Measurement of cosmogenic 32P and 33P activities in rainwater and seawater

We have developed a new method for the collection, purification, and measurement of natural levels of P-32 and P-33 in rain, marine particulates, and dissolved constituents of seawater. P-32 and P-33 activities were measured using a recently developed ultra-low-level liquid scintillation counter. Measurement by liquid scintillation counting allows, for the first time, simultaneous measurement of both P-32 and P-33, Furthermore, P-33 activities are measured with high efficiency (>50%), regardless of the amount of stable phosphorus in the sample. Liquid scintillation also produces energy specific beta spectra which has enabled us to identify previously unrecognized beta-emitting contaminants in natural samples, In order to remove these contaminants, new methods of purification have been developed which utilize a series of precipitations and anion and cation exchange columns. Rainwater and dissolved seawater samples were extracted from large volumes of rain- and seawater, 5-20 and >5000 L, respectively, using iron-impregnated polypropylene filters. On these filters, it was possible to load between 25 and 30% Fe(OH)(3) by weight over twice that loaded on previously utilized materials. Using our collection, purification, and liquid scintillation counting techniques, it was possible to obtain specific P-32 and P-33 activities with less than 10% error (2 sigma) in rainwater and 20% error (2 sigma) in seawater.