Y. Segal

Considerations in bond strength evaluation by ultrasonic guided waves

Acoustic wave propagation in a three‐layer waveguiding configuration is analyzed. Considering an adhesive layer as a waveguide structure, it is shown that the propagation of guided modes is affected by the bonding quality. A comprehensive study demonstrates the possibility of utilizing measurements on guided wave propagation to detect interfacial weakness between an adhesive and adherend.

Point spread functions due to neutron scattering in thermal neutron radiography of aluminum, iron, zircaloy and polyethelene objects

Abstract Recently, image restoration methods have penetrated to the nondestructive testing field. Statistical and averaging methods are not adequate for the extraction of thicknesses and dimensions. The present work deals with the calculation of the point spread function (PSF) in thermal neutron radiography. The contribution of the scattering of neutrons in the radiographed object is calculated using Monte Carlo computational methods. Calculations were performed for polyethylene, iron, zircaloy and aluminum. The results are based on the physical phenomena, therefore, a restoration operator based on it has to be preferred over a general statistical operator. However, one has to bear in mind that scattering is not the only contributor to the image blurring. A complete operator has to take into account the other phenomena as well.

Limitations in gap width measurements by X-ray radiography

Abstract The use of radiography as a quantitative tool for determining the width and depth of cracks is discussed. It is shown that in most cases the extraction of dimensional information from radiographs may lead to erroneous results. The effects of oblique geometry and a blurring line spread function are modelled. The calculated results are compared with experimental findings.

Resolving power of dynamic radiation gauges

The characteristic functions of dynamic gauges, based on nuclear or atomic radiation, were developed. These gauges are applied to the examination of material whose properties may vary continuously with time. The approach presented takes into consideration contributions to the uncertainty and blurring from various effects, such as radiation scattering, gauge geometry, and the systems time constant. The analysis is based on the concept of the line spread function obtained from the derivation of the response to a step change in the inspected property. The response and relative resolving functions were demonstrated for a rectangular change with a gamma-through transmission gauge. The procedure provides a systematic method of obtaining the optimal values for the design parameters of the radio gauge, such as radiation energy, source emission rate, detection efficiency, detector-sample distance, and measurement time. The time constant, for example, reveals a pronounced minimal value for large relative velocity. Due to the radiation scattering in the examined material, there is an advantage to large detector-material distance. The design values may differ considerably more for the dynamic gauge than for a static gauge, i.e., a gauge applied to samples whose properties do not vary during the measurement period.

Gamma transmission gauge for assay of integral water content in soil

Abstract A photon transmission gauge applied for integral water content measurement in a soil layer was analyzed. The gauge may be used as a control unit for automatic irrigation in a field, or as a scanner employed for establishing an irrigation policy. The characteristic functions of the gauge; response and relative resolving power were developed. The functions provide parameter study at the design stage and interpretational ability at the operational stage. The model led to a design which eliminates sensitivity to water distribution in the examined soil. It is shown that a resolving power of 2% was obtained for a 2.3 mCi 137 Cs source at 53 cm below surface, in measuring water content of 0.2 g water/cm 3 soil during 1000 s.

Interaction of a guided wave with a nonuniform adhesion bond

This paper presents theoretical considerations for the determination of the diffraction of ultrasonic guided waves propagating in a nonuniform elastic adhesive layer. The nonuniformity results from changes in the adhesion bond characteristics between the adhesive and the adherent layer. The bond strength is assumed to change both locally as well as periodically. The problem is solved by using the perturbation theory. The field of the reflected and transmitted waves is given in natural modes of the elastic waveguide layer. The theoretical model derived serves as a reference for extracting acoustic wave parameters. These parameters are correlated to adhesion strength.

Backscattering of 137Cs gamma rays by finite barriers

Abstract Angular differential number and energy albedo were measured at a scattering angle of 60° for narrow beam of 137Cs gamma rays normally incident on finite thickness scattering media of various atomic numbers. Measurements were made using a collimated 3 cm3 Ge(Li) detector with suitable electronics and a 400 channel pulse-height analyzer. The calculation of the energy spectrum of the scattered photons was carried out by using a response matrix with 51 energy intervals over the range 0·04−0·3 MeV.

Dual Gauging Utilizing Penetrating and Scattered Photon Fluxes

The scattered photon flux of primary photons in the energy ranges from 640 to 680 keV, from 340 to 360 keV, and from 200 to 220 keV was calculated by Monte Carlo methods. The results were computed for cylindrical geometry. A semi-empirical formula was fitted to the calculated values. To expand the usefulness of the response functions obtained, a composition characterization parameter phi was defined and used. A method for analyzing the errors associated with multiple gauging of composition and density has been developed. It is shown that a gamma-ray gauging technique using primary transmitted photons in conjunction with a scattered component represents a very powerful combination of assay methods.

Gap width measurements in fuel elements

Abstract The analysis of 11 neutron radiographs, five of pin CEP-E1 no. 4 and six of pin CEP-E1 no. 7 are presented. The dimensions of the gaps between adjacent pellets were determined by three methods: projection microscopy measurements, the derivative method and the convolution method. The errors associated with the gap width measurements were in some cases over 100%.

Radiogauge for adsorbate concentration in adsorbent bed

Abstract A photon transmission gauge employed for the measurement of adsorbate concentration in adsorbent bed and its uptake were analyzed. The gauges responses and uncertainties were derived. The relative resolving power functions of the gauge were used to obtain the optimal photon energy and source emission rate. The significance of other design parameters is also shown. As an example, a specific bed used in adsorption study of PbCl 2 on alumina, is presented. The mathematical procedure described may serve for the study of similar processes dealing, for example, with packed columns, fluidized beds or chromatography systems.