The concentration of 210Pb is determined by alpha spectrometry through its granddaughter 210Po, assuming radioactive equilibrium between the two radionuclides. An acid digestion of the sediment is carried out by using HNO3 and HF, followed by another digestion using H3BO3 in order to eliminate salts formed during the first digestion.
After digestion, the resulting solution is transferred to a Teflon beaker and is evaporated to incipient dryness. Small amounts of concentrated HCl are added to dissolve the sample residuals and to ensure the elimination of HNO3. Afterwards, samples are diluted to 50-100 ml 1M HCl and approximately 50-100 mg of ascorbic acid is added to reduce the iron Fe(III) to Fe(II) while heating at 80 ℃.
Finally, polonium isotopes are auto-plated onto silver disks at 80 ℃ while stirring for 8 hours. After polonium deposition, Po isotopes emissions are measured by alpha spectrometry using Passivated Implanted Planar Silicon, PIPS detectors
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