Keywords: Rare-isotope beam, Fragment separator, 300 MeV/nucleon PACS numbers:More than 99% of the mass in the visible universethe material that makes up ourselves, our planet, stars -is in the atomic nucleus. Although the matter has existed for billions of years, only over the past few decades have we had the tools and the knowledge necessary to get a basic understanding of the structure and dynamic of nuclei. Nuclear physicists around the world have made tremendous strides by initiating a broad range of key questions that can be best attacked with various experimental probes at different beam energies. Moreover, through these efforts, we have gained access to the origin of elements and the nucleosynthesis processes that were and still are shaping the world we are living in.The energy region at around 300 MeV gives rise to the so-called energy window for nuclear structure studies. At this energy range, the distortion effects on the projectile wave functions are relatively small due to the weak strength of the scalar-isoscalar interaction, which further suppresses the multistep processes in the nuclear reaction mechanism. This brings advantages in studying nuclear spin and isospin excitations [1] and nucleon density distribution of very exotic nuclei characterized by short lifetimes and very different isospins from the stable ones [2,3]. Quantitive investigations in the two topics can yield precision information on the weak interaction processes and on how protons and neutrons are distributed in atomic nuclei. They play important roles not only in nuclear physics but also in astrophysics for stellar events such as supernovae explosions.Experimentally, such investigations are closely linked to the availability of separators and spectrometers to select and identify the rare isotopes of interest at relativistic energies of around 300 MeV/nucleon (about 65% of the speed of light). Among all the separators operating at energies more than300 MeV/nucleon worldwide, the Second Radioactive Ion Beam Line in Lanzhou (RIBLL2), one of the key components in the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR) [4] at IMP, China, is unique to have an asymmetric double achromatic configuration.RIBLL2 was constructed in 2007 connecting the synchrotron cooler storage main ring (CSRm) and the experimental storage ring (CSRe) in the HIRFL-CSR complex. It has been utilized to deliver radioactive isotopes into the CSRe for mass measurements [5]. Yet its full potential as an individual experimental terminal has not been explored. The schematic layout of RIBLL2 and external target facility (ETF) is shown in Fig. 1(a).RIBLL2 has four independent sections, each consisting of a 25• dipole magnet and a set of quadrupole magnets before and after the dipole to fulfill first-order focusing conditions. Additional 8 hexapole and 4 octupole magnets are equipped for higher-order corrections. The whole separator is about 55 meters long, while the first half (F0-F2) and the second half (F2-F4) are about 26 and 29 meters, respectively. Shown in Fig...

Plastic scintillation detectors for Time-of-Flight (TOF) measurements are almost essential for event-byevent identification of relativistic rare isotopes. In this work, a pair of plastic scintillation detectors of 50 × 50 × 3 t mm 3 and 80 × 100 × 3 t mm 3 have been set up at the external target facility (ETF), Institute of Modern Physics. Their time, energy and position responses are measured with 18 O primary beam at 400 MeV/nucleon. After the off-line walk-effect and position corrections, the time resolution of the two detectors are determined to be 27 ps (σ) and 36 ps (σ), respectively. Both detectors have nearly the same energy resolution of 3% (σ) and position resolution of 2 mm (σ). The detectors have been used successfully in nuclear reaction cross section measurements, and will be be employed for upgrading RIBLL2 beam line at IMP as well as for the high energy branch at HIAF.

In typical nuclear physics experiments with radioactive ion beams (RIBs) selected by the in-flight separation technique, Si detectors or ionization chambers are usually equipped for the charge determination of RIBs. The obtained charge resolution relies on the performance of these detectors for energy loss determination, and this affects the particle identification capability of RIBs. We present an approach on improving the resolution of charge measurement for heavy ions by using the abundant energy loss information from different types of existing detectors along the beam line. Without altering the beam line and detectors, this approach can improve the charge resolution by more than 12% relative to the multiple sampling ionization chamber of the best resolution.

Abstract. The time-of-flight (TOF) mass spectrometry (MS), a high-resolution magnetic spectrometer equipped with a fast particle tracking system, is well recognized by its ability in weighing the most exotic nuclei. Currently such TOF-MS can achieve a mass resolution power of about 2 10 -4 . We show that the mass resolution can be further improved by one order of magnitude with augmented timing and position detectors. We report the progress in developing ultra-fast detectors to be used in TOF-MS.

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