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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.

Tritium in a firn core from the coastal zone of Adelie Coast, Antarctica, has been determined by gas-counting after samples were enriched by thermal diffusion. Measurements have been made down to a depth of 10 meters, which corresponds to a water equivalent of 5.35 meters. Each sample represents about 15 cm of water equivalent. Mean annual snow accumlation has been determined by tritium fallout from nuclear tests of 1954 and by radioactive decay of natural tritium. The values found by fallout and by radioactive decay are, respectively, 21 and 20 g cm−2 yr−1. The agreement with data obtained by other methods is very good. Mean natural tritium content at the time of precipitation is 11.3 tritium units (TU), which corresponds to a rate of precipitation of natural tritium of 0.5 tritium atom cm−2 sec−1. Important fluctuations arise in the natural tritium content of precipitation. An attempt to correlate tritium precipitation and solar activity is made difficult by the irregularity of snow accumulation at the site of the core.

Deuterium and tritium measurements were made on firn samples taken along a central axis across Greenland. Accumulation values determined from tritium profiles decrease regularly from 54.7 cm of water per year on the west coast to 18.1 cm of water per year on the east coast. A correlation is demonstrated between the tritium deposition rate and the altitude of the precipitation collection site.