The 15N Calibration Method

Methods       Results
 
 

The Method

Hydrogen can be analyzed under high-vacuum by bombarding it with 15N ions from a linear accelerator.  The nuclear reaction scheme is shown below.  The 4.4 MeV gamma ray is emitted proportionally to the amount of H present in the sample.  By varying the energy of the incident 15N beam, it is possible to vary the depth the N beam penetrates into the sample before the nuclear resonance is excited.  In this way, a hydrogen depth profile can be measured.


 
 

This is an actual nuclear reaction profile obtained by the Frankfurt group on a kimberlite-hosted megacryst olivine from Kaalvallei, South Africa.  It shows a high concentration of 'water' on the surface of the crystal and a much lower internal OH content.

Results

These results represent the state of the art for our analyses of olivine.  Near linear calibrations are obtained with minerals with several 10's to a few 100's ppm hydrogen (expressed as water) in the sample.
 

Reference:   Bell DR, Rossman GR, Maldener J, Endisch D, Rauch F (2001).  Hydroxide in olivine: A quantitative determinatin of the absolute amount and calibration of the IR spectrum. Submitted to Journal of Geophysical Research