Effective Cutoff Energies Research Articles

A modified BCS theory of heavy fermion superconductivity

In this paper we derive an expression for the superconducting gap equation for U and Ce based heavy fermion (HF) systems within a modified weak coupling theory of superconductivity. The calculated gap equation presents a mixture of pairing amplitudes of two different quasi-particle bands α and β. These two gap equations are solved numerically and self-consistently within the cut-off energy which arises due to the Kondo energy. It is found that the energy dependence of the enhanced density of states for the HF systems clearly manifests itself in the theory and the Kondo energy naturally takes the role of cut-off energy (ωC), as long as the effective cut-off energy is large in comparison with the Kondo energy. The numerical analysis confirms this result and shows that superconducting transition temperature is independent of effective cut-off energy employed within this approach. The temperature dependence of gap equations are studied by varying the model parameters like position of f-level, hybridization and coupling constants of the HF systems.

A modified BCS theory of heavy-fermion superconductivity

In this paper we derive an expression for the superconducting transition temperature of a uranium-based heavy-fermion system within a modified weak-coupling theory of superconductivity. It is found that the energy dependence of the enhanced density of states for the heavy-fermion system clearly manifests itself in the theory, and the Kondo energy naturally takes the role of cut-off as long as the effective cut-off energy is large in comparison. The numerical analysis confirms this result and shows that the superconducting transition temperature is indeed independent of the effective cut-off energy employed within the approach.

Epicadmium neutron activation analysis (ENAA) based on the k0-comparator method

The applicability of the k0 standardization concept in ENAA has been investigated by comparing for 32 isotopes the experimentally determined ke, 0-values with those calculated from well-known k0 and Q0=l0/σ0 factors. It is concluded that the k−-comparator method can be extended and applied in general to epicadmium (n, γ) activation analysis. Attention is also paid to some specific problems, such as the deviation from the ideal epithermal neutron flux distribution, the uncertainty in the effective Cd cut-off energy for the Cd-covers used, and the cadmium epithermal neutron transmission factor for which a literature survey is presented.

Calculations of Cadmium Cutoff Energies

This paper develops the integral forms for the effective cadmium cutoff energy for different geometrical configurations such as: (a) infinite slab, (b) infinite cylinder, and (c) infinite slab abso...

Epithermal Measurements of Capture and Fission Resonance Integrals in 235U, 233U, 239Pu, and 241Pu

The resonance integrals for capture and fission and their ratios, a, have been measured for 233U, 235U, 239Pu, and 241Pu. Small samples of high isotopic enrichment were irradiated in a water channel of a swimming pool reactor. The number of captures was determined by mass spectrometry and the number of fissions was determined by 137Cs analysis. A combination of cadmium and rhodium neutron filters was used to provide effective cutoff energies in the 2- to 4-eV range. The measured values of a above 3.0 eV are 0.148 ± 0.006, 0.615 ± 0.019, 0.723 ± 0.044, and 0.285 ± 0.015 for 233U, 235U, 239Pu, and 241Pu, respectively. The corresponding values calculated from ENDF/B cross sections are 0.162, 0.608, 0.650, and 0.212.

Neutron Transmission Properties of Cd and B Filters in Moderating Media and Its Application in the Determination of 1/E-Spectrum

The energy dependent neutron transmission function of the Cd-filter covering a cylindrical 1/ν-detector was calculated with consideration given to the perturbation effect in the surrounding medium. The results were found to agree well with experiments using lead slowing-down time spectrometer.The effective Cd cut-off energy for 1mm thick Cd was calculated from the above transmission function, and found to be about 50% larger than the reported values.The validity of the assumption of 1/E1+β spectrum in a graphite moderator is discussed, and the β-value determined with an accuracy of 0.01 from the reaction rate ratio of BF3-counters covered with the different thicknesses of Cd- and B-filters. The region of the 1/E-spectrum neutron field in the graphite standard pile was determined by using this technique.

Effective Cadmium Cutoff Energies for Finite Cylindrical Filters with Finite-Size Detectors

Effective Cadmium Cutoff Energies for Finite Cylindrical Filters with Finite-Size Detectors

Effective cadmium cut-off energies in cycindrical geometry for fissile and [formula omitted] detectors

The importance of geometry in detector-filter arrangements used for integral neutron spectrum measurements is discussed, and cadmium transmission functions are presented for a number of detectors ranging from cylinders of 0·040 in. o.d. to slabs of finite thickness and infinite extent, with close-fitting filters of thickness 0·030, 0·040 and 0·050 in. The transmission function as defined in this paper is dependent on the physical size of the detector and the importance of this consideration is also demonstrated. In addition the transmission functions have been used to determine the effective cadmium cut-off energies for 239Pu, 235U, 233U and 1 V detectors.

Calculation of Effective Cutoff Energies taking into account Scattering and Higher Resonances of Filters

A refinement on the calculation of the effective cutoff energies of neutron filters has been made by taking into account the scattering and higher resonances of the filters. The effect of scattering is found to be considerable, especially in the case of resonance detectors. With Sm and Gd filters the higher resonances introduce marked deviations of the cutoff energies from those calculated without taking their effect into account. These two factors of scattering and higher resonances cause the epithermal neutron flux from the 1/E-spectrum to strongly affect the cutoff energies.

Effective Cadmium Cutoff Energies for Non-1/VDetectors

Effective cadmium cutoff energies were calculated for 239Pu, 235U, 115In, Au, 119Ir and 176Lu as a function of the cadmium filter thickness, the mast probable energy of the Maxwellian flux and the epi-thermal index. An infinite slab geometry and isotropic flux were assumed in the calculations. The calculated values of the cutoff energies are compared with those for 1/V detector, and are related to the resonance energies near the cutoff energy. If the resonance energy is lower than that of the 1/V detector, and the neutron spectrum and filter are same, the cutoff energy is lower than that of the 1/V detector. Such cases include 235U and 176Lu with thin filter, 191Ir with thick filter, and 239Pu with either thin or thick filter. If the resonance energy is higher than the E c of the 1/V detector, the cutoff energy is higher, such cases being 191Ir with thin filter, 176Lu with thick filter and 115In with either thin or thick filter. And if the resonance energy is very much higher than the E c of the 1/V detec...

Effective Cadmium Cutoff Energies for Non-1/V Detectors

Effective cadmium cutoff energies were calculated for 239Pu, 235U, 115In, Au, 119Ir and 176Lu as a function of the cadmium filter thickness, the mast probable energy of the Maxwellian flux and the epi-thermal index. An infinite slab geometry and isotropic flux were assumed in the calculations. The calculated values of the cutoff energies are compared with those for 1/V detector, and are related to the resonance energies near the cutoff energy. If the resonance energy is lower than that of the 1/V detector, and the neutron spectrum and filter are same, the cutoff energy is lower than that of the 1/V detector. Such cases include 235U and 176Lu with thin filter, 191Ir with thick filter, and 239Pu with either thin or thick filter. If the resonance energy is higher than the E c of the 1/V detector, the cutoff energy is higher, such cases being 191Ir with thin filter, 176Lu with thick filter and 115In with either thin or thick filter. And if the resonance energy is very much higher than the E c of the 1/V detector, as in the case of Au with thin filter, the cutoff energy approaches the value of the 1/V detector.

Calculation of Effective Cutoff Energies taking into account Scattering and Higher Resonances of Filters

Calculation of Effective Cutoff Energies taking into account Scattering and Higher Resonances of Filters

Effective Cadmium Cutoff Energies for Cylindrical Detectors with Cylindrical Filters

The effective cutoff energies for cylindrical detectors with cylindrical filters in isotropic neutron flux were studied. The reactor spectra used in calculating the effective cutoff energy were those for infinite homogeneous media using the free gas model of deuterium and carbon. The values of the effective cutoff energies for cylindrical geometry in isotropic neutron flux are intermediate between those in isotropic and beam neutron fluxes for slab geometry. Change of detector position in the filter considerably influences the value of the effective cutoff energy. The self-shielding effect is negligibly small in micro counters.

Effective Cadmium Cutoff Energies for Cylindrical Detectors with Cylindrical Filters

The effective cutoff energies for cylindrical detectors with cylindrical filters in isotropic neutron flux were studied. The reactor spectra used in calculating the effective cutoff energy were those for infinite homogeneous media using the free gas model of deuterium and carbon. The values of the effective cutoff energies for cylindrical geometry in isotropic neutron flux are intermediate between those in isotropic and beam neutron fluxes for slab geometry. Change of detector position in the filter considerably influences the value of the effective cutoff energy. The self-shielding effect is negligibly small in micro counters.

Effective Cutoff Energies for Boron, Cadmium, Gadolinium, and Samarium Filters

Effective Cutoff Energies for Boron, Cadmium, Gadolinium, and Samarium Filters

The Calculation of Effective Cutoff Energies in Cadmium, Samarium, and Gadolinium

A set of effective cutoff energies for 1/v detectors covered by cadmium, samarium, and gadolinium filters is presented. These cutoff energies have been calculated for both isotropic and beam fluxes...

放射化法におけるデータ解析の現状

Foil techniques play an important role in the experiment in reactor physics. It is always necessary for reactor physicists to compile the newest information on foil techniques in order to conduct fruitful experiments and to make proper interpretation of the results. Then, we present a short note for the latest papers about the analysis and interpretation of foil data which appeared in journal and so on. Information is included on the thermal neutron flux perturbation by foils, neutron self-shielding effect in resonance foils and effective cadmium cutoff energies. Integral measurements of neutron energy spectra are also discussed with the emphasis on the experience accumulated in Japan.

An Experimental Study of the Relative U235Fission Activation as a Function of Energy in Slightly Enriched Uranium-Water Lattices

Measurements of the relative U/sup 235/ fission rates as a function of energy were made for the TRX facility, a slighly enriched uranium, light water moderated critical assembly. The parameter directly measured is the ratio of the activity of a bare U/sup 235/ foil to that of a similar foil enclosed in a box of absorbing material, which was either cadmium, boron, or gadolinium. The energy dependence associated with these ratios was obtained by the introduction to effective cutoff energies for the absorbing shields. A comparison is made with calculated values, based upon a simplified model for the neutron energy spectrum present, and the agreement is considered ade quate. (auth)

Effective Cadmium Cutoff Energies

Effective cutoff energies for point 1/υ absorbers inside of spherical and cylindrical cadmium filters have been calculated for thermal reactor neutrons. The neutron spectrum was assumed to consist of a Maxwellian plus a 1/E component, and the parameters varied were the thickness of filter, the Maxwellian temperature, and the Maxwellian to 1/E flux ratio. Because of the sensitivity of the effective cutoff to Maxwellian flux parameters for thin filters it is recommended that filter thicknesses of about 40 mils be used. Forty-mil filters show effective cutoffs at about 0.50 to 0.55 ev for temperatures up to about 500°A (or about 0.045 ev). Effective cutoff energies for boron filters were also calculated for purposes of comparison.