rat sized cortical bone samples, caution should be used when reporting the heterogeneity. [ABSTRACT FROM AUTHOR]

Based on security issues and regulations airports are provided with luggage cargo scanners. These scanners utilize ionizing radiation that in principle present health risks toward humans. The study aims to investigate the amount of backscatter produced by passenger luggage and cargo toward airport personnel who are located at different distances from the scanners. To approach our investigation a Thermo Electron Radeye-G probe was used to quantify the backscattered radiation measured in terms of dose-rate emitted from airport scanners, Measurements were taken at the entrance and exit positions of the X-ray tunnel at three different distances (0, 50, and 100 cm) for two different scanners; both scanners include shielding curtains that reduce scattered radiation. Correlation was demonstrated using the Pearson coefficient test. Measurements confirmed an inverse relationship between dose rate and distance. An estimated occupational accumulative dose of 0.88 mSv/y, and 2.04 mSv/y were obtained for personnel working in inspection of carry-on, and cargo, respectively. Findings confirm that the projected dose of security and engineering staff are being well within dose limits. [ABSTRACT FROM AUTHOR]

Purpose In this investigation, we sought to characterize X-ray beam qualities and quantitate percent depth dose (PDD) curves for fluoroscopic X-ray beams incorporating added copper (Cu) filtration, such as those commonly used in fluoroscopically guided interventions (FGI). The intended application of this research is for dosimetry in soft tissue from FGI procedures using these data. Methods All measurements in this study were acquired on a Siemens (Erlangen, Germany) Artis zeego fluoroscope. X-ray beam characteristics of first half-value layer (HVL), second HVL, homogeneity coefficients (HCs), backscatter factors (BSFs) and kVp accuracy and precision were determined to characterize the X-ray beams used for the PDD measurements. A scanning water tank was used to measure PDD curves for 60, 80, 100, and 120 kVp X-ray beams with Cu filtration thicknesses of 0.0, 0.1, 0.3, 0.6, and 0.9 mm at 11 cm, 22 cm, and 42 cm nominal fields of view, in water depths of 0 to 150 mm. Results X-ray beam characteristics of first HVLs and HCs differed from previous published research of fluoroscopic X-ray beam qualities without Cu filtration. PDDs for 60, 80, 100, and 120 kVp with 0 mm of Cu filtration were comparable to previous published research, accounting for differences in fluoroscopes, geometric orientation, type of ionization chamber, X-ray beam quality, and the water tank used for data collection. PDDs and X-ray beam characteristics for beam qualities with Cu filtration are presented, which have not been previously reported. Conclusions The data sets of X-ray beam characteristics and PDDs presented in this study can be used to estimate organ or soft tissue doses at depth involving similar beam qualities or to compare with mathematical models. [ABSTRACT FROM AUTHOR]

SAR (Synthetic Aperture Radar) imaging plays a central role in Remote Sensing due to, among other important features, its ability to provide high-resolution, day-and-night and almost weather-independent images. SAR images are affected from a granular contamination, speckle, that can be described by a multiplicative model. Many despeckling techniques have been proposed in the literature, as well as measures of the quality of the results they provide. Assuming the multiplicative model, the observed image Z is the product of two independent fields: the backscatter X and the speckle Y. The result of any speckle filter is bX, an estimator of the backscatter X, based solely on the observed data Z. An ideal estimator would be the one for which the ratio of the observed image to the filtered one I = Z/bX is only speckle: a collection of independent identically distributed samples from Gamma variates. We, then, assess the quality of a filter by the closeness of I to the hypothesis that it is adherent to the statistical properties of pure speckle. We analyze filters through the ratio image they produce with regards to first- and second-order statistics: the former check marginal properties, while the latter verifies lack of structure. A new quantitative image-quality index is then defined, and applied to state-of-the-art despeckling filters. This new measure provides consistent results with commonly used quality measures (equivalent number of looks, PSNR, MSSIM, b edge correlation, and preservation of the mean), and ranks the filters results also in agreement with their visual analysis. We conclude our study showing that the proposed measure can be successfully used to optimize the (often many) parameters that define a speckle filter. [ABSTRACT FROM AUTHOR]

Advanced imaging technologies (AIT) are being developed for passenger airline transportation. They are designed to provide enhanced security benefits by identifying objects on passengers that would not be detected by methodologies now used for routine surveillance. X-ray backscatter imaging is one AIT system being considered. Since this technology is based on scanning passengers with ionizing radiation, concern has been raised relating to the health risks associated with these exposures. Recommendations for standards of radiation safety have been proposed by the American National Standards Institute published in ANSI/HPS N43.17-2009. A Monte Carlo based methodology for estimating organ doses received from an X-ray backscatter AIT system is presented. Radiological properties of a reference scanner including beam intensity, geometry and energy spectra were modeled based on previous studies and physical measurements. These parameters were incorporated into a Monte Carlo source subroutine and validated with comparison of simulated versus measured data. One extension of this study was to calculate organ and effective dose on a wide range of potential passengers. Computational phantoms with realistic morphologies were used including adults of 5th, 25th, 50th, 75th and 95th percentile weight, children of 5th, 50th and 95th percentile weight, and the developing fetus of 15, 25, and 38 weeks after conception. Additional sensitivity studies were performed to evaluate effects of passenger positioning within the scanner, energy spectrum and beam geometry, as well as failure mode analyses. Results for routine operations yielded a maximum effective dose to the adult and pediatric passengers of 15 and 25 nSv per screen, respectively. The developing fetus received a maximum organ dose and whole body dose of 16 nGy and 8.5 nGy per screen, respectively. The sensitivity analyses indicated that variations in positioning, energy spectra, and beam geometry yielded a range of effective doses per screen that were an order of magnitude below the ANSI recommendation. [ABSTRACT FROM AUTHOR]

Quantitative ultrasound (QUS) methods based on the backscatter coefficient (BSC) are typically model-based. The BSC is estimated from experiments and is fit to a model. The fit parameters are often termed QUS estimates and are used to characterize the scattering properties of the tissue under investigation. Nevertheless, for physical interpretation of QUS estimates to be accurate, the scattering model chosen must also be accurate. The goal of this work was to investigate the use of the structure factor model (SFM) to take into account coherent scattering from high volume fractions of scatterers. The study focuses on comparing the performance of two sparse models (fluid-filled sphere and Gaussian) and one concentrated model (SFM) to estimate QUS parameters from simulations and cell pellet biophantoms with a range of scatterer volume fractions. Results demonstrated the superiority of the SFM for all investigated volume fractions (i.e., from 0.006 to 0.30). In particular, the sparse models underestimated scatterer size and overestimated acoustic concentration when the volume fraction was greater than 0.12. In addition, the SFM has the ability to provide the volume fraction and the relative impedance contrast (instead of only the acoustic concentration provided by the sparse models), which could have a great benefit for tissue characterization. This study demonstrates that the SFM could prove to be an invaluable tool for QUS and could help to more accurately characterize tissue from ultrasound measurements. [ABSTRACT FROM PUBLISHER]

While recent years have seen considerable progress in image denoising, the leading techniques have been developed for digital photographs or other images that can have very different characteristics than those encountered in X-ray applications. In particular here we examine X-ray backscatter (XBS) images collected by airport security systems, where images are piecewise smooth and edge information is typically more correlated with objects while texture is dominated by statistical noise in the detected signal. In this paper, we show how multiple estimates for a denoised XBS image can be combined using a variational approach, giving a solution that enhances edge contrast by trading off gradient penalties against data fidelity terms. We demonstrate the approach by combining several estimates made using the non-local means (NLM) algorithm, a widely used patch-based denoising method. The resulting improvements hold the potential for improving automated analysis of low-SNR X-ray imagery and can be applied in other applications where edge information is of interest. [ABSTRACT FROM AUTHOR]

Backscatter differential phase δ within the melting layer has been identified as a reliably measurable but still underutilized polarimetric variable. Polarimetric radar observations at X band in Germany and S band in the United States are presented that show maximal observed δ of 8.5° at X band but up to 70° at S band. Dual-frequency observations at X and C band in Germany and dual-frequency observations at C and S band in the United States are compared to explore the regional frequency dependencies of the δ signature. Theoretical simulations based on usual assumptions about the microphysical composition of the melting layer cannot reproduce the observed large values of δ at the lower-frequency bands and also underestimate the enhancements in differential reflectivity ZDR and reductions in the cross-correlation coefficient ρ hυ. Simulations using a two-layer T-matrix code and a simple model for the representation of accretion can, however, explain the pronounced δ signatures at S and C bands in conjunction with small δ at X band. The authors conclude that the δ signature bears information about microphysical accretion and aggregation processes in the melting layer and the degree of riming of the snowflakes aloft. [ABSTRACT FROM AUTHOR]

The backward second harmonic generation (SHG) in mouse tissues is studied with a confocal multiphoton microscopy system. The total backward collected SHG (B-SHG) consists of the backward generated SHG and the backward-scattered forward-generated SHG (BS-SHG), which can be modeled by a Gaussian and a uniform distribution, respectively, at the confocal pinhole plane. By varying the pinhole size with a series of collection fibers, the proportion of the BS-SHG to the B-SHG and the proportion of BS-SHG to the forward generated SHG can be obtained. The approach is first validated by Monte Carlo simulation. It is then applied to two types of mouse tissues: mouse tail tendon and Achilles tendon. It is found that the BS-SHG contributes less to the B-SHG for the tail tendon than Achilles tendon with thicknesses of ~300 µm. With the thickness of the Achilles tendon tissue increased to 1000 µm but the focal plane kept at the same depth, as high as ~10% of the total forward SHG is backscattered and collected. The results indicate that BS-SHG may not be the major source of B-SHG in the tail tendon, but it may be the major source in the Achilles tendon. These methods and results provide a noninvasive method and supporting information for investigating the generation mechanism of SHG and help with optimizing backward SHG microscopy and spectroscopy measurements. [ABSTRACT FROM AUTHOR]

The article discusses the issue related to full body scanning at airports and privacy violation. It mentions technologies for full body scanning, which includes millimeter wave and backscatter to detect external objects attached to the body. It mentions that current judicial and scholarly discussions, as of November 2013, assume that use of body scanners violates privacy.

Abstract: The objective of this study was to assess the value of ultrasonic backscatter signals and the backscatter coefficient (BSC) in the analysis of bone status in neonates and to analyze the relationships between the BSC and gestational age, birth weight, length, head circumference and gender. A total of 122 neonates participated in the study, including 83 premature infants and 39 full-term infants. Their BSCs were measured by ultrasound after birth. The results revealed a significant correlation between the BSC and gestational age (R = 0.47, p < 0.001), birth weight (R = 0.47, p < 0.0001) and length at birth (R = 0.43, p < 0.001) at a frequency of 5.0 MHz. This study suggests that the use of ultrasonic backscattering and the BSC is feasible for assessment of the bone status of neonates. [Copyright &y& Elsevier]

The author reflects on the issue of police use of mobilized backscatter technology or ZBVs on automobiles for unreasonable searches and seizures. It describes the fourth amendment which guarantees people's security against unreasonable searches and warrants. It discusses the process of backscatter technology and its use to bolster national security at the airport and along the border. It suggests public awareness related to the use of ZBVs.

Multi-Beam Echo Sounders are often used for classification of seabed type, as there exists a strong link between sonar backscatter and sediment characteristics of the seabed. Most of the methods for seabed classification from MBES backscatter create a highly-dimensional data set of statistical features and then use a combination of Principal Component Analysis and k-means clustering to derive classes. This procedure can be time consuming for contemporary large MBES data sets with millions of records. This paper examines the complexity of one of most commonly used classification approaches and suggests an alternative where feature data set is optimised in terms of dimensionality using computational and visual data mining. Both the original and the optimised method are tested on an MBES backscatter data set and validated against ground truth. The study found that the optimised method improves accuracy of classification and reduced complexity of processing. This is an encouraging result, which shows that bringing together methods from acoustic classification, visual data mining, spatial analysis and remote sensing can support the unprecedented increases in data volumes collected by contemporary acoustic sensors. [ABSTRACT FROM AUTHOR]

Most of the existing backscatter factors for the dosimetry of clinical diagnostic x-ray beams have been calculated for 15 cm thick phantoms; these data are used for skin dose determinations which in general ignore the influence of phantom material and thickness. The former should strictly be required whenever dosimetry measurements are made on phantom materials different from those used for the backscatter factor calculations. The phantom or patient thickness is of special importance when skin dose determinations are made for infants or paediatric patients. In this work, the recently published formalism for reference dosimetry and comprehensive database of backscatter factors for clinical beams and water phantoms have been extended using two correction factors which account for phantom material and thickness. These were determined with simulations using the PENELOPE Monte Carlo system, for PMMA to analyse the influence of the phantom material relative to water, and for a broad range of thicknesses of water and PMMA to investigate the role of this parameter in patient dose estimates. The material correction factor was found to be in the range 3-10%, depending on the field size and the HVL. The thickness correction factor was in the range 2-12% for a 5 cm thick phantom and square field sizes between 5 and 35 cm, reaching a plateau of about ±1% for thicknesses beyond 13 cm. Expressions in the form of surface fits over the calculated data are provided which streamline the determination of backscatter factors for arbitrary thicknesses and phantom materials, as well as field sizes. Results demonstrate the inadequacy of using conventional backscatter factors (calculated for 15 cm thick phantoms) without correction factors that take into account the phantom material and its thickness. [ABSTRACT FROM AUTHOR]

This article examines whole body imaging technologies in contemporary airport security contexts. Situating these technologies more broadly within histories of aviation and theories of mobility, we examine how discourses of technological efficiency and freedom of movement work to obscure the ever-expanding surveillance practices of the state. While whole body imaging technologies are marketed as objective and neutral, we investigate how they draw upon, and reinscribe, existing social inequalities. Using Angela Davis' theory of the strip search as a form of state-sponsored sexual assault, we assess contemporary uses of whole body scanners by the state and allied corporate interests not only as alleged privacy violations, but also as potential acts of violence by the state on marginalized subjects. By demonstrating the disproportionate impact of whole body imaging technologies on particular communities, including the intersections of transgendered travelers, travelers with disabilities, and racialized and religious communities, we show that whole body imaging technologies continue and expand upon the tradition of stratified mobilities that has always been a component of air travel. We also argue that the alleged non-invasiveness and efficiency of the “virtual strip search” marks a troubling trend in which the state consolidates power through increasingly concealed surveillance practices. [ABSTRACT FROM PUBLISHER]

The article looks at the issues concerning Rapiscan Systems Inc.'s backscatter full-body X-ray security screening system in airports in the U.S. It examines the standard radiation dose limits for people screening set by radiation safety organizations and the concerns raised by scientists regarding the potential health risks from screening with a general-use X-ray scanner. It also notes the contestation between the biological effects of radiation and the safety of full-body X-ray scanners.

The article discusses results of a study that examines the negative effects of radiation from the full-body x-ray scans. It debunks the misconception that radiation that is emitted by backscatter x-ray scanners increases cancer risks. An overview of full-body scanners installed in various U.S. airports by order of the Transportation Security Administration (TSA) is given. It discusses common sources of exposure to ionizing radiation, including industry and medicine. It concludes that there is no risk from scanner radiation.

The article discusses if the airport scanners using the "Backscatter" and "Millimeter Wave" technologies which produce body images of passengers constitute an invasion of privacy and violate the Fourth Amendment which protects persons from unreasonable searches. Presented are various decided cases in which legitimate government interests and risk to lives and property justified warrantless searches. It is believed that the scanners will be deemed constitutional in the face of terrorist threats.

The article focuses on the aspects of the use of the U.S. Customs and Border Protection (CBP) of the backscatter technology (BT) at borders. It states that the CBP uses BT in borders with drive-through vehicle inspection systems. It says that CBP also uses BT-equipped vehicles to inspect contraband and security threats. Moreover, BT under the Fourth Amendment is also discussed.

Objectives: This study sought to determine the accuracy of 3-dimensional, quantitative measurements of coronary plaque by computed tomography angiography (CTA) against intravascular ultrasound with radiofrequency backscatter analysis (IVUS/VH). Background: Quantitative, 3-dimensional coronary CTA plaque measurements have not been validated against IVUS/VH. Methods: Sixty patients in a prospective study underwent coronary X-ray angiography, IVUS/VH, and coronary CTA. Plaque geometry and composition was quantified after spatial coregistration on segmental and slice-by-slice bases. Correlation, mean difference, and limits of agreement were determined. Results: There was significant correlation for all pre-specified parameters by segmental and slice-by-slice analyses (r = 0.41 to 0.84; all p < 0.001). On a segmental basis, CTA underestimated minimal lumen diameter by 21% and overestimated diameter stenosis by 39%. Minimal lumen area was overestimated on CTA by 27% but area stenosis was only underestimated by 5%. Mean difference in noncalcified plaque volume and percent and calcified plaque volume and percent were 38%, −22%, 104%, and 64%. On a slice-by-slice basis, lumen, vessel, noncalcified-, and calcified-plaque areas were overestimated on CTA by 22%, 19%, 44%, and 88%. There was significant correlation for percentage of atheroma volume (0.52 vs. 0.54; r = 0.51; p < 0.001). Compositional analysis suggested that high-density noncalcified plaque on CTA best correlated with fibrous tissue and low-density noncalcified plaque correlated with necrotic core plus fibrofatty tissue by IVUS/VH. Conclusions: This is the first validation that standardized, 3-dimensional, quantitative measurements of coronary plaque correlate with IVUS/VH. Mean differences are small, whereas limits of agreement are wide. Low-density noncalcified plaque correlates with necrotic core plus fibrofatty tissue on IVUS/VH. [Copyright &y& Elsevier]

The article discusses the Fourth Amendment to the U.S. Constitution that challenges the Transportation Security Administration's decision to install body scanners and pat-downs at the airports in the U.S. which were put in place after the 2001 terrorist attacks. It mentions rising cases of dissatisfaction over the Advanced Imaging Technology and pat-downs. It highlights that passenger-neutral scanning should take place to secure passenger privacy and to provide highest level of security.

Objective: The goal of this study was to evaluate the radiation received by the practitioner when performing percutaneous vertebroplasty guided by CT and fluoroscopy for specific anatomical sites: orbits, hands, ankles, and thorax (under lead-lined apron).Materials and Methods: Twenty-four vertebroplasties were performed on 18 patients.Results: The anatomical site that was most exposed to radiation was the right hand (0.37 mSv on average). This study demonstrates a significant correlation between the irradiation dose and fluoroscopy duration, reflecting both the quantity of primary-beam radiation and backscattered radiation. The right hand (P = 0.03), left hand (P = 0.02), and the left orbit (P < 0.0001) are the anatomical zones that are the most affected by the combination of these two types of radiation, with cumulative irradiation doses of 0.45, 0.2, and 0.14 mSv, respectively. There was a significant correlation between the patient weight and radiation of the left hand (P = 0.03), the left orbit (P = 0.03), and the thorax (P = 0.02), confirming the major influence of backscattered radiation.Conclusions: The most irradiated anatomical sites limiting the number of interventions are the left orbit and the right hand. [ABSTRACT FROM AUTHOR]

Abstract: Compton profiles for the elements C, N and O, which are important both in medical science and security screening, are represented here as weighted sums of three Gaussians. Simple scaling relationships describe the dependence on atomic number (Z) of the amplitudes and standard deviations of the component Gaussians, which are identified with the Compton profiles of the 1s, 2s and 2p orbitals. This representation of the Compton profile agrees with tabulated values for C, N and O to a rms deviation of the order of 1% of the mean profile amplitude over the momentum range 0≤q≤4, where q is expressed in units of the hydrogen ground state momentum. This representation allows a “mean atomic number” for mixtures and compounds dominated by second period elements to be assigned on the basis of experimental measurements of the Doppler broadening of back-scattered X-ray K characteristic lines. Processed spectra of water and ethanol from a Compton spectrometer equipped with a room-temperature semiconductor detector are compared with the Compton profiles synthesized as suggested here, and a satisfactory agreement between the measured and theoretical mean atomic numbers and the profile shapes is found. [Copyright &y& Elsevier]

Doped Si films were deposited by controlled coevaporation or Ga( p) of Sb(n) and Si at room temperature on an atomically clean Si substrate in ultrahigh vacuum. The amorphous films were then crystallized at 230 Å/min by heating the substrate to 575 °C. Good crystal quality results, judged by Rutherford backscattering and transmission electron microscopy. Advantages over normal evaporative doping during molecular beam epitaxial growth at ∼750 °C include (1) unity sticking coefficient of the dopant, (2) no smearing or carry-over of the dopant, (3) better mobility (bulk values for n or p∼1018 cm-3), and (4) higher doping levels (>8×1018 cm-3 for Ga, 8×1019 cm-3 for Sb). [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to an article about the uncertainties concerning the effective dosage per screening from the Compton backscattering screening system along with the authors' response to the correspondence.