In this article, the effect of admixture gas on the heating and cooling of pinched plasma directly related to the enhancement or reduction of 18 F production through the 16 O( 3 He, p) 18 F is considered in the plasma focus devices. It is shown that by controlling the velocity of added Oxygen particles mixed with the working helium gas into the plasma focus chamber, one can increase the current and decrease the confinement time (plasma heating) or vice verse (plasma cooling). The highest level of nuclear activities of 18 F was found around 16% of the Oxygen admixture participation and was about 0.35MBq in the conditions of 20kJ, 0.1Hz and after 2min operating of Dena PF. However, in the same condition, but for the frequency of 1Hz, the level of activity increased up to 3.4MBq.