Dating of sediment cores using Lead-210 

 

Sediment 

 

The geochronology of recent sediment materials can be determined by the 210Pb dating method.

Applications are in the areas of Late Quaternary geochronology, sedimentology and biochronology.

 

Please discuss your proposal with the appropriate ANSTO Contact Scientist before submitting your proposal as they will assist you in making the correct capability selection.


Capability Selections

 

  • 210Pb dating (by alpha spectrometry) 
  • 210Pb dating and 137Cs (by gamma spectrometry) 
  • 137Cs dating (by gamma spectrometry)

 


Pb-210 dating (by alpha spectrometry)


One of the techniques which can be used for 210Pb dating is alpha spectrometry. The technique uses the decay of excess 210Pb activity (half-life = 22.3 years) to determine the rate of sediment accumulation. About 5 g of dried sample, from various depths of the sediment core, is required. The samples are processed to prepare 210Po and 226Ra alpha sources. The activities of these sources are determined by alpha spectrometry to calculate excess 210Pb activities.

 

This technique is more sensitive than gamma spectrometry and is suitable when a small quantity of sample is available for analysis. However the method is destructive and other radionuclides such as 137Cs will need to be analysed by a different technique such as gamma spectrometry. 137Cs activities in sediment cores are analysed to verify 210Pb chronologies.


Pb-210 dating and Cs-137 (by gamma spectrometry)


210Pb dating can be undertaken by gamma spectrometry technique. 30-50g of dried sample is required for analysis using a standard gamma spectrometer or 5g using a Well detector. There is no radiochemical processing required with this technique. The samples are simply packed into petri dishes or vials, left to equilibrate for three weeks and then counted on a High Purity Germanium (HP-Ge) gamma spectrometry system. Radionuclides such as 210Pb, 226Ra, 137Cs, 7Be, 228Ra, 228Th, 238U and 40K can be measured simultaneously. This technique is non-destructive.


Cs-137 dating (by gamma spectrometry)


137Cs analyses by gamma spectrometry are performed to validate the chronology of sediment cores which had been dated using the 210Pb method by alpha spectrometry. The depth at which 137Cs activity is the highest most likely indicates the year 1964. At least 6 samples are required from varying depths to construct the 137Cs profile. The analysis is usually performed using the Well detector gamma spectrometer, which requires 5g of sample.

 


 

 

For further information contact:


Atun Zawadzki
Phone: +61 2 9717 3480
atun.zawadzki@ansto.gov.au