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Cerium-doped lanthanum bromide – LaBr3(Ce) – scintillators offer better resolution and greater stopping power compared to conventional thallium-doped sodium iodine – NaI(Tl) – scintillators.

A typical lanthanum bromide scintillator achieves a 2.5% FWHM @ 662 keV resolution compared to a 6-7% resolution of a sodium iodine detector. In terms of geometry, a 1.5″ high by 1.5″ diameter lanthanum bromide crystal is roughly equivalent to a 2″ high by 2″ diameter sodium iodine crystal in terms of sensitivity.

Advantages of Lanthanum Bromide Detectors

The advantages of LaBr3(Ce) scintillators over NaI(Tl) are:

  • 3x better resolution;
  • 2x smaller volume at the same sensitivity;
  • Fast (100 ns) peaking time allows for much faster counts (10x faster than sodium iodine);
  • Exceptional linearity.

Disadvantages of Lanthanum Bromide Detectors

The drawbacks of LaBr3(Ce) compared to NaI(Tl) are:

  • Much higher price: a 1.5″ x 1.5″ high-resolution (e.g. 2.5% FWHM @ 662 keV) lanthanum bromide gamma detector costs almost $10,000;
  • Self-activity of lanthanum bromide produces peaks at 30 keV and 1.5 MeV, with the latter being especially unwelcome since it overlaps with the important 40K line.

Do the advantages outweigh the disadvantages? With the exception of 40K, the answer is a definite ‘yes’.

Maximus Energy LaBr3 Detectors

Maximus Energy have recently introduced a new affordably priced LaBr3 gamma detector based on CapeSym 1.4 x 1.4 x 2.5 cm crystal – Fig. 1.

Fig. 1. Maximus Energy LaBr3 gamma detector.

The detector comes in a compact 2 x 3 x 1″ enclosure and requires a 5V power. The built-in charge-sensitive preamplifier outputs positive-polarity pulses (via an SMA connector) with an internal jumper-selectable 10- or 50-μs time constant suitable for processing with an MCA-PRO or any other multi-channel analyzer / pulse processor.

Also, the detector contains a temperature sensor, which automatically adjusts the preamplifier gain in order to keep the output pulse height constant regardless of the ambient conditions thus eliminating the temperature related calibration drift.

PulseCounter Preset

The recommended PulseCounter preset is as follows:

  • Sampling Rate: 10 MHz;
  • Range: 1-2V;
  • Pulse Shaping Mode: Trapezoidal;
  • Shaping Time / Flat Top: 0.5 μs / 0.5 μs;
  • Threshold: 4 mV;
  • Trigger: Absolute;
  • Baseline: 1 μs.

Sample Spectra

The sample spectra captured using the Maximus Energy LaBr3 gamma detector detector connected to an MCA-PRO are shown on Fig. 2-4.

Fig. 2. 137Cs gamma spectrum captured using the Maximus Energy LaBr3 gamma detector; FWHM @ 662 keV = 2.5%.
Fig. 3. 57Co gamma spectrum captured using the Maximus Energy LaBr3 gamma detector; note the 14.4 keV peak.
Fig. 4. 133Ba, 137Cs, 57Co, and 60Co gamma spectrum captured using the Maximus Energy LaBr3 gamma detector.

The detector was calibrated using the three reference energies (122 keV, 661.7 keV, and 1.332 MeV). The resulting quadratic calibration curve provided excellent fit for all energies across the captured spectra.

Background Spectrum

The background gamma spectrum captured over 10 hours is shown on Fig. 5.

Fig. 5. The background gamma spectrum captured using the Maximus Energy LaBr3 gamma detector (note the logarithmic scale).

The 32 keV x-ray and 1436+32 keV gamma-ray peaks are evident.

Conclusion

Maximus Energy offers an affordable small form factor LaBr3 gamma detector characterized by excellent resolution, good sensitivity, near-perfect energy calibration linearity and satisfactory temperature stability. This detector makes an excellent choice for replacing legacy NaI(Tl) detectors for gamma spectroscopy.