Gamma-Ray Spectrum Stabilization in a Borehole Probe Using a Light Emitting Diode

A borehole probe which has a Light Emitting Diode (LED) implanted in a NaI detector has been constructed to collect spectral gamma-ray data for uranium exploration. The LED is pulsed to simulate light from gamma-ray interactions in the detector, and the resulting light is used as a reference to gain stabilize the detection system. The LED allows optimum gain sensitivity by producing a peak higher in the energy spectrum than the natural gamma-ray peaks, and the LED has no Compton scattering to interfere with the natural spectrum as do isotopic gamma-ray sources used in gain stabilization. A temperature-sensitive resistance network is used to compensate the LED for the extreme temperature variations encountered in the borehole environment. Diagrams of the probe and LED system are given along with test results.