In the paper, a theoretical study to calculate the value of the radioactivity ‎of nitrogen-13 isotope required for use in positron emission tomography (PET) has been presented. The isotope is produced by deuteron beams from NX2 dense plasma focus ‎device. First the effect of three factors was studied, namely, the deuterium gas density, exposure ‎time and the repetition rate of the device. ‎The results showed an increase in radioactivity as deuterium gas pressure decreased. It was next possible to obtain four radioactivity values, suitable for use in PET, by varying the two rest factors.