In so doing, the first detector logs photons (gamma quantum) passed through the wellstream pipe not interacting with wellstream components.

The detector element (1) consists of two or more different conversion units (11, 12), which react to the absorption of a gamma quantum (y) with light emissions (λ1, λ2) of different spectral composition.

Using said detector module (1) a method to determine the 3D-coordinates of a point of interaction of a gamma quantum (Ϝ1, Ϝ2) with said detector module (1) is disclosed method.