NaIL (NaI:Tl, Li) a large volume neutron-gamma scintillator with exceptional pulse shape discrimination

Transcription

1 NaIL (NaI:Tl, Li) a large volume neutron-gamma scintillator with exceptional pulse shape discrimination Kan Yang Peter R. Menge Saint-Gobain Crystals Hiram, Ohio USA Vladimir Ouspenski Saint-Gobain Recherche Aubervilliers, France IEEE NSS MIC 29 Oct. 5 Nov., 2016 Strasbourg, France

2 OUTLINE Introduction of NaIL (NaI:Tl, Li) n-γ pulse shape discrimination (PSD) Scintillation properties High temperature performance Neutron detection efficiency Conclusions 2

3 INTRODUCTION NaIL NaI:Tl is the most widely used γ-ray scintillator. Fully industrialized Large volume production Low cost Mature detector designs Introducing efficient neutron detection to NaI:Tl by Li doping. n + 6 Li t (2.75 MeV) + α (2.05 MeV) NaI - LiI forms solid solution at any ratio. Polycrystalline NaI:Tl,Li does not have sufficient PSD.* Our researches focus on large format single crystals of NaI:Tl, Li (NaIL ) [Tl] = 0.1 at%; [Li] = 0 8 at% *Brubaker et al., IEEE NSS/MIC Conf. Rec.(2011) Nagarkar et al., IEEE NSS/MIC Conf. Rec.(2013) 3

4 PULSE SHAPE DISCRIMINATION Room temperature, measured with 252 Cf 662 kev 3.2 MeVee Gamma * PSD Ratio Gamma Neutron Neutron 1% 6 Li in crystal PSD FoM = 2.8 Energy (MeVee) Typical PSD FoM is 2 4 depending on [Li]. Better than 10-8 gamma rejection *FFT based PSD algorithm, 8 µs integration time K. Yang, et al., IEEE NSS-MIC Conf. Rec., NPO1-73 (2013) 4

5 DECAY CONSTANTS AND PULSE SHAPES Room temperature 0.7% Li Gamma 2.2% Li Neutron 7.7% Li Averaged neutron pulses Decay constants of NaI:Tl, Li Neutron pulses decay faster than gamma pulses. Both fast and slow decay times increase with [Li]. ~ 250 ns with 1% Li loading; ~ 290 ns with 2% Li loading 5

6 LIGHT YIELD AND ENERGY RESOLUTION [Li] = 0 8% in crystal LY decreases gradually with increasing [Li]. ~ 34,000 ph/mev with 1% Li loading ~ 31,000 ph/mev with 2% Li loading E/E is comparable to standard NaI:Tl. LY and E/E are relatively insensitive to [Li]. Synthesis process is not yet optimized. 6

7 IMPROVED HIGH TEMPERATURE LIGHT YIELD NaI:Tl + 1% Li in crystal LY o C < 10% NaIL (1% Li) Standard NaI:Tl Shaping time = 12 µs Better high temperature stability than standard NaI:Tl 7

8 PSD AT DIFFERENT TEMPERATURES NaI: Tl + 1% Li PSD is enhanced between o C. *Measured with Photonis XP2020 PMT through a 1 quartz light pipe; PSD FoM s were scaled based on reference points of which the sample were coupled directly to PMT. Excellent neutron-gamma PSD up to 160 o C 8

9 NEUTRON DETECTION EFFICIENCY SMALL FORM FACTOR Simulation Results Trade-off between performance, cost and amount of Li loading Question: how much Li loading is needed? Example #1 : 50 mm x 50 mm NaIL Detector, 6 Li enriched Handheld, backpack, SPRD, oil-well logging etc. thermal neutron detection efficiency Det. Eff. (NaI + 2% 6 Li) = 74% Det. Eff. (NaI + 1% 6 Li) = 53% 50mm x 50mm NaIL Li doping (%at.) 2 x2 CLLB w/ 6 Li 2 x2 CLYC w/ 6 Li 3 He 0.5 x2 tube, 8atm ( 12 mm x 50 mm) 9

10 NEUTRON DETECTION EFFICIENCY SMALL FORM FACTOR Simulation Results Trade-off between performance, cost and amount of Li loading Question: how much Li loading is needed? Example #1 : 50 mm x 50 mm NaIL Detector, 6 Li enriched 25 2 x2 CLLB w/ 6 Li n th detection efficiency * area Handheld, backpack, SPRD, oil-well logging etc. (ε*a, cm 2 ) NaIL + 2% 6 Li = C 6 LYC of the same size NaIL + 1% 6 Li = 3x a typical handheld 3 He tube NaIL % 6 Li 5 = a typical handheld 3 He tube 3 He 0.5 x2 tube, 8atm ( 12 mm x 50 mm) 50mm x 50mm NaIL Li doping (%at.) 2 x2 CLYC w/ 6 Li 10

11 NEUTRON DETECTION EFFICIENCY LARGE FORM FACTOR Simulation Results Example #2 : 50 x 100 x 400 mm 3 NaIL Detector (2 x4 x16 ) Standard PNNL setup Diminishing gain if 6 Li is increased beyond 3% Four 2x4x16 Simulated with MCNPX Detectors share one standard moderator box 3 He tube 2 2.9atm Three 2x4x16 Two 2x4x16 Three 2x4x16 NaIL + 2% 6 Li = a standard portal 3 He tube One 2x4x16 Four 2x4x16 NaI + 1% 6 Li = a standard portal 3 He tube Spectroscopic portal, RPM standoff and mobile system Promising solution for spectroscopic portal < 3% enriched 6 Li loading is needed for most detection applications. 11

12 SUMMARY AND CONCLUSIONS NaI:Tl, Li (NaIL ) is an excellent n-γ dual mode scintillator with exceptional PSD. Production of large volume detector (> 500 cm 3 ) is planned. Scintillation performance of NaIL is comparable to standard NaI. NaIL maintains excellent LY and n-γ PSD from room temperature up to 160 o C. NaIL with < 3 % enriched 6 Li is sufficient for most detection applications. Higher doping is possible if needed. Production scale-up progress Pilot trials (8 / 200 mm) currently underway Full size production trials (>600 mm) planned by year end Patents pending Thank you! Visit us at booth 56/57 50 mm NaIL detector First 200 mm NaIL pilot ingot 12