Characterization of large volume 3.5″×8″ LaBr3:Ce detectors

Abstract

The properties of large volume cylindrical 3.5" x 8" (89 mm x 203 mm) LaBr 3 :Ce scintillation detectors coupled to the Hamamatsu R10233-100SEL photo-multiplier tube were investigated. These crystals are among the largest ones ever produced and still need to be fully characterized to determine how these detectors can be utilized and in which applications. We tested the detectors using monochromatic ray sources and in-beam reactions producing  rays up to 22.6 MeV; we acquired PMT signal pulses and calculated detector energy resolution and response linearity as a function of -ray energy. Two different voltage dividers were coupled to the Hamamatsu R10233-100SEL PMT: the Hamamatsu E1198-26, based on straightforward resistive network design, and the "LABRVD", specifically designed for our large volume LaBr 3 :Ce scintillation detectors, which also includes active semiconductor devices. Because of the extremely high light yield of LaBr 3 :Ce crystals we observed that, depending on the choice of PMT, voltage divider and applied voltage, some significant deviation from the ideally proportional response of the detector and some pulse shape deformation appear. In addition, crystal non-homogeneities and PMT gain drifts affect the (measured) energy resolution especially in case of high-energy  rays. We also measured the time resolution of detectors with different sizes (from 1"x1" up to 3.5"x8"), correlating the results with both the intrinsic properties of PMTs and GEANT simulations of the scintillation light collection process. The detector absolute full energy efficiency was measured and simulated up to -rays of 30 MeV

Characterization of Large Volume 3.5″ x 8″ LaBr3:Ce Detectors for the HECTOR+array

“…The Figure 1 shows the energy spectra measured in the reaction 23 Na+p = 24 Mg with a proton energy of 1416.9 keV (left panel) and 11 B + p = 12 C with a proton energy of 7250 keV (right panel) [13]. In both spectra of figure 1 it is evident that the full energy peak and the first escape one are well separated.…”

“…The high-energy gamma-ray spectra measured with a large volume LaBr 3 :Ce 3.5"x8" and analogue electronics for monochromatic gamma rays of 6.13, 8.9 and 22.6 MeV [13].…”

“…In the left panel, the measurements with digital electronics are shown while in the right panel those taken with the analogue one are displayed. The dashed line shows the expected (E) 1/2 trend while in the continuous line a term linear with energy was added [13].…”

“…[11] and references therein) and even less information is available for large volume LaBr 3 :Ce detectors (see ref. [12,13] and references therein). It is also important to point out that the properties of large volume LaBr 3 :Ce crystals cannot be easily derived from those of small and medium sized detectors.…”

“…It is also important to point out that the properties of large volume LaBr 3 :Ce crystals cannot be easily derived from those of small and medium sized detectors. In fact, several factors may affect the detector performances: i) self absorption, ii) possible crystal internal non-homogeneities that may result in variation of the crystal light yield depending on the detector area affected by the interacting γ ray (both of which are more likely to appear with scaled up dimensions), iii) the much longer mean free path of the scintillation light towards the photo-cathode and iv) non-ideal photo-multiplier tube (PMT) properties [13]. …”