Neutron Capture Cross Section Measurement of Praseodymium in the Energy Region from 0.003 eV to 140 keV

The neutron capture cross section of praseodymium (¹⁴¹Pr) has been measured relative to the ¹⁰B(n,αγ) standard cross section in the energy region from 0.003 eV to 140 keV by the neutron time-of-flight (TOF) method with a 46-MeV electron linear accelerator (linac) of the Research Reactor Institute, Kyoto University (KURRI). An assembly of Bi₄Ge₃O₁₂ (BGO) scintillators was used for the capture cross section measurement. In addition, the thermal neutron cross section (2,200 m/s value) of the ¹⁴¹Pr(n, γ)¹⁴²Pr reaction has been also measured by an activation method at the heavy water thermal neutron facility of the Kyoto University Reactor (KUR). The thermal neutron flux was monitored with the ¹⁹⁷Au(n, γ)¹⁹⁸Au standard cross section. The above TOF measurement has been normalized to the current activation data (11.6±1.3 b) at 0.0253 eV.

The evaluated data in JENDL-3.3, ENDF/B-VI, and JEF-2.2 have been in general agreement with the current result, except that the JENDL-3.3 and the JEF-2.2 values are clearly lower than the measurement in the cross section minimum region from about 10 to 500 eV.     

Measurement of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 167 Er

The neutron capture cross sections and capture γ-ray spectra of ¹⁶⁷Er were measured in the neutron energy region of 10 to 90keV and at 550 keV. Using a neutron time-of-flight method with a 1.5-ns pulsed neutron source by the ⁷Li(p, n)⁷Be reaction, the measurement was performed by detecting prompt γ rays from an enriched capture sample with a large anti-Compton Nal(Tl) spectrometer. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to extract capture yields. The capture cross sections were derived with the error of about 5% by using the standard capture cross sections of ¹⁹⁷Au. The present results were compared with the evaluated values of ENDF/B-VI and the previous measurement. The present measurement at 550 keV was the first one. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. An anomalous shoulder was clearly observed around 3 MeV in the γ-ray spectra and the energy position of the shoulder was consistent with the systematics obtained in our previous work. The multiplicities of the observed γ rays were derived from the γ-ray spectra.     

Measurement of Neutron Total Cross Section of Silicon at 146-and 53.5-keV Windows

The process constituting the elements of the method for treating high-level liquid waste with addition of reducing agent at temperatures above 1,873 K were examined applying thermogravimetry and X-ray diffractometry to sample mixtures of the platinum metal oxides RuO₂, Rh₂O₃, PdO and of Re₂O₇, with and without addition of TiN as reducing agent. The addition of TiN reducing agent proved to induce reduction of the platinum metal oxides at temperatures far below those of thermal decomposition occurring in the absence of reducing agent. The presence of reducing agent further proved to reduce Re₂O₇ to ReO₃ at 373K, to ReO₂ at 773 K and to Re metal at 1,073 K. At around 773 K disproportionation reconverted part of the ReO₃ formed at 373K to ReO₂ and Re₂O₇. Thus, sublimation of the Re₂O₇ in starting material which occurs at 523 K in the absence of TiN was eliminated, and occurred only at 773 K on the Re₂O₇ that was regenerated at that temperature by disproportionation of the converted ReO₃. Alloys of Ru, Rh and Pd resulting from the above treatment with TiN proved to agree with what is indicated from phase diagrams. Among the alternative compounds existing in the Rh-Ti and Rh-Ti binary systems, however, solely Ru-Ti proved to have been produced.     

Measurement of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 209Bi

The capture cross sections and capture γ-ray spectra of ²⁰⁹Bi were measured in a neutron energy region from 5 to 80keV and at 520 keV, using pulsed keV neutrons from the ⁷Li(p, n)⁷Be reaction and a time-of-flight method. The capture γrays from a bismuth or standard gold sample were detected with a large anti-Compton NaI(Tl) spectrometer. The capture yield of the bismuth or gold sample was obtained by applying a pulse-height weighting technique to the corresponding capture y-ray pulse-height spectrum. The derived capture cross sections from 5 to 80 keV were in good agreement with recent measurements, but that at 520 keV was about half of previous measurements. This large discrepancy at 520 keV was ascribed to the incorrect background-subtraction in the previous measurements from a comparison between the present and previous capture γray spectra. Strong transitions from the capture states to low lying states of ²¹⁰Bi were observed in the present γray spectra. The multiplicities of observed y rays were obtained from the γray spectra.     

Total Neutron Cross Sections of Magnesium,Aluminum, Silicon,Zirconium, Niobium and Molybdenum in Energy Range from 0.001 to 0.3 eV

Total neutron cross sections of Mg, Al, Si, Zr, Nb and Mo at room temperature have been measured in the energy range of 0.001–0.3 eV using a chopper and TOF facility of the Musashi Institute of Technology Research Reactor. The experiments were performed for solid and powdered samples. For these samples inelastic and elastic scattering cross sections were respectively calculated with the THRUSH code assuming Debye-type frequency spectrum and with the UNCLE-TOM code using crystal structure and lattice constants of each sample.

For solid samples the measured cross sections agreed well with the calculations below the Bragg cut-off energies. For the powdered samples there were good agreements above the Bragg cut-off, and the measurements were larger than the calculations below the Bragg cut-off.

The experimental cross section, adopting the results of powdered and solid samples for energy ranges above and below the Bragg cut-off respectively, agreed well with the calculation which was performed for the samples in perfect polycrystalline state.     

Measurement of ke V-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 147,148,149,150,152,154Sm

The neutron capture cross sections and capture γ-ray spectra of ^{147,148,149,150,152,154}Sm were measured in the neutron energy region of 10 to 90 keV and at 550 keV. A neutron time-of-flight method was adopted with a 1.5-ns pulsed neutron source by the ⁷Li(p, n)⁷Be reaction and with a large anti-Compton NaI(Tl) γ-ray spectrometer. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to derive capture yields. The capture cross sections were obtained with the error of about 5% by using the standard capture cross sections of ¹⁹⁷Au. The present results were compared with the evaluated values of JENDL-3.2 and previous measurements. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. An anomalous shoulder was clearly observed around 3 MeV in the γ-ray spectra of ^150,152,154Sm, and the energy position of the shoulder was consistent with the systematics obtained in our previous work.     

Average Neutron Capture Cross Sections of 151Eu and 153Eu from 3 to 100 keV

Neutron capture cross sections of europium isotopes ¹⁵¹Eu and ¹⁵³Eu were measured in the neutron energy range of 3~100keV. Experiments were carried out with the time-of-flight facility at the 52 m station of the JAERI Electron Linear Accelerator. Prompt capture γ-rays were detected by a large liquid scintillation detector and the neutron flux shape was determined with a ⁶Li glass scintillation detector. The average capture cross sections were examined in terms of energy independent strength functions for ¹⁵¹Eu and ¹⁵³Eu.     

Measurements of Total Neutron Cross Sections at 24-keV by means of Iron-Filter Method

Sputtering of the solid hydrogens by light ions has shown isotope effects which are greater than for any other solid targets. These hydrogenic solids are unique because of the extreme volatility and because the first step of the electronic sputtering process is identical for all hydrogenic solids. The sputtering for protons in the energy range from 5 to 10 keV can be qualitatively described by an electronic spike of cylindrical geometry. The sputtering yield of solid tritium has been evaluated on the basis of results for solid H₂, D₂ and HD.     

Total Neutron Cross Section in Heavy Ice at 77 and 15 K for Neutron Energies between 0.3 and 100 meV

A 10MW High Temperature Gas Cooled Reactor (HTR-10) designed by the Institute ofNuclear Energy Technology (INET) of Tsinghua University is being constructed now. The steam generator (SG) of the HTR-10 is one of the most important facilities for reactor safety. In order to investigate the thermal-hydraulic performance of the SG, a full scale HTR-10 Steam Generator Two Tube Engineering Model Test Facility (SGTM-10) was installed and tested at INET. This paper describes the SGTM-10 in detail. The test assembly of the SGTM-10 simulates practical thermal and structural parameters of the HTR-10. The SGTM-10 consisted of three separated loops, primary-helium loop, secondary-water loop, and third-cooling water loop. There are two parallel tubes arranged in the test assembly. The main experimental equipment is shown in this paper. Analysis shows that for once-through steam generator simulation experiment, the electric-heated simulation method could not match practical operating condition. The results may not reflect true phenomena. The main results of experiments, for example effects of the outlet pressure, effects of the heating power, effects of the inlet sub-cooling are described. Experiments indicated, when the heat load of the HTR-10 is more than 30% the SG will be stable.     

Measurement of keV-Neutron Capture Cross Section of 96Zr

The neutron capture cross section of ⁹⁶Zr at incident neutron energies from 15 to 100 keV has been measured by the time-of-flight method. Capture γ-rays were detected with an anti-Compton NaI(Tl) spectrometer, and the pulse-height weighting technique was applied to derive the neutron capture cross section. The present measurement provided the capture cross section as a function of incident neutron energy in the keV region. The results were compared with previous measurements and cross section data in the evaluated nuclear data libraries, JENDL-4.0, JENDL-3.3, ENDF/B-VII.0, and ENDF/B-VI.8. The present results revealed considerable underestimation of the evaluated cross sections in the high-energy region of 35–100 keV.     

Measurement of Neutron-Production Double-Differential Cross Sections for Intermediate Energy Pion Incident Reaction

Neutron-production double-differential cross sections for 870-MeV π⁺ and π ^- and 2.1-GeV π⁺ mesons incident on iron and lead targets were measured with NE213 liquid scintillators by time-of-flight technique. NE213 liquid scintillators 12.7cm in diameter and 12.7cm thick were placed in directions of 15°, 30°, 60°, 90°, 120° and 150°. The typical flight path length was 1.5 m. Neutron detection efficiencies were derived from the calculation results of SCINFUL and CECIL codes. The experimental results were compared with the cascade-evaporation calculation code NUCLEUS. The calculation results are higher typically by a factor of two than the experimental data at neutron energies below about 30MeV. NUCLEUS overestimates π^+-incident neutron-production cross sections in forward angles at neutron energies of 100 to 500 MeV.     

Assessment of Neutron Cross Sections for Titanium with Neutron Spectrum in Titanium Pile

The measurement of angular neutron spectrum in a quasi-spherical pile of Ti was carried out by the linac time-of-flight method for the assessment of neutron cross sections for Ti in the energy range from a few keV to a few MeV. The measured spectrum in the pile is generally in good agreement with the calculated one from ENDF/B-IV (MAT = 1,286 for Ti) except in the energy range from about 60 keV to a few 100 keV, where the calculation gives considerably lower neutron flux than the measurement.

In order to investigate the cause of this discrepancy between the measured and calculated spectra, the total cross sections for Ti were measured by the transmission method. The results give larger values of total cross sections for Ti by about 30% than ENDF/B-IV below 200 keV, and smaller values by about 10% above 200 keV. These results were ensured at 55 and 147 keV by the measurement using a Si-filtered neutron beam. The calculation based on the measured cross sections shows better agreement with the measured spectrum than that based on ENDF/B-IV. The discrepancy is still observed around 100 keV.

The sensitivity analysis shows the importance of cross sections above 1 MeV and elastic cross sections in the resonance energy region to solve the disagreement between the measured spectrum and the calculated one.     

Measurement of Gamma-Ray Production Cross Sections of Iron for Incident Neutron Energies between 6 and 33 MeV

Measurement of differential γ-ray production cross sections, i.e. (n, x γ) cross sections, of Fe was made for neutron energies from 6 to 33 MeV. Neutrons used in the experiment were white neutrons produced with (p, n) reactions by 35 MeV protons using a thick Be target. The neutron energy was analyzed by the time-of-flight method and bunched into 3 MeV wide energy bins, for each of which the spectrum of secondary γ-rays produced in an Fe sample was measured by a BGO scintillator at an angle of 144° to the neutron beam direction.

The obtained (n, xγ) cross sections agreed well with other data and the evaluated data file of ENDF/B-IV at neutron energies below 15 MeV where data were existing. The JENDL-3 file overestimated the γ-ray spectra at γ-ray energies of 3 to 7 MeV. The present work newly provided the data in the neutron energy range above 20 MeV. The GNASH calculation made by Young reproduced the measured data fairly well even at these higher energies.     

Measurement of Fast Neutron Induced Fission Cross Section Ratios of Pu-240 and Pu-242 Relative to U-235

Fission cross section ratios of ²⁴⁰Pu and ²⁴²Pu relative to ²³⁵U were measured by using the 4.5 MV Dynamitron accelerator of Tohoku University. The measurement using mono-energetic neutrons was performed in the neutron energy range of 0.6–7 MeV with the time-of-flight method. Prior to the measurement, a fast timing back-to-back fission chamber was developed with good time resolution to reduce the backgrounds due to α-particles and spontaneous fissions. Furthermore, we took account of the effect of the nonuniformity of fission sample thickness for accurate determination of fission cross section ratio. The uncertainty was estimated by analyzing the correlation between the error sources. The correlation matrix between the measured data was given. The overall uncertainty of the present results is about 2%. For both nuclides, the present results agree well with those by Meadows and by Kuprijanov et al. The JENDL-3 evaluation generally has good agreement with the present results. However, the evaluated data are slightly higher around 1 MeV and lower above 6 MeV than the present results.     

R-Matrix Analysis of 239Pu Neutron Transmissions and Fission Cross Sections in Energy Range from 1.0 keV to 2.5 keV

Abstract

The results of the ²³⁹Pu high resolution neutron transmission measurements of Harvey et al. and of the ²³⁹Pu high resolution fission cross section measurements of Weston & Todd performed at the Oak Ridge Electron Linear Accelerator (ORELA) were analysed in the energy range from 1 keV to 2. 5 keV by the Bayesian code SAMMY using the Reich-Moore approximation of the R-matrix theory. The results obtained in a previous analysis in the energy range from thermal to 1 keV were updated by taking into account the recent renormalization of the experimental fission data by Weston & Todd. The statistical properties of the parameters of the resonances identified in the energy range from thermal to 2. 5 keV were examined and improved values of the average parameters were obtained. The resonance parameters are given in an ENDF-6 format file available from JAERI Nuclear Data Center and from NEA Data Bank (OECD).     

Measurements of Double-Differential Neutron Emission Cross Sections of 6Li, 7Li and 9Be for 11.5 MeV and 18.0 MeV Neutrons

Double-differential neutron emission cross sections (DDXs) of ⁶Li, ⁷Li and ⁹Be were measured for 18.0 MeV and 11.5 MeV incident neutrons produced by the T(d, n) and ¹⁵N(d, n) reactions respectively, using the Tohoku University Dynamitron time-of-flight (TOF) spectrometer. The data were obtained at 13 laboratory angles, and angular-differential cross sections (ADXs) of elastic and inelastic scattering neutrons were derived from the DDXs. For 11.5 MeV neutrons, we obtained the neutron emission spectra over the secondary neutron energies by newly employing the double TOF method as well as the conventional one. In the measurements at 18.0 MeV, we achieved better energy resolution than in our previous studies by using a neutron detector that has a larger solid angle and a thinner tritium target. The experimental results of DDXs and ADXs were compared with our previous results and the evaluated data given in JENDL-3.2, JENDL Fusion File and ENDF/B-VI. It is found that the JENDL data reproduce the experimental ones very well.     

A Method Using Nuclear Emulsions for Measuring the Anisotropy of Fast Neutron Fluxes due to Arrangement of Fast Core Cell

Measurements using nuclear emulsions have been made on the neutron spectra and on the fine structure of neutron fluxes in the cell of the I-4 core of the fast critical assembly at the Japan Atomic Energy Research Institute. The I-4 core is a graphite-diluted fast core with 3:1 volume ratio of 20% enriched metallic uranium and graphite. The nuclear emulsions were irradiated in two typical patterns of arrangement of the cell (systems with graphite plates (a) bunched and (b) distributed among fuel plates).

For the distributed graphite plate system a marked discrepancy was found between the direct measurements and calculations based on the Monte Carlo method. This is attributed to anisotropy in the incident neutron flux due to the parallel plate arrangement of the simulated materials. It is concluded that Reines' formula requires correction to amount for such anisotropy, even when the emulsions are irradiated at the core center. A simple method for treating this anisotropy is proposed for use in fine structure analysis. The method utilizes, in part, the calculated results.     

Measurement of Double-Differential Neutron Emission Spectra from Uranium-238

We have performed the measurement of neutron emission spectra from ²³⁸U using a time-of-flight technique, and deduced the following data; (1) the prompt fission neutron spectra for 2 MeV incident neutrons at two emission angles of 90° and 135°, (2) the double-differential neutron emission cross sections at the incident energies of 1.2, 2.0, 4.2, 6.1 and 14.1 MeV. The emission spectra and the cross sections for scattering process were also deduced by subtracting the fission neutrons from the experimental spectra. The experimental results were compared with other experiments and the evaluations of JENDL-3 and ENDF/B-IV.

From the fission spectrum data ranging from 2 to 12 MeV, we have derived the best fit parameters for the Maxwellian and Watt type distribution functions. The experimental spectra are described with the Maxwellian spectrum with temperature of 1.24–1.26 MeV and are softer than both evaluations.

The spectra and cross sections for inelastic-scattering showed substantial disagreement with the evaluations concerning the discrete levels between 0.5 and 1.2 MeV, and continuum neutrons due to evaporation and pre-equilibrium processes. The secondary neutron angular distributions at 14 MeV incident energy were reproduced fairly well with the systematics.