Search

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.

International audience; Isochronous mass spectrometry based on heavy-ion storage rings is a powerful tool for direct mass measurements of very short-lived nuclei. Owing to the nature of in-flight separation of high-energy reaction products, many ion species with different mass-to-charge ratios (m/q) can be transmitted to and stored in the ring in one shot. However, high mass resolving power can be achieved only for a limited range of ion species with velocities well matching the isochronous condition of the ring. The knowledge of velocities of each stored ions is required to overcome this restriction. For this purpose, two time-of-flight (TOF) detectors were installed 18 m apart in one straight section of the cooler-storage ring CSRe in Lanzhou. The time sequences measured by the two TOF detectors for each stored ion were used for the precision determination of its velocity. A relative precision of the velocity is achieved to the level of 10-5 for individual ions. The betatron oscillations of the ion motion in the ring were clearly identified in the data and were taken into account in the analysis. The presented technique can be used for measurements of machine tunes and their dependence on particle momenta.

To achieve high-resolution selection and separation of mono-isotopic beams through projectile fragmentation or in-flight fission and to efficiently transport the secondary beams to the Rare-RI Ring (R3) for mass determination, the BigRIPS separator combined with the High-resolution Achromatic (HA) beam-line of SHARAQ is served as a two-stage separator. The first stage from F0 to F2 is used for separation of the nuclei of interest through a Bρ-ΔE-Bρ method and the second stage from F3 to S0 is employed for identification of the beam with a Bρ-ΔE-TOF method. With this scheme, all the secondary ions can be well separated on an event by event basis and be utilized for mass measurements by two complementary methods: the conventional magnetic-rigidity-time-of-flight (Bρ-TOF) method employing the BigRIPS-HA beam-line to measure exotic nuclides within 1 μ s and the newly established isochronous mass spectrometry (IMS) approach via the R3 with a measurement duration less than 1 ms. This report presents the technique advances of the BigRIPS-HA-SHARAQ-R3 as a separator/spectrometer and give a brief description of its application to the complementary TOF methods for mass measurements at RIBF.

An electrostatic time-of-flight detector named E-MCP has been developed for quick diagnostics of circulating beam and timing measurement in mass spectrometry at the Rare-RI Ring in RIKEN. The E-MCP detector consists of a conversion foil, potential grids, and a microchannel plate. Secondary electrons are released from the surface of the foil when a heavy ion hits it. The electrons are accelerated and deflected by 90$^\circ$ toward the microchannel plate by electrostatic potentials. A thin carbon foil and a thin aluminum-coated mylar foil were used as conversion foils. We obtained time resolutions of 69(1) ps and 43(1) ps (standard deviation) for a $^{84}$Kr beam at an energy of 170 MeV/u when using the carbon and the aluminum-coated mylar foils, respectively. A detection efficiency of approximately 90% was obtained for both foils. The E-MCP detector equipped with the carbon foil was installed inside the Rare-RI Ring to confirm particle circulation within a demonstration experiment on mass measurements of nuclei around $^{78}$Ge produced by in-flight fission of uranium beam at the RI Beam Factory in RIKEN. Periodic time signals from circulating ions were clearly observed. Revolution times for $^{78}$Ge, $^{77}$Ga, and $^{76}$Zn were obtained. The results confirmed successful circulation of the short-lived nuclei inside the Rare-RI Ring.

We developed a time-of-flight (TOF) detector for mass measurements of rare radioactive isotopes (RIs) with a storage ring, called the Rare-RI Ring, in RIKEN. For successful mass measurements, a time resolution of less than 100 ps and a detection efficiency close to 100% are required. Additionally, the change of ion velocity in the detector should be as small as possible ( 1 0 − 4 ). To satisfy these requirements, the TOF detector utilizes ion-induced secondary electrons emitted from a thin foil and the crossed static electric and magnetic fields to transport the electrons isochronously to the microchannel plate detectors. The TOF detector was tested in both offline test with an alpha source and online test with heavy ions. In the online test with 84Kr ions of 200 MeV/nucleon, a time resolution of 38.6(2) ps in sigma and a position-averaged detection efficiency of 95.2(2)% were achieved in the entire area of 45-mm-diameter aluminum-coated Mylar foil. This good performance is attributed to the electromagnetic field achieved, which is the strongest thus far for a detector with this design.

A time detector is under development for the mass measurement with the Rare-RI (radioactive iso- tope) Ring at the RI beam factory (RIBF) in RIKEN. To perform successful mass measurement, a time detector requires a small energy loss of the ion beams, a good time resolution, and a suf- ficient detection efficiency. To satisfy these requirements, our time detector utilizes isochronous transport of the secondary electrons emitted from a thin foil. The isochronous transport of the electrons from the foil to the micro-channel plate (MCP) detector is provided by the crossed electromagnetic field. To improve the detection efficiency, the transport time of the electrons is reduced by a factor of two using a strong magnetic field. An experiment to test the performance of the time detector was carried out with heavy ion beams. The time resolution was σ < 100 ps with a maximum detection efficiency of 99% for heavy ion beams. The details of the detector are presented in this contribution.