Shusuke Nishiyama

Floating zone growth and scintillation characteristics of cerium-doped gadolinium pyrosilicate single crystals

Growth of cerium-doped gadolinium pyrosilicate (Gd₂Si₂O₇:Ce) single crystals, which show 2.5 times greater light output for gamma-rays and five times greater light output for alpha particles than GSO single crystals, is accomplished using floating zone growth method (FZ method). Although growth of Gd₂Si₂O₇ (GPS) single crystal is considered to be difficult because it melts incongruently according to the phase diagram in a Gd₂O₃-SiO₂ system, we attempted crystal growth of Ce:GPS because the possibility exists that heavy Ce doping changes the phase diagram. Transparent single crystals were obtained, but cracks were observed in the crystals. The crystal structure was triclinic with space group P_/1 and density of 5.5 g/cm³. Two peaks were observed by photoluminescence spectrum measurement at 374 nm and 394 nm caused by 5d-4f transition in Ce³⁺ ion. Decay times of Ce:GPS were 46 ns for gamma-ray and 39 ns for alpha particles; its density was 5.5 g/cm³. We consider that the energy resolution of 23% will be improved by fabrication of large crystals and improvement of crystal perfectability.

Phase unwrapping for noisy phase maps using rotational compensator with virtual singular points

In the process of phase unwrapping for an image obtained by an interferometer or in-line holography, noisy image data may pose difficulties. Traditional phase unwrapping algorithms used to estimate a two-dimensional phase distribution include much estimation error, due to the effect of singular points. This paper introduces an accurate phase-unwrapping algorithm based on three techniques: a rotational compensator, unconstrained singular point positioning, and virtual singular points. The new algorithm can confine the effect of singularities to the local region around each singular point. The phase-unwrapped result demonstrates that accuracy is improved, compared with past methods based on the least-squares approach.

Scintillation Characteristics of

Cerium-doped gadolinium pyrosilicate single crystals Ce:Gd2Si2O7 (Ce:GPS) with various Ce concentrations of 2.5-30 mol% with respect to the total rare-earth sites were prepared by the floating zone method. Their scintillation performances were investigated under irradiation of gamma rays of 137Cs. The Ce concentration dependence of scintillation characteristics and high-performance scintillation characteristics were obtained: 3-6 times greater light output than that of BGO single crystals, rapid decay, and good energy resolutions of 5.1-8.4%. Furthermore, X-ray diffraction patterns of Ce:GPS revealed Ce concentration dependence of the crystal structure of Ce:GPS.

{\rm Ce}:{\rm Gd}_{2}{\rm Si}_{2}{\rm O}_{7}

Phase unwrapping for a noisy image suffers from many singular points. Singularity-spreading methods are useful for the noisy image to regularize the singularity. However, the methods have a drawback of distorting phase distribution in a regular area that contains no singular points. When the singular points are confined in some local areas, the regular region is not distorted. This paper proposes a new phase unwrapping algorithm that uses a localized compensator obtained by clustering and by solving Poissons equation for the localized areas. The numerical results demonstrate that the proposed method can improve the accuracy compared with other singularity-spreading methods.

(Ce 2.5–30 mol%) Single Crystals Prepared by the Floating Zone Method

The spatial distribution of OH radical density was measured in an atmospheric-pressure dc helium glow plasma produced between a nozzle anode and an electrolyte cathode. Laser-induced fluorescence imaging spectroscopy was applied to measuring OH density. To obtain the accurate distribution of OH density, we carefully examined the spatial distributions of collisional quenching frequency and rotational temperature. The distribution of OH radical density indicates that the surface of the electrolyte cathode works as the sink of OH radicals, suggesting the transport of OH radicals from the gas phase into the inside of the electrolyte.

Phase unwrapping for noisy phase map using localized compensator

Phase unwrapping still plays an important role in many data-processing chains based on phase information. Here, we introduce a new phase unwrapping approach for noisy wrapped phase maps of continuous objects to improve the accuracy and computational time requirements of phase unwrapping using a rotational compensator (RC) method. The proposed algorithm is based on compensating the singularity of discontinuity sources. It uses direct compensation for adjoining singular point (SP) pairs and uses RC for other SP pairs. The performance of the proposed method is tested through both simulated and real wrapped phase data. The proposed algorithm is faster than the original algorithm with the RC and has proved efficiency compared to other phase unwrapping methods.

Spatial distribution of OH radical density in atmospheric-pressure dc helium glow plasma in contact with electrolyte solution

Authors have been working in particle accelerator wake field analysis by using the Time Domain Boundary Element Method (TDBEM). A stable TDBEM scheme was presented and good agreements with conventional wake field analysis of the FDTD method were obtained. On the other hand, the TDBEM scheme still contains difficulty of initial value setting on interior region problems for infinitely long accelerator beam pipe. To avoid this initial value setting, we adopted a numerical model of beam pipes with finite length and wall thickness on open scattering problems. But the use of such finite beam pipe models causes another problem of unwanted scattering fields at the beam pipe edge, and leads to the involvement of interior resonant solutions. This paper presents a modified TDBEM scheme, Scattered-field Time Domain Boundary Element Method (S-TDBEM) to treat the infinitely long beam pipe on interior region problems. It is shown that the S-TDBEM is able to avoid the excitation of the edge scattering fields and the involvement of numerical instabilities caused by interior resonance, which occur in the conventional TDBEM.

Reliable phase unwrapping algorithm based on rotational and direct compensators

Phase unwrapping still plays an important role in the optical metrology field. The phase unwrapping process has direct influence on the accuracy of final results. The aim of this article is to evaluate the performance of several well-known phase unwrapping algorithms for noisy phase measurement. The results of the examined algorithms on simulated and real phase data are presented, and the conclusions regarding the performances of each studied algorithm are given.

Scattered-field time domain boundary element method and its application to transient electromagnetic field simulation in particle accelerator physics

Dependence of crystal structure and luminescence property of Gd2Si2O7(Ce:GPS) was investigated using poly-crystalline samples synthesized by a solid state reaction method. Three types of crystal structures and different luminescence spectra were observed according to concentration of cerium. The largest luminescence intensity was observed for orthorhombic structure whose cerium concentration was between 0.75 and 2.5 mol%.

Performance Evaluation of Phase Unwrapping Algorithms for Noisy Phase Measurements

Abstract The multiple reciprocity boundary element method (MRBEM) has been employed to solve the three-dimensional Helmholtz equation, ▿ 2 gf + k 2 gf = 0. In the present technique, the Helmholtz equation is arranged as ▿ 2 gf + k 0 2 gf + gf / γ = 0 where k 0 is an estimate of k and λ is equal to ( k 2 − k 0 2 ) −1 . As the term gf/λ is treated as a source, the power iteration technique with Wielandts spectral shift is used to find the value of λ. The boundary integral equation is formulated with the fundamental solution to ▿ 2 gf + k 0 2 gf + δ i = 0. The domain integral related to the above source is transformed into a series of boundary integrals, with the aid of the higher order fundamental solutions based on the spherical Bessel functions. The eigenvalue k 2 can also be described using only boundary integrals. Test calculations demonstrate that the present technique is efficient for finding k 2 and easier to handle than the conventional determinant search scheme.