Light Output Uniformity of Long CsI(Tl) crystals - the “bottle-neck” for gamma and proton spectroscopy Light Output Uniformity for CsI(Tl) as supplied by manufacturers… …and Energy Resolution for gammas, measured by a APD ( 5x5), when irradiating the whole crystal volume… * CsI(Tl), L=110 mm source 20x20 Lund-Dubna, VC_2007_12_13 L=110 mm

Effect of crystal Light Output nonuniformity ( a)- 5%, b)-10% on the Light collected by Photodetector. Calculated for Protons. For Gammas – the picture looks similar, but with energy scaled by factor 1/4 - 1/5. Conclusion – dLO/LO must be less than 1% along the length of crystal Straggling and Nonlinearity for Protons and Gammas due to dL/L Lund-Dubna, VC_2007_12_13

Test with highly uniform in Light Output Crystal, L=110 mm, dL/L <0.7% CsI(Tl) – 20x20 – 110 – 23x23 mm**3 Irradiated for 110 mm distance… Photodetectors: PD – 10x10 mm**2 APD – 5x5 mm**2 / =40 APD – 10x10 mm**2 / =50 Our data… compare APD of 5x5 and 10x10 mm**2 !!!! Published data, 10x10x10 mm**3 CsI(Tl)+ 10x10 APD !!! Lund-Dubna, VC_2007_12_13

a) b) Effect of VM200 ( ESR) Light Guide reflector on Light collection and Energy Resolution a)- Active area of APD = Active area of Light Guide, 10x10 mm**2. S_ APD /S_ LG =1.0 b)- Active area of APD = 0.25 of Active area of Light Guide, 5x5 mm**2. S_ APD /S_ LG =0.25 Light Collection coefficient, L(5x5)/L(10x10) = 0.65, due to the VM2000 (ESR) reflector, covering an extra surface By using an APD of 10x10 mm**2 we can gain around 12% in the energy resolution as compared with the APD of 5x5 mm**2 Lund-Dubna, VC_2007_12_13

Some Conclusions and Plans for Future R&D Lund-Dubna, VC_2007_12_13 1.Light Output uniformity for Long crystals is more important than the active area of the APD 2.For the highly uniform in L.O. crystals we can get almost ideal Energy Resolution 3.New groups must be involved in the Uniformity Problem for real Califa geometries Plans for nearest future: 1.Light Uniformity adjustment for the real CALIFA crystal geometry 2.Tests with APD’s, PMT’s / like R7400U-3, 20 – insensitive to magnetic field 3.To mount CsI(Tl) “demonstrator” for bench and in-beam tests