海洋沉积物 32 Si测年方法研究

32 Si generates from the spallation reaction of cosmic rays and argon in atmosphere, which is ingested by siliceous organisms such as diatoms after falling into the lakes and sea from atmosphere. The cosmogenic radioactive isotope 32 Si, with a half-life of approximately 150 a, represents an excellent dating tool for the age range of approximately 100-1 000 a. 32 Si, with a single source and a constant production rate, is of importance to the ancient environments and paleoclimatology. The method of determining 32 Si activity in the marine sediments was established. The main steps were as follows:(1) sample pretreatment; (2) separating and purifying biogenic silica; (3) separating and purifying phosphorus from biogenic silica; (4) preparation of phosphorus and counting 32 P by β counter. The experimental process was monitored by acidic silicomolybdenum blue spectrophotometry and phosphomolybdenum blue spectrophotometry to control loss of silicon and phosphorus during the process. The specific activity of 32 Si in sediments from Nansha sea area varies from 8.39 mBq/kg to 33.34 mBq/kg, with 16.60 mBq/kg as the mean value. The average specific activity of 32 Si in SiO 2 is 0.356 Bq/kg. The average specific abundance of 32 Si in biogenic silica is 1.29×10 -16 ( 32 Si/SiO 2 ). Sedimentary rates of sediment cores from deep water (1 335-1 537 m) and shallow water (121-141 m) are 0.106 cm/a and 0.191 cm/a respectively. The average setting flux of 32 Si is 2.14×10 -6 Bq/(cm 2 ·a), within the range of references.