A cryogenic gas target for high-intensity radioactive ion beam production at HIRFL-RIBLL

Abstract

A liquid-nitrogen-cooled cryogenic gas target system has been developed and installed for radioactive ion beam (RIB) production at the Radioactive Ion Beam Line in Lanzhou (RIBLL). Light-element gases (${\mathrm{H}}_2$, ${\mathrm{D}}_2$, and ${}^4\mathrm{He}$) filled in the target cell were cooled to cryogenic temperatures, with the gas-cell outlet temperature typically monitored at 82--86 K during beam irradiation and operating pressures up to 1000 mbar. The system was used to produce ${}^7\mathrm{Be}$, ${}^{16}\mathrm{N}$, and ${}^{15}\mathrm{O}$ RIBs via the ${}^1\mathrm{H}{(}^7\mathrm{Li}{,}^7\mathrm{Be})n$, ${}^2\mathrm{H}{(}^{15}\mathrm{N}{,}^{16}\mathrm{N})p$, and ${}^1\mathrm{H}{(}^{15}\mathrm{N}{,}^{15}\mathrm{O})n$ inverse kinematics reactions, yielding purities of 85\%, 99\%, and 95\%, with intensities of $1.02\times 10^6$, $2.7\times 10^5$, and $1.0\times 10^5$ pps, respectively. A ${}^{93m}\mathrm{Mo}$ isomer beam was also produced via the ${}^4\mathrm{He}{(}^{94}\mathrm{Zr},5n{)}^{93m}\mathrm{Mo}$ reaction, achieving an intensity of $5.38\times 10^3$ pps and a purity of 20\% (which can be further improved to $\sim$50\% with offline time-of-flight gating). By delivering a broader range of high-intensity secondary RIBs, this setup establishes a robust platform at RIBLL for low- and medium-energy nuclear astrophysics and reaction studies.