The aim of the irradiation described below is a test of drift
under radiation with the sensor fixed on a stainless steel support
which is not supposed to vary under irradiation (Fig. 6). The
drift can be measured through the difference of cavity length
from the start of the reactor to the end of the cycle; but it can also
be assessed continuously during irradiation as far as the temperature
is keep constant, which is necessary since the sensor is not
completely temperature compensated (the amount of variation
with temperature depends on how the thermal dilatations of the
support and the sensor are similar).