Analysis of The Effect of Irradiation Time Variation On Radionuclide Activity Accumulation In Aluminum Target Holders For Cu-64 Radioisotope Production Using PHITS Simulation

Abstract

Cu-64 is an important radionuclide in nuclear medicine due to its applicability in both PET imaging and radionuclide therapy. One common production method is proton irradiation of a nickel-64 target via the ⁶⁴Ni(p,n)⁶⁴Cu reaction, in which the surrounding aluminum holder may become activated by secondary particles, producing radioactive by-products. This study aims to analyze the effect of irradiation time variation on the accumulated activity of by-product radionuclides in the aluminum holder using PHITS Monte Carlo simulation version 3.360 together with the DCHAIN-PHITS module, employing a 30 MeV proton beam and irradiation times ranging from 0.5 to 3 hours. The simulation results show that the activities of Na-24 and H-3 increase nearly linearly with irradiation time, rising approximately 5.7-fold and 6-fold, respectively, from 0.5 to 3 hours, while the total holder activity remains relatively constant as it is dominated by extremely short-lived radionuclides that reach saturation early in the irradiation process. Na-24 was identified as the most relevant by-product for post-irradiation radiation safety due to its high activity and half-life (15 hours), which influences the required cooling time before the holder can be safely handled, whereas H-3 constitutes a long-term residue despite its small contribution. This study concludes that extending irradiation time consistently increases the accumulated activity of by-product radionuclides, which should be considered in determining irradiation duration and radiation safety procedures in Cu-64 production.