Towards the full realization of the RIBLL2 beam line at the HIRFL-CSR complex

Abstract

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...

Improvement of charge resolution for radioactive heavy ions at relativistic energies using a hybrid detector system

“…Secondary beams were produced via the projectile fragmentation reactions. Radioactive nuclei of interest were produced, separated in flight at a velocity of around 70% speed of light with the first half of RIBLL2 and then delivered to the external target facility (ETF) [14]. The experiment setup is shown in Fig.…”

Isotopic production cross sections of fragmentation residues produced by 18O ions on a carbon target near 260 MeV/nucleon*

“…The experiment was conducted at the HIRFL-CSR facility [20,21] in Lanzhou (China). The 18 O primary beam was transported to the entrance of the second Radioactive Ion Beam Line in Lanzhou (RIBLL2) [22] to impinge on a primary Be target.…”

Charge-changing cross section measurements of atomic nuclei and charge radii

“…MeV/nucleon能区开展的Li同位素链的截面测量 [15] , 另 一个是Chulkov等人 [16] Chulkov等人 [16] 的工作也触发了一系列的理论研 究. Meng等人 [17] 在Glauber模型的框架下, 利用由相对 主要针对稳定线附近的原子核进行系统测量 [20,21] ; 德 国GSI主要关注1 GeV/nucleon等较高能量条件下Z<10 不稳定原子核的截面测量 [22~25] ; 日本RIKEN因具备当 前性能最好的次级束流条件, 主要瞄准质量更重、产 额更低的奇特原子核, 如 30 Ne和 [32][33] Na [26] . 相对于较高 能量, 在较低能量开展电荷改变反应截面的测量工作 面临着一些难点, 既有因产物角分布过大而对探测装 置接受度的挑战, 也有对反应产物能谱进行精确解析 的分析困难.…”