Measurements of environmental radioactivity with germanium 'well type' detectors at high efficiency and very low background

During the last 15 years most developments of gamma spectrometry using H.P Germanium detectors have been devoted to conventionally shaped detectors, i.e a cylinder on which the sample is directly laid. Very few 'well type' detectors in which the Ge diode surround the sample were used. Indeed such 'well type' crystals are known to present several disadvantages when compared with their conventionally shaped counterparts: loss of about 10% in resolution, impossibility of using a linear energy calibration curve due to problems of summed peaks detection, a limitation to only 2 to 3 cm3 sample volume placed in the well. We demonstrate here, however, that for many applications to environmental studies a large, low background 'well type' detector is a good choice. (authors). 4 figs., 1 tab., 7 refs