The Study Of Determination Of ²²⁶Ra In Ultra-Pure Water By Manganese Fiber Enrichment-Ejection Method

In high-energy physics research,a large amount of ultra-pure water is required for neutrino detection.Ultra-pure water has high requirements for radioactive materials.For example,the Daya Bay neutrino experiment requires ²²²Rn for shielding water to be less than0.2Bq/m³.²²²Rn is one of the radioactive daughters of ²²⁶Ra.If ²²⁶Ra is contained in water,²²²Rn is inevitably produced.In general,the content of radium in natural water is about 4.5 Bq/m³,which is slightly lower in seawater,it is about 3.3 Bq/m³ in seawater.These concentrations are an order of magnitude higher than 0.2 Bq/m³.Ultra-pure water is natural water treated through special processes.It may still contain extremely low level of ²²⁶Ra.In order to prevent ²²²Rn in ultra-pure water from interfering with neutrino detection,it is necessary to measure the ²²⁶Ra accurately.The determination of very low content ²²⁶Ra in water by the method of manganese fiber enrichment-emission method has its unique advantages.Manganese fiber has a very high adsorption selectivity for²²⁶Ra in water samples.The ²²⁶Ra in water samples can be efficiently adsorbed by a small amount of manganese fiber,and the gas coefficient of ²²⁶Rn adsorbed on manganese fiber is very high when ²²²Rn is produced.On the other hand,the process of Sampling and measurement with manganese fiber avoids the use of barium and lead salt reagents,which can greatly reduce the ²²⁶Ra background during the experiment,thereby improving the sensitivity and accuracy of the ²²⁶Ra measurement.This method facilitates the enrichment and measurement of ²²⁶Ra in ultra-pure water.In this paper,we explored the interference in the process of enriching ultra-pure water ²²⁶Ra,the preparation of low ²²⁶Ra background manganese fiber and the chemical yield determination of"²²⁶Ra in ultra-pure water by manganese fiber enrichment-ejection method"using standard liquid ²²⁶Ra.Using this method to measure ²²⁶Ra in tap water,deionized water and ultra-pure water used in the Daya Bay neutrino experiment.Studies have shown that the method of soaking and scrubbing the manganese fiber with acid,isolating the sealing plug at both ends of the adsorption tube from radon,and using the activated carbon radon removal device decanting device to remove radon from the air used in the experiment can effectively reduce the Background interference of ²²⁶Ra enriching and measuring in ultra-pure water.The specific activity of ²²⁶Ra in the prepared manganese fiber is less than0.1 mBq/g,which satisfies the research needs of the subject.The chemical yield of ²²⁶Ra with the method is 92.4%.The method was applied to measure ²²⁶Ra in tap water,laboratory deionized water and ultra-pure water used in the Daya Bay neutrino experiment.The concentration of ²²⁶Ra in tap water and laboratory deionized water is3.1Bq/m³ and 3.1Bq/m³.The concentration of ²²⁶Ra in ultra-pure water used in the Daya Bay neutrino experiment is 0.1⁰.13Bq/m³,which is lower than 0.2Bq/m³.The results of this study can provide reference for the measurement of the ultra-pure water in the Daya Bay neutrino experiment and the Jiangmen neutrino experiment.