RADRISK Inspector: a mobile application for shielding design and safety distance calculation in industrial gamma radiography

Industrial gamma radiography is a widely used non-destructive testing (NDT) technique, but it involves significant radiological risks that require precise planning of shielding and safety distances. Current practices rely heavily on in-situ radiometric measurements, which are time-consuming and may increase unnecessary operator exposure during setup and verification stages. This work presents RADRISK Inspector (RRI), a cross-platform mobile application that enables real-time radiological safety planning through physics-based calculations. The system estimates minimum safety distances, required shielding thickness, and risk zoning based on radionuclide activity, exposure parameters, and material attenuation properties. In addition, RRI integrates interactive zoning maps, exposure timers, and automated dosimetric reporting compliant with international standards (IAEA, CSN), supporting full digitalization of radiological risk management workflows. The application was preliminarily verified under real industrial conditions during pipeline weld inspections using an Ir-192 source. In this field case, RRI estimated an operator safety distance of 66 m, compared with 22 m obtained from in-situ dose-rate measurements, indicating conservative behaviour consistent with its safety-first planning approach. Accordingly, RRI is not intended to replace in-situ radiometric verification or high-fidelity radiation transport modelling, but to support conservative pre-inspection planning, risk zoning and traceable professional reporting in industrial gamma radiography. RRI represents a novel and beneficial application of radioactivity in modern industry, enabling proactive radiological protection, reducing unnecessary exposure, and improving operational efficiency in gamma radiography. Its compatibility with ATEX-certified devices further supports deployment in hazardous environments. This work supports a shift in radiographic NDT from reactive measurement-based practices to predictive, physics-based safety planning.

Industrial gamma radiography is a widely used non-destructive testing (NDT) technique for inspecting welds and structural components in critical industries such as energy, petrochemical, and infrastructure (IAEA, 2017; Yenumula et al., 2019; Vetter et al., 2018). Despite the increasing need for digital support in radiological risk management, current solutions for gamma radiography remain fragmented and limited in scope (ICRP, 2007; Clairand et al., 2008). In current practice, safety distances are generally estimated theoretically before industrial radiography operations, while in-situ radiometric measurements are subsequently performed after source exposure for verification purposes. Although this workflow provides an essential safety check, it may still be time-consuming and may increase operator exposure during setup and verification stages. These limitations highlight the need for predictive, physics-based tools that enable proactive radiological safety planning before inspection activities are carried out (Kasim et al., 2018; Suffo et al., 2023).

Operational Intervention Levels (OILs) (CSN, 2022) are defined as ionising radiation thresholds which, when exceeded, trigger protective actions to safeguard workers and the public (NIOS, 2023; Directive, 2013/59/Euratom, 2013). They are a crucial component of radiological protection in Spain and worldwide. Similar to the Seveso Directives that establish threshold values for the quantities of hazardous substances stored (Suffo and Nebot, 2015; Suffo et al., 2015; Suffo and Nebot, 2016), OILs guide radiological protection but do not prevent risks proactively.

However, regulatory thresholds alone are insufficient to prevent radiological risks in practice. The increasing number of industrial activities involving ionising radiation, supported by advanced inspection technologies, has led to a growing need for effective radiological risk management. In this context, gamma radiography inspections may pose significant risks to operators, surrounding infrastructure, and the public if not properly controlled (Kasim et al., 2018; Kasim et al., 2019). These operations require comprehensive planning that integrates pre-inspection assessment, on-site protection measures, and post-inspection evaluation, forming a complete radiological risk management process (Craciun, 2015).

Among these, gamma radiography stands as a cornerstone non-destructive testing (NDT) technique for detecting internal defects in welds and engineering materials (Rosado et al., 2010; Ashok Reddy, 2017; Siengsanoh et al., 2018). Since these techniques involve ionising radiation, strict safety measures are essential.

Gamma radiography is performed by guiding a sealed radioactive source through a remote-control hose to the inspection area, where a collimator is used to direct the photon beam and reduce unnecessary exposure (IAEA, 2017). Despite these protective measures, the source emits ionizing radiation continuously, making radiological risk control essential throughout the operation. Compliance with international and national radiation protection frameworks requires that exposure to workers and the public remains within established dose limits (ICRP, 2007). In practice, radiological protection in industrial gamma radiography depends on the combined control of three key variables: distance, shielding, and exposure time. However, increasing distance is often constrained by site layout and hose length, while reducing exposure time depends on source activity, material thickness, and inspection requirements. Under these conditions, shielding and accurate safety-distance estimation become critical for minimizing restricted areas and ensuring safe operation (Nazemi et al., 2018). Nevertheless, current practice still relies heavily on in-situ radiometric verification, which limits proactive planning and may expose personnel unnecessarily during setup (Kasim et al., 2018; Kasim et al., 2019). These limitations support the need for predictive tools based on standardized dose, distance, and shielding models for pre-inspection radiological safety planning (Craciun, 2015).

Digital tools are increasingly essential for managing the large volumes of dosimetric data generated during industrial radiography operations, including individual records of inspector identity, absorbed dose, exposure time, and inspection history, which are required for regulatory compliance and audit processes. Despite the increasing need for digital support in radiological risk management, current solutions for gamma radiography remain fragmented and limited in scope. Existing tools, such as the “Waygate Technologies Exposure App”, provide basic exposure-time calculations but do not support integrated shielding design, safety-distance estimation, or risk zoning. In addition, the use of conventional mobile devices is restricted in hazardous environments, where compliance with the ATEX Directive 2014/34/EU is mandatory (ATEX, 2014). In this context, to address these limitations, a new digital solution is required. Such a solution should provide comprehensive radiological risk management for gamma radiography NDT, integrating physics-based calculations for shielding, safety distances, and risk zoning with real-time visualization and automated dosimetric reporting, and ensuring compatibility with ATEX-certified devices for deployment in explosive atmospheres.

This study presents RADRISK Inspector (RRI), a novel cross-platform mobile application for real-time radiological safety planning in industrial gamma radiography. The system integrates physics-based algorithms to estimate safety distances, shielding requirements, and risk zoning based on radionuclide activity, collimator configuration, exposure parameters, and material attenuation properties. In addition, RRI provides interactive visualization tools, exposure monitoring, and automated dosimetric reporting to support comprehensive radiological risk management workflows. The application was preliminarily verified during industrial pipeline weld inspections using an Ir-192 source. The field case showed that RRI provides conservative safety-distance estimates, with a predicted operator safety distance of 66 m compared with 22 m obtained from in-situ dose-rate measurements. This difference is consistent with the intentionally conservative assumptions adopted for pre-inspection planning, particularly the open-field approximation used to avoid underestimation of radiological risk. Furthermore, the system is fully compatible with ATEX-certified devices, enabling safe deployment in hazardous industrial environments. Therefore, the scientific contribution of RRI lies primarily in the integration of established radiological protection calculations, risk zoning, exposure control and dosimetric reporting into a single mobile workflow, rather than in the development of a high-fidelity radiation transport model.

Radiological risk management framework

This study evaluates the performance of RADRISK Inspector (RRI) within a radiological risk management framework structured into three operational stages of industrial gamma radiography: prevention, protection, and evaluation. This sequence reflects the temporal progression of radiographic inspections and is consistent with established safety intervention approaches, in which preventive actions are implemented before exposure, protective measures are applied during operation, and evaluation is carried out afterwards to assess compliance and improve future practice (Dyreborg et al., 2022). Within this framework (see Figure 1a), the prevention stage is focused on estimating the shielding requirements and minimum safety distances associated with a specific inspection scenario before field deployment. The protection stage applies these calculated parameters during the inspection in order to support safe operator positioning, restricted-area delimitation, and exposure control. Finally, the evaluation stage compiles the dosimetric information generated during the inspection process, enabling traceable documentation and subsequent regulatory review.

The methodological basis of RRI is that radiological safety in gamma radiography depends on the control of dose rate and total absorbed dose as a function of five main variables: radionuclide activity, source-to-operator distance, exposure time, collimation conditions, and shielding properties. For each inspection scenario, dose criteria are first defined for occupationally exposed workers and for the public, in accordance with radiological protection principles and international safety standards (IAEA, 2017).

From these criteria, the corresponding dose-rate thresholds and minimum safe distances are determined (see Figure 1b). When increasing distance is not feasible because of operational limitations, the required shielding thickness is estimated from the attenuation properties of the selected material, following the numerical approach previously developed for ionising-radiation shielding applications (Suffo et al., 2023).

Following (IAEA, 2017), the individual dose “D t ”, the corresponding dose rate “T t ” and the minimum safety distance “d lim ” are determined using Equation 1, which is explicitly applied for each radioactive source.

Where:

T t = Operational dose-rate estimate at distance d lim, expressed in mSv/h.

Γ = gamma dose-rate constant, expressed in mSv·m 2 ·h -1 ·GBq −1, used to estimate the operational dose-rate quantity at 1 m from a radionuclide with an activity of 1 GBq.

A = Radionuclide activity, expressed in GBq.

d lim = distance from the source to the point where the dose rate is evaluated, expressed in m.

The symbol Tt is used here to denote the operational dose-rate estimate, following the notation adopted in Suffo et al. (2023), and should not be confused with the occupancy factor T commonly used in shielding calculations. In this work, Tt is used for radiological protection planning purposes and does not imply the explicit application of tissue weighting factors. In the current version of RRI, the occupancy factor is not implemented as an independent user-defined parameter. For the preliminary safety-distance calculations, a conservative full-occupancy assumption was adopted, equivalent to an occupancy factor of T = 1 at the evaluated point.

Once T t is calculated, it is multiplied by the exposure time t exp using Equation 2 to obtain the total dose.

Where: D t = Total dose in mSv

T t = Dose rate in mSv/h

t exp = Exposure time in hours

Using these relationships, RRI calculates the minimum safe distance required to keep exposure below predefined limits for both authorised personnel and members of the public. In parallel, the system estimates the shielding thickness required for materials such as steel, lead, and concrete when spatial constraints prevent sufficient source separation. These outputs constitute the basis for pre-inspection planning, allowing the definition of safety zones and the establishment of radiological protection measures before the inspection begins.

In addition to preventive and operational support, the framework incorporates a post-inspection evaluation component. After each inspection, individual dosimetric data, including received dose, number of exposures, and exposure time, are recorded in the application. These records provide the basis for periodic reporting and support traceable radiological safety management throughout the inspection workflow.

RRI development and operational functionality

RADRISK Inspector (RRI) was developed as a cross-platform mobile application designed to support radiological risk management in industrial gamma radiography. The system integrates three core operational functions: risk zoning calculation, shielding thickness estimation, and dosimetric data recording and reporting, enabling full coverage of the radiographic workflow from pre-inspection planning to post-inspection evaluation.

The application is compatible with both conventional smartphones and ATEX-certified mobile devices, allowing its use in standard industrial environments as well as in hazardous areas where explosive atmospheres may be present. To ensure traceability and controlled access to radiological data, the system includes company-linked user management with three roles: administrator, operator, and coordinator, supporting both individual and team-level dosimetric monitoring. Before an inspection, the user enters the main radiological parameters of the scenario, including radionuclide type, source activity, collimator configuration, and shielding material and thickness when applicable. Based on these inputs, RRI calculates the minimum safety distances required for authorised personnel and for the public, and estimates the shielding thickness necessary when distance constraints prevent adequate separation from the source. These calculations are directly linked to the methodological framework described in Section 2.1 and provide the basis for preventive planning before field deployment. To facilitate operational use, the application generates real-time visual and numerical outputs, including interactive safety-zone maps and dose–distance reference tables. In addition, RRI provides an exposure timer to support accurate control of irradiation periods and ensures consistent execution of inspection procedures. The complete operational workflow of the application, from user access to dosimetric reporting, is illustrated in Figure 2. After inspection, individual exposure data, including received dose, number of exposures, and total exposure time, are recorded in a digital dosimetric log. These data are used to automatically generate periodic reports, including monthly and annual summaries, which support regulatory compliance and audit processes. Examples of these reports are shown in Figure 3.

From a software-engineering perspective, RRI was implemented using JavaScript with React Native, enabling cross-platform deployment for Android and iOS, and built with the Expo framework. The backend architecture is based on Firebase, using Cloud Firestore for real-time data storage and synchronization, and Firebase Authentication for user management. Security is ensured through SHA-256 password hashing, TLS 1.2+ encrypted communication, and role-based database access control. Application distribution through official app stores enables continuous updates without disrupting field operations.

Overall, this architecture provides the portability, reliability, and security required for industrial radiography applications, while ensuring full functionality on ATEX-certified mobile devices deployed in hazardous environments.

Preliminary field validation methodology

The practical performance of RADRISK Inspector (RRI) was evaluated through a preliminary field validation study conducted during an industrial gamma radiography inspection of a pipeline welded joint in an open trench environment. This field case was intended to verify the conservative behavior and operational applicability of the application under real industrial conditions, rather than to provide a statistically representative validation across all possible radiographic configurations. The inspection site and experimental setup are shown in Figure 4.

The validation procedure followed the operational workflow defined in Section 2.2 and illustrated in Figure 2, ensuring consistency between the application design and its real-world implementation. The methodology was structured into three sequential stages: Pre-inspection planning.

The inspection scenario was defined within the RRI application by introducing the relevant radiological parameters, including radionuclide type (Ir-192), source activity (80 Ci), and collimator configuration. No additional shielding was considered, as the inspection was performed in an open trench environment. Based on these inputs, RRI calculated the minimum safety distances for authorised personnel and the public, and generated interactive risk zoning maps and dose–distance reference tables. These outputs were used to define the inspection perimeter and access restrictions prior to field deployment, based on the risk zoning criteria implemented in the application (Figures 2f,g, 5). 2. On-site implementation.

During the inspection, the calculated safety distances were applied to position operators and delimit controlled areas. The operational configuration assumed a maximum operator distance constrained by the remote-control hose length (10 m), as illustrated in Figure 6. For modelling purposes, the scenario was treated as an open-field condition, which represents a conservative assumption since it does not account for additional attenuation effects provided by trench geometry. This approach ensures that calculated safety distances are not underestimated. 3. Field verification and data acquisition.

Once the inspection was initiated, in-situ dose-rate measurements were performed using a calibrated radiometer to validate the safety distances predicted by RRI. The measured dose rates were used to determine the actual distance required to reach the regulatory dose threshold for operators, allowing direct comparison between predicted and observed values (Figure 6a). Because only one industrial configuration was available for this study, the comparison was interpreted as a preliminary field verification of the conservative performance of RRI, not as a full statistical validation of the calculation model. No additional measurements for public-distance verification or shielding-thickness validation were available during this field campaign; therefore, these outputs are reported as calculated planning values rather than experimentally validated quantities.

In parallel, individual exposure data were recorded using a personal dosimeter (Figure 6b) and subsequently logged in the RRI system. These data enabled the generation of daily records and periodic dosimetric reports consistent with the application workflow (Figure 3).

The experimental setup, combining predictive calculations with in-situ radiometric measurements and personal dosimetry, allowed a preliminary assessment of the RRI methodology under realistic industrial conditions. This approach enabled the evaluation of conservatism and practical applicability, while acknowledging that broader validation requires additional field scenarios.

Mobile devices used in the field tests

RADRISK Inspector (RRI) was tested across multiple hardware platforms to ensure system robustness, cross-platform compatibility, and operational reliability under different usage conditions. The application was tested on a range of commercial mobile devices, including smartphones and tablets with different operating systems, as well as on an Android emulator environment.

Specifically, the tests were performed using the following devices: an iPhone 13, a Xiaomi Redmi Pro smartphone, a Samsung Galaxy Tab tablet, and an Android emulator implemented through Android Studio (Android 15.0). In addition, the system was deployed and evaluated on an ATEX-certified IS540.1 smartphone, confirming its functionality in hazardous environments where the use of conventional mobile devices is restricted.

This multi-platform validation demonstrates the portability and stability of the application, ensuring consistent performance across both standard consumer devices and industrial-grade ATEX-certified equipment.

The preliminary field validation indicated that RADRISK Inspector (RRI) provides conservative and operationally useful estimates for industrial gamma radiography planning. The main result of the study was the comparison between the operator safety distance predicted by the application and the value obtained from in-situ radiometric verification. For the inspected pipeline weld scenario using an Ir-192 source (80 Ci) with tungsten collimator, RRI estimated a minimum operator safety distance of 66 m, whereas the measured distance required to reach the operator dose-rate threshold was 22 m (Table 1; Figure 6a). This discrepancy indicates that the application overestimated the required safety distance by a factor of approximately three in this specific field scenario. Rather than indicating an error in the in-situ measurement, this difference reflects the conservative modelling assumptions implemented in RRI, particularly the open-field approximation and the exclusion of trench-related attenuation effects. Other site-specific factors, such as source orientation, local shielding effects, scattering conditions, and the geometry of the trench, may also have contributed to the lower measured distance in the real field configuration. Therefore, the predicted distance should be interpreted as a preventive planning value rather than as an exact reconstruction of the measured field condition.

This conservatism is consistent with the modelling assumptions used by RRI. In the preliminary validation scenario, the inspection was represented as an open-field condition constrained only by hose length, without incorporating the additional attenuation and natural shielding effects provided by trench geometry (Figure 4). As a result, the model intentionally prioritizes safety by avoiding underestimation of radiological risk. From a radiation protection perspective, this behaviour is desirable, since it supports preventive planning while maintaining a safety-first criterion under variable field conditions.

Several uncertainty sources may affect the comparison between calculated and field-derived safety distances, including source activity, decay correction, gamma constant selection, collimator configuration, source orientation, detector positioning, local attenuation, scattering conditions and simplified geometry. In the current version of RRI, these factors are not modelled with the level of detail provided by advanced radiation transport simulations. Consequently, the calculated distances should be interpreted as conservative planning values intended to support pre-inspection decision-making and risk zoning, while final radiological protection decisions must continue to rely on in-situ dose-rate verification and applicable regulatory requirements.

Beyond the numerical comparison, the results demonstrate a clear operational advantage. By generating safety distances, shielding estimates, and zoning criteria before inspection, RRI reduces dependence on iterative field measurements and supports proactive radiological planning. The application therefore transforms gamma radiography workflow from a reactive approach based on source-exposed radiometric verification to a predictive approach based on pre-inspection calculation and controlled execution (Figures 2f,g). This improvement is especially relevant in industrial NDT contexts, where reducing setup time and minimizing unnecessarily large restricted areas can substantially improve operational efficiency.

The results also confirm the practical value of the dosimetric management functions integrated into the application. Individual exposure data recorded after inspection can be automatically incorporated into monthly and annual reports, providing traceable documentation for radiological safety monitoring and audit processes (Figure 3). This digital workflow replaces manual recordkeeping with a more efficient and consistent reporting process.

Although personal dosimetry was recorded during the field inspection, the limited number of measurements did not allow a robust quantitative comparison between calculated personnel dose and measured personal dosimeter values. Future validation campaigns will therefore include systematic paired comparisons between RRI-calculated doses and personal dosimeter records.

An additional relevant outcome is the successful deployment of the application on an ATEX-certified mobile device. The adaptation of the RRI interface to the IS540.1 smartphone demonstrated that the application maintains full functionality in hazardous industrial environments where conventional mobile devices cannot be used (Figure 7). This expands the applicability of the system to sectors such as refineries, pipelines, and other explosive-atmosphere scenarios, where digital radiological planning tools are especially valuable.

Despite these positive results, the present study has several limitations. First, the field verification was based on a single real inspection scenario. Although this case provided valuable evidence of the conservative behavior and practical applicability of RRI, it does not constitute a statistically representative validation dataset. Additional field measurements under different source activities, collimator configurations, geometries, shielding conditions, and radionuclides are required to quantify prediction uncertainty and define scenario-dependent correction factors. Second, the current model is based on a simplified point-source outdoor approximation and does not explicitly account for complex geometries or multiple-scattering effects. Third, experimental verification was performed using a single radionuclide configuration, specifically Ir-192, and should be extended to other industrially relevant isotopes such as Co-60 and Se-75. Future work should therefore focus on incorporating more advanced radiation transport models, including scattering corrections and geometry-dependent attenuation, as well as broadening the field validation dataset across additional inspection scenarios and source types.

Overall, the results support RRI as a robust and practical tool for industrial gamma radiography, combining conservative radiological predictions, digital workflow integration, and compatibility with ATEX-certified devices. In this sense, the application contributes to a new operational paradigm in radiographic NDT, in which preventive, physics-based planning improves both radiological safety and inspection efficiency.

This study presents RADRISK Inspector (RRI), a novel cross-platform mobile application for real-time radiological safety planning in industrial gamma radiography. The system integrates physics-based calculations for safety distance estimation, shielding design, and risk zoning within a unified digital workflow. Preliminary field validation under real industrial conditions indicated that RRI provides conservative safety-distance estimates, with a calculated operator distance of 66 m compared with 22 m obtained from in-situ dose-rate measurements. This result supports the safety-first nature of the model, showing that radiological risks are not underestimated under the conservative assumptions adopted, while also highlighting the need for additional field measurements to broaden the validation dataset. Therefore, RRI should be interpreted as a beta-version conservative planning and radiological risk management tool, not as a replacement for in-situ radiometric verification, regulatory assessment or high-fidelity radiation transport modelling. Beyond numerical validation, RRI enables a transition from reactive, measurement-based practices to predictive, pre-inspection planning. This approach reduces operational uncertainty, improves efficiency, and supports more effective management of restricted areas in industrial radiography. The integration of automated dosimetric reporting further enhances traceability and simplifies compliance with regulatory requirements.

The successful deployment of the application on ATEX-certified mobile devices demonstrates its applicability in hazardous environments, expanding its use to industrial sectors where conventional digital tools cannot be employed. Future work will focus on extending the model to incorporate complex geometries and scattering effects, as well as validating the system with additional radionuclides, source activities, collimator configurations, shielding conditions, and inspection scenarios.

Overall, RRI establishes a practical and scalable solution for improving radiological safety and operational efficiency in gamma radiography, contributing to the digital transformation of industrial non-destructive testing.