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BigRIPS is a powerful two-stage in-flight separator for the research with exotic nuclei studied in frontier experiments since more than a decade. The ion-optical system is very versatile due to the multi-stage structure of BigRIPS combined with the ZeroDegree spectrometer or the Superconducting Ring Cyclotron (SRC). Various optical modes can be flexibly realized according to the purpose of experiments. Two categories of developments are presented here. One is a new operating mode of BigRIPS aiming at higher ion-optical resolving power. BigRIPS itself has a two-stage structure. Spatial isotope separation is made at both the first and second stages. In the standard operating mode of BigRIPS, at the second stage the two spatial separations with energy degraders are subtractive in their resolving powers. Here, we present the additive mode. With the resulting increased spatial separation power, the isotopic background can be substantially reduced. Higher ion-optical resolving powers of the first and second BigRIPS degrader stages are also investigated with the goals to reduce further the background and to yield access to new isotopes of heavier elements. The other development is a dispersion-matched system with BigRIPS for high-resolution spectrometer experiments. The BigRIPS and ZeroDegree spectrometer are presently two independent, coupled achromatic systems. A new dispersion-matched mode of BigRIPS and ZeroDegree will enable novel experiments. For high-resolution spectroscopy experiments with high-intensity light projectiles, SRC and BigRIPS can be operated as a dispersion-matched system. The described different ion-optical developments are a base for a new category of experiments exploring exotic nuclei and mesic atoms. Characteristic future experiments with these new ion-optical developments are exemplified in this report.

A beam monitor is developed at the Rare-RI Ring storage ring facility at the RI beam factory at RIKEN. Because the Rare-RI Ring stores only a single exotic ion according to the operation principle, conventional beam instruments cannot be employed. In the present study, we design a simple monitoring system to confirm particle storage. The system comprises a thin foil and scintillators with photon sensors. When an ion passes through the foil, secondary electrons, including δ -rays, are emitted and are detected by a set of scintillation detectors without any guiding field. A beam test using 78 Ge with 175 MeV/nucleon successfully demonstrates the periodic revolution of the stored ions.

We have combined the low-energy neutron detector WINDS (Wide-angle Inverse-kinematics Neutron Detectors for SHARAQ) and the SAMURAI spectrometer at RIKEN Nishina Center RI Beam Factory (RIBF) in order to perform ( p , n ) reactions in inverse kinematics for unstable nuclei in the mass region around A ∼ 100 . In this setup, WINDS is used for detecting recoil neutrons and the SAMURAI spectrometer is used for tagging decay channel of heavy residue. The first experiment by using the setup was performed to study Gamow–Teller transitions from 132 Sn in April 2014. The atomic number Z and mass-to-charge ratio A / Q of the beam residues were determined from the measurements of time of flight, magnetic rigidity and energy loss. The obtained A / Q and Z resolutions were σ A / Q = 0.14 % and σ Z = 0.22 , respectively. Furthermore, owing to the large momentum acceptance ( 50 % ) of SAMURAI, the beam residues associated with the γ , 1n and 2n decay channel were measured in the same magnetic field setting. The kinematic loci of the measured recoil neutron energy and laboratory angle are clearly seen. It shows that the excitation energy up to about 20 MeV can be reconstructed.

Low-pressure multi-wire drift chambers have been developed to track high-intensity radioactive isotope beams at the energies of around 200 MeV/nucleon. In order to minimize the effect of multiple scattering by radioactive isotope beam, the thickness of the detectors were minimized by using isobutane gas at low pressure (10 kPa). The performance of the position resolution, the tracking efficiency, and the beam intensity capability were evaluated as a function of atomic number and applied voltage. As a result, an overall position resolution of 300 μm was achieved for radioactive isotope beams with an intensity of 1 MHz. The details of the design specifications and performances of the low-pressure multi-wire drift chambers are described.

An isochronous mass spectroscopy system using a newly constructed storage ring named the “rare-RI ring” is expected to be implemented at the RIKEN Nishina Center to determine the masses of short-lived rare nuclei including those in the r-process region with a relative precision of the order of 10 - 6 even for only one particle. In an isochronous storage ring, the mass is determined by measuring the revolution time of each nucleus. Our rare-RI ring consists of six magnetic sectors, and each sector consists of four bending magnets. To precisely optimize the isochronous conditions of the circulating particles for large acceptance, we install ten trim coils to half of the bending magnets. A fast-response and fast-charging kicker system enables selective and efficient injection of the produced rare nuclei into the ring one by one, along with facilitating efficient extraction of the circulating particles for time-of-flight measurement. Construction of the rare-RI ring was begun in the middle of the fiscal year 2012 at the RIKEN RI Beam Factory, and the ring is expected to be fully functional by 2015.

Proton polarization at room temperature, produced in a p-terphenyl crystal by using electron population difference in a photo-excited triplet state of pentacene, was enhanced by utilizing an intense laser with an average power of 1.5 W. It was shown that keeping the sample temperature below 300 K is critically important to prevent the rise of the spin–lattice relaxation rate caused by the laser heating. It is also reported that the magnitude of proton polarization strongly depends on the time structure of the laser pulse such as its width and the time interval between them.

The paper describes recent developments of diamond detector at CNS and discusses the timing signal transfer system suitable for optimizing its performance. The diamond detector is well known to have good properties as a radiation detector such as fast response and good radiation hardness. Consequently, it is an excellent candidate for serving as a high-resolution thin timing detector. CNS and NSCL/MSU started a collaboration to develop diamond detectors, and manufactured a detector with a size of 28 × 28 mm2 and thickness of 200 μm. An irradiation experiment of the detector was performed by using a 32-MeV α beam to check its basic performance. The CNS detector had almost 100% efficiency and a timing resolution of 27 ps ( σ ). Jitter in long optical-fiber signal-transfer lines was examined and found to be 10.7 ps ( σ ). Diamond detectors and signal transfer system using a optical fiber enable us to provide time-of-flight measurements with extremely high resolution.

The new heavy-ion storage ring project Rare-RI Ring at the RIKEN RI Beam Factory launched in 2012 aims at precision isochronous mass spectrometry for single ions of exotic nuclides. To precisely tune the storage-ring ion optical conditions to the isochronous field setting, Schottky noise pick-up technique will be employed. Pillbox-type resonant cavity, similar to the Schottky pick-up system successfully operating at the experimental storage ring ESR at GSI, is adopted for the pick-up probe. To determine the design values of the cavity, we systematically performed a simulation study of three-dimensional electromagnetic field calculations in the high frequency region. High shunt impedance obtained in the simulation will enable us to detect stored single ions with charge down to q ≃ 15 .

We are presently working on a new project ‘pionic atom factory project’ at RIBF. The project aims at precision spectroscopy of the energy spectrum of the pionic atom for a wide range of elements, using missing-mass spectroscopy of the (d,3Hed,3He) reaction near the π-π- emission threshold. For this project, we developed a new ion optics for BigRIPS using the dispersion-matching method. In this optics the BigRIPS beam line is used as a high resolving-power forward angle spectrometer to momentum-analyze 3He. We are aiming for a spectral resolution of

A large time-of-flight (TOF) detector has been developed for the Rare-RI Ring. This detector consists of a Multi Channel Plate (MCP) and a carbon foil. Secondary electrons from the carbon foil are transported to the MCP by crossed electric and magnetic fields. In order to cover the beam size of the ring, a large and thin carbon foil (100 mm × 50 mm2 and 60 μ g/cm2) is used as a sensitive material. The time resolution of σ ≈ 130 ps, the detection efficiency about 56% and a position dependence of the TOF about 1 ns are obtained. A calculated position dependence of TOF adopting experimental (inhomogeneous) electric field and a homogeneous magnetic field is in agreement with the experimental one. These results suggest that the homogeneity of electric field is important to improve the time resolution in the large size detector.

The high-resolution SHARAQ spectrometer is now under construction at RI Beam Factory (RIBF) of RIKEN. The spectrometer will be used in nuclear physics experiments in combination with a variety of radioactive isotope (RI) beams. It is designed to achieve a high momentum resolution of δp/p = 1/14,700 and a high angular resolution of δθ ∼ 1 mrad. Details of the ion-optical design and the newly-constructed magnets making up the spectrometer are described.

The high resolution beam line for the SHARAQ spectrometer was designed to satisfy the lateral and angular dispersion matching conditions based on the precise ion optical calculation using the measured magnetic field maps of the beam line magnets. The higher order aberration due to the large emittance of the secondary RI-beams was corrected by employing the three octupole magnets. A Monte Carlo calculation was carried out to examine the beam profile on the SHARAQ target, and it was found that the octupole magnets actually correct the higher order aberration.

Isochronous Mass Spectrometry (IMS) in heavy-ion storage rings is an excellent experimental method for precision mass measurements of exotic nuclei. In the IMS, the storage ring is tuned in a special isochronous ion-optical mode. Thus, the mass-over-charge ratios of the stored ions are directly reflected by their respective revolution times in first order. However, the inevitable momentum spread of secondary ions increases the peak widths in the measured spectra and consequently limits the achieved mass precision. In order to achieve a higher mass resolving power, the ring aperture was reduced to 60 mm by applying a mechanical slit system at the dispersive straight section. The momentum acceptance was reduced as well as better isochronous conditions were achieved. The results showed a significant improvement of the mass resolving power reaching $5.2 \times 10^{5}$, though at the cost of about 40\% ion loss., Comment: 6 pages, 6 figures, proceeding of EMIS2018