Cu is an important trace metal which plays a role in many biological processes. The radioisotope ⁶⁴Cu is often used to study such processes. Furthermore, ⁶⁴Cu finds applications in cancer diagnostics as well as therapy. For all of these applications ⁶⁴Cu having high specific activity is needed. ⁶⁴Cu can be produced in cyclotrons or in nuclear reactors. In this paper we study the effect of gamma dose on the production of ⁶⁴Cu according to the Szilard-Chalmers reaction using Cu(II)-phthalocyanine as a target. For this purpose, irradiations were performed in the nuclear reactor of the Delft University of Technology using a novel irradiation facility helping to limit the dose produced by gammas present in the reactor pool. The obtained ⁶⁴Cu activity yield was in general above 60% in accordance to the theoretical expected value. An increase in gamma dose has no significant influence on the obtained activity yield but increases the loss of Cu from Cu(II)-phthalocyanine up to 0.9% and hence decreases the specific activity that can be obtained. However, without optimisation, when reducing the gamma dose specific activities in the order of 30 TBq/g can be achieved.