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
CRYSTALS
OUTLINE
Introduction of NaIL™ (NaI:Tl, Li)
n-γ pulse shape discrimination (PSD)
Scintillation properties
High temperature performance
Neutron detection efficiency
Conclusions
CRYSTALS
2
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 + 6Li → 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)
CRYSTALS
3
PULSE SHAPE DISCRIMINATION
Room temperature, measured with 252Cf
662 keV
3.2 MeVee
Gamma
PSD Ratio
*
Gamma
Neutron
Neutron
1% 6Li 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)
CRYSTALS
4
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
CRYSTALS
5
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.
CRYSTALS
6
IMPROVED HIGH TEMPERATURE LIGHT YIELD
NaI:Tl + 1% Li in crystal
LY loss @160 oC < 10%
NaIL™ (1% Li)
Standard NaI:Tl
Shaping time = 12 µs
Better high temperature stability than standard NaI:Tl
CRYSTALS
7
PSD AT DIFFERENT TEMPERATURES
NaI: Tl + 1% Li
PSD is enhanced between 40 – 120 oC.
*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 oC
CRYSTALS
8
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, 6Li enriched
thermal neutron detection efficiency
1
Handheld, backpack,
SPRD, oil-well logging etc.
2”x2”CLLB w/ 6Li
0.8
2”x2” CLYC w/ 6Li
Det. Eff. (NaI + 2%6Li) = 74%
0.6
3He
⌀0.5”x2” tube, 8atm
(⌀12 mm x 50 mm)
Det. Eff. (NaI + 1%6Li) = 53%
0.4
0.2
50mm x 50mm NaIL™
0
0
2
4
6
Li doping (%at.)
8
10
CRYSTALS
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, 6Li enriched
25
th
2”x2” CLYC w/ 6Li
20
2
(ε*A, cm )
n detection efficiency * area
2”x2”CLLB w/ 6Li
NaIL™ + 2%6Li
= C6LYC of the same size
15
NaIL™ + 1%6Li
= 3x a typical handheld 3He tube
10
NaIL™ + 0.25%6Li
= a typical handheld 3He tube
5
3He
0.5”x2” tube, 8atm
(⌀12 mm x 50 mm)
50mm x 50mm NaIL™
Handheld, backpack,
SPRD, oil-well logging etc.
0
0
2
4
6
Li doping (%at.)
8
10
CRYSTALS
10
NEUTRON DETECTION EFFICIENCY – LARGE FORM FACTOR
Simulation Results
Example #2 : ⌀ 50 x 100 x 400 mm3 NaIL™ Detector (2”x4”x16”)
Standard PNNL setup
Diminishing gain if 6Li is
increased beyond 3%
Four 2x4x16
3He
Three 2x4x16
tube
2”x72” @ 2.9atm
Simulated with MCNPX 2.6.0.
Detectors share one standard moderator box
Two 2x4x16
Three 2x4x16 NaIL™ + 2%6Li
= a standard portal 3He tube
One 2x4x16
Four 2x4x16 NaI™ + 1%6Li
= a standard portal 3He tube
Spectroscopic
portal, RPM standoff and mobile
system
Promising solution for spectroscopic portal
< 3% enriched 6Li loading is needed for most
detection applications.
CRYSTALS
11
SUMMARY AND CONCLUSIONS
NaI:Tl, Li (NaIL™) is an excellent n-γ dual mode scintillator
with exceptional PSD. Production of large volume detector
(> 500 cm3) 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 oC.
NaIL™ with < 3 % enriched 6Li 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
Thank you!
Patents pending
Visit us at booth 56/57
⌀ 50 mm
NaIL™ detector
First ⌀ 200 mm
NaIL™ pilot ingot
CRYSTALS
12