[en] A digital data acquisition system for monitoring plant variables has been designed and implemented at the University of Michigan's Ford Nuclear Reactor (FNR), a 2-MW open-pool research reactor. The digital data provided by this system will be useful for: improved operator training, real-time experimental calculations, noise analysis, closed-loop control, and expert system applications. This paper describes the analog-to-digital (A/D) transitions and the associated applications and benefits experienced

[en] Since the data sizes in fully 3D PET imaging are very large, iterative image reconstruction algorithms must converge in very few iterations to be useful. One can improve the convergence rate of the conjugate-gradient (CG) algorithm by incorporating preconditioning operators that approximate the inverse of the Hessian of the objective function. If the 3D cylindrical PET geometry were not truncated at the ends, then the Hessian of the penalized least-squares objective function would be approximately shift-invariant, i.e. G'G would be nearly block-circulant, where G is the system matrix. We propose a Fourier preconditioner based on this shift-invariant approximation to the Hessian. Results show that this preconditioner significantly accelerates the convergence of the CG algorithm with only a small increase in computation

[en] A digital data acquisition system for monitoring plant variables has been designed and implemented at the University of Michigan's Ford Nuclear Reactor (FNR), a 2 Megawatt, open-pool, research reactor. The digital data provided by this system is useful for: closed loop control, real time experimental calculations, advanced simulation-as-knowledge techniques, improved operator training, and expert system applications. The purpose of this paper is to discuss the transition to the digital data world and the anticipated applications and benefits

[en] This paper describes a digital data acquisition and display system for research reactor applications. Prototype and commercially available hardware is presented for the analog and digital signals. Particular problems encountered in actually implementing the system are highlighted. Three applications showing the advantages of the digital monitoring system are presented

[en] The KENO-NR Monte Carlo code was developed to simulate the measurement of R(ω) = G₁₂(ω)G₁₃(ω)/G₁₁(ω)G₂₃(ω), a ratio of spectral densities measured by the ²⁵²Cf source-driven noise analysis (CSDNA) method for determining subcriticality. From a direct comparison of simulated and measured R(ω), cross sections and the physical system model can be benchmarked and then used in standard criticality codes for determining k_eff for a multiplying system. This procedure eliminates the dependence of the CSDNA method on the point-kinetics model and allows cross-section and geometry models to be validated for noncritical configurations. For a set of uranium cylinders (93.2 wt % ²³⁵U and 17.7-cm outer diameter) of varying height, the simulated and the measured R(ω) values in the low-frequency limit and the prompt neutron decay constant α agreed to within 10%. These results indicate that the approach of validating a simulation of the direct experimental data should lead to improved neutronic parameters for fissile systems

[en] The authors have examined the feasibility of compartmental analysis of ^99mTc-teboroxime kinetics in measuring physiological changes in response to adenosine-induced coronary vasodilation. To evaluate the effect of tracer recirculation on ^99mTc-teboroxime kinetics in the myocardium, they also compared compartmental analysis with washout analysis (monoexponertial fitting), which does not account for this effect. Eight healthy male volunteers were imaged using fast dynamic SPECT protocols (5 sec per tomographic image) at rest and during adenosine infusion. A two-compartment model was used and compartmental parameters K1 and k2 (characterizing the diffusion of ^99mTc-teboroxime from the blood to the myocardium and from the myocardium to the blood, respectively) were fitted from myocardial time-activity curves and left ventricular input functions. Both K1 and washout estimates for the whole left ventricular myocardium changed significantly in response to coronary vasodilation. Mean stress-to-rest (S/R) ratios were almost two times higher for K1 (S/R = 2.7 ± 1.1) than for washout estimates (S/R = 1.5 ± 0.3). Estimation of K1 for all local regions, except the septal wall, is feasible because variations in K1 estimates for all local regions, except the septum during stress, are comparable with those for the global region. The authors conclude that quantitative compartmental analysis of ^99mTc-teboroxime kinetics provides a sensitive indicator for changes in response to adenosine-induced coronary vasodilation. 39 refs., 7 figs., 1 tab

[en] The ²⁵²Cf-source-driven noise analysis method has successfully measured the subcritical neutron multiplication factor k for a wide variety of fissile systems. The recent modifications of the KENO Va Monte Carlo code to calculate directly the measured noise analysis data allow the use of this experimental data for validation of calculational methods and cross sections. High sensitivity of noise-measured parameters to small changes in fissile systems has been observed in several measurements. To investigate this sensitivity, a series of calculations was performed for a 3 by 3 array of PWR spent-fuel elements in unborated water. The macroscopic fission-product cross sections were changed, and the resulting ratios of spectral densities, coherence between detectors, and values of k were obtained from this Monte Carlo simulation of the measurement. The sensitivity of the ratios of spectral densities and coherences to changes in fission-product cross sections were a factor of 10 and 4 degrees, respectively, more than that of k. These Monte Carlo calculations have shown that this type of subcritical measurement can be used to benchmark fission-product cross sections for spent PWR fuel and, because of the high sensitivity of the noise analysis quantities, would provide a more stringent test of the fission-product cross sections than comparison of calculation with experiments at delayed criticality, even though the value of k can be measured more accurately at delayed criticality

[en] Modern SPECT instrumentation allows attenuation correction in cardiac scans by using transmission measurements. Simultaneous transmission and emission measurements are feasible with different geometries in multihead SPECT systems and are already commercially available. The selection of the transmission nuclide affects the quality of data, depending on the emission nuclide used. Iterative reconstruction methods have to be implemented to get accurate results in the case of heterogeneous attenuation distributions. Methodological aspects concerning simultaneous scatter and attenuation correction have to be studied in future. The clinical significance of routine attenuation correction measurements for myocardial perfusion has to be shown in a large patient population. (orig.)