High energy resolution scintillators for nuclear nonproliferation applications

Abstract

The detection of ionizing radiation is important in numerous applications related to national security ranging from the detection and identification of fissile materials to the imaging of cargo containers. A key performance criterion is the ability to reliably identify the specific gamma-ray signatures of radioactive elements, and energy resolution approaching 2% at 662 keV is required for this task. In this work, we present discovery and development of new high energy resolution scintillators for gamma-ray detection. The new ternary halide scintillators belong to the following compositional families: AM 2 X 5 :Eu, AMX 3 , and A 2 MX 4 :Eu (A = Cs, K; M = Ca, Sr, Ba; X = Br, I) as well as mixed elpasolites Cs 2 NaREBr 3 I 3 :Ce (RE = La, Y). Using thermal analysis, we confirmed their congruent melting and determined crystallization and melting points. Using the Bridgman technique, we grew 6, 12 and 22 mm diameter single crystals and optimized the Eu concentration to obtain the best scintillation performance. Pulse-height spectra under gamma-ray excitation were recorded in order to measure scintillation light output, energy resolution and light output nonproportionality. The KSr 2 I 5 :Eu 4% showed the best combination of excellent crystal quality obtained at fast pulling rates and high light output of ~95,000 photons/MeV with energy resolution of 2.4% at 662 keV.

Crystal growth and spectroscopic performance of large crystalline boules of CsCaI3:Eu scintillator

“…In recent years, the search for new ternary compositions with similar performance to the aforementioned binary compositions have yielded many new materials which may offer reduced cost of development with improved performance over current technology utilizing NaI:Tl [4,5]. Each new ternary composition poses unique advantages and disadvantages to their development such as activator distribution, optical quality, and mechanical strength.…”

Crystal growth and characterization of europium doped KCaI3, a high light yield scintillator

“…The orthorhombic crystal belongs to the ABX 3 family of perovskite-type compounds (A = Cs, K; B = Ca, Sr, Ba; X = Cl, Br, I) with a density of q = 3.81 g/cm 3 and adopts the Cmcm space group (a = 4.561 Å, b = 15.086 Å, c = 11.639 Å) [6]. KCaI 3 :Eu was first reported as one of the most promising of the ABX 3 compounds with a previously reported light yield of %70,000 ph/MeV and energy resolution of 3.8% at 662 keV [7]. The earlier report remarked upon our early attempts at crystal growth of KCaI 3 :Eu which often encountered difficulties in attaining sizable crystals which tend to grow with a needle-like morphology due to the somewhat layered structure.…”

Improvement in the optical quality and energy resolution of CsSrBr3: Eu scintillator crystals

“…Similarly, europium ( [3]- [7]. The effort towards developing scintillators with promising performance have yielded many new materials, which may offer lower cost of development in addition to improved performance 34 over current scintillators like NaI: Tl [8], [9]. These new materials include ternary compound 35 scintillators such as CsCaBr 3 : Eu which possesses a light yield of ~29,000ph/MeV and an energy resolution of 9.3% at 662 keV [10], and CsSrBr 3 : Eu which has been previously reported with a 37 light yield of ~31,300ph/MeV and an energy resolution of 8.8% at keV [11].…”