Airborne spectrometry: Extraction of low energy γ-rays using two or three spectral windows

Airborne γ-ray spectrometry with NaI(Tl) is a recognized tool for emergency mapping. The maps produced usually look for natural isotopes (⁴⁰K, ²³⁸U, ²³²Th) and ¹³⁷Cs due to the Chernobyl accident. Nowadays a new thematic emerges as nuclear materials tracking. Such materials emitting at low energies require new algorithms and a new method is presented here based on counts observed in two or three spectral windows. Since altitude is an important factor to be taken into account, an improvement is proposed to follow flight altitude changes. An extension to medium energies is proposed and compared to windows methods and to peak detection.