Abstract
Groundwater age has significant hydrogeological implication for groundwater renewal and solute transport. The period between 50 to 1000 years, marked by increased human activity, which is also a gap of groundwater dating. Cosmogenic 32Si with a half-life of 144±11 a, is the only viable dating tool for this range but is seldom used due to complex pretreatment and time-consuming and expensive detection. Radiogenic 32P, as a daughter isotope of 32Si, decays by emitting high-energy β- particles and is easily detected. 32Si and 32P reaches radioactive equilibrium within 3 months, meaning they maintain consistent activity levels in groundwater aged between 50 and 1000 years. Therefore, 32P can be used to date groundwater in the range of 50–1000 a. 32P is enriched and extracted using Mg(OH)2 co-precipitation method. The 32P solution is then mixed with a solvent mixture containing Triton X-100 and Permafluor and detected using an ultra-low background liquid scintillation spectrometer. The counting time ranges from 2500 to 3000 min with an efficiency of 65 %, and the 32P count peak surface is observed between channels 600 and 900. Comparing the 32P ages with the 14C and 32Si ages of groundwater samples from the Jianghan Plain, Central China, reveals that 32P ages and 14C ages exhibit similar trends, and the 32P ages and 32Si ages are approximately consistent in the range of 50–1000 a. Therefore, radiogenic 32P dating groundwater in the range of 50–1000 a is feasible, convenient and reliable.
Published Version
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