Performance of large lanthanum bromide scintillators

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 579; no. 1; pp. 6 - 10
• Main Authors: Menge, Peter R., Gautier, G., Iltis, A., Rozsa, C., Solovyev, V.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 21-08-2007
• Subjects: Energy linearity; Energy resolution; LaBr 3:Ce; Scintillation crystals; γ-detection; 29.40.Mc; LaBr 3:Ce; Energy resolution; 29.30.Lw; Scintillation crystals; γ-detection; Energy linearity
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2007.04.002

Cerium-doped lanthanum bromide, LaBr
3(Ce), scintillator possesses several outstanding properties that make it an attractive choice for security, medical, and geophysical radiation detection applications. Among these properties are good density (5.1
g/cc), excellent energy resolution (∼3% full-width at half-maximum (FWHM) at
E
γ=662
keV), brightness (>65,000
photon/MeV), and speed, (
τ
d
<20
ns). Unfortunately, the development of many prospective devices using this scintillator has been hampered by the lack of large crystals (>100
cc). The anisotropic thermal expansion exhibited by this material makes it difficult to grow large ingots due to the build up of internal stresses as it cools, causing fracturing. Recently, Saint–Gobain Crystals has achieved successful growths of large unfractured ingots, from which large detectors have been assembled (>150
cc). The outstanding properties seen in small pieces are retained up to at least 155
cc (the largest assembled into a single detector thus far). A cylindrical LaBr
3(Ce=5%) crystal with dimensions of diameter=51
mm, and length=76
mm achieves energy resolution of 3.1% FWHM at 662
keV, and brightness of 165% of NaI with good uniformity throughout the crystal. Scintillation light yield and energy resolution have been examined as a function of crystal size and γ-ray energy. Spatial mapping of a large crystal was examined and shown to be uniform. Large crystals enable accurate measurements of the intrinsic γ-ray background from
138La (0.09% nat. abun., γ-ray emission at 1436 and 789
keV). This background is shown to scale appropriately in size with theoretical calculations.