Optimizing tote transfer cycle time in a gamma irradiator via pneumatic system redesign: A case study of IGMP Indonesia

A low-cost mechanical–control retrofit for the Merah Putih Gamma Irradiator (IGMP) is presented, aimed at shortening tote-transfer cycle time and improving simulated dose uniformity without altering the source or shielding. The intervention simplifies the pneumatic sequence from nine to six stages and slightly reassigns two tote positions to preserve path symmetry relative to the 60 Co racks. Based on operational logs and prototype testing, the average cycle time decreased from ∼65.3 s to ∼43.2 s per cycle (≈33.7 %), reducing the minimum batch duration from ∼78 to ∼50 min and widening the operating window for low-dose services (e.g., phytosanitary treatment, sprout inhibition). To evaluate potential dose effects, a comparative MicroShield v7 calculation was performed across all 72 irradiation positions on two quasi-2D planes. The simulated range narrowed primarily by lifting the minimum from 91.98 mSv to 130.86 mSv, while the peak remained at 1050.34 mSv. Consequently, the Dose Uniformity Ratio (DUR) improved from 11.4 to 8.0, indicating better homogeneity. Position-level analysis shows tote #37 increasing from 91.98 mSv to 131.04 mSv after reassignment, whereas tote #55 remains essentially unchanged (∼145.69 mSv). Assuming total simulated dose is represented by sampled points, the 72-cycle total rises from 32,896.96 mSv to 32,935.02 mSv (≈+0.12 %). Limitations: the six-stage sequence has not yet been deployed in production; results are based on full-scale prototype testing and simulations using a free-field approximation (no bunker scatter). Therefore, validation by field dose mapping under production conditions is required. Overall, the retrofit offers a transferable sequencing framework for tote-based irradiators in resource-constrained settings.