Proton induced gamma-ray emission measurements of sodium in unopened fluid inclusions in geological samples

Proton induced gamma-ray emission (PIGE) is applied to the quantitative analysis of sodium in unopened fluid inclusions. The Na is identified through the (p,p'gamma) reaction which provides a good sensitivity of measurement. Two methods for quantifying Na in unopened fluid inclusions or other "buried" samples are described. The first method is based on the calibrated gamma-ray yield with depth of the target material at a specific bombarding energy. This method relies on the measurement of the thickness of the "cap" of the fluid inclusion. The second method is based on the identification of a certain resonance in the cross-section of the (p, p'gamma) reaction. This method provides an accurate measurement of the concentration of Na in fluid inclusions or buried samples without accurate knowledge of the thickness of the cap. The advantage and the disadvantage of these methods are discussed. The average value of the measured concentrations of Na in unopened fluid inclusions in quartz from the Panasqueira tungsten deposit, Beira Baixa, Portugal, using the first method is 1.33 wt.% with an uncertainty of 58%. Salinity estimations employing standard microthermometric technique are in the range of 5 wt.% to 10 wt% equivalent. Because of the problem of Na contamination in the Queen's University's external beam proton microprobe the second method could not be applied for quantifying potential of this approach has been demonstrated herein. The limit of detection of Na for different depths of the buried sample at bombarding energies of 3 MeV and 2 MeV is also presented. Na in these inclusions. However, the potential of this approach has been demonstrated herein. The limit of detection of Na for different depths of the buried sample at bombarding energies of 3 MeV and 2 MeV is also presented.