Preliminary application of low-background gamma-spectrometry to volcanic ground water

Abstract

To enrich cosmogenic ⁷Be and ²²Na, artificial ¹³⁷Cs and natural radium isotopes, three chemical methods were applied to large volumes (100–300 l) of ground water from Daisen Volcano, Japan. The co-precipitation method using BaSO₄, Fe(OH)₃ and AMP, yielded ⁷Be, ¹³⁷Cs and radium isotope levels of nearly 100%. An ordinary ion-exchange column method, selectively recovered ²²Na (77%) through two continuous column operations. ⁴⁰K was satisfactorily removed in both, the co-precipitation and column methods. In addition, the simple batch method was suitable for rapid treatment even on the slope of a volcano without sacrificing yields. Low-background γ-spectrometry combined with these chemical treatments enabled the determination of extremely low-levels of ⁷Be, ²²Na, ¹³⁷Cs and radium isotopes (0.01–4 mBq/l) in ground water samples. The measurement of these nuclides of Daisen ground water provide new information on the flow system of volcanic water, including residence time, the mixing of precipitation, and the aquifer’s environment.