Khairi M.S. Abdullah, Tran., “A Method to Determine Doublet Photopeak Area 137Cs and 214Bi, in NORM Soil by NaI-detector”, Int.J. Fundam. Phys. Sci, vol. 5, no. 2, pp. 32–37, Jun. 2015, doi: 10.14331/ijfps.2015.330083.