Disclosed herein are a method and an apparatus to identify alpha-emitting radionuclides and to measure absolute alpha radioactivity using a low temperature detector. A 4π metallic absorber which encloses a radioactive material containing alpha-emitting radionuclides absorbs the total alpha decay energy in the form of thermal energy. The corresponding temperature changes are measured by a low temperature detector attached to the 4π absorber with high energy resolution. The identification of alpha-emitting radionuclides is declared by comparing the measured temperature signal with characteristic decay energy of radionuclides. The absolute amount of the radionuclides is determined by counting the number of the pulses for each of the identified nuclides.