Katsuhei Kobayashi

Utilization of coherent transition radiation from a linear accelerator as a source of millimeter-wave spectroscopy

A spectroscopic system for the millimeter-wave region has been constructed on the coherent radiation beamline at the KURRI-LINAC of the research reactor institute, Kyoto University. Coherent transition radiation has been used as the light source. The observed spectrum of radiation was distributed throughout the entire millimeter-wave region and the intensity was four orders of magnitude larger than that of the conventional light source which has the continuous spectrum, i.e., a mercury-arc lamp. The interference between wave packets emitted from successive bunches was observed. It showed that the spectrum of coherent transition radiation was constituted of the higher harmonics of the L-band radio frequency (1.3 GHz) and that the high resolution spectrum was not a continuous spectrum. The diameter of the light beam at the position of a sample was about 9 mm (full width half maximum) and it increased as the wavelength became long because of the diffraction effect for the finite sizes of the optical componen...

The spherical harmonics method for the multigroup transport equation in x−y geometry

Abstract A spherical harmonics equation in the form of a second-order differential equation is derived for the 2-D x − y geometry, including higher-order scattering within a group. Using this equation, a multigroup transport code for the spherical harmonics method of a general order of approximation is developed. Some numerical examples, including typical problems for the ray effect, are presented and compared with those obtained by the discrete-ordinates method. It is shown that the present method gives more accurate results than the discrete-ordinates method, although this spherical harmonics code requires more computer memory than the discrete-ordinates code.

MEASUREMENTS OF AVERAGE CROSS SECTIONS FOR SOME THRESHOLD REACTIONS FOR NEUTRONS WITH FISSION-TYPE REACTOR SPECTRUM.

The fast neutron spectrum in the core of the Kyoto University Reactor (KUR) was measured by using seven threshold reactions, a 6Li sandwich counter and also nuclear emulsion plates, and the results were compared with theoretical calculations by the Sn method. It was found that the shape of the fast neutron spectrum was approximately the same as that of fission neutrons. Making use of these neutrons with fission-type spectrum, measurements were made of the average cross sections for twelve threshold reactions (46Ti(n, p)46Sc, 47Ti(n, p)47Sc, 46Ti(n, p)48Sc, 28Si(n, p)28Al, 29Si(n, p)29Al, 30Si(n, α)27Mg, 51V(n, α)48Sc, 64Zn(n, p)64Cu, 92Mo(n, p) 92mNb(n, 2n)92mNb, 204Pb(n, n1 )204mPb and 204Pb(n, 2n)203Pb). For the purpose of comparison, the average cross sections for six among these reactions were measured also with neutrons from a fission plate. The results agreed within experimetal error with those obtained for neutrons in the KUR core. A Ge(Li) counter was mainly used for the measurement of γ-rays emit...

Measurement of Neutron Capture Cross Section of 237Np by Linac Time-of-Flight Method and with Linac-driven Lead Slowing-down Spectrometer

The neutron capture cross section of 237Np has been measured relative to the 10b(n, α) standard cross section by the neutron time-of-flight (TOF) method in the energy range of 0.005 eV to 10keV using a 46MeV electron linear accelerator (linac) at the Research Reactor Institute, Kyoto University (KURRi). In order to experimentally prove the result obtained, the supplementary cross section measurement has been made from 0.15 eV to 1 keV using the Kyoto University Lead slowing-down Spectrometer (KULS) coupling to the linac. The relative measurement by the TOF method has been normalized to the reference value (181 b) at 0.0253 eV and the KULS measurement to that by the TOF method. The existing experimental data and the evaluated capture cross sections in ENDF/b-Vi and JENDL-3.2 have been compared with the current measurements by the linac TOF and the KULS experiments. The energy dependency of the KULS data is close to that of the TOF data which are energy-broadened by the resolution function of the KULS. It has been found that the data measured by Weston and Todd and evaluated in ENDF/b-Vi and JENDL-3.2 are in general agreement with each current measurement, although those data are systematically lower by about 15% above about 0.2 eV. However, the data by Hoffman et al. are low obviously in the relevant energy region.

Measurements of Thermal Neutron Cross Section and Resonance Integral for 237Np(n, γ)238Np Reaction

Making use of a standard neutron spectrum field with a pure Maxwellian distribution, the thermal neutron cross section for the 237Np(n, γ)238Np reaction was measured at a neutron energy of 0.0253 eV by the activation method. The result is 158±3 b, which is obtained relative to the reference value of 98.65±0.09 b for the 197Au(n, γ)198Au reaction. Although the data in JENDL-3 is larger by about 15% than the present value, the recently revised data in JENDL-3.2 is close to the present. The ENDF/B-V, ENDF/B-VI, JEF-2 and Mughabghabs data are also larger by 7–15%. Old measurements are larger by 7–18% than the present data. The resonance integral for the 237Np(n, γ)238Np reaction was also measured relative to the reference value of 1,550±28 b for the 197Au(n, γ)198Au reaction with a 1/E standard neutron spectrum field. By defining the Cd cut-off energy as 0.5 eV for the 237Np(n, γ)238Np reaction, the present resonance integral is 652 ± 24 b, which is in good agreement with the JENDL-3, -3.2, ENDF/B-V, -VI, JE...

Measurement of Neutron Capture Cross Section of 237Np from 0.02 to 100 eV

The neutron capture cross section of 237 Np has been measured relative to the 10B (n, α)7Li* cross section by the time-of-flight method in the energy range from 0.02 to 100 eV. The 46 MeV electron linear accelerator at the Research Reactor Institute, Kyoto University, was used as a pulsed neutron source. The BGO scintillation detector was employed in conjunction with the flash ADC-based data taking system for measurement and data accumulation. For the first time the capture cross section of 237 Np in resonance energy range was measured using the total energy gamma-ray detector. The results of present measurements have been compared with the evaluated capture cross sections of ENDF/B-VI and JENDL-3.3, as well as with the data measured by other authors.

Calibrated fission and fusion neutron fields at the Kyoto University Reactor

Thermal-neutron-driven fast neutron fields using a fission plate and a 6LiD converter are briefly reviewed. The characteristics of a large (27-cm-diam × 1.1-cm-thick) fission plate made of highly e...

Rigorous derivation of nodal equations for coupled reactors

Abstract Static and kinetic nodal equations whose unknowns are the total fission source for each reactor are derived rigorously for coupled reactors from static or time-dependent multigroup diffusion equations. Explicit expressions are given for coupling coefficients and neutron lifetime which are consistent with the nodal equations. These equations are exact independently of the strength of the coupling, and they can also be applied to a single reactor dividing the core into appropriate subregions.

Radiochemistry and secondary reactions for the diagnostics of laser‐driven fusion plasmas

Radiochemical measurements have been developed for the diagnostics of laser‐driven implosion plasmas. The excellent calibration for neutron‐yield measurement has been done using β‐γ coincidence technique. The multiactivable tracer method has been examined for measuring the pusher areal density by means of a high‐purity germanium detector. The first experimental success of the secondary nuclear fusion reaction method is also demonstrated for the direct measurement of the fuel ρR.

Assessment and Propagation of the 237Np Nuclear Data Uncertainties in Integral Calculations by Monte Carlo Techniques

Abstract A new method to produce covariance or dispersion matrices for the resonance parameters of neutron cross sections was developed. The technique uses resonance shape analysis in association with Monte Carlo treatment of the uncertainties. The method was implemented in the error propagation tool MCFIT. This program provides a user-friendly textual interface for the shape analysis code REFIT. It was designed to take into account the main sources of uncertainties involved in time-of-flight measurements. Its capability is illustrated with the simultaneous analysis of 237Np capture and transmission data. The covariance matrix obtained in this work was used to interpret oscillation measurements of 237Np samples carried out in the Minerve reactor located at Cadarache.