For field mapping applications, a 𝛾-ray detector is needed that has a response that should be high enough to obtain sufficient statistics to identify individual nuclide activity concentrations of natural soil, rock or sediment in about 10 s. Moreover, the system should be able to withstand rough conditions  where cooling with liquid nitrogen is not straightforward. Therefore, often a scintillation crystal is chosen. The measurement of natural 𝛾-radiation in the field is not new, but has been applied in boreholes (see e.g. Tittle, 1989) and airborne surveys (see e.g. Darnley, 1991), but also in seafloor measurements (Jones, 1994).  In most of these cases NaI scintillation crystals are used. These crystals have a combination of properties that make them appropriate for many of these applications: they are available in large crystals, have a moderate resolution and can be used at normal temperatures. In recent years other detector materials have also been used.

Detector materialdensity (kg/l)hygroscopicbrittleother
CeBr35.2YesYesextremely high resolution

The properties described above and the application for the measurement determine which system is preferred. An app on: describes how fast you can survey or how long you have to measure at different accuracies.