摘要:

AbstractSamples of uranium enriched in233U and in235U have been irradiated with cobalt monitors in high-flux facilities in both cadmium-covered and bare assemblies. Radiometric analyses of irradiation samples provide data concerning thermal and epithermal capture and fission reactions from which experimental results are obtained. The epithermal capture-to-fission cross-section ratios of233U and235U at infinite dilution are 0.175±0.006 and 0.499±0.016, respectively, for a l/Espectrum with a low-energy cutoff of 0.50 eV. Resonance integrals for capture and fission are evaluated in terms of cobalt cross sections.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17804

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractIntercalibrated values of fission-spectrum-averaged cross sections have been obtained for the24Mg (n,p),46Ti (n,p),54Fe (n,p),5eFe (n,p),58Ni (n,p),59Co (n,α),92Mo (n,p), and115In (n,n') threshold reactions. All values are given relative to an assumed value of 0.61 mb for27Al (n,α)24Na. Irradiations were performed in a specially designed Converter Facility, located in a beam port near the thermal column of the Ispra-I Reactor. The converter is a disk of enriched uranium-aluminum alloy suspended in an essentially material-free cavity. Spectral purity correction factors were calculated using the Monte Carlo code TIMOC. The measured values are compared to the results of other workers.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17805

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractAn experimental method for the measurement of thermal-neutron spectra by neutron-induced radioactivities in selected isotopes is described. Criteria from theoretical and experimental considerations are developed and applied for the selection of such detectors. The applications and limitations of the method are discussed. The experimental technique has been applied to investigate neutron spectra in borated H2O solutions, using four detectors:164Dy,176Lu,151Eu, and197Au. The spectra obtained are in good agreement with the known spectra.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17806

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractCalculations have been performed of scattering and absorption self-shielding effects in the activation of bare and cadmium-covered Au, In, and 1/υdetectors in infinite slab geometry in both monodirectional (beam) and isotropic flux, for a range of detector thicknesses. Energy loss on scattering is included. It is found that the calculated activation rates agree well with published data on detector activity vs cadmium thickness and with measurements of the sandwich type. The effect of scattering is to increase the activity of the detectors over what would be observed in the absence of scattering, in a beam flux, and to decrease it in an isotropic flux. These effects are due almost entirely to scattering from the cadmium covers rather than from the detector. The contribution to the activation from neutrons scattered once in the cover is found to decrease markedly with detector thickness for the resonance detectors, and to remain more or less constant for 1/υdetectors, over a range of practical thicknesses. Effective cadmium cutoff energies have also been computed for the zero-thickness detectors and are in agreement with previously published tabulations. Tables of correction factors for scattering and for absorption self-shielding are presented.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17807

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractInvariant imbedding method is applied to compute the energy-dependent, time-dependent transmission and reflection of neutrons in slab geometry. A set of“characteristic functions”(which are a generalization of Chandrasekhar'sX- andY-functions) can be defined when the scattering kernel is degenerate. A computational scheme is outlined which makes use of these functions to obtain the time decay constant, the time-asymptotic leakage flux, and, for a steady-state case, the thermal utilization factor for a heterogeneous system.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17808

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractNumerical results for the time asymptotic neutron flux in a pulsed experiment, and for the thermal utilization factor in an infinite slab lattice, are derived using invariant imbedding. An isotropic separable kernel is assumed. It is shown that, though the neutron spectrum is strongly dependent on the shape of the kernel and thus cannot hope to be accurately predicted with a separable kernel, the qualitative behavior is in good agreement with previous computations. Moreover, some other features (the angular dependence of the flux, and the thermal utilization factor) are shown to have less dependence on the thermalization model, and are thus accurately predicted.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17809

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractA use of the variational method which has been neglected in reactor theory is discussed. This is the invariance theorem of E. Noether which has been widely utilized in other areas of mathematical physics. Following a derivation of the theorem, its use to obtain solutions of the time-independent diffusion equation is demonstrated. The theorem is used to construct a complete analogy between the time-dependent diffusion process and classical mechanics. Certain“conservation laws”arise in the construction of this analogy and their possible application is discussed. An analogy between the neutron diffusion equation and the time-dependent Schroedinger equation is also given. Several suggestions for generalizations of Noether's theorem for use in reactor theory are made.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17810

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractFormal development of the theory for harmonic analysis of neutron multiplying systems is carried out completely in the frequency domain. From basic probability theory, and an assumed reactor model, the problem is expressed as the Fokker-Planck equation in terms of the characteristic function, thus enabling the moments required for a statistical analysis to be obtained. Second-moment calculations include investigation into the bias in estimates of the power spectral density arising from the existence of finite record lengths. It is seen that for even very long records large biases can result, particularly at the lower frequencies. Variance analysis for estimates of the power spectral density investigates all moments up to and including the fourth for neutrons, delayed neutron precursors, and Fourier coefficients. The results show that for the most part, the variances can be described by a single parameter in which the extraneous neutron source plays a particularly important role. For reactors with large sources, the Fourier coefficients are shown to be Gaussian. For systems with small sources, variance in estimates of the power spectral density can become very large, and even the classical smoothed estimate is not consistent.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17811

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractSeveral aspects of the physics of periodically pulsed reactors and boosters are treated on the basis of the point neutron kinetics model. Steady-state operating conditions are established from delayed-neutron precursor and energy balances. The dependence of the power pulse characteristics and, in particular, the power pulse halfwidth on the principal reactor parameters is derived for both types of systems. Relations for the kinetics of pulsed reactors and boosters are given and the relative sensitivities to reactivity changes are discussed. Design examples are given to illustrate the pulse characteristics achievable in practical systems. Physics design requirements and performance limitations for high-power pulsed reactors and pulsed boosters are mentioned

ISSN:0029-5639    

DOI:10.13182/NSE67-A17812

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractThe effective resonance capture integral of ThO2has been measured at temperatures of 300 and 1200°K for rods ranging in diameter from 0.4 to 3.0 cm. The measurements were done by an activation technique relative to the dilute resonance integral of thorium. Calculated resonance integrals obtained using current cross sections and calculational methods are found to be in good agreement with the experimental results.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17813

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor