For measuring accurately the energy of relativistic high energy charged particles, we have constructed a novel transition radiation detector (TRD) utilizing superheated superconducting microspheres of tin with diameters in the range of 20-40 μm In order to enhance transition radiation for higher sensitivity, the TRD is in a special dilution refrigerator operated at~100 mK. Test has been conducted in a high energy electron beam facility at the CERN PS in the energy range of 1-10 GeV showing an energy dependence of the TR X-ray photon produced and hence the value γ=E/mc^2 of the charged particle.
