10 research outputs found
Development of fast-response PPAC with strip-readout for heavy-ion beams
A strip-readout parallel-plate avalanche counter (SR-PPAC) has been developed
aiming at the high detection efficiency and good position resolution in
high-intensity heavy-ion measurements. The performance was evaluated using 115
MeV/u Xe, 300 MeV/u Sn, and 300 MeV/u Ca beams. A
detection efficiency beyond 99% for these beams is achieved even at an incident
beam intensity of 0.7 billion particles per second. The best position
resolution achieved is 235 um (FWHM).Comment: 16 pages, 18 figures, 2 table
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
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
Performance of prototype Dual Gain Multilayer Thick GEM with high-intensity heavy-ion beam injections in low-pressure hydrogen gas
A prototype Dual Gain Multilayer Thick Gas Electron Multilyer (DG-M-THGEM)
with an active area of 10 cm 10 cm was manufactured aiming at the
production of a large-volume active-target time projection chamber which can
work under the condition of high-intensity heavy-ion beam injections. The
DG-M-THGEM has a alternating structure of electrodes and insulators. Effective
gas gains of two regions, which are called beam and recoil regions, are
separately controlled. Performance of the prototype DG-M-THGEM in hydrogen gas
at a pressure of 40 kPa was evaluated. Irradiating a Xe beam, an
effective gas gain lower than 100 with a charge resolution of 3% was achieved
in the beam region while the effective gas gain of 2000 was maintained in the
recoil region. Position distributions of measured charges along the beam axis
were investigated in order to evaluate gain uniformity in the high intensity
beam injection. The gain shift was estimated by simulations considering space
charges in the drift region. The gain shift was suppressed within 3% even at
the beam intensity of 2.5 10 particles per second.Comment: 19 pages, 14 figures, 3 table
Mass measurements of neutron-rich <math><mrow><mi>A</mi><mo>≈</mo><mn>90</mn></mrow></math> nuclei constrain element abundances
International audienceAtomic masses of the neutron-rich isotopes Ga83,84, Ge82–86, As82–89, Se82,84–91, Br85,86,89–92, Kr89,91,92, and Rb91 have been measured with high precision and accuracy using the multi-reflection time-of-flight mass spectrograph at the RIBF facility. The masses of As88,89 were measured for the first time and the mass uncertainties of Ge86 and Se90,91 were significantly reduced from several hundred keV to below the 10 keV scale. Investigation of shell evolution and potential subshell closures are proceeded by analysis of two-neutron separation energy systematics. As a result of the precise mass measurements, no prominent change on the slope of the two-neutron separation energy beyond N=56 is observed in Se isotopes, indicating the subshell closure effect at N=56 of Se does not exist. Also, various leading mass models are compared with the measurements. The impact of the more precisely known data on r-process nucleosynthesis calculations is investigated in light of these new mass measurements, showing a remarkable reduction of reaction-rate uncertainties
First direct mass measurement for neutron-rich <math><mmultiscripts><mi>Mo</mi><mprescripts/><none/><mn>112</mn></mmultiscripts></math> with the new ZD-MRTOF mass spectrograph system
International audienceThe atomic masses of Ag111,113, Pd111–113, Rh111–113, Ru111–113, and Mo111,112 have been measured during the online commissioning experiments of the ZeroDegree multi-reflection time-of-flight Mass Spectrograph (ZD MRTOF-MS) at the RIKEN RI beam factory. The mass of Mo112 has been determined. For the previously known masses, a good agreement between our results and the 2020 Atomic Mass Evaluation has been observed in most cases. The determined two-neutron separation energies for Mo isotopes up to N=70 show a smooth trend. In this work, the performed experiment and analysis procedure are presented. The theoretical interest in the measured region is highlighted, and the results are discussed in terms of the various mass surface formulas including the new mass data. Furthermore, a comparison between our results and global theoretical mass models is given, and we provide a benchmark for results from a Bayesian machine learning algorithm for future mass extrapolation