彩色数码相机光强响应特性的标定实验

当前高动态彩色数码相机的光强响应具有强烈的非线性,针对于此,用多项式这种非线性模型对彩色数码相机红、绿、蓝三通道的光强响应特性予以描述。建立了一种利用曝光时间测量CCD彩色数码相机光强响应特性的方法,通过调整快门速度获得不同的光强。同时,设计了标定实验,选用OLYMPUSE20数码相机对上述理论分析成果进行了实验验证,分别采用多项式模型和幂模型对实验数据进行拟合。实验结果表明,光强响应标定方法是可行的,多项式模型更适于描述彩色数码相机光强响应特性。     

The time-of-flight technique for the HERMES experiment

This paper describes the use of the time-of-flight (TOF) technique as a particle identification method for the HERMES experiment. The TOF is measured by two scintillation hodoscopes that initially were designed only for the first-level trigger. However, the suitable time structure of the HERA electron beam allows an extension of their functions to also measure the TOF for low momentum hadron identification. Using only these conventional hodoscopes, good particle identification was achieved for protons and pions in the momentum range up to and for kaons up to .     

Magnetic shielding of a large volume for an experiment on quasi free neutron oscillation

Results of the shielding against the Earth's magnetic field on a large volume are given. The experimental procedure is based on a multilayer μ-metal shield and a series of correcting electric coils. A final average value of (8.1±4.4) mG is obtained in a volume of about 20 m³.     

Digital-holographic interferometry with an image-intensifier system

A method for recording digital holograms on an image intensifier coupled with a CCD sensor is presented. The advantage of the image intensifier is that it can be gated (electronic shutter action produced by controlling of the image intensifier's photocathode voltage). This allows us to record holograms with a short exposure time. Two holograms of an object submitted to dynamical displacements (e.g., vibrations) are recorded by two short exposures. The phase of the wave front recorded at different times is calculated from the recorded intensity by use of a digital Fourier-transform method. By comparison of the phases recorded it is possible to get the displacement of the object during a short interval. Experimental results are presented, and the problems related to the noise and to the spatial resolution are discussed.     

Moiré effects in neutron interferometry and their use in the experimental search for an electric charge of the neutron

The operation of neutron interferometers is analyzed with particular emphasis on the Moiré effects present. The high sensitivity of neutron interferometers to deflection of the incident and propagating beams is shown to make these instruments a promising tool in the experimental search for an electric charge on the neutron. The corresponding estimates for interferometers of different types are given.It is shown that by using diffraction grating interferometers for very cold neutrons, the present-day upper limit for the neutron charge can be lowered by several orders of magnitude.     

Calibration of neutron albedo dosemeters

It is shown that by calibrating neutron albedo dosemeters under the proper conditions, two complicating effects will essentially cancel out, allowing accurate calibrations with no need for explicit corrections. The 'proper conditions' are: a large room (> or = 8 m on a side). use of a D2O moderated 252Cf source, and a source-to-phantom calibration distance of approximately 70 cm.     

Interframe intensity correlation matrix for self-calibration in phase-shifting interferometry

A new method of estimating reference phase shifts in phase-shifting interferometry is proposed. The reference phase shifts are determined from a matrix that represents the interframe intensity correlation (IIC) of phase-shifted interferograms. The root-mean-square error of intensity measurement is automatically obtained from the smallest eigenvalue of the IIC matrix. The proposed method requires only four interferograms, unlike others, and can extract phase shifts reliably even from interferograms without well-defined fringes, such as speckle patterns. In typical conditions, reference phase shifts and wave-front phases can be determined with an accuracy of lambda/6310 and lambda/150, respectively. The validity of the method is tested by comparing it with other methods in experiments and simulations.     

Some aspects of a time-domain neutron optics experiment

We report on recent progress in the observation of time-dependent matter wave optics with very cold neutrons (VCN). We have performed an experiment where a VCN beam was amplitude modulated by a high-frequency chopper. The resulting diffraction in time was measured with a special time-of-flight spectrometer that achieving an energy resolution of 22 neV. The measured spectra of different cases are discussed qualitatively.     

Calibration of an electronic multisensor system for measuring highpressures

An electronic system for measuring high pressures is considered. Its functioning is based on three fiber-optic transducers whose static characteristics are nonmonotonic and significantly influenced by temperature. A method for static calibration of this system is proposed, based on the use of spline functions of one variable. Its applicability in the considered case is demonstrated using synthetic data generated after an idealized model of the transducers. A method for valuation of the quality of calibration is also proposed and used for quantitative characterization of the impact of the number and errors of the data used for calibration on the quality of calibration     

Silicon multilayer target for a high intensity charm photoproduction experiment

The silicon active target for the high intensity heavy flavour photoproduction experiment NA14 has been tested satisfactorily. The standard deviation of the Gaussian noise distribution of the associated electronics was, on average, 17 keV. The stability of the energy-scale calibration was better than about 1% in a month. However it can be improved to 0.5% by monitoring the system over shorter periods.     

Mueller matrix error correction for a fringe-free interferometry system

We present an automated surface profiling system based on a shearing interferometer, in which precise measurement of the polarization states eliminates fringe ambiguity. A full error correction based on Mueller matrices allows comparatively inaccurate but rapidly switchable liquid-crystal wave plates to be used, enabling unambiguous profile information to be obtained in real time.     

Calibration method for high-accuracy measurement of long focal length with Talbot interferometry

In this paper, a new calibration method for accurate long focal-length measurements, based on Talbot interferometry, is presented. Error analysis is derived in detail by the numerical method, and an effective way to improve the accuracy is proposed. By this method, the systematic errors that are the main factors effecting accuracy are calibrated and reduced. Both simulation and experiments have been carried out to prove the effectiveness and advantages of the proposed method as compared to conventional approaches. The experimental results reveal that the relative error is lower than 0.02%, and the repeatability is better than 0.05%. This method is especially useful for measuring long focal-length lenses.     

Calibration for cylindrical specimens in grazing-incidence interferometry via integration of difference measurements

Cylindrical specimens may be tested advantageously by using grazing-incidence interferometry. A multiple positions test in combination with rotational averaging has recently been used to separate the surface deviations of the specimen from the interferometric aberrations. To reduce the measuring time and to check whether the results are reliable, a second procedure is now investigated, which uses the principle of the multiple positions test to determine quantities proportional to the difference quotients of the surface deviations. After numerical integration, the results can be compared with those obtained previously by rotational averaging. The measurement principle is described, and calibration results are presented.     

Investigation of the Cauchy-Riemann equations for one-dimensional image recovery in intensity interferometry

A method of image recovery using noniterative phase retrieval is proposed and investigated by simulation. This method adapts the Cauchy-Riemann equations to evaluate derivatives of phase based on derivatives of magnitude. The noise sensitivity of the approach is reduced by employing a least-mean-squares fit. This method uses the analytic properties of the Fourier transform of an object, the magnitude of which is measured with an intensity interferometer. The solution exhibits the degree of nonuniqueness expected from root-flipping arguments for the one-dimensional case, but a simple assumption that restricts translational ambiguity also restricts the space of solutions and permits essentially perfect reconstructions for a number of non-symmetric one-dimensional objects of interest. Very good reconstructions are obtained for a large fraction of random objects, within an overall image flip, which may be acceptable in many applications. Results for the retrieved phase and recovered images are presented for some one-dimensional objects and for different noise levels. Extensions to objects of two dimensions are discussed. Requirements for signal-to-noise ratio are derived for intensity interferometry with use of the proposed processing.     

Analysis of spatial resolution of an experiment on verification of the equivalence principle for a neutron by the diffraction method

Investigations of the spatial resolution of a setup for verification of the equivalence of inertial and gravitational masses of a neutron by the method of diffraction in a perfect crystal have been performed. Tests were conducted at Bragg angles of 74°–82°. A decrease in spatial resolution at Bragg angles >78° is detected.     

Normalization of a collimated 14.7 MeV neutron source in a neutron spectrometry system for benchmark experiments

In the present study a method used to normalize a collimated 14.7 MeV neutron beam is introduced. It combined a measurement of the fast neutron scalar flux passing through the collimator, using a copper foil activation, with a neutron transport calculation of the foil activation per unit source neutron, carried out by the discrete-ordinates transport code DOT 4.2. The geometry of the collimated neutron beam is composed of a D-T neutron source positioned 30 cm in front of a 6 cm diameter collimator, through a 120 cm thick paraffin wall. The neutron flux emitted from the D-T source was counted by an NE-213 scintillator, simultaneously with the irradiation of the copper foil. Thus, the determination of the normalization factor of the D-T source is used for an absolute flux calibration of the NE-213 scintillator.The major contributions to the uncertainty in the determination of the normalization factor, and their origins, are discussed.     

Calibration of a microwave system for measuring grain moisturecontent

This paper relates to a microwave system for grain moisture content determination which is based on simultaneous measurements of two parameters: attenuation and phase shift, of the electromagnetic wave transmitted through the layer of material. The calibration of such a system consists of identifying a function modeling the relationship between these parameters and the measured moisture content, taking into account an influence quantity-temperature T. Two algorithms for calibration are proposed and studied. The results of calibration show that the moisture of hard red winter wheat can be determined with uncertainty less than 0.5% moisture, at the 95% confidence level, in the moisture range of 10% to 19% at grain temperatures between -1°C and 42°C, independent of the grain bulk density