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Scintillation Detectors and Materials Scintillation Detectors and Materials
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Cerium activated Lanthanum bromide (LaBr3:Ce) was reported in 2002 by van Loef et al. as a new scintillator that can perform with better energy resolution than that of NaI:Tl. After a lull in the discovery of bright scintillators capable of competing with NaI:Tl performance, the discovery of Ce activated LaBr3 helped reenvigorate the search for bright scintillators. LaBr3:Ce has a mass density of 5.06 g cm−3, and with relatively large atomic constituents of 57 (La) and 35 (Br), it has good gamma-ray absorption efficiency. The primary interaction efficiency as a function of gamma-ray energy and detector thickness is shown in Fig. 13.19. The material is very hygroscopic and brittle, and has a hexagonal crystal structure that cleaves easily along the {100} planes.18 The probable emission wavelength for LaBr3:Ce λmax is 380 nm, which matches well-enough with common PMTs. The refractive index is 1.9 that produces a critical angle of 52.1° with a glass interface. The absolute light yield is 63,000 photons/MeV, and its photoelectron response with a bi-alkali PMT ranges between 130% to 165% of that measured for NaI:Tl. The energy resolution achieved is quite excellent for a scintillation, with reported values below 2.9% FWHM at 662 keV for various crystal sizes. The excellent energy resolution is a combined effect of the absolute light yield and the good relative light yield proportionality. It is also a fast scintillator with a decay constant of τ = 16 ns, a time which requires that the light detection device be capable of following such a fast and bright light output without causing space charge buildup.20
Accelerator Technology for Well Logging: Advances, Challenges, and Opportunities
Published in Nuclear Science and Engineering, 2023
Both generators and scintillators used in monitoring tools have evolved. For example, between 1962 and 1992, D-T generators used by one major logging company went from glass type producing 9 × 107 n/s with a size of 1.25 × 9 in. to ceramic type with a neutron output of 3 × 108 n/s and a size of 1 × 7 in. (Ref. 33). Tools too have evolved from using a single detector to multiple detectors to extract multiple parameters.34–42Figure 4 displays a representative set of dual-detector and multidetector monitoring devices from the four major logging companies. Note that scintillators have evolved from NaI to a range of advanced crystals. Table I displays the key properties of the scintillators in use (the scintillator acronyms are included in Fig. 4). In view of its superior energy resolution and faster decay time, lanthanum bromide (LaBr3) crystal is emerging as the scintillator of choice for spectroscopy measurements in the industry. Its internal radioactivity did not affect the data needed in monitoring but could adversely impact the spectral data in energy ranges of interest in other applications.