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

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 $\mathrm{^4He}$) filled in the target cell were cooled to approximately 82-86 K with pressures up to 1000 mbar. Utilizing this target, high-quality $^{7}\mathrm{Be}$, $^{16}\mathrm{N}$, and $^{15}\mathrm{O}$ RIBs were successfully produced via the $^{1}\mathrm{H}(^{7}\mathrm{Li}, n)^{7}\mathrm{Be}$, $^{2}\mathrm{H}(^{15}\mathrm{N}, p)^{16}\mathrm{N}$, and $^{1}\mathrm{H}(^{15}\mathrm{N}, n)^{15}\mathrm{O}$ inverse kinematics reactions, yielding high purities of 85%, 99%, and 95%, with intensities of $1.02\times10^{6}$, $2.7\times10^{5}$, and $1\times10^{5}$ pps, respectively. Notably, a $^{93m}\mathrm{Mo}$ isomer beam was also produced via the $\mathrm{^4He(^{94}Zr, 5n)}$ reaction, achieving an intensity of $5.38\times10^{3}$ pps and an purity of 20% (which can be further improved to $\sim$50% with offline TOF gating). A broader range of high-intensity secondary RIBs is expected to be accessible using this setup, widely facilitating low- and medium-energy experiments in nuclear astrophysics and reaction mechanisms.