Low level environmental measurements by gamma spectroscopy

An automatic sample changer for low level environmental measurement is here described. All individual components including detector assembly, liquid nitrogen cryostat and shielding chamber are made from carefully selected materials. The 225 cm3 U-type Ge detector is attached to a 20 l Dewar. The 150 mm thick lead shield prevents background counts due to external sources. A 8 mm copper graded liner at the inside of the shielding chamber prevents interference by lead X-rays. This measurement system reduces dramatically counting time and improves lower limits of detection. (authors). 2 figs., 4 ills., 2 refs