In this study, a Monte Carlo code was used to simulate a proton beam flux to calculate the Tc-94m production yield from the Mo-94(p,n)Tc-94m reaction. An experimental yield of 3.465 GBq/mu Ah was measured for 48 min of irradiation at 1 mu A. An estimated value of 3.048 GBq/mu Ah was calculated for the yield produced based on the MCNPX proton flux in the same situation. These results demonstrate the usefulness and precision of MCNPX as a tool to design targets for the production of PET radionuclides. The yield of isotopic impurities from the Mo-94(p,xn)(94g,) (93m,) Tc-93g, 93gTc reactions was also calculated by the MCNPX code. (C) 2013 Elsevier Ltd. All rights reserved.