Rafael Lima Rodrigues

Naturally occurring radioactive material (NORM) oily sludges are heterogeneous multiphase systems in which radiochemical partitioning does not necessarily translate into physical separability. This review critically compares reported radium distributions, host phases and oily-sludge separation studies and proposes a coupled framework combining the apparent distribution coefficient, K _d , with a radium-bearing-solids recovery efficiency, η _s . Quantitative evidence shows strong but matrix-dependent radium association with sulfate solids, while fine particles, colloids and emulsions can limit recovery. Isotope-specific activity-balance closure is proposed as a primary criterion for evaluating centrifugal volume reduction and its limitations.

Separating isotope-specific evidence from detection capability prevents non-detection from being interpreted as radionuclide absence and supports defensible reporting of complex NORM measurements.

Radium-bearing naturally occurring radioactive material is a recurring radiation safety concern in oil and gas production. The radionuclides ²²⁶ Ra and ²²⁸ Ra may be mobilized in formation water, transported with produced water, and concentrated in scale, sludge, filters, tanks, separators, pigging residues, soils, and sediments. This paper proposes a semi-quantitative occurrence susceptibility index for radium-bearing scale and sludge to inform radiation safety survey planning. The framework combines five weighted components: radium mobilization potential, scale precipitation potential, produced-water burden, deposition and accumulation potential, and operational trigger potential. Empirical radiological evidence is treated separately through a noncompensatory trigger so that an elevated field indication or confirmed radium-bearing material cannot be diluted by low scores in other components. A data quality index reduces false confidence when information is incomplete. Four worked operational scenarios demonstrate how the core score, empirical trigger, and data quality alter survey sequence, portable instrument use, targeted sampling, high-purity germanium gamma-spectrometric confirmation, and work controls. The framework is a rule-based decision-support structure, not a validated predictive model, probability estimate, or substitute for direct measurement, regulatory requirements, or site-specific dose assessment. No field-validated improvement in efficiency or cost savings is claimed. Its present purpose is to make provisional survey planning transparent and testable until field calibration and validation are completed.

Beach sands may contain elevated concentrations of naturally occurring radionuclides because of sediment provenance, hydraulic sorting and local accumulation of heavy minerals. This study establishes an HPGe-based radiological baseline for beach sands from Rio de Janeiro State, Brazil, and evaluates external gamma exposure through an uncertainty-propagated screening approach. Forty-seven surface sand samples were collected from recreational beach sectors and analysed by high-purity germanium gamma-ray spectrometry. Activity concentrations of ²²⁶ Ra, ²²⁸ Ra, ²²⁸ Th and ⁴⁰ K were determined, and their reported analytical uncertainties were propagated to derived exposure quantities. To avoid double counting when applying a conventional whole-series thorium dose coefficient, a central ²³² Th-series screening equivalent was calculated as the arithmetic mean of the ²²⁸ Ra and ²²⁸ Th indicators. Sensitivity calculations using ²²⁸ Ra alone and ²²⁸ Th alone were also performed. Activity concentrations ranged from 1.10 to 1408.10 Bq kg ⁻¹ for ²²⁶ Ra, 0.03–5449.93 Bq kg ⁻¹ for ²²⁸ Ra, 0.42–6957.21 Bq kg ⁻¹ for ²²⁸ Th and 2.07–1008.36 Bq kg ⁻¹ for quantified ⁴⁰ K results. Canto was the dominant point-specific anomaly, with a central calculated absorbed dose-rate estimate of 4420 ± 169 nGy h ⁻¹ . Excluding Canto, the mean absorbed dose rate was 38.6 nGy h ⁻¹ , whereas the complete-dataset median was 16.8 nGy h ⁻¹ . Under all three thorium-series assumptions, the same eight sampling points exceeded the comparative outdoor value of 55 nGy h ⁻¹ and only Canto exceeded 1 mSv y ⁻¹ under the frequent local-use scenario. All short-term tourist-use estimates remained below 0.3 mSv y ⁻¹ . The 55 nGy h ⁻¹ value is used only for comparison and not as a regulatory or action level. Most sampling points therefore represent lower-priority external gamma exposure conditions, whereas a limited number of local anomalies require confirmatory sampling, in situ dose-rate mapping and mineralogical characterisation before any beach-wide radiological protection conclusion is drawn.

Radium isotopes are central to marine radioecology and environmental radiological protection because they connect natural decay series, sediment–water exchange, offshore oil and gas naturally occurring radioactive material (NORM), technologically enhanced NORM and exposure of humans and non-human biota. Marine sediments are often described as radionuclide repositories, yet for radium they may function as reactive interfaces where activity is generated, adsorbed, coprecipitated, remobilised, buried, resuspended or incorporated into low-solubility sulfate phases such as radiobarite. This review develops a framework-guided synthesis of ²²⁶ Ra and ²²⁸ Ra in marine sediments, produced water, NORM scale, oily sludge, sediment–water exchange, analytical methods and radiological risk assessment. The proposed framework organises the evidence into five domains: source terms, host phases, mobility processes, analytical observability and exposure relevance. Recent studies show that produced-water radium can precipitate as micron-sized radiobarite or radiostrontiobarite particles, radium-bearing barite scales may preserve strong mineralogical control over solubility and release and ecological dose assessment depends on exposure geometry, partitioning assumptions, mineral incorporation, progeny ingrowth, sediment mixing depth and organism occupancy. Bulk activity concentration alone is therefore insufficient for interpreting radiological significance. Future monitoring should integrate ²²⁶ Ra and ²²⁸ Ra activity, isotope ratios, porewater measurements, Ba–Sr–Ca–SO ₄ chemistry, mineralogical characterisation, phase-specific activity, leaching tests, site-specific K _d values and tiered dose modelling. By reframing marine sediments as active radium reaction zones, this review provides a practical basis for improved monitoring, offshore NORM management and environmental radiation protection.