Bing Tang

A PLASEN (Precision LAser Spectroscopy for Exotic Nuclei) system, consisting of a compact radio-frequency quadrupole cooler buncher (RFQ-cb) and a collinear resonance ionization spectroscopy setup, has now been fully commissioned with radioactive ion beams at the Beijing Radioactive Ion-beam Facility (BRIF). Using both stable and radioactive Rb ion beams from BRIF, we demonstrated that the large beam energy spread observed at BRIF has been successfully handled by employing the RFQ-cb, enabling the delivery of high-quality bunched radioactive ion beams for collinear resonance ionization spectroscopy experiments. Under these conditions, we performed laser spectroscopy of exotic nuclei, achieving high resolution ( ∼ 100 MHz spectral linewidth) and high sensitivity ( ∼ 1 : 200 efficiency). This fully operational PLASEN system will serve as a state-of-the-art experimental platform at BRIF for research in multiple fields such as nuclear, atomic, and molecular physics.

The Beijing Radioactive ion beam facility Isotope Separator On-Line (BRISOL) is a radioactive ion beam facility based on a 100MeV cyclotron providing 200μA proton beam bombarding the thick target to produce radioactive nuclei, which are transferred into an ion source to produce singly charged ion beams. A surface ion source had been developed for BRISOL, and the first radioactive beams ( ³⁷ K ⁺ , ³⁸ K ⁺ , ⁴² K ⁺ , etc.) were produced by bombarding a CaO target with a 100MeV proton beam from the cyclotron in 2015. A FEBIAD ion source with MgO target are successfully used in the first physics experiments, including the decay study of ²⁰ Na with the energy of 110keV and the elastic scattering study of ²¹ Na and ²² Na beams, post-accelerated by a 13MV tandem. The refractory carbide targets such as SiC, LaC ₂ and UC ₂ are also developing for more radioactive beams. The first online test of SiC target has been completed recently, and radioactivity beams of ²⁵ Al, ²⁶ Al, and ²⁸ Al were produced. The details of the development of BRISOL facility and the online experimental results will be presented in this paper.

A negative helium ion source for tandem accelerator has been developed and built. The system consists of a multi-cusp ion source, a beam extraction and focusing system, a charge exchange cell (CEC), and a beam analysis and measurement system. The yield of He ⁻ was optimized by adjusting both the temperature of the CEC and the injection energy of He ⁺ beam. The results indicate that the He ⁺ beam current of up to 200 μA (20 keV) can be generated without CEC, and the maximum yield of the He ⁻ beam is 1.5 μA (6 keV) using cesium as a charge exchange medium, and 2 μA (7 keV) with rubidium as the charge exchange medium.

Present and future rare isotope accelerator facilities provide new opportunities to explore the structure of unstable nuclei. We report the measurements of the elastic scattering angular distributions of ²¹Na and ²²Na on the doubly magic ⁴⁰Ca above the Coulomb barrier energies, using high-purity post-accelerated ISOL beams from Beijing Radioactive Ion Beam Facility (BRIF). Angular distributions were measured with a silicon detector telescope array, and relative cross sections were determined with a CaF₂ target on Au backing. The data were well reproduced by optical model calculations with Woods–Saxon and USNP potentials, the latter giving better agreement. These results confirm the stable operation and performance of the BRIF ISOL production and post-acceleration system, demonstrate its capability to provide radioactive beams of useful intensity and purity for future investigations of reaction dynamics and astrophysically relevant processes involving proton-rich nuclei, and simultaneously extend proton-rich elastic scattering studies to heavier systems.