Response Matrix Of System Research Articles

Response matrix validation of a [formula omitted]-based multi-shell neutron spectrometer

A new type of compact multi-shell neutron spectrometer (MuNS) was developed at PNRI. It consists of a series of concentric polyethylene shells that can be combined to form Bonner spheres with different diameters ranging from 5 cm to 30 cm. With respect to conventional Bonner spheres, this system is more flexible and portable. MuNS can accommodate either passive or active neutron detectors. The response matrix of the MuNS with a cylindrical 3He proportional counter (He-MuNS) was calculated using Monte Carlo simulations for incident neutrons with energies ranging from 1 meV to 100 MeV. Anisotropy effect was investigated through simulations and is found to be at most 90% for the smallest configuration, indicating that He-MuNS should have a specific orientation during deployment. Validation of the calculated response matrix and calibration of the He-MuNS system were performed using a 252Cf reference source and the shadow cone method. The quotient of the measured and calculated neutron counts in the 3He detector was computed for every sphere and the value was found to be constant within 5.1%. Results confirm the validity of the He-MuNS model and the simulated response matrix.

Axial Movement Parameter Study on Preclinical Slit-Slat SPECT

One challenge to discrete detector slit-slat SPECT is that the system’s resolution and sensitivity vary significantly in the axial direction. The objective of this work was to reduce the variation by introducing axial movement and to determine the corresponding parameters, i.e. step size (D) and total length (L). We calculated the system response matrix of the slit-slat SPECT system and evaluated the system’s axial-direction resolution and sensitivity as functions of axial positions in the field of view. A series of scan protocols with combined rotational and axial movements, that is, helical scans, were applied to simulated phantom studies to select the preferred L and D values. Introducing axial movement effectively improved the system’s axial-direction sensitivity uniformity and reconstructed image resolution in both axial direction and in transverse plane, and it also reduced the artifacts in the transverse plane. The preferred choice of L is the cycle of the periodic pattern formed by the slat collimator’s and detector crystals. As about the value of D, a smaller D value is preferred for better uniformity as well as resolution improvement but practical constraints would apply.

Influence of Gaussian function index of deformable mirror on iterative algorithm adaptive optical system

Among all kinds of wavefront reconstruction algorithms in adaptive optical systems, the standard and mostly used algorithm is the direct gradient wavefront reconstruction algorithm. As the number of sub-apertures in Shack-Hartmann wavefront sensor and the actuators for deformable mirror increases, the reconstruction matrix in direct gradient wavefront reconstruction algorithm takes too much space and the number of multiplication in the algorithm increases sharply. So, the iterative algorithm is adopted in wavefront reconstruction for the high-resolution adaptive optical system. The number of multiplication and the required space of the iterative algorithm are directly related to the sparseness of both iterative matrix and slope response matrix. In an adaptive optical system, the sparseness of these two matrixes is connected with the system parameters. Therefore, it is necessary to study how to choose the proper parameters for an adaptive optical system when it uses iterative wavefront reconstruction algorithm. In this paper, the sparseness of slope response matrix and iterative matrix are analyzed based on a 613-actuator adaptive optical system. The influence of the Gaussian function index of deformable mirror on the sparsenesses of slope response matrix, iterative matrix, stability and correction qualities of the adaptive optical system are also studied under the condition of constant actuator spacing and coupling coefficient. A larger Gaussian function index results in a lower sparseness of the slope response matrix and the iterative matrix. Too large or too small a Gaussian function index will degrade the stability and the correction quality of an adaptive optical system. Finally, the optimal range of the Gaussian function index is provided by balancing the sparseness of slope response matrix, the correction quality, and the stability of the adaptive optical system.

Neutron spectrum unfolding using genetic algorithm in a Monte Carlo simulation

A spectrum unfolding technique GAMCD (Genetic Algorithm and Monte Carlo based spectrum Deconvolution) has been developed using the genetic algorithm methodology within the framework of Monte Carlo simulations. Each Monte Carlo history starts with initial solution vectors (population) as randomly generated points in the hyper dimensional solution space that are related to the measured data by the response matrix of the detection system. The transition of the solution points in the solution space from one generation to another are governed by the genetic algorithm methodology using the techniques of cross-over (mating) and mutation in a probabilistic manner adding new solution points to the population. The population size is kept constant by discarding solutions having lesser fitness values (larger differences between measured and calculated results). Solutions having the highest fitness value at the end of each Monte Carlo history are averaged over all histories to obtain the final spectral solution. The present method shows promising results in neutron spectrum unfolding for both under-determined and over-determined problems with simulated test data as well as measured data when compared with some existing unfolding codes. An attractive advantage of the present method is the independence of the final spectra from the initial guess spectra.

Response matrix of a neutron spectroscopy system comprised of successive BF3and H2O arrays

The response matrix of a neutron spectroscopy system is studied. The system is comprised of successive rectangular parallel layers of BF 3 followed sequentially by water layers. In total, ten BF 3 (96% 10 B) layers and nine H 2 O ones are configured in periodic order. Two different geometries are investigated; system A and system B. MCNP-4C is used to estimate the response functions of both systems. The response matrix of system A shows higher magnitude than those obtained from system B. In addition, the response matrix of system A shows more distinctive behavior than that obtained from system B.

Deconvolution of continuous internal bremsstrahlung spectra of 32P, 85Kr and 143Pr

AbstractAn efficient method of deconvolution of the internal bremsstrahlung (IB) spectra accompanying the β‐decay in 32P, 85Kr and 143Pr is presented. Experimental data is taken from the literature. The usual experimental values are folded with the response matrix of the detector system, and the Gold iteration technique is employed to deconvolve the detector response function for the continuous IB photon spectra. The response function of the detector is calculated using the peak to total ratio and the energy resolution of the detector. The results of the deconvolved IB spectra along with the theoretical calculations are presented. Copyright © 2007 John Wiley & Sons, Ltd.

Electron–acoustic-phonon energy-loss rate in multicomponent electron systems with symmetric and asymmetric coupling constants

We consider electron-phonon (\textit{e-ph}) energy loss rate in 3D and 2D multi-component electron systems in semiconductors. We allow general asymmetry in the \textit{e-ph} coupling constants (matrix elements), i.e., we allow that the coupling depends on the electron sub-system index. We derive a multi-component \textit{e-ph}power loss formula, which takes into account the asymmetric coupling and links the total \textit{e-ph} energy loss rate to the density response matrix of the total electron system. We write the density response matrix within mean field approximation, which leads to coexistence of\ symmetric energy loss rate $F_{S}(T)$ and asymmetric energy loss rate $F_{A}(T)$ with total energy loss rate $ F(T)=F_{S}(T)+F_{A}(T)$ at temperature $T$. The symmetric component F_{S}(T) $ is equivalent to the conventional single-sub-system energy loss rate in the literature, and in the Bloch-Gr\"{u}neisen limit we reproduce a set of well-known power laws $F_{S}(T)\propto T^{n_{S}}$, where the prefactor and power $n_{S}$ depend on electron system dimensionality and electron mean free path. For $F_{A}(T)$ we produce a new set of power laws F_{A}(T)\propto T^{n_{A}}$. Screening strongly reduces the symmetric coupling, but the asymmetric coupling is unscreened, provided that the inter-sub-system Coulomb interactions are strong. The lack of screening enhances $F_{A}(T)$ and the total energy loss rate $F(T)$. Especially, in the strong screening limit we find $F_{A}(T)\gg F_{S}(T)$. A canonical example of strongly asymmetric \textit{e-ph} matrix elements is the deformation potential coupling in many-valley semiconductors.

Response matrix of an extended Bonner sphere system

We have developed a system of Bonner spheres designed for use around high-energy accelerators. The upper energy limit of the system was extended using a lead radiator, which acts as an energy converter via the (n, xn) reaction. In addition, we use 11C activation as an additional component integrated into the system and the spectra unfolding process. In the first version of the system, the lead radiator was present in only one sphere with diameter of 30.48 cm. The object of the present work was to investigate the geometry of the lead radiator and its use in moderators of several different sizes. As a result, we have developed a modular design and calculated the response matrix of the new system.

Density functional theory for a model of nonuniform liquid metal in partially ionized states

The problem of the electronic, ionic and atomic density profiles in a nonuniform liquid metal which can locally exist in partially ionized states is examined using the density functional formalism. Ions and electrons are allowed to bind into atoms through a «reaction» governed by the mass action law. Formally exact equations for the density profiles are given in terms of the inverse response matrix of the nonuniform system, which consists of two terms: the first corresponding to to a mixture of ions, electrons and structureless atoms and the other to the atomic internal degrees of freedom. Approximate schemes are proposed for both contributions, stressing, in partieular, i) how ionization of the atoms arises with increasing density and the relation with Mott’s criterion for the metal-insulator transition, and ii) the usefulness of a weak-coupling assumption for interspecies correlations. This formalism used together with properly parametrized trial functions for the density profiles should be particularly useful for studying the liquid-vapour interface of alkali metals.

Internal bremsstrahlung accompanying the second-forbidden beta decay inCs137

The internal bremsstrahlung spectrum accompanying the nonunique second-forbidden ..beta.. decay in /sup 137/Cs has been measured using the magnetic deflection technique. The internal bremsstrahlung data beyond 760 keV are investigated due to the presence of a 662 keV ..gamma..-ray line. The pileup effect is corrected for by graphical integration. The theoretical spectra of Knipp and Ulhenbeck, Bloch, Lewis and Ford, and Chang and Falkoff are folded with the response matrix of the detector system and compared with the experimental spectrum. The agreement between measurement and theory is poor throughout the energy range of the present investigation, though the experimental points are closer to the second-forbidden scalar theory of Chang and Falkoff.

Incomplete state feedback design of linear regulators

A time-domain approach for the design of an incomplete state feedback control law for linear regulators is presented by comparing the impulse response matrix of the suboptimal system with that of the optimal system. A computational procedure is given for the design of the suboptimal control law.