A new ADC circuit for nuclear spectroscopy based on digital signal processing techniques

A 12-bit analog-to-digital converter (ADC) circuit for nuclear spectroscopy applications was developed using a digital signal processor (DSP) as the central processing element.

The DSP runs a program that builds the distribution function of data collected by the ADC (the multichannel analyzer algorithm) and simultaneously corrects the ADC differential nonlinearity (DNL) by the sliding scale method. The acquisition routine runs in 4 μs.

The conversion time, when the faster versions of the ADC are used, is well below 10 μs. The resulting DNL is better than 0.4% and the integral nonlinearity <0.002%.     

Effect of the method of measurement of ADC and DAC linearity on the yield of acceptable microcircuits

Translated from Izmeritel'naya Tekhnika, No. 4, pp. 5–6, April, 1991.     

A new method for momentum measurement of particle tracks in nuclear emulsions

A new type of emulsion spectrometer for a momentum determination of high energy charged particles has been developed.The spectrometer consists of a spacer and emulsion sandwich placed in a magnetic field. The accuracy for momentum determination ΔP/P by the spectrometer is calculated to be approximately 14%. The experimental result is consistent with the theoretical calculation.     

A new method for nuclear ADCs using the vernier approximation technique

The paper describes a new method of analog-to-digital conversion. The method named the vernier approximation technique utilizes two scales made of chains of resistors sliding over each other, one being called the main scale and the other the vernier scale. The vernier scale is moved by applying the input analog voltage as a voltage shift at both ends. This voltage shift is digitized using the comparators connected between the corresponding points on main and vernier scales. All the quantization steps are derived from a single quantization step using the process of sliding and vernier scaling resulting in high differential linearity. The scheme uses a balancing technique to balance the points on the main scale with the corresponding points on the vernier scale. The scheme works with the speed of a “sequential parallel approximation technique” giving a higher speed of operation than either the Wilkinson technique or the successive approximation technique used for nuclear ADCs. The technique gives high accuracy even with use of ordinary components such as 1% resistors.     

A new method for reducing DNL in nuclear ADCs using an interpolation technique

The paper describes a new method for reducing the DNL associated with nuclear ADCs. The method named the “interpolation technique” is utilized to derive the quantisation steps corresponding to the last n bits of the digital code by dividing quantisation steps due to higher significant bits of the DAC, using a chain of resistors. Using comparators, these quantisation steps are compared with the analog voltage to be digitized, which is applied as a voltage shift at both ends of this chain. The output states of the comparators define the n bit code. The errors due to offset voltages and bias currents of the comparators are statistically neutralized by changing the polarity of quantisation steps as well as the polarity of analog voltage corresponding to last n bits) for alternate A/D conversion. The effect of averaging on the channel profile can be minimized. A 12 bit ADC was constructured using this technique which gives DNL of less than ±1% over most of the channels for conversion time of nearly 4.5 μs. Gatti's sliding scale technique can be implemented for further reduction of DNL. The interpolation technique has a promising potential of improving the resolution of existing 12 bit ADCs to 16 bit, without degrading the percentage DNL significantly.     

A convergent method for cyclic plasticity analysis with application to nuclear components

A new method for elastic-plastic analysis of pressure vessels subject to cyclic mechanical and thermal loading is proposed. The method is shown to lead to a highly convergent solution when applied in conjunction with Prager's complete kinematic hardening rule. The plastic strain increments are written in terms of the total strains, thus leading to a consistent formulation when the analysis is done by an incremental iterative process. The proposed method is applied to the analysis of a long cylinder in the state of generalized plane strain and subject to cyclic loading. Cyclic plasticity and creep are considered in one of the problems analysed. The finite difference method is used in the solution of the compatibility and equilibrium equations. It is shown that the computation time using the proposed method is very small compared to other techniques.     

A new method for high speed nuclear ADCs using commercially available ADCs and DACs

This paper describes a new and simple method for high speed nuclear ADCs using commercially available high speed ADCs and monolithic DACs. The digital code corresponding to the input analog voltage, which is first determined with an accuracy of $\text{±}\text{1}\text{2}$ LSB using a commercial ADC (conversion time 2.5 μs), is corrected using a corrected monolithic DAC and external comparators to yield a DNL of better than ± 2% (without Gatti's scheme) with a total conversion time of 3.5 μs. The advantage of the method is the smaller size of the circuit and higher speed of operation compared with other methods. The recent improvements in speed, size and cost of commercial ($\text{±}\text{1}\text{2}\text{LSB}$) ADCs are directly utilized to improve the corresponding factors in nuclear ADCs. Use of Gatti's sliding scheme can further reduce the DNL to 0.2%.     

A new method for evaluating the order parameter in application to nickel and beta-brass

An analysis of experimental data on the resistivity and thermal expansion coefficient for nickel and beta-brass reveals a simple relationship between the order parameter and the isobaric thermal strain of these materials. Expressions are obtained for evaluation of the order parameter of ferromagnetic metals and ordered alloys from the results of the resistivity and thermal expansion measurements.     

A new method to simulate the micro-thermo-mechanical behaviors evolution in dispersion nuclear fuel elements

The large-deformation constitutive relations and stress update algorithms in a co-rotational framework are formulated respectively for the fuel particles, the matrix and cladding in dispersion nuclear fuel elements undergoing irradiation, with the main irradiation-induced effects within them considered. Their specific consistent tangent stiffness moduli are also developed. Correspondingly, the user subroutines UMAT have been programmed for definition of their mechanical constitutive relations. Besides, the user subroutines UMATHT have been written to define their thermal constitutive relations, in which degradation of the thermal conductivity of fuel particles are involved. An efficient method is established for modeling the irradiation-induced micro-thermo-mechanical behaviors evolution in dispersion nuclear fuel elements. The developed methodology is validated with the simulation results of the thermo-mechanical behaviors in fuel elements under an assumed irradiation condition. This study lays a foundation for optimal design of dispersion fuel elements.     

Some new formulae for posterior expectations and Bartlett corrections

Some new accurate approximations for posterior expectations and Bartlett corrections are derived. These approximations are modifications of formulae based on signed root log-likelihood ratios obtained in Sweeting (1996) and are designed to address two problems that arise in the practical application of these formulae in the multiparameter case. The first problem is a computational one associated with inversion of signed root log-likelihood ratios. The second concerns the form of the posterior expectation formula, which is not in a particularly convenient form for the computation of predictive densities. The theory is illustrated by two examples.     

A new method to evaluate alternate AC power source effects in multi-unit nuclear power plants

In order to evaluate accurately a station blackout (SBO) event frequency of a multi-unit nuclear power plant that has a shared alternate AC (AAC) power source, an approach has been developed which accommodates the complex inter-unit behavior of the shared AAC power source under multi-unit loss of offsite power conditions. The SBO frequency at a target unit of probabilistic safety assessment could be underestimated if the inter-unit dependency of the shared AAC power source is not properly modeled.The approach is illustrated for two cases, 2 units and 4 units at a single site, and generalized for a multi-unit site. Furthermore, the SBO frequency of the first unit of the 2-unit site is quantified. The methodology suggested in the present paper is believed to be very useful in evaluating the SBO frequency and the core damage frequency resulting from the SBO event. This approach is also applicable to the probabilistic evaluation of the other shared systems in a multi-unit nuclear power plant.     

A new method for low-capacitance probing

A method is suggested for cancelling the input capacitance of instruments and probes used in measurements. This approach is proposed as an alternative to conventional attenuating passive and active probes. The idea is demonstrated with a practical device that is able to nullify the parasitic capacitance to less than 2 pF without introducing signal attenuation     

核电站核安全相关结构基于性能指标的抗震概率设计评估方法探究

本文介绍了美国核电站基于性能指标的核安全相关抗震概率设计方法(performance-based method,PBM)的发展,较为系统地对PBM方法进行了阐述和讨论。在目前的研究成果和现有的规范标准归纳和总结的基础上,阐明了PBM的主要内容,其中包括:根据不同的性能要求对系统、结构和部件进行分级;确定系统、结构或部件的性能要求指标;确定基于概率地震危害性评价(PSHA)的地震动输入;系统、结构或部件概率极限值(fragility)计算;保证系统、结构或部件概率极限值有足够的裕度,以达到规定的性能指标5个方面。对PBM的进一步研究和发展提出了建议。     

A new quadrature algorithm consisting of volume and integral domain corrections for two-dimensional peridynamic models

International Journal of Fracture - Peridynamic (PD) models using the equation of motion in the integral form are applied to describe the failure and damage of materials. At present, the most...     

A new method for checking optical quadrants

Summary The above equipment is simple and provides, with great productivity, accurate checking of quadrants by means of a simple procedure.