Centre Européen
de Recherche et d'Enseignement
des Géosciences de l'Environnement

LN2C - ASTER AMS

 

Presentation

The ASTER facility is an Accelerator Mass Spectrometer (AMS) installed in 2006 at CEREGE. It constitutes the backbone of the LN2C by ensuring the measurement of samples prepared at CEREGE or sent by partner laboratories.

A detailed description of the ASTER instrument is available here (in French).

 

Accelerator Mass Spectrometry (AMS)

Mass spectrometry is the key analytical technique of isotopic geochemistry. It allows the measurement of various isotope ratios down to 10-6. In the case of cosmogenic nuclides, such as 10Be, their very low abundance implies isotopic ratios (for example 10Be/9Be) of the order of 10-12-10-8 for atmospheric varieties and 10-15-10-12 for in situ varieties. In addition, the existence of isobars (isotopes of different elements with the same mass number: 10B and 10Be, 36S and 36Cl or 26Mg and 26Al), with natural abundances much higher than the ones of cosmogenic nuclides, constitutes a major difficulty for these techniques based on mass separation.  

Specific methods must therefore be implemented to lower the detection threshold by several orders of magnitude and ensure good separation of the isobars. Accelerator Mass Spectrometry (AMS) combines (1) the classical approaches of mass spectrometry allowing selection by differential deflection of ion beams in magnetic fields according to the number of mass with (2) accelerators techniques, used in nuclear physics, allowing high energy peeling of the ion beam and separation of isobars by differential energy losses as a function of the charge number.

The following isotope ratios are routinely measured by the ASTER instrument.

  • 10Be/9Be
  • 26Al/27Al
  • 36Cl/35Cl

Development

Maintaining the instrument at the best international level of activity requires constant development and performance optimization. The characteristics of the instrument are thus permanently adapted to provide the highest level of quality for the measurements carried out.

A recent important development project is the installation of a Gas Filled Magnet (GFM), allowing a significant gain in precision on the measurement of the 26Al/27Al ratio , with major implications for the determination of burial ages.