Nuclear density measurements rely on the attenuation of a radiation field of known intensity traversing a region of interest. Such an attenuation measurement technique requires the determination of the radiation field intensity before entering and after exiting the region of interest. In a downhole environment, density measurements are typically performed in a single cylindrical downhole tool.
In typical downhole gamma-gamma density measurements, the downhole tool contains both one or more photon detectors and a gamma radiation source of known intensity. The formation density of interest is probed when photons emitted from the radiation source exit the bore-hole region and scatter off the formation back into the bore-hole again, where they are detected by a detection unit on the downhole tool.
One of the disadvantages to such methods is that the downhole tool electronics are submitted to the harsh wellbore conditions, which requires more system maintenance. In addition, more deployment time and money are required because the tool must be repeatedly conveyed and retrieved from the wellbore to perform such maintenance.