The Cumulative Distribution Of Radon And Its Characteristic Progeny In The Surface Soil During Spontaneous Combustion Of Coal

The key to the prevention of spontaneous combustion in mines lies in the precise detection of the location of the fire source.The isotope radon method has been widely used in the detection of serious spontaneous fire areas because of its simple operation,low cost,no terrain limitation,and suitability for deep fire detection.How to accurately detect the spontaneous combustion area of coal under complex conditions by obtaining accurate abnormal information of radon concentration on the surface is a key technical challenge faced by the radon measurement technology.At present,the?-cup method is mainly used to obtain abnormal information on radon on the surface.This method is susceptible to the influence of seasons,weather,sunshine,wind,instrument vibration and other human factors,which restricts the effective collection and accurate analysis of field data.Affected by the spontaneous combustion of coal,radon continuously decays into inactive solid long-lived daughters with inactive physical and chemical properties during transportation to the surface.Once formed,these daughters adsorb and stay in the nearby soil,and their concentration is not easy to change with the environment,etc.Changes in external factors can directly reflect the cumulative value of parent radon in a certain period of time.Therefore,using the characteristic progeny accumulated in the soil at different depths as a tracer is expected to obtain accurate information on the abnormal concentration of radon,but the cumulative distribution of radon and its characteristic progeny on the surface is unclear,making its feasibility questionable.To this end,this article carried out experiments to explore the cumulative distribution of the two in the topsoil layer.In this paper,by comparing the physical and chemical properties of the three characteristic daughters of radon,based on the radiation background and the difficulty of detection,the daughter ²¹⁰Po is selected as the tracer for the abnormal information of radon concentration in the topsoil.Based on theoretical analysis,a comprehensive comparison of the soil radon precipitation process under natural conditions and the changes caused by high-temperature flue gas generated by coal spontaneous combustion are comprehensively compared to obtain soil characteristic parameters that can affect radon transport and the accumulation of ²¹⁰Po daughters.Carry out experiments to explore how soil characteristic parameters affect the correlation between radon concentration and polonium content,compare the different accumulation characteristics of radon concentration and polonium content under different soil textures and analyze the reasons for their formation.Select a known fire source location and implement the ²¹⁰Po analysis method in the fire area.The fire source location judged by the ²¹⁰Po distribution of different sampling depths is consistent with the known fire source location,which verifies that the ²¹⁰Po analysis method can be used for coal spontaneous combustion fire source location.At the same time,in view of the abnormality of²¹⁰Po distribution at different depths,interpret the radon concentration distribution,and try to provide a basis for the actual use of the ²¹⁰Po analysis method in terms of sampling depth and sampling location.Studies have shown that the factors that can affect the transport of radon and the accumulation of ²¹⁰Po daughters in the soil are the ejection coefficient,diffusion coefficient and seepage velocity.The corresponding soil characteristic parameters include soil texture,soil water saturation and porosity,and soil particle size;There is a correlation between the radon concentration and polonium content in the topsoil layer,but this correlation is affected by the comprehensive influence of soil water saturation and porosity,soil particle size,and soil texture.In different soil textures,the correlation between radon concentration and polonium content in clay soil is higher than that in sandy soil.Soil water saturation is inversely proportional to effective porosity,when the water saturation is low,with the increase in saturation,The soil porosity decreases,and the correlation index between soil radon concentration and polonium content increases.When the water saturation continues to increase,the correlation index shows a downward trend,too high or too low soil water saturation will affect the soil radon concentration and polonium content The ²¹⁰Po analysis method is more suitable for use in soils with a certain degree of water saturation,the correlation between soil radon and polonium gradually decreases with the increase of soil particle size.