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A water calorimeter based on thermistor is developed in this paper, and for the correction of chemical thermal defects in the absolute measurement of absorbed dose to water from proton beam, the design of gas saturated ultrapure water system is completed. By filling the ultrapure water inside the calorimeter core with high purity gas to form saturation condition, the effect of radiation chemical reaction is minimized. And the irradiation reaction of O2 in the ultrapure water is fully occurred through pre-irradiation experiment after the encapsulation of the calorimeter core, so that the water environment inside reaches a stable state without heat loss,which successfully developed a stable zero heat loss water calorimeter and the influence of heat loss on the absolute measurement of absorbed dose to water is minimized, which provides an important basis for the subsequent absolute measurement of absorbed dose to water.

Absolute measurement has consistently been the primary focus in the development of precision linear and angular displacement measurements. The scheme design of binary zero position codes is an important factor for absolute measurement. Designing and optimizing high-bit zero position codes with over 100 bits face considerable challenges. Simultaneously, the working parameters of zero position codes [unit code width (b), distance (d), and yaw angle (α)] remarkably affect their post-installation performance, particularly in absolute positioning and limit code application in multi-degree-of-freedom measurement schemes. This study addresses these challenges by proposing a design method for zero position codes that considers diffraction based on generative adversarial networks and aims to explore a design with increased efficiency and accuracy as well as optimization for high-bit zero position codes. Additionally, the tolerance range of zero positioning performance for each working parameter is examined. By leveraging the adversarial network structure, this study generates the optimization of a 150-bit code and processes the tests of the zero position code by using simulation results. The following working parameter ranges for code design are recommended on the basis of theoretical and experimental results: b greater than 10 μm, d and α within 1000 μm and 3490 μrad, and avoidance of intervals with sharp changes in the full width at half maximum. The proposed code design and parameter optimization lay a solid foundation for research and engineering applications in absolute measurement field and have considerable potential for generalization and wide applicability. Highlights: This article is the first to use deep learning adversarial networks to generate absolute positioning binary codes; This article analyzes the influence of installation and unit code width parameters on positioning performance based on the principle of diffraction propagation and the positioning performance labels; This article establishes a comprehensive model (ZD-GAN) for generating absolute positioning codes through deep learning. The model can select the best absolute positioning code and provide guidance for the optimal installation and usage parameter range. [ABSTRACT FROM AUTHOR]

Efficient and ultra‐sensitive measurements of micro‐angle are critical technological requirements in various fields. Traditional measurement approaches have disadvantages in terms of accuracy and system complexity. Here, a micro‐angle measurement scheme based on the pixelated metasurface is reported. By utilizing the interaction between a C‐band optical frequency comb (OFC) laser source and the plasmonic metasurface, precise angle encoding is achieved, enabling each meta‐pixel within the pixelated metasurface to exhibit ultra‐sensitive responses to angular changes. Experimental results demonstrate a resolution as low as 2.8 μrad for angle sensing. Furthermore, by controlling the dimensions of the meta‐atom structural dimensions and designing specific combinations of meta‐pixels, the unique angle response of individual pixels is manipulated, effectively creating an angle barcode. This technique allows for highly efficient acquisition of angle information, and based on this, it demonstrates absolute angle measurement with an average error at 7 μrad. The robustness and stability of the proposed scheme is also evaluated. [ABSTRACT FROM AUTHOR]

BackgroundMost of domestic radiation therapy doses can only be traced back to air kerma of 60Co γ-ray at present in China. The uncertainty of directly tracing radiation therapy dose to absorbed dose to water is much smaller compared to tracing radiation therapy dose to air kerma, which must be converted to absorbed dose to water.PurposeThis study aims to solve the problem of traceability and transfer of 60Co γ-ray absorbed dose to water, as well as the problem that the dose measurement of radiotherapy cannot be directly traced through the absorbed dose to water, NIMTT (National Institute of Measurement and Testing Technology) has established an absolute measurement device of 60Co γ-ray absorbed dose to water.MethodsAn absolute measurement device of 60Co γ-ray absorbed dose to water was established by National Institute of Measurement and Testing Technology (NIMTT) using water calorimeterfor direct measurement of absorbed dose to water. The correction factors for water absorbed dose measurement were obtained by experimental and simulation methods. A comparison of laboratory reproducing results was made between NIMTT and NRC (National Research Council, Canada) using the method of transmitting standard to further verify the accuracy and consistency of the measurement of 60Co γ-ray absorbed dose to water. Two PTW ionization chambers were used as the transfer standard.ResultsThe reproduced results of two laboratories for absolute measurement of 60Co γ-ray absorbed dose to water are consistent within the relative standard uncertainty of 0.71%, and the normalized error value of En is -0.45.ConclusionsThe comparison results have verified that NIMTT laboratory has the ability of traceability and transmission of absorbed dose to water. The results of this study provide a reference for the absolute measurement of absorbed dose to water for 60Co γ-ray.

Due to the fact that there is no static reference point in ocean space, relative measurement sensors such as laser sensors cannot be applied to the measurement of ship motion. In order to collect the motion signal of a ship in the ocean more accurately, an absolute measurement method for the motion of a ship is proposed. Firstly, the acceleration signal in the heave direction of the ship is obtained by using an acceleration sensor; secondly, the time–frequency domain integration algorithm is used to avoid the problem of the quadratic trend item and the influence of the low-frequency signal, and the ship's heave displacement value is obtained by integration; finally, the displacement signal measured by the laser sensor and the integrated displacement signal of the acceleration sensor are compared with each other to verify the effectiveness of the absolute measurement of the heave displacement of the ship based on the acceleration sensor. At the same time, an angle sensor is used to measure the roll angle and pitch angle in the motion of the ship, form an absolute measurement system for the motion of the ship, and verify that the measurement points are arranged on the ship, which proves that the system can collect data from the ship in sea areas far from the coast. Motion signals are more advantageous. [ABSTRACT FROM AUTHOR]

An absolute-type four-degree-of-freedom (four-DOF) grating encoder that can simultaneously measure the three-axis pose (θx, θy, θz) and one-axis out-of-plane position (Z) of an object with high accuracy is demonstrated for the first time in this research. This grating encoder is composed of a stationary reading head and a movable grating reflector. A light beam from the reading head is projected onto the grating, and three diffracted beams (0th-, +1st-, and −1st-order) are generated, collimated, and received by three separate quadrant photodetectors (QPDs). The information of θx, θy, θz, and Z is coded into spot positions of these three diffracted beams on the QPDs. Thus, the modeling and decoupling algorithms were investigated, and an independent calculation of these four-DOF absolute positions was theoretically guaranteed. A prototype was then designed, constructed, and evaluated. Experimental results verified that the proposed grating encoder could achieve the absolute measurement of four-DOF θx, θy, θz, and Z with an accuracy of sub-arcseconds and sub-micrometers. To the best of our knowledge, the proposed encoder in this research is the first one to achieve absolute simultaneous measurements of four-DOF position and pose with a large measurement range. The success of this new grating encoder can benefit various multi-DOF positioning applications, especially for large-scale synthetic aperture optics (SAO), including stitching off-axis parabolic mirrors and pulse compression grating. [ABSTRACT FROM AUTHOR]

• The signal analysis step has been adopted in absolute surface error calibration for filtering out undesirable rotations angle. • The algorithm validation technology of the calibration was conducted using randomly generated surface profiles with power spectral density from experiment. • Quantitative analysis and calibration were performed to assess errors introduced by clamping stress, vibrations, airflow disturbances, angular errors and eccentricity. • The verification was conducted with standard mirror to prove the robustness, accuracy, and responsiveness. A novel absolute surface calibration method for interferometer testing based on power spectral density analysis has been proposed. The method involves obtaining the loss of signal at different frequencies as a function of various rotation angles by signal analysis to choose the rotation angle for calibration. A model is developed to evaluate the calibration method by creating random surface shapes based on the Power Spectral Density. Using this algorithm, the precision of the absolute testing method during the testing process exceeds 0.28 %. Error propagation during the experimental process, such as testing optic clamping, angular errors, eccentricity, vibrations and airflow disturbances, were calibrated. Ultimately, the absolute detection test results were verified using high-precision flat mirrors. The experimental result indicates an RMS of 4.275 nm, 4.263 nm, and 4.265 nm in different rotation angle, and the calibrated result shows an RMS of 4.880 nm. The shape of surface errors in the absolute test results and calibration results is consistent. [ABSTRACT FROM AUTHOR]

This article proposes an absolute-type inductive angle sensor for detecting the position of the YRT turntable bearing. The sensor comprises a multispeed incremental measuring unit and a single-speed absolute measuring unit sharing the same stator, rotor, and excitation circuit. The stator is composed of a ferromagnetic gear groove, two groups of excitation coils, and one group of induction coils arranged according to certain rules. The end cover of the YRT turntable bearing is machined as rotor and it rotated eccentrically relative to the rotation of the stator. A bridge circuit is used to acquire and process the sensor signal from the single-speed measuring unit. Compared with the traditional dual-channel absolute measurement, the proposed measurement method avoids the effects of different magnetic circuit disturbances on signal quality and measurement accuracy, and has more advantages in the volume and weight of the sensor. The structure and working principles of the sensor are presented in detail, the feasibility of sensing scheme is verified via simulation, and a sensor prototype is designed for the final experiment. Experimental results show that the accuracy of the sensor prototype is –0.06758° to 0.1203° before compensation and –0.001139° to 0.0015° after compensation in the range of [0°, 360°], respectively. [ABSTRACT FROM AUTHOR]

Due to the fact that there is no static reference point in ocean space, relative measurement sensors such as laser sensors cannot be applied to the measurement of ship motion. In order to collect the motion signal of a ship in the ocean more accurately, an absolute measurement method for the motion of a ship is proposed. Firstly, the acceleration signal in the heave direction of the ship is obtained by using an acceleration sensor; secondly, the time–frequency domain integration algorithm is used to avoid the problem of the quadratic trend item and the influence of the low-frequency signal, and the ship’s heave displacement value is obtained by integration; finally, the displacement signal measured by the laser sensor and the integrated displacement signal of the acceleration sensor are compared with each other to verify the effectiveness of the absolute measurement of the heave displacement of the ship based on the acceleration sensor. At the same time, an angle sensor is used to measure the roll angle and pitch angle in the motion of the ship, form an absolute measurement system for the motion of the ship, and verify that the measurement points are arranged on the ship, which proves that the system can collect data from the ship in sea areas far from the coast. Motion signals are more advantageous.

A design of a new, absolute sensor for measurement of an angular micro-displacement is presented. In this sensor deflections of incident laser beam generate changes of the constant of the interference fringes that are created by the double arm special interferometer. Fringe constant is determined using a CCD camera and proposed analysis algorithms. Sensor's operating principle and metrological properties are presented. Sensor was tested using reference interferometer. Obtained measurement uncertainty is equal to ±10 μrad in the multi-milliradian range. The concept of a two-sensor system for increasing twice the measuring range is presented. • New method for absolute measurement of angular micro-displacement is proposed. • Compact and low-cost, interference sensor with CCD camera was designed. • Metrological properties of the sensor were tested. • Obtained measurement uncertainty is ±10 microradians. [ABSTRACT FROM AUTHOR]

An absolute-type four-degree-of-freedom (four-DOF) grating encoder that can simultaneously measure the three-axis pose (θx, θy, θz) and one-axis out-of-plane position (Z) of an object with high accuracy is demonstrated for the first time in this research. This grating encoder is composed of a stationary reading head and a movable grating reflector. A light beam from the reading head is projected onto the grating, and three diffracted beams (0th-, +1st-, and −1st-order) are generated, collimated, and received by three separate quadrant photodetectors (QPDs). The information of θx, θy, θz, and Z is coded into spot positions of these three diffracted beams on the QPDs. Thus, the modeling and decoupling algorithms were investigated, and an independent calculation of these four-DOF absolute positions was theoretically guaranteed. A prototype was then designed, constructed, and evaluated. Experimental results verified that the proposed grating encoder could achieve the absolute measurement of four-DOF θx, θy, θz, and Z with an accuracy of sub-arcseconds and sub-micrometers. To the best of our knowledge, the proposed encoder in this research is the first one to achieve absolute simultaneous measurements of four-DOF position and pose with a large measurement range. The success of this new grating encoder can benefit various multi-DOF positioning applications, especially for large-scale synthetic aperture optics (SAO), including stitching off-axis parabolic mirrors and pulse compression grating.

• This study proposed a new surface reconstruction method for the absolute measurement of shift rotation. It linearizes the surface distribution function based on the Taylor expansion and constructs a linear system of equations between the surface distribution function and the differential wavefront. The coefficient matrix of this linear system of equations is sparse, so the absolute surface distribution can be obtained quickly and accurately. Compared with existing methods, it has the following advantages: • It can obtain a full-aperture surface distribution regardless of the translation ratio of the test mirror. Then it can significantly reduce the effect of tilt errors by increasing the translation ratio. • It requires only three measurements, and the test mirror can be rotated at almost any angle. • It can reduce the effect of the measurement noise. • It can reduce the effect of translation error, rotation error and eccentricity error. We propose a new surface reconstruction method for the absolute measurement of shift rotation that can obtain a full-aperture surface distribution. Our approach reduces the effect of tilt errors on surface reconstruction by increasing the translation ratio of the test mirror. This method requires the test mirror to be measured once in situ , after translation, and after rotation. Because the known measured wavefront is a nonlinear function of the absolute surface distribution, the function of the surface distribution is linearized by performing a Taylor expansion to achieve fast surface reconstruction. Finally, a linear system of equations is constructed to solve the absolute surface distribution. The coefficient matrix is sparse and can quickly and accurately reconstruct the absolute surface distribution. In the simulation, the root mean square error (RMSE) of the reconstructed surface distribution of the method discussed in this study can reach to 0.012nm. Moreover, our method can significantly reduce the effect of tilt errors compared with typical methods, thereby yielding a new, high-precision solution for absolute measurements in interferometry. [ABSTRACT FROM AUTHOR]

Accurate absolute measurement of existing lines is a task of fundamental importance to provide scientific basis for reconstruction. Traditional railway track survey methods in combination with classical geodetic surveying apparatus such as total stations cannot meet the requirements of surveying efficiency. Accurate, reliable and fast existing railway surveying applications call for an innovative method that can obtain high-precision, continuous and uniform railway track axis position in short time without interrupting the railway traffic. This paper provides an innovative solution to track axis surveying based on the integrated technique of global navigation satellite system (GNSS), inertial navigation system (INS) and odometer. GNSS/INS/odometer system does not depend on a high-precision track control network, which can operate in mobile surveying mode and significantly improve the measuring speed from 0.15 km/h to 5 km/h compared to conventional methods. Compared with satellite surveying methods, this solution for the measurement of existing line axis can obtain continuous and high-precision results in the absence of satellite signals. The results of field tests on the Zhengzhou-Xuzhou high-speed railway track show that the measurement errors are less than 0.6 cm and 1.1 cm in horizontal and vertical directions, respectively, and this measuring system is able to maintain high precision of 5 cm with a GNSS outage of 700 s, which can meet the accuracy requirements of China Specifications for Survey Engineering of High-speed Railway and serve visualization, assessment and design process of existing railways.

The paper presents a number of signal processing approaches for the spectral interferometric interrogation of extrinsic Fabry-Perot interferometers (EFPIs). The analysis of attainable microdisplacement resolution is performed and the analytical equations describing the dependence of resolution on parameters of the interrogation setup are derived. The efficiency of the proposed signal processing approaches and the validity of analytical derivations are supported by experiments. The proposed approaches allow the interrogation of up to four multiplexed sensors with attained resolution between 30 pm and 80 pm, up to three times improvement of microdisplacement resolution of a single sensor by means of using the reference interferometer and noise-compensating approach, and ability to register signals with frequencies up to 1 ​kHz in the case of 1 ​Hz spectrum acquisition rate. The proposed approaches can be used for various applications, including biomedical, industrial inspection, and others, amongst the microdisplacement measurement.

An approach for suppressing the abrupt half the wavelength errors in case of spectral interferometric interrogation of optical fiber sensors is proposed. The approach was derived from theoretical analysis of least-squares fitting of interference signal and is based on estimating the additional phase shift in the interference scheme. The approach was experimentally validated through estimation of the Gouy phase in an extrinsic Fabry-Perot interferometer and eliminating abrupt half the wavelength errors which took place when the interferometer was simultaneously heated and bent. The proposed signal processing approach can be applied for increasing sensing resolution and robustness of low-cost fiber-optic interferometric sensors, paving the way for their wide-spread use. [ABSTRACT FROM AUTHOR]

The paper exploits absolute distance measurement with traceability to the international system (SI) of units of length. In the present work, the diode pumped Nd:YVO4/KTP polarised green laser is used to measure a distance Δl between two positions without the need for a reference standard. To comprise a synthetic wavelength λs suitable to the range of the distance, the output wavelength generated by the frequency doubling is shifted by Δλ by controlling the injection current, and a set of shifted wavelengths are produced to form λs. The output signal is sent to the interferometer by an optical fibre after being enhanced with a speckle removal unit. The measurement starts by identifying the zero position where no shift in the interference fringes is observed during sweeping the wavelengths, while at the distance Δl a deviation in the interference pattern is observed. This deviation is analysed by Fourier transformation to extract the phase change Δθ and determine the distance value. To prove the reliability of absolute distance measuring interferometer, some measurements are made for various ranges with evaluation of both repeatability and uncertainty. The discussed technique can measure 100 mm with uncertainty ±16 µm. [ABSTRACT FROM AUTHOR]

The indication error, as a characteristic of the interferometer, can be obtained through verification and calibration, and the uncertainty during measurement represents the reliability of the indication error. This paper employed the modified absolute measurement method to gain the indication error. First, the improved absolute algorithm was derived. Then, the absolute measurements were conducted with a 150-mm-aperture Fizeau interferometer. The measured indication error conforms to the maximum allowable error of the interferometer. Finally, the measurement uncertainty evaluation was carried out based on the method to characterize the indication error's dependability, which was much less than one-third of the maximum allowable error. • Through the improved absolute measurement method, the indication error is 0.0034 wave (PV), which less than the maximum allowable error. • The improved absolute measurement method can obtain three absolute profiles simultaneously and ensure the repeatability of the measurement. • The expanded uncertainty is λ / 192 far less than one-third of the maximum allowable error, indicating the measurement repeatability is well controlled. [ABSTRACT FROM AUTHOR]

This re-examination of the earliest version of Maxwell's most important argument for the electromagnetic theory of light—the equality between the speed of wave propagation in the electromagnetic ether and the ratio of electrostatic to electromagnetic measures of electrical quantity—establishes unforeseen connections between Maxwell's theoretical electrical metrology and his mechanical theory of the electromagnetic field. Electrical metrology was not neutral with respect to field-theoretic versus action-at-a-distance conceptions of electro-magnetic interaction. Mutual accommodation between these conceptions was reached by Maxwell on the British Association for the Advancement of Science (BAAS) Committee on Electrical Standards by exploiting the measurement of the medium parameters—electric inductive capacity and magnetic permeability—on an arbitrary scale. While he always worked within this constraint in developing the ‘ratio-of-units’ argument mathematically, I maintain that Maxwell came to conceive of the ratio ‘as a velocity’ by treating the medium parameters as physical quantities that could be measured absolutely, which was only possible via the correspondences between electrical and mechanical quantities established in the mechanical theory. I thereby correct two closely-related misconceptions of the ratio-of-units argument—the counterintuitive but widespread notion that the ratio is naturally a speed, and the supposition that Maxwell either inferred or proved this from its dimensional formula. [ABSTRACT FROM AUTHOR]

During the 1860s, the Committee on Electrical Standards convened by the British Association for the Advancement of Science (BAAS) attempted to articulate, refine, and realize a system of absolute electrical measurement. I describe how this context led to the invention of the dimensional formula by James Clerk Maxwell and subsequently shaped its interpretation, in particular through the attempts of William Thomson and Fleeming Jenkin to make absolute electrical measurement intelligible to telegraph engineers. I identify unit conversion as the canonical purpose for dimensional formulae during the remainder of the nineteenth century and go on to explain how an operational interpretation was developed by the French physicist Gabriel Lippmann. The focus on the dimensional formula reveals how various conceptual, theoretical, and material aspects of absolute electrical measurement were taken up or resisted in experimental physics, telegraphic engineering, and electrical practice more broadly, which leads to the conclusion that the integration of electrical theory and telegraphic practice was far harder to achieve and maintain than historians have previously thought. This ultimately left a confusing legacy of dimensional concepts and practices in physics. [ABSTRACT FROM AUTHOR]

The paper presents a novel wide range absolute displacement sensor based on polarized light detection principle. The sensor comprises of two sets of polarized light detecting systems which are coupled by pulleys. The inherent disadvantage in optic system like light source intensity drift is solved and absolute measurement with wide-range is achieved. A prototype and the relevant test bed have been built. The test results are in good agreement with expectation. Its measurement range is 540 mm, and its linearity is better than 0.05%.

When proportional counters are employed in charge integration mode to determine the magnitude of a radiation pulse, so intense that individual detection events take place in a time too short to produce individual output pulses, mostly in pulsed neutron sources, the strong build-up of positive space charge reduces the electric multiplication factor of the proportional detector. Under such conditions the ensuing measurement underestimates the amount of radiation that interacted with the detector. If the geometric characteristics, the filling gas pressure and the voltage applied to that detector are known, it becomes possible to apply an analytical correction method to the measurement. In this article we present a method that allows to determine the absolute value of the detected radiation burst without the need to know the characteristics of the employed detectors. It is necessary to employ more than one detector, taking advantage of the Influence Method. The “Influence Method” is conceived for the absolute determination of a nuclear particle flux in the absence of known detector efficiency and without the need to register coincidences of any kind. This method exploits the influence of the presence of one detector in the count rate of another detector, when they are placed one behind the other and define statistical estimators for the absolute number of incident particles and for the efficiency (Rios and Mayer, 2015 [1,2] ). Its practical implementation in the measurement of a moderated neutron flux arising from an isotopic neutron source was exemplified in (Rios and Mayer, 2016 [3] ) and the extension for multiple detectors in (Rios and Mayer 2016 [4] ). [ABSTRACT FROM AUTHOR]

Competitiveness analysis of countries and regions stands in the foreground in recent years. Different methods as well as indicators are used to assess competitiveness, but no single procedure is considered to be the main one and it can hardly be stated, which of the measurement approaches is the most proper. The IMD World Competitiveness Online database represents one of such tools, containing the Overall Competitiveness ranking that evaluates 59 world countries by more than 300 individual indicators in 2012. The paper proposes an original Analytic Hierarchy Process (AHP) model for competitiveness ranking of selected countries. The model is based, due to the high number of indicators and countries, on absolute measurement and expert evaluation. The results given by the AHP model are compared to IMD competitiveness ranking. Differences of both results are analysed and discussed. [ABSTRACT FROM AUTHOR]

The “Influence Method” is conceived for the absolute determination of a nuclear particle flux in the absence of known detector efficiency and without the need to register coincidences of any kind. This method exploits the influence of the presence of one detector in the count rate of another detector, when they are placed one behind the other and define statistical estimators for the absolute number of incident particles and for the efficiency ( Rios and Mayer, 2015a ). Its detailed mathematical description was recently published ( Rios and Mayer, 2015b ) and its practical implementation in the measurement of a moderated neutron flux arising from an isotopic neutron source was exemplified in ( Rios and Mayer, 2016 ). With the objective of further reducing the measurement uncertainties, in this article we extend the method for the case of multiple detectors placed one behind the other. The new estimators for the number of particles and the detection efficiency are herein derived. [ABSTRACT FROM AUTHOR]

A 4π(β + +γ) integral counting method using 4πβ–4πγ detector configuration composed of a large well type NaI(Tl) scintillation detector and stacked plastic scintillators positioned in the center of the well and coupled with a slender PMT was adopted for activity measurement of 68 Ge– 68 Ga. Several source preparation schemes were studied to reduce the activity loss due to volatility. The possible contribution of EC events were rejected with pulse-height discrimination. Owing to the high counting efficiencies in both channels and the multiplicity of photons and β-particles emitted, the 4π(β + +γ) integral counting system gives a count rate very nearly equal to the positron emission rate. The activity can be determined simply from this value divided by the positron emission branching ratio. The remaining overall inefficiency was evaluated by the EGS5 code. [ABSTRACT FROM AUTHOR]

The “Influence Method” is conceived for the absolute determination of a nuclear particle flux in the absence of known detector efficiency. This method exploits the influence of the presence of one detector, in the count rate of another detector when they are placed one behind the other and define statistical estimators for the absolute number of incident particles and for the efficiency. The method and its detailed mathematical description were recently published (Rios and Mayer, 2015 [1] ). In this article we apply it to the measurement of the moderated neutron flux produced by an 241 AmBe neutron source surrounded by a light water sphere, employing a pair of 3 He detectors. For this purpose, the method is extended for its application where particles arriving at the detector obey a Poisson distribution and also, for the case when efficiency is not constant over the energy spectrum of interest. Experimental distributions and derived parameters are compared with theoretical predictions of the method and implications concerning the potential application to the absolute calibration of neutron sources are considered. [ABSTRACT FROM AUTHOR]

Non-linear interaction of waves with contact interfaces has been widely applied in non-destructive evaluation fields such as bonding quality evaluation, and the detection of closed microcracks and composite delamination. This paper proposes an absolute measurement of the ultrasonic non-linearity parameter using a piezoelectric detection method for two aluminum alloy blocks of different lengths. The results of a two-dimensional finite element method model verified by models for hard and soft contact interfaces, depending on the interface property, were compared with the measured non-linearity parameter. The measured values show good agreement with the modelled results, indicating good potential for measuring the non-linearity parameter at interfaces experimentally and numerically. [ABSTRACT FROM PUBLISHER]