Study of the concentrations of Kr and Ar in high-purity nitrogen of JUNO

Purpose In the JUNO, the LS serves as the medium for detecting neutrinos. When purifying the LS using HPN, it is essential to ensure low background levels of radioactive krypton and argon in the HPNMethods Using the low-temperature physical adsorption properties of activated carbon to adsorb and separate radioactive gases such as radon, krypton, and argon from nitrogen in a liquid nitrogen environment.
Results Our results indicated that the ⁸⁵Kr concentration in the HPN purified by HP activated carbon is 6.84 μBq/m³, and the ³⁹Ar concentration is 3.6 μBq/m³ for overground HPN, while the ⁸⁵Kr concentration is 31.4 μBq/m³ for underground HPN. The ⁸⁵Kr concentration in the nitrogen purified by coconut shell activated carbon is 0.46 μBq/m³.
Conclusions After adsorption with activated carbon, the content of ⁸⁵Kr and ³⁹Ar in HPN is lower than the 50 μBq/m³ required by JUNO. This work validates that the ⁸⁵Kr and ³⁹Ar concentrations in HPN is fit the JUNO requirement.