Lanthanum bromide

Lanthanum bromide (LaBr₃) is a bromide of lanthanum, an inorganic compound. It has the appearance of a white powder or hexagonal crystals with melting point 789 °C. It is highly hygroscopic and well-soluble. It is used as a source of lanthanum in chemical synthesis. Its CAS number is [13536-79-3] and its EINECS number is 236-896-7. Its molecular weight is 378.62 g/mol, and its density is 5.06 g/cm³.[1] The CAS number of the hydrate (LaBr₃.xH₂O) is [13465-19-5].

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Cerium activated lanthanum bromide is the recent inorganic scintillator which has a combination of high light yield and the best energy resolution.

Lanthanum bromide scintillation detector

Recent advances in scintillator material have resulted in the development of cerium activated lanthanum bromide (LaBr₃) detectors. LaBr₃ was discovered in 2001 ^[1]. These detectors offer improved energy resolution, fast emission and excellent temperature and linearity characteristics. Typical energy resolution at 662 keV is 3% as compared to sodium iodide detectors at 7% ^[2]. The improved resolution is due to a photoelectron yield of 160% that achieved with sodium iodide. Another advantage of LaBr₃ is the nearly flat photo emission over a 70 °C temperature range (~1% change in light output).

Today LaBr₃ detectors are offered with bialkali photomultiplier tubes (PMT) that can be two inches in diameter and 10 or more inches long. However, miniature packaging can be obtained by the use of silicon drift detectors (SDD). These UV enhanced diodes provide excellent wavelength matching to the 380 nm emission of LaBr₃. A recent paper presented at the 2005 IEEE Nuclear Science Symposium shows that the SDD has a higher quantum efficiency over the PMT^{[citation needed]}. Moreover the SDD is not as sensitive to temperature and bias drift. The reported spectroscopy performance of the SDD configuration resulted in a 2.8% energy resolution at 662 keV for the detector sizes considered.

LaBr₃ introduces an enhanced set of capabilities to a range of isotope identification systems used in the homeland security market. Isotope identification utilizes several techniques (known as algorithms) which rely on the detector’s ability to discriminate peaks. The improvements in resolution allow more accurate peak discrimination in ranges where isotopes often have many overlapping peaks. This leads to better isotope classification. Screening of all types (pedestrians, cargo, conveyor belts, shipping containers, vehicles, etc.) often requires accurate isotopic identification to differentiate concerning materials from non-concerning materials (medical isotopes in patients, naturally occurring radioactive materials, etc.) Heavy R&D and deployment of instruments utilizing LaBr₃ is expected in the upcoming years. (List of companies who manufacture commercial off-the-shelf Radiation Isotope Identifiers for Homeland Security: Canberra Industries, ORTEC, Berkeley Nucleonics, Polimaster ^[3] )

References

1. ^ E. V. D. van Loef, P. Dorenbos, C. W. E. van Eijk, K. W. Kraemer and H. U. Guedel Appl. Phys. Lett. 79 2001 1573
2. ^ Knoll, Glenn F., Radiation Detection and Measurement 3rd ed. (Wiley, New York, 2000).
3. ^ http://www.polimaster.com