Experimental test of the possible violation of the Pauli exclusion principle by photo-activation analysis of carbon content in pure boron

Experiments which search for chemically boron-like carbon nuclei in samples of pure boron were carried out by a photo-activation technique. Use was made of the ¹²C(γn)¹¹C reaction with irradiation by bremsstrahlung photons of below 30 MeV. The resulting positron active isotope carbon-11 has a half-life of 20 min, and there are no radioactive nuclides formed by boron. These features of carbon-11 allow use of the rather sensitive and selective γ-γ coincidence technique to detect carbon nuclei. Special radiochemical procedures were developed for purification of the samples from initial carbon and metal impurities in the samples. Experimental results provided an estimate of the lifetime of atomic electrons relative to the Pauli exclusion principle of T > 10²¹ yr.