Molina Porras Arnold, Condomines Michel, Seidel Jean Luc
HydroSciences, Montpellier Univ., 34090 Montpellier, France; University of Costa Rica, 11501-2060 San José, Costa Rica.
Geosciences, Montpellier Univ., 34090 Montpellier, France.
Appl Radiat Isot. 2017 Feb;120:119-125. doi: 10.1016/j.apradiso.2016.12.010. Epub 2016 Dec 9.
A new portable sampling system was developed to extract Radium isotopes from large volumes (up to 300L) of fresh surface- and ground-waters of low Ra-activities (<5mBq/L). Ra is quantitatively adsorbed on a small amount (6.5g) of MnO-coated acrylic fibers, which are then dried and burned at 600°C in the laboratory. The resulting Mn-oxide powder (about 2cm when compacted) is then analyzed through gamma-ray spectrometry which allows measurement of the whole Ra quartet (Ra, Ra, Ra and Ra) in a single counting of a few days. The usual relative standard combined uncertainties (1σ) are 2-3% for Ra, Ra and Ra; and less than 10% for Ra. This method was applied to the analysis of Ra in karstic waters of the Lez aquifer, and surface- and ground-waters of the upper and middle Vidourle watershed (South of France). The analyzed waters have relatively low Ra activities (1-4mBq/L) in both cases, regardless of the contrasted geology (Mesozoic limestone vs crystalline Variscan basement), but clearly distinct (Ra/Ra) ratios in agreement with the differences in Th/U ratios of the two drained areas. Short-lived Ra isotopes (Ra and Ra) appear to be mainly influenced by near-surface desorption/recoil processes for most of the sampling sites.
开发了一种新型便携式采样系统，用于从大量（高达300升）低镭活度（<5毫贝克勒尔/升）的新鲜地表水和地下水中提取镭同位素。镭被定量吸附在少量（6.5克）涂有MnO的丙烯酸纤维上，然后在实验室中干燥并在600°C下燃烧。然后通过伽马射线光谱法分析所得的氧化锰粉末（压实后约2厘米），这使得能够在几天的单次计数中测量整个镭四重态（镭-226、镭-228、镭-224和镭-223）。对于镭-226、镭-228和镭-224，通常的相对标准合成不确定度（1σ）为2-3%；对于镭-223，不确定度小于10%。该方法应用于分析莱兹含水层岩溶水以及维杜尔勒河上游和中游流域（法国南部）的地表水和地下水。在这两种情况下，分析的水的镭活度相对较低（1-4毫贝克勒尔/升），无论地质情况如何不同（中生代石灰岩与华力西期结晶基底），但（镭-226/镭-228）比值明显不同，这与两个排水区域钍/铀比值的差异一致。对于大多数采样点，短寿命镭同位素（镭-22４和镭-223）似乎主要受近地表解吸/反冲过程的影响。
