W. Kosiński, K. Saxton, and R. Saxton, “Second sound speed in a crystal of NaF at low temperature”, Arch. Mech., vol. 49, no. 1, pp. 189–196, Jan. 1997, Accessed: Jan. 17, 2026. [Online]. Available: http://am.ippt.gov.pl/index.php/am/article/view/v49p189