Scintillation efficiency of nuclear recoils in a CaF2(Eu) crystal for Dark Matter search

The scintillation efficiency (quenching factor) of fluorine and calcium nuclei recoiling in a CaF2(Eu) crystal was measured in an energy region relevant to Dark Matter searches. The recoiling nuclei were obtained via the 19F(n,n′) and 40Ca(n,n′) reactions, where the neutron beam was provided via the d(d,n)3He reaction. The quenching factor of F and Ca nuclei in the CaF2(Eu) crystal was found to be 11–20%, and 9–23% relative to the electron equivalent energy for 53–192 keV and 25–91 keV recoil energies, respectively, and the energy dependence was observed. The quenching factor we measured here is a little larger than that of previous studies, which may depend on the Eu doping concentration of the crystal.