1. É. M. Krisyuk, ?Radioactivity standards for building materials,? Gigiena Sanitariya, No. 12, 32?34 (1980).
2. NRB-76 Radiation Safety Standards and OSP-72/80 Health Regulations [in Russian], Énergoizdat, Moscow (1981), p. 19.
3. Ionizing Radiation-Sources and Biological Effects, UNSCEAR Report 1982, UN, N.Y. (1982), Vol. 1, p. 220.
4. V. I. Karpov and É. M. Krisyuk, Photon Emission of Natural Radionuclides [in Russian], Preprint NKRZ 79-14, Atomizdat, Moscow (1979), p. 19.
5. Evaluated Nuclear-Physical Characteristics of Radioactive Nuclides Used in the National Economy (Handbook) [in Russian], Énergoizdat, Moscow (1982).