Method for Shielding Evaluation of Industrial Radiography with 192Ir

Background: Iridium-192 (192Ir) is one of the radioisotopes most commonly utilized for industrial radiography worldwide. In accordance with the Nuclear Safety Act of the Republic of Korea, the use of projectors containing 192Ir sources requires conducting a shielding evaluation for a given workplace. This evaluation usually uses gamma constants and half-value layers (HVLs). However, significant differences in these values among references can result in over- or underestimation of values.Materials and Methods: The radiological characteristics of the gamma constant and HVL of 192Ir sources employed in industrial radiography were studied with a focus on the effects of source configurations and usage conditions. The source configurations were categorized into point source, volume source (lateral/upward direction), and encapsulated source. The usage conditions, defined by variations in the lead thickness and the distance among the source, lead shield, and tally, enabled derivation of the HVL. Monte Carlo N-Particle version 6.2 (MCNP6.2) was used in these calculations.Results and Discussion: The gamma constant substantially varied depending on the source configuration, exhibiting up to 43%-lower dose rates for the volume source oriented in an upward direction in comparison to the point source. In contrast, usage conditions substantially affected the HVL, which increased from 3.27 mm to 5.51 mm depending on the lead thickness under the broad-beam geometry. Furthermore, the HVLs under narrow-beam conditions were approximately 16.49% lower than those under the broad-beam geometry.Conclusion: A method with new data on the gamma constants and HVLs for shielding evaluation of industrial radiography with 192Ir was presented. The relevant findings resolve inconsistencies in the data presented in the literature and enhance shielding evaluation accuracy. The proposed method not only provides practical standards for shielding evaluations but also ensures regulatory consistency.