A system for collecting MNCs to be treated with irradiation comprises a fluid circuit comprising a product container for receiving a MNC product. The system comprises a separator to work in association with the fluid circuit, the separator comprising a chamber for separation into RBCs, plasma, and an interface carrying MNCs between the RBCs and the plasma. A microprocessor-based controller is in communication with the separator, wherein the controller receives input of a target hematocrit for the MNC product. The controller also receives input for a total volume of whole blood and a number of cycles, and directs the interface and a portion of the RBCs into the product container for a resulting product volume comprising a volume of MNCs and a volume of RBCs. The controller automatically adjusts a RBC volume so that a ratio of RBCs within the MNC product to MNC product equals the target hematocrit.
