AMS ASTER

The ASTER instrument is a Accelerator Mass Spectrometer (SMA) installed at CEREGE in 2006. It forms the backbone of the LN2C, measuring samples prepared at CEREGE or sent by partner laboratories.

Accelerator Mass Spectrometry (AMS)

Mass spectrometry is the central analytical technique of isotope geochemistry. It allows the measurement of isotope ratios of up to 10^-6. In the case of cosmogenic nuclides, such as ¹⁰Be, their very low abundance involves isotope ratios (e.g. ¹⁰Be/⁹Be) of the order of 10^-12-10^-8 for atmospheric varieties and 10^-14-10^-12 for in situ varieties. In addition, the existence ofisobars (isotopes of different elements with the same mass number: ¹⁰B and ¹⁰Be, ³⁶S and ³⁶Cl or ²⁶Mg and ²⁶Al), whose natural abundances are much higher than the cosmogenic nuclide of interest, represents a major difficulty for these techniques based on mass separation.

Specific methods must therefore be implemented to lowering the detection threshold by several orders of magnitude and ensure good isobar separation. Accelerator Mass Spectrometry (AMS) combines the classical approaches of mass spectrometry for differential deflection selection of ion beams in magnetic fields as a function of mass number, using the techniques of acceleratorsused in particle physics, enabling the ion beam to be peeled off at high energy and isobars to be separated by differential loss of energy as a function of charge number.

The following isotope ratios are routinely measured by the ASTER instrument.
. ¹⁰Be/⁹Be
. ²⁶Al/²⁷Al
. ³⁶Cl/³⁵Cl

Developments

Maintaining the instrument at the highest level of international activity requires constant work by development andoptimization performance. In this way, the instrument's characteristics are constantly adapted to provide the highest level of quality for the measurements taken.

A major current development project is the introduction of a Gas Filled Magnet (GFM), allowing a major gain in accuracy on the measurement of the ²⁶Al/²⁷Al, with major implications for the implementation of burial dating.