Low energy γ-ray scintillation detection with large area avalanche photodiodes

The energy resolution of NaI:Tl, CsI:Tl, LSO and YAP crystals coupled to 16 mm diameter large area avalanche photodiodes (LAAPD) was studied for low energy γ-rays. Energy resolutions of 11.3% and 8.4% were obtained for 59.6 keV γ-rays from ²⁴¹Am and 122 keV γ-rays from ⁵⁷Co sources, respectively, as measured with a 10 mm diameter by 10 mm high NaI:Tl crystal. The optimization of the LAAPD performance is presented, being essential for improvement of energy resolution at low energy γ-rays. Measured numbers of primary electron-hole pairs produced in LAAPDs and evaluation of the noise contribution of these devices allowed for quantitative discussion of the results. Particularly, the intrinsic energy resolution of the crystals vs. the energy of γ-rays has been evaluated. Obtained data for a NaI:Tl crystal showed a good agreement (within 30%) with the calculated component due to nonproportional light yield for energies above 50 keV