arXiv subjects

S. Harada

Publications and source records attributed to S. Harada.

6 recordsLinked to original sources

arXiv2025

Neutron emission during fission and its impact on fission-fragment mass distribution studied by Langevin model

Actinide nuclei exhibit mass-asymmetric fission at low energy due to shell structure. The fission-fragment mass distributions produced at high energy tend to have a symmetric shape due to smearing of shell effects. On the other hand, the distribution can be changed by neutron emission occurring before fission, as this decreases the excitation energy of the fissioning nucleus, and thus revives the shell structure. In so called multichance fission, neutron emission is considered prior to fission at the initial nuclear shape, and competition between fission and neutron emission is determined with the framework of the statistical model. In the present work, we describe fission in the Langevin equations, and neutron emission is treated throughout the fission process. The calculation reproduces experimentally observed mass distributions, and for a wide range of initial compound-nucleus excitation energy up to 60 MeV. The results show that, while neutron emission dominates at the ground-state shape, it occurs along the shape evolution path to the scission point.

nucl-th↗

arXiv2019

Sub-pixel Response of Double-SOI Pixel Sensors for X-ray Astronomy

We have been developing the X-ray silicon-on-insulator (SOI) pixel sensor called XRPIX for future astrophysical satellites. XRPIX is a monolithic active pixel sensor consisting of a high-resistivity Si sensor, thin SiO$_2$ insulator, and CMOS pixel circuits that utilize SOI technology. Since XRPIX is capable of event-driven readouts, it can achieve high timing resolution greater than $\sim 10{\rm ~\mu s}$, which enables low background observation by adopting the anti-coincidence technique. One of the major issues in the development of XRPIX is the electrical interference between the sensor layer and circuit layer, which causes nonuniform detection efficiency at the pixel boundaries. In order to reduce the interference, we introduce a Double-SOI (D-SOI) structure, in which a thin Si layer (middle Si) is added to the insulator layer of the SOI structure. In this structure, the middle Si layer works as an electrical shield to decouple the sensor layer and circuit layer. We measured the detector response of the XRPIX with D-SOI structure at KEK. We irradiated the X-ray beam collimated with $4{\rm ~\mu m\phi}$ pinhole, and scanned the device with $6{\rm ~\mu m}$ pitch, which is 1/6 of the pixel size. In this paper, we present the improvement in the uniformity of the detection efficiency in D-SOI sensors, and discuss the detailed X-ray response and its physical origins.

astro-ph.IM↗

arXiv2013

Phonon anomaly and anisotropic superconducting gap in non-centrosymmetric Li2(Pd1-xPtx)3B

We report the systematic investigation of the specific heat of the noncentrosymmetric supercon- ductor Li2(Pd1-xPtx)3B as a function of x. There is a large deviation of the phononic specific heat from the conventional Debye specific heat for Pt-rich samples. In contrast with the fully-gapped con- ventional behavior for small x, a power-law temperature dependence of the electronic specific heat is observed even at x = 0.5. This results manifest a strongly-anisotropic or nodal superconducting gap even at x = 0.5 and a nodal superconducting gap for x >~ 0.9.

cond-mat.supr-con↗

arXiv2012

Abrupt enhancement of non-centrosymmetry and appearance of the spin-triplet superconducting state in Li_2(Pd_{1-x}Pt_{x})_3B beyond x=0.8

We report synthesis, ^{195}Pt, ^{11}B and ^{7}Li NMR measurements, and first-principle band calculation for non-centrosymmetric superconductors Li_{2}(Pd_{1-x}Pt_{x})_{3}B (x=0, 0.2, 0.5, 0.8, 0.84, 0.9 and 1). For 0 \leq x \leq 0.8, the spin-lattice relaxation rate 1/T_1 shows a clear coherence peak just below T_c, decreasing exponentially at low temperature, and the Knight shift ^{195}K decreases below T_c. For x=0.9 and 1.0, in contrast, 1/T_1 shows no coherence peak but a T^3 variation and ^{195}K remains unchanged across T_c. These results indicate that the superconducting state changes drastically from a spin-singlet dominant to a spin-triplet dominant state at x=0.8. We find that the distortion of B(Pt,Pd)_6 increases abruptly above x=0.8, which leads to an abrupt enhancement of the asymmetric spin-orbit coupling as confirmed by band calculation. Such local structure distortion that enhances the extent of inversion-symmetry breaking is primarily responsible for the pairing symmetry evolution. The insight obtained here provides a new guideline for searching new NCS superconductors with large spin-triplet component.

cond-mat.supr-con↗

arXiv2011

Magnetic Phase Diagram of Li_2(Pd_{1-x}Pt_x)_3B by AC Susceptometry

The H-T phase diagram and several superconducting parameters for Li_2(Pd_{1-x}Pt_x)_3B have been determined as a function of cation substitution x. Notably, the coherence length may be linear in platinum concentration. Despite the superconducting pairing state and band structure apparently changing fundamentally, the H-T phase diagram is essentially unchanged. Unusual aspects of the shape of the H-T phase diagram are discussed. The upper critical field H_c2(0) is not anomalously high for any Pt content, likely due to an absence of high carrier masses - in such a case, the value of H_c2(0) would not serve as a probe for novel physics.

cond-mat.supr-con↗

arXiv2003

Development of a pipeline CAMAC controller with PC/104-Plus single board computer

A pipeline CAMAC controller with PC/104-Plus single board computer has been developed. The architecture of the pipeline CAMAC controller is completely different from that of traditional CAMAC controller. The pipeline CAMAC controller adopted truly pipelined command and data paths from/to computer memory to/from CAMAC. The pipeline method enabled the controller maximum speed of CAMAC, approximately up to 3 MB/sec with 24-bit data. The controller also has a DAQ function such as event numbering for co-existence with other equipment such as VME. Not only the functionality and the performance but also the pipeline architecture and the design concept are described.

physics.ins-det↗