Cross-checking groundwater age by 4He and 14C dating in a granite, Tono area, central Japan

Krypton 81: A New Method of Paleogroundwater Dating

“…They also used a control isotope 85 Kr to assist their experiment [15]. Generally, to correctly measure the age of groundwater samples, three steps are required: (1) the extraction of dissolved gas from groundwater, (2) the isolation and purification of krypton from dissolved gas, (3) and the measurement of krypton radioactive isotopes. The sample size of 81 Kr required for ATTA measurement is 6-8µL, which means about 100-200L groundwater samples, also means 2L dissolved gas should be extracted.…”

“…The results show that the groundwater is getting older from west to east in the North China Plain, and the most ancient groundwater is aged from 0.85 to 1.15 Ma. In Guanzhong Basin by applying the method of degassing membrane extraction from eight groundwater water samples (each sample 100L to 160L) and the separation and purification of krypton, as well as the atomic trap trace analysis technique (ATTA), Pang Zhonghe [3] measured the content of 81 Kr and estimated the age of groundwater in Guanzhong basin in the depth of 5000m, and compared the results with 14 C, 4 He and 36 Cl, indicating that the estimated age of groundwater by 81 Kr is basically consistent with other methods. He also illustrated that the age characteristics of groundwater estimated by 81 Kr can reveal the rules of groundwater movement in Cenozoic rift basin, and to some extent, it can reflect the temperature of paleoclimate on the scale of millions of years.…”

“…Recently, a large number of radioactive isotopes are used in groundwater dating studies [1]. For example, 3 H, 85 Kr and 3 He/ 3 H can be used to measure the age of young groundwater (about 50 years); 39 Ar is used to measure the age of groundwater from 50 to 1000 years. The method of using 39 Ar as isotope tracer to determine the age of groundwater makes up for the blank stage between the range determined by 3 H/ 3 He (< 50 years) and 85 Kr (>1000 years) [2]; 14 C is used to measure the age of groundwater between 1,000 and 40,000 years old.…”

“…The method of using 39 Ar as isotope tracer to determine the age of groundwater makes up for the blank stage between the range determined by 3 H/ 3 He (< 50 years) and 85 Kr (>1000 years) [2]; 14 C is used to measure the age of groundwater between 1,000 and 40,000 years old. Although the 14 C dating method is not absolutely accurate, it is an important method in solid phase or mesoscale measurement [3]. It is also very effective to use 4 He for groundwater dating, whose accumulation can be calculated by the amount of U decay [4].…”