arXiv subjects

H. Hirayama

Publications and source records attributed to H. Hirayama.

3 recordsLinked to original sources

arXiv2021

First high-precision direct determination of the atomic mass of a superheavy nuclide

We present the first direct measurement of the atomic mass of a superheavy nuclide. Atoms of $^{257}$Db ($Z$=105) were produced online at the RIKEN Nishina Center for Accelerator-Based Science using the fusion-evaporation reaction $^{208}$Pb($^{51}$V, 2n)$^{257}$Db. The gas-filled recoil ion separator GARIS-II was used to suppress both the unreacted primary beam and some transfer products, prior to delivering the energetic beam of $^{257}$Db ions to a helium gas-filled ion stopping cell wherein they were thermalized. Thermalized $^{257}$Db$^{3+}$ ions were then transferred to a multi-reflection time-of-flight mass spectrograph for mass analysis. An alpha particle detector embedded in the ion time-of-flight detector allowed disambiguation of the rare $^{257}$Db$^{3+}$ time-of-flight detection events from background by means of correlation with characteristic $α$-decays. The extreme sensitivity of this technique allowed a precision atomic mass determination from 11 events. The mass excess was determined to be $100\,063(231)_\textrm{stat}(132)_\textrm{sys}$~keV/c$^2$. Comparing to several mass models, we show the technique can be used to unambiguously determine the atomic number as $Z$=105 and should allow similar evaluations for heavier species in future work.

nucl-ex↗

arXiv2003

Development of an Interface for Using EGS4 Physics Processes in Geant4

As simulation system, the variety of physics processes implemented is one of the most important functionalities. In that sense, Geant4 is one of the most powerful simulation toolkits. Its flexibility and expansibility brought by object-oriented approach make it possible for us to easily assimilate external simulation packages into the Geant4 system as modules of physics processes. We developed an interface for using EGS4, which is another of the most well-known simulation package for electromagnetic physics, in Geant4. By means of this interface, EGS4 users can share Geant4 powerful resources, such as geometry, tracking, etc. It is also important that it can provide a common environment for comparison tests between EGS4 and Geant4. In this paper, we describe our design and implementation of the interface.

physics.comp-ph↗

arXiv2001

Electron microscopy of the strain on the Si(111)$7\times7$ surface induced by the STM tip

The Si(111)7x7 surface was observed by reflection electron microscopy (REM) and scanning tunneling microscopy (STM) simultaneously in an ultra-high vacuum electron microscope. The distance between the STM tip and the Si surface was detected from the REM image, which showed the real and the mirror image of the tip. We approached the tip to the surface or retracted from the surface by a piezo drive to observe the strain induced on the Si(111)7x7 surface as a function of the tip-surface distance. This investigation was done with and without the bias voltage between the tip and the substrate. With bias voltage of 1.0 V on the sample, the tip was approached to 1.6 nm above the sample surface for the tunneling current of 0.8 nA, no detectable order of strain (10^{-4}) was induced on the sample surface. When the bias decreased within the range of -0.3 - +0.5 V, the surface was compressed over the Si surface area of 100 nm. Without the bias voltage, tensile and compressive strain was detected as the tip-surface distance changed from attractive to the repulsive interaction regime. The strain field extended over 50 - 140 nm, and the force became neutral at the tip-substrate distance of 0.45 nm.

cond-mat.mtrl-sci↗