Horodek, P., L. H. Khiem, K. Siemek, L. A. Tuyen, and A. G. Kobets. “Positron Annihilation Spectroscopy in Material Studies”. Communications in Physics, vol. 29, no. 4, Dec. 2019, p. 501, doi:10.15625/0868-3166/29/4/14282.