Development of polarized nuclear targets using dynamic nuclear polarization of mechanically ground nano-particles dissolved in ethanol matrix with TEMPO

La-139 is one of the candidates for the polarized nuclear targets in the T-violation measurement experiment, NOPTREX at J-PARC. Dynamic Nuclear Polarization (DNP) of LaAlO₃ crystal achieved rather high polarizations of La-139, up to +47.5 % and -56.5 %. However, there are technical difficulties on growing a large crystal with good purity, controlling the density of the polarized agency Nd₃⁺, and handling of the target material, whose crystal axis must be aligned with a magnetic field for DNP. In order to overcome these difficulties, we propose an alternative and simple method, which can be widely applied for polarizing the nuclei in other materials. LaF₃ was ground into nanoparticles with a size of 30 nm at maximum by using a planetary ball-milling machine. The nanoparticles were dispersed in an ethanol matrix containing a free radical, TEMPO. At a magnetic field of 2.5 T and temperature of 0.9K, DNP of the nanoparticles was performed. The polarization of F-19 in the nanoparticles reached about 3 %, which was 2/3 as high as those for H-1 in the ethanol. The polarization difference may indicate polarization mechanism. Details of the target material preparation and results of the DNP test will be presented.