  A new digital logarithmic airborne gamma ray spectrometer is designed in this
study. The spectrometer adopts a high-speed and high-accuracy logarithmic
amplifier (LOG114) to amplify the pulse signal logarithmically and to improve
the utilization of the ADC dynamic range, because the low-energy pulse signal
has a larger gain than the high-energy pulse signal. The spectrometer can
clearly distinguish the photopeaks at 239, 352, 583, and 609keV in the
low-energy spectral sections after the energy calibration. The photopeak energy
resolution of 137Cs improves to 6.75% from the original 7.8%. Furthermore, the
energy resolution of three photopeaks, namely, K, U, and Th, is maintained, and
the overall stability of the energy spectrum is increased through potassium
peak spectrum stabilization. Thus, effectively measuring energy from 20keV to
10MeV is possible.
