Customized calibration sources in the JUNO experiment

We customized a laser calibration system and four radioactive $\gamma$-ray calibration sources for the Jiangmen Underground Neutrino Observatory (JUNO), a 20-kton liquid scintillator-based neutrino detector. The laser source system was updated to realize the isotropic light emission timing within $\pm 0.25$~nsec level and to allow the tuning of the laser intensity covering more than four orders of magnitude. In addition, methods to prepare four different radioactive sources (${}^{18}\mathrm{F}$, ${}^{40}\mathrm{K}$, ${}^{226}\mathrm{R}\mathrm{a}$, and ${}^{241}\mathrm{A}\mathrm{m}$), covering energies from O(10)~keV to O(1)~MeV, for the JUNO detector were established in this study. The radioactivity of each source and the risk of impurities leaking into the detector from the source were confirmed to meet the experimental requirements.