arXiv subjects

T. Itoh

Publications and source records attributed to T. Itoh.

10 recordsLinked to original sources

arXiv2025

Measurement of radiant spectrum for excess heat generation in NiCu and Ni thin film during hydrogen gas desorption

Heat production in Ni-based thin films interacting with hydrogen gas was studied using a radiation calorimeter equipped with a composite photon-detector system. Measurements were performed on pure Ni foil and NiCu composite thin films. Electromagnetic radiation emitted from samples heated to approximately 1100 K in vacuum was recorded over the energy range of 0.05 - 2.5 eV. In this study,detailed spectra were obtained, particularly in the low-energy region below 0.5 eV. The peak of the thermal radiation spectrum was observed around 0.2 eV, deviating from that expected for simple graybody radiation. Spectral variations depending on the presence or absence of hydrogen differed between the NiCu and pure Ni samples. The total radiated energy was determined directly from the measured radiation power, without relying on radiation models. The excess heat generated in the NiCu sample was estimated to be approximately 1.1 W. A comparable but slightly smaller excess heat generation was also observed in Ni. Long-term measurements of the NiCu sample demonstrated sustained excess heat production for at least 215 hours, with a decay time exceeding 2000 hours.

physics.ins-det↗

arXiv2023

Photon radiation calorimetry for anomalous heat generation in NiCu multilayer thin film during hydrogen gas desorption

In order to investigate the anomalous heat effect (AHE) in NiCu multilayer thin film, photon radiation calorimetry has been developed. Three types of photon detectors are employed to cover a wide range of wavelengths from 0.3 um to 5.5 um, i.e., photon energies from 0.2 to 1.8 eV. In the present work, the usefullness of the calorimetry is demonstrated for excess heat measurements with samples of Ni pure, NiCu composite layers, and Cu layer deposited on the Ni substrate. Direct comparisons of photon radiation spectra with and without H2 easily showed sample-specific differences in excess heat power. The samples of NiCu composite layer produced larger excess heat. By incorporating the measured radiant power into a heat flow model, the excess heat was deduced to be 4 - 6 W. The energy generated in 80 hours reached to 460 +/- 120 kJ: the generated energy per hydrogen was at least 410 +/- 108 keV/H atom. This is definitely not a chemical reaction, but producing energy at the level of nuclear reactions.

physics.ins-det↗

arXiv2015

Probing astrophysically important states in $^{26}$Mg nucleus to study neutron sources for the $s$-Process

The $^{22}$Ne($α$,n)$^{25}$Mg reaction is the dominant neutron source for the slow neutron capture process ($s$-process) in massive stars and contributes, together with the $^{13}$C($α$,n)$^{16}$O, to the production of neutrons for the $s$-process in Asymptotic Giant Branch (AGB) stars. However, the reaction is endothermic and competes directly with the $^{22}$Ne($α,γ)^{26}$Mg radiative capture. The uncertainties for both reactions are large owing to the uncertainty in the level structure of $^{26}$Mg near the alpha and neutron separation energies. These uncertainties are affecting the s-process nucleosynthesis calculations in theoretical stellar models. Indirect studies in the past have been successful in determining the energies, $γ$-ray and neutron widths of the $^{26}$Mg states in the energy region of interest. But, the high Coulomb barrier hinders a direct measurement of the resonance strengths, which are determined by the $α$-widths for these states. The goal of the present experiments is to identify the critical resonance states and to precisely measure the $α$-widths by $α$ transfer techniques . Hence, the $α$-inelastic scattering and $α$-transfer measurements were performed on a solid $^{26}$Mg target and a $^{22}$Ne gas target, respectively, using the Grand Raiden Spectrometer at RCNP, Osaka, Japan. Six levels (E$_x$ = 10717 keV , 10822 keV, 10951 keV, 11085 keV, 11167 keV and 11317 keV) have been observed above the $α$-threshold in the region of interest (10.61 - 11.32 MeV). The rates are dominated in both reaction channels by the resonance contributions of the states at E$_x$ = 10951, 11167 and 11317 keV. The E$_x$ =11167 keV has the most appreciable impact on the ($α,γ$) rate and therefore plays an important role for the prediction of the neutron production in s-process environments.

nucl-ex↗

arXiv2008

X-Ray Spectral Variability of the Seyfert Galaxy NGC 4051 Observed with Suzaku

We report results from a Suzaku observation of the narrow-line Seyfert 1 NGC 4051. During our observation, large amplitude rapid variability is seen and the averaged 2--10 keV flux is 8.1x10^-12 erg s^-1 cm^-2, which is several times lower than the historical average. The X-ray spectrum hardens when the source flux becomes lower, confirming the trend of spectral variability known for many Seyfert 1 galaxies. The broad-band averaged spectrum and spectra in high and low flux intervals are analyzed. The spectra are first fitted with a model consisting of a power-law component, a reflection continuum originating in cold matter, a blackbody component, two zones of ionized absorber, and several Gaussian emission lines. The amount of reflection is rather large (R ~ 7, where R=1 corresponds to reflection by an infinite slab), while the equivalent width of the Fe-K line at 6.4 keV is modest (140 eV) for the averaged spectrum. We then model the overall spectra by introducing partial covering for the power-law component and reflection continuum independently. The column density for the former is 1x10^23 cm^-2, while it is fixed at 1x10^24 cm-2 for the latter. By comparing the spectra in different flux states, we identify the causes of spectral variability. (abridged)

astro-ph↗

arXiv2006

Hard X-ray Detector (HXD) on Board Suzaku

The Hard X-ray Detector (HXD) on board Suzaku covers a wide energy range from 10 keV to 600 keV by combination of silicon PIN diodes and GSO scintillators. The HXD is designed to achieve an extremely low in-orbit back ground based on a combination of new techniques, including the concept of well-type active shield counter. With an effective area of 142 cm^2 at 20 keV and 273 cm2 at 150 keV, the background level at the sea level reached ~1x10^{-5} cts s^{-1} cm^{-2} keV^{-1} at 30 keV for the PI N diodes, and ~2x10^{-5} cts s^{-1} cm^{-2} keV^{-1} at 100 keV, and ~7x10^{-6} cts s^{-1} cm^{-2} keV^{-1} at 200 keV for the phoswich counter. Tight active shielding of the HXD results in a large array of guard counters surrounding the main detector parts. These anti-coincidence counters, made of ~4 cm thick BGO crystals, have a large effective area for sub-MeV to MeV gamma-rays. They work as an excellent gamma-ray burst monitor with limited angular resolution (~5 degree). The on-board signal-processing system and the data transmitted to the ground are also described.

astro-ph↗

arXiv2006

In-Orbit Performance of the Hard X-ray Detector on board Suzaku

The in-orbit performance and calibration of the Hard X-ray Detector (HXD) on board the X-ray astronomy satellite Suzaku are described. Its basic performances, including a wide energy bandpass of 10-600 keV, energy resolutions of ~4 keV (FWHM) at 40 keV and ~11% at 511 keV, and a high background rejection efficiency, have been confirmed by extensive in-orbit calibrations. The long-term gains of PIN-Si diodes have been stable within 1% for half a year, and those of scintillators have decreased by 5-20%. The residual non-X-ray background of the HXD is the lowest among past non-imaging hard X-ray instruments in energy ranges of 15-70 and 150-500 keV. We provide accurate calibrations of energy responses, angular responses, timing accuracy of the HXD, and relative normalizations to the X-ray CCD cameras using multiple observations of the Crab Nebula.

astro-ph↗

arXiv2001

Resonant excitation and anti-Stokes luminescence of GaAs single quantum dots

We have investigated micro-photoluminescence ($μ$-PL) and excitation ($μ$-PLE) spectra of a single GaAs/AlGaAs quantum dot grown on a GaAs (411)A surface. We observed sharp resonant lines in both $μ$-PL and $μ$-PLE spectra, corresponding to the discrete energy levels of the dot. When the sample was excited at one of the resonant lines, resonant luminescence lines appear not only in Stokes side but also in anti-Stokes side. We discuss the possible origins of the anomalus anti-Stokes luminescence.

cond-mat.mes-hall↗

arXiv2000

Low thermal conductivity of the layered oxide (Na,Ca)Co_2O_4: Another example of a phonon glass and an electron crystal

The thermal conductivity of polycrystalline samples of (Na,Ca)Co_2O_4 is found to be unusually low, 20 mW/cmK at 280 K. On the assumption of the Wiedemann-Franz law, the lattice thermal conductivity is estimated to be 18 mW/cmK at 280 K, and it does not change appreciably with the substitution of Ca for Na. A quantitative analysis has revealed that the phonon mean free path is comparable with the lattice parameters, where the point-defect scattering plays an important role. Electronically the same samples show a metallic conduction down to 4.2 K, which strongly suggests that NaCo_2O_4 exhibits a glass-like poor thermal conduction together with a metal-like good electrical conduction. The present study further suggests that a strongly correlated system with layered structure can act as a material of a phonon glass and an electron crystal.

cond-mat.str-el↗

arXiv1999

Transport Properties in (Na,Ca)Co_2O_4 Ceramics

The resistivity and thermopower of polycrystalline (Na,Ca)Co_2O_4 were measured and analyzed. Both the quantities increase with x, suggesting that the carrier density is decreased by the substitutions of Ca^{2+} for Na^{+}. Considering that the temperature dependence of the resistivity show a characteristic change with x, the conduction mechanism is unlikely to come from a simple electron-phonon scattering. As a reference for NaCo_2O_4, single crystals of a two-dimensional Co oxide (Bi,Pb)_2M_3Co_2O_9 (M=Sr and Ba) were studied. The Pb substitution decreases the resistivity, leaving the thermopower nearly intact.

cond-mat.str-el↗

arXiv1999

Na-site substitution effects of the thermoelectric properties of NaCo_2O_4

The resistivity and thermopower of Na$_{1+x}$Co$_2$O$_4$ and Na$_{1.1-x}$Ca$_x$Co$_2$O$_4$ are measured and analyzed. In Na$_{1+x}$Co$_2$O$_4$, whereas the resistivity increases with $x$, the thermopower is nearly independent of $x$. This suggests that the excess Na is unlikely to supply carriers, and decreases effective conduction paths in the sample. In Na$_{1.1-x}$Ca$_x$Co$_2$O$_4$, the resistivity and the thermopower increase with $x$, and the Ca$^{2+}$ substitution for Na$^+$ reduces the majority carriers in NaCo$_2$O$_4$. This means that they are holes, which is consistent with the positive sign of the thermopower. Strong correlation in this compound is evidenced by the peculiar temperature dependence of the resistivity.

cond-mat.str-el↗