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A new device for measuring air content in polar ice has been designed, built and tested with 22 samples of Antarctic ice. The new technique is based on the barometric method which implies: (1) air extraction under vacuum by melting refreezing of the ice sample placed in a calibrated cell, and (2) accurate air-pressure and temperature measurements. The new apparatus simplifies the experimental procedure, decreases the duration of measurement and can eventually be used in the field. It provides results with an accuracy equivalent to or better than other methods previously used.

A multistep photoionization with three resonant polarized photons has been used to separate the odd and even isotopes of gadolinium. Due to their hyperfine structure (I= 3 2 ), the 155,157Gd isotopes can be photoionized via a J=2→2→1→0 scheme with three п photons whereas the even isotopes cannot. If a time delay is introduced between the three laser pulses we show that the presence of a low intensity dc magnetic field affects the selectivity. The effect of this weak field on the 156Gd photoionization rate has been calculated independently of the optical pumping and the result is in good agreement with the experiment.