Neodymium neutron cross section measurements

Neutron capture and transmission measurements were performed by the time-of-flight technique at the Rensselaer Polytechnic Institute LINAC using metallic neodymium samples. The capture measurements were made at the 25-m-long flight station with a 16-segment NaI(Tl) multiplicity detector, and the transmission measurements were performed at 15 and 25 m flight stations with a 6Li glass scintillation detector. After the data were collected and reduced, resonance parameters were determined by simultaneously fitting the transmission and capture data with the multilevel R-matrix Bayesian code SAMMY. The resonance parameters for all naturally occurring neodymium isotopes lie within the energy range of 1.0-500 eV. The resulting resonance parameters were used to calculate the capture resonance integral with this energy region and were compared to calculations obtained when using the resonance parameters from ENDF-B/VI. The RPI parameters gave a resonance integral value of 32 +/- 0.5 b that is approximately 7% lower than that obtained with the ENDF-B/VI parameters. The current measurements significantly reduce the statistical uncertainties on the resonance parameters when compared with previously published parameters.     

A method for determining relative ionization gauge sensitivities using cross section measurements

The authors propose an original molecular collision method for the determination of vacuum ionization gauge sensitivity coefficients. The knowledge of scattering gas pressure p is necessary to determine absolute scattering cross sections σ, using molecular beam techniques. Inversely the knowledge of σ allows the absolute measurement of the pressure. The cross section σ is first measured using a beam of molecules A and a target gas B for which the gauge calibration is known. By interchanging A and B the gauge can be calibrated for the gas A. Theoretical conditions of application of this method are discussed, the principal point being that the beam has to be effusive. Sensitivity coefficients have been determined for several gases.     

Novel transmission detector used for total cross section measurements

A new apparatus for total cross section measurements was developed and tested at Saturne II, Sacalay. The transmission ratios are determined using a ring-counter system coded in the Gray code, involving an exclusive four-fold coincidence between 4 counters among 8. Beam rate effects are suppressed by an electronic device which permits reaching an accuracy of better than 10^?4 in any transmission ratio. The apparatus was first used at SIN for the measurements of the total polarized proton-proton cross section difference Δσ_L and of the spin correlation parameter A_00kk in pp → pp and pp → dπ⁺ reactions, and then at Saturne II for Δσ_γ and Δσ_L measurements in p-p scattering.     

Relative measurements of stopping cross section factors by back-scattering

A procedure for evaluating relative stopping cross section factors from the ratios of two heights in a single back-scattering spectrum is described. The method, which requires a two-layered target, is used to test the stopping cross sections of 1–2 MeV⁴He⁺ ions incident on Au, Ag, Cu, Si and Al. The ratios of the heights of Au, Ag and Cu are consistent with published stopping cross section data. The Au-Al height ratio is within the errors quoted for the Au and Al stopping cross section measurements. The Al-Si height ratio differs significantly from the expected value. It is also shown that the height ratio changes slightly as a function of the thickness of the surface layer.     

Topography characterization of a deep grating using near-field imaging

Using near-field optical microscopy at the wavelength of 633 nm, we image light intensity distributions at several distances above an approximately 2-microm-deep and a 1-microm-period glass grating illuminated from below under the condition of total internal reflection. The intensity distributions are numerically modeled, and an inversion procedure based on a least-squares-fit optimization is employed to extract the grating geometry from the optical images.     

Neutron cross section measurements at ORELA for improved nuclear data and their application

To support the Nuclear Criticality Safety Program, the Oak Ridge Electron Linear Accelerator (ORELA) has been used to measure the total and capture neutron cross sections of several nuclides in the energy range from 100 eV to -600 keV. Concerns about the use of existing cross section data in nuclear criticality calculations have been a prime motivator for the new cross-section measurements. Our new capture cross sections of aluminium, silicon, chlorine, fluorine and potassium in the energy range from 100 eV to 600 keV are substantially different from the cross sections in evaluated nuclear data files of ENDF/B-VI and JENDL-3.2.     

Error estimates in coordinate measurements of the cross section parameters of cylindrical surfaces

A simulation method and the results of simulating the errors in coordinate measurements of the cross section parameters of cylindrical surfaces are discussed. Data are presented from experimental studies that confirm the simulations.     

一种有源微波近场成像系统

针对早期乳腺癌检测等近场目标的探测成像,设计了一种基于2.45GHz连续波信号的微波近场成像实验系统,主要由硬件电路和成像算法组成.系统电路用小体积、高性能和低成本的射频微波集成芯片实现,大大缩小了系统的体积并降低了成本,电路由天线模块、收发模块和数据采集控制模块构成.成像算法采用有限元微波共焦算法,完成对被测区域日标的探测成像.     

Theory of near-field magneto-optical imaging

Scanning near-field optical microscopy has been recently applied to the imaging of magnetic samples. It was shown experimentally that an apertureless microscope suffers a substantial loss of resolution when used for magneto-optical imaging compared with that for conventional imaging. No such change is observed for aperture microscopes. We explain this observation by developing a model for the imaging process that incorporates the response of the probe. We calculate real observable properties such as the rotation of polarization at the detector or the circular dichroism signal and thus simulate magneto-optical images of a domain structure in cobalt for both aperture and apertureless microscopes.     

Utilization of X-ray spectrometry for cross section ratio measurements of 14 MeV neutron reactions

X-ray spectrometry by means of a hyperpure Ge detector has been used in the measurement by the activation technique of some cross section ratios. The method and calculations are given in detail for the following reactions ¹¹⁵In(n, 2n) ^114m.gln; ¹¹³In(n, 2n) ^112m.gln; ¹¹⁵ln(n, n′) ^115mln and ¹¹³ln(n, n′) ^113mln. The much better known gamma spectrometry has been parallelly used and the results of both methods were compared. Other cross section ratios were measured for the reactions ¹⁰⁷Ag(n, 2n) ^106m.gAg and ¹⁹⁷Au(n, 2n) ^196m.gAu.     

Radar imaging

Radar systems combining coherent signals with frequency and angular diversity offer the possibility of synthesizing images of complex objects with spatial resolution of a few wavelengths. The availability of high-quality microwave sources and components, high-speed digital computers, and efficient signal-processing algorithms allows radar imaging to be implemented in laboratory environments using commercially-available equipment. The paper summarizes fundamental issues by addressing conceptual and practical limits of radar imaging and presents examples obtained from results of measurements in a laboratory environment. Implementation details of sophisticated operational imaging radars are not covered.©1993 John Wiley & Sons Inc     

Defect imaging and characterization in composite structures using near-field microwave nondestructive testing techniques

The use of composites as building materials in different industries, aircrafts, cars, ships, buildings, bridges, etc., is rapidly growing. Composite structures become weaker than expected due to the presence of an inhomogeneity or a disbond within their layers. The presence of these defects can cause catastrophic results unless their presence is detected and their effects are assessed. Microwave nondestructive imaging techniques have several unique attributes which make them attractive for inspecting composite structures. Near-field microwave imaging is based on transmitting a wave into a dielectric structure, which is located in the near-field of a sensor, and using a signal proportional to the magnitude or phase of the transmitted or reflected wave to create a two or three dimensional image of the structure under investigation. To analyze the features and properties of an experimental image, it is important to form and optimize the image theoretically before application. In this paper, we will present the image formation model and illustrate its potential on optimizing the detection capability of subsurface inclusions in multi-layered composites.     

A spectrometer for double-differential neutron-emission cross section measurements in the energy range 1.6 to 16 MeV

A neutron spectrometer for the measurement of double-differential neutron-emission cross sections has been set up.An electron linac (GELINA) is used as a pulsed white neutron source. The energy of the incident neutrons is determined by the time-of-flight method. The secondary neutron spectra are determined by unfolding the pulse-height distributions observed in eight NE213-scintillators surrounding the sample.The measured spectra are normalised to the shape of the incident neutron flux measured with a ²³⁵U-fission chamber, and afterwards converted to absolute cross sections using as standard the carbon differential elastic scattering cross section below 2 MeV.     

Possibility of using the “Groza” aircraft radar in radio-meteorological measurements

The possibility of constructing a ground-based radio-meteorological system using the “Groza” aircraft radar is considered. The results of investigations of the short-term and long-term stability of the main parameters of the transmitter are presented. Recommendations are made on increasing the accuracy of radar reflectivity measurements. Translated from Izmeritel'naya Tekhnika, No. 2, pp. 52–54, February, 1996.     

Interference effect in apertureless near-field fluorescence imaging

Apertureless scanning near-field optical microscopy has been used to image fluorescent latex spheres with a resolution of a few tens of nanometers and good signal-to-noise ratio. The near-field fluorescence images reveal optical interference with several highly contrasted fringes located around the spheres. The origin of the interference is discussed in detail, and models are used to explain their formation. Spatial coherence is also discussed.     

Biological imaging with a near-field optical setup

Noncontact scanning near-field optical microscope (SNOM) systems can be used to optically resolve samples in atmospheric conditions at theoretical resolutions comparable to those of transmission electron microscope and atomic force microscope systems. SNOM systems are also increasingly used to image biological samples. In this study we custom built a SNOM system with the aim of further demonstrating the potential applications of near-field optical examination of biological material. In this study we were able to image both fixed whole-cell samples in air and liquid environments and live whole-cell samples in liquids. The images acquired were of a relatively low resolution, but this work has shown that SNOM systems can be used to monitor the dynamics of living cells at subnanometric resolutions in the z axis and for fluorescent imaging of whole cells in a liquid medium.     

Optical near-field Raman imaging with subdiffraction resolution

We report optical near-field Raman imaging with subdiffraction resolution (approximately 120 nm) without field enhancement effects. Chemical discrimination on tetracyanoquinodimethane organic thin films showing localized salt complexes is accomplished by detailed Raman maps. Acquisition times that are much shorter than previously reported are due to the high Raman efficiency of the materials and to careful collection and detection of the optical signals in our near-field Raman spectrometer.     

Phase aberration correction using near-field signal redundancy. I. Principles [Ultrasound medical imaging

The signal redundancy principle in the near field is analyzed quantitatively. It is found that common midpoint signals are not identical (or redundant) for echoes coming from arbitrary target distributions in the near field. A dynamic near-field correction is proposed to reduce the difference between common midpoint signals for echoes coming from the region of interest. When phase aberrations are present, it is shown that the dynamic correction can generally be done assuming no phase aberration, and the relative time-shift between common midpoint signals can be used to measure phase-aberration profiles. A phase-aberration correction algorithm based on that principle is proposed. In this algorithm, after common midpoint signals are collected they are dynamically corrected for near-field effects and cross-correlated with one another. In a related way, the phase errors are measured from peak positions of these cross-correlation functions. The phase-aberration profile across the array is derived from these measurements. The relationship between the errors in the derived phase aberration profile and the errors in the measured relative time-shift between common midpoint signals is derived. A method for treating the situation of different transmission and reception phase-aberration profiles is also proposed. This algorithm works for general target distributions, iteration is not required, and it can be used in other near-field, pulse-echo, imaging systems.     

Fluorescence lifetime imaging with near-field scanning optical microscopy

Near-field scanning optical microscopy (NSOM) is a high-resolution scanning probe technique capable of obtaining simultaneous optical and topographic images with spatial resolution of tens of nanometers. We have integrated time-correlated single-photon counting and NSOM to obtain images of fluorescence lifetimes with high spatial resolution. The technique can be used to measure either full fluorescence lifetime decays at individual spots with a spatial resolution of <100 nm or NSOM fluorescence images using fluorescence lifetime as a contrast mechanism. For imaging, a pulsed Ti:sapphire laser was used for sample excitation and fluorescent photons were time correlated and sorted into two time delay bins. The intensity in these bins can be used to estimate the fluorescence lifetime at each pixel in the image. The technique is demonstrated on thin films of poly(9,9'-dioctylfluorene) (PDOF). The fluorescence of PDOF is the results of both inter- and intrapolymer emitting species that can be easily distinguished in the time domain. Fluorescence lifetime imaging with near-field scanning optical microscopy demonstrates how photochemical degradation of the polymer leads to a quenching of short-delay intrachain emission and an increase in the long-delay photons associated with interpolymer emitting species. The images also show how intra- and interpolymer species are uniformly distributed in the films.