47 research outputs found
The new MRTOF mass spectrograph following the ZeroDegree spectrometer at RIKEN's RIBF facility
A newly assembled multi-reflection time-of-flight mass spectrograph
(MRTOF-MS) at RIKEN's RIBF facility became operational for the first time in
spring 2020; further modifications and performance tests using stable ions were
completed in early 2021. By using a pulsed-drift-tube technique to modify the
ions' kinetic energy in a wide range, we directly characterize the dispersion
function of the system for use in a new procedure for optimizing the voltages
applied to the electrostatic mirrors. Thus far, a mass resolving power of is reached within a total time-of-flight of only
, making the spectrometer capable of studying short-lived
nuclei possessing low-lying isomers. Detailed information about the setup and
measurement procedure is reported, and an alternative in-MRTOF ion selection
scheme to remove molecular contaminants in the absence of a dedicated
deflection device is introduced. The setup underwent an initial on-line
commissioning at the BigRIPS facility at the end of 2020, where more than 70
nuclear masses have been measured. A summary of the commissioning experiments
and results from a test of mass accuracy will be presented.Comment: 13 pages, 11 figure
First Direct Mass Measurements of Nuclides around Z=100 with a Multireflection Time-of-Flight Mass Spectrograph
The masses of 246Es, 251Fm, and the transfermium nuclei 249−252Md and 254No, produced by hot- and cold-fusion reactions, in the vicinity of the deformed N=152 neutron shell closure, have been directly measured using a multireflection time-of-flight mass spectrograph. The masses of 246Es and 249,250,252Md were measured for the first time. Using the masses of 249,250Md as anchor points for α decay chains, the masses of heavier nuclei, up to 261Bh and 266Mt, were determined. These new masses were compared with theoretical global mass models and demonstrated to be in good agreement with macroscopic-microscopic models in this region. The empirical shell gap parameter δ2n derived from three isotopic masses was updated with the new masses and corroborates the existence of the deformed N=152 neutron shell closure for Md and Lr
A new study of the and shell gap for Ti and V by the first high-precision MRTOF mass measurements at BigRIPS-SLOWRI
The atomic masses of Sc, Ti, and V have been
determined using the high-precision multi-reflection time-of-flight technique.
The radioisotopes have been produced at RIKEN's RIBF facility and delivered to
the novel designed gas cell and multi-reflection system (ZD MRTOF), which has
been recently commissioned downstream of the ZeroDegree spectrometer following
the BigRIPS separator. For Ti and V the mass uncertainties
have been reduced down to the order of , shedding new light
on the shell effect in Ti and V isotopes by the first high-precision
mass measurements of the critical species Ti and V. With the new
precision achieved, we reveal the non-existence of the empirical
two-neutron shell gaps for Ti and V, and the enhanced energy gap above the
occupied orbit is identified as a feature unique to Ca. We
perform new Monte Carlo shell model calculations including the
and orbits and compare the results with conventional shell model
calculations, which exclude the and the orbits. The
comparison indicates that the shell gap reduction in Ti is related to a partial
occupation of the higher orbitals for the outer two valence neutrons at
Beta decay of the axially asymmetric ground state of 192Re
The β decay of 75192Re117, which lies near the boundary between the regions of predicted prolate and oblate deformations, has been investigated using the KEK Isotope Separation System (KISS) in RIKEN Nishina Center. This is the first case in which a low-energy beam of rhenium isotope has been successfully extracted from an argon gas-stopping cell using a laser-ionization technique, following production via multi-nucleon transfer between heavy ions. The ground state of 192Re has been assigned Jπ=(0−) based on the observed β feedings and deduced logft values towards the 0+ and 2+ states in 192Os, which is known as a typical γ-soft nucleus. The shape transition from axial symmetry to axial asymmetry in the Re isotopes is discussed from the viewpoint of single-particle structure using the nuclear Skyrme-Hartree-Fock model
Paricle identification at VAMOS++ with machine learning techniques
Multi-nucleon transfer reaction between 136Xe beam and 198Pt target was performed using the VAMOS++ spectrometer at GANIL to study the structure of n-rich nuclei around N=126. Unambiguous charge state identification was obtained by combining two supervised machine learning methods, deep neural network (DNN) and positional correction using a gradient-boosting decision tree (GBDT). The new method reduced the complexity of the kinetic energy calibration and outperformed the conventional method improving the charge state resolution by 8%
Laser Ram Microprobe Analysis of Graphite Exposed to Edge Plasma in the TEXTOR Tokamak
An isotropic fine grain graphite (EK98) block has been exposed to the edge plasma in the TEXTOR tokamak and studied by Raman spectroscopy. Spectra from the net erosion area and deposition area where co-deposits (hard layer) were created by the tokamak discharges, are remarkably different. The spectra at the net erosion areas consist of two sharp peaks: the D-peak (1355 cm-') and the G-peak (approximate to 1580 cm(-1)). The spectra at the net deposition areas were very broad, which are similar to the Raman spectra of amorphous carbon. Fitting analyses of the Raman spectra for the net erosion area exhibit a linear relationship between the G-peak width (FWHMG) and the peak intensity ratio (I-D/I-G). Comparison with the diagram derived for ion-irradiated graphite revealed that thermally unstable defects of single vacancies scarcely remained due to the power loading in this plasma exposure condition but thermally stable defects such as the dislocation dipoles could be accumulated. (c) 2007 Elsevier B.V. All rights reserved