Some classes of (mostly older) neutrino-detection experiments detect single radionuclides in many tons of material. https://en.wikipedia.org/wiki/Homestake_exp

Some classes of (mostly older) neutrino-detection experiments detect single radionuclides in many tons of material. https://en.wikipedia.org/wiki/Homestake_experiment https://en.wikipedia.org/wiki/Homestake_experiment is perhaps the most-famous, but GALLEX and SAGE use a similar approach. https://en.wikipedia.org/wiki/SAGE_(Soviet%E2%80%93American_Gallium_Experiment) https://en.wikipedia.org/wiki/SAGE_(Soviet%E2%80%93American_...