In the late 1970s,a well logging radiation source was lostted accidentally during geological exploration.Preliminary instrument checks indicated that the source might be dropped at the depth of 497 to 543 meters.Despite several attempts,the source was salvaged due to technological limitations at that time,and ultimately leading to the sealing of the borehole with the lost source in.The lost radiation source,identified as 60Co,had an initial activity of approximately 5.143×10-4 Bq,classified as a Class Ⅱ radiation source.Because the borehole was situated within the planned mining area of a coal mine,the lost radioactive source cause the potential risks to mining safety as the source's location may coincide with the primary coal seams.Therefore,it is imperative to assess the status and impact of the radiation source before mining commences.This study conducted a comprehensive analysis of potential geological strata and radiation pathways of the source by utilizing existing data and considering its characteristics.Monte Carlo simulations were employed to assess the extent and range of radiation impact within the geological strata,supplemented by isotope analysis of groundwater around the coal seams.The analysis results indicated that the lost source had minimal impact on the groundwater environment.Simulation results suggested that the source hosting geological strata under actual shielding conditions significantly restricted the impact range of the radiation within 0.3 meters,while without geological shielding,the impact range may extend up to 3 meters.The study recommended the protective measures for the mining design,such as leaving coal pillars or implementing real-time monitoring during mining operations.The pillar retention method ensures no external contact with the radiation source.Alternatively,real-time monitoring during mining should initiate boundary surveillance beyond the radiation impact range under unshielded conditions.Any abnormal monitoring readings should prompt immediate evacuation and reporting to higher authorities to prevent a radiation source mishap.This study is the first application of Monte Carlo methods for assessing radiation impact from sources within geological strata and proposes corresponding protective measures tailored to mining practices,which provides valuable insights and practical guidance for addressing similar incidents.
radiation assessmentradiation source60CoMonte Carlo methodcole mining
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