Kenji Ishibashi

Brief Calculation of Neutrino Energy Spectra by the Use of Nuclear Data Files

Nuclear reactors generate a highly intense flux of electron-antineutrinos from fission products through β− decay, and a slight amount of electron-neutrinos through either β+ decay or electron capture. Neutrino energy spectra are usually calculated by the β decay theory. Since the reactor neutrinos are emitted from a great number of nuclides, the calculation requires a lot of level scheme of these nuclides. Nuclear data files, however, are available these days. It is possible to evaluate the electron-antineutrino and -neutrino spectra for a nuclear reactor on the basis of nuclear data files (JENDL-FP-Decay-Data-File-2000, JENDL-3.3)1, 2). In the study, we consider β transition of 420 nuclides for electron-antineutrino spectra and 120 nuclides for electron-neutrinos. We derive electron-neutrino and -antineutrino spectra in the energy range of 10 keV to 8 MeV from nuclear data files. The method gives good agreement with other studies for electron-antineutrino spectra. We show a simple method to estimate the reactor neutrino spectra without complicated computation.

Measurement of Continuous-Energy Neutron-Incident Neutron-Production Cross Section

Continuous energy neutron‐incident neutron‐production double differential cross sections were measured at the Weapons Neutron Research (WNR) facility of the Los Alamos Neutron Science Center. The energy of emitted neutrons was derived from the energy deposition in a detector. The incident‐neutron energy was obtained by the time‐of‐flight method between the spallation target of WNR and the emitted neutron detector. Two types of detectors were adopted to measure the wide energy range of neutrons. The liquid organic scintillators covered up to 100 MeV. The recoil proton detectors that constitute the recoil proton radiator and phoswich type NaI (Tl) scintillators were used for neutrons above several tens of MeV. Iron and lead were used as sample materials. The experimental data were compared with the evaluated nuclear data, the results of GNASH, JQMD, and PHITS codes.

Purity measurement of liquid methane by using the drift property of ionized electrons

The purity is important parameter for the collection of electrons ionized in an ionization chamber filled with the liquid methane. The methane gas purification system was developed for the liquid methane ionization chamber. After the condensation of the purified methane gas in the ionization chamber mounted with 241 Am alpha source, ionized electrons were collected by a charge sensitive preamplifier. The concentration of impurity of oxygen gas was obtained by analyzing a collected charge distribution. Pulse height distributions of a charge sensitive preamplifier were obtained for the detection of y rays and neutrons emitted from 60Co, 137Cs and Am-Be sources located outside the cryostat of the liquid methane chamber.

Measurement of Neutron‐Production Double‐Differential Cross Sections for Continuous‐Energy‐Neutron‐Incidence on Fe and Pb by Liquid Organic Scintillator

The neutron‐production double‐differential cross sections for the neutron‐induced reaction were measured on iron and lead samples up to 100 MeV. Neutrons produced by a 800 MeV proton‐bombarded spallation target were used as incident particles. The energies of incident neutrons were determined by their flight times on the path between the neutron source and the detectors. A fission ionization detector was utilized to determine the incident‐neutron flux. NE213 liquid organic scintillators were employed to detect outgoing neutrons which were emitted from the sample. As a part of this experiment, the response functions of NE213 detectors for neutrons were also measured by using the spallation neutrons. The energy spectra for outgoing neutrons were derived from their deposition‐energy spectra and the measured response functions of the detectors with unfolding technique. The results were presented at incident energies around 100 MeV, and were compared with GNASH calculations.

Development of 1.8 K HTS current feedthrough using large-sized YBCO bulk conductors

In Phase II experiment of a large helical device (LHD) of the National Institute for Fusion Science (NIFS), the helical coils are planned to be operated at 1.8 K by employing pressurized superfluid cooling to raise the magnetic field up to 4 T using a current of 17.3 kA. It is important to develop a 20 kA-class current feedthrough into the 1.8 K region with high current capacity and low heat leakage in the maximum leakage magnetic field of 1 T. The YBCO bulk conductors of 20 mm in width, 140 mm in length and 10 mm in thickness were assembled into a prototype 1.8 K current feedthrough. The current transport tests of the prototype 1.8 K current feedthrough were carried out successfully for currents up to 20 kA with liquid helium bath cooling at 4.2 K. The transport current was held at 20 kA for longer than 300 seconds. During the 20 kA operation, the current transport section of the YBCO bulk conductor remained in the superconducting state and the voltage drop between the YBCO bulk conductors and the copper electrode was constant. The contact resistance and the Joule heat generation in the joint region between the YBCO bulk conductors and the copper electrode were 1.8 n/spl Omega/ and 0.72 W, respectively when operated at 20 kA. We demonstrated the feasibility of a 1.8 K HTS current feedthrough using large-sized YBCO bulk conductors for the Phase II experiment of the LHD.