Bromide Scintillation Detectors Research Articles

Determining initial enrichment, burnup, and cooling time of pressurized-water-reactor spent fuel assemblies by analyzing passive gamma spectra measured at the Clab interim-fuel storage facility in Sweden

The purpose of the Next Generation Safeguards Initiative (NGSI)–Spent Fuel (SF) project is to strengthen the technical toolkit of safeguards inspectors and/or other interested parties. The NGSI–SF team is working to achieve the following technical goals more easily and efficiently than in the past using nondestructive assay measurements of spent fuel assemblies: (1) verify the initial enrichment, burnup, and cooling time of facility declaration; (2) detect the diversion or replacement of pins; (3) estimate the plutonium mass [which is also a function of the variables in (1)]; (4) estimate the decay heat; and (5) determine the reactivity of spent fuel assemblies. Since August 2013, a set of measurement campaigns has been conducted at the Central Interim Storage Facility for Spent Nuclear Fuel (Clab), in collaboration with Swedish Nuclear Fuel and Waste Management Company (SKB). One purpose of the measurement campaigns was to acquire passive gamma spectra with high-purity germanium and lanthanum bromide scintillation detectors from Pressurized Water Reactor and Boiling Water Reactor spent fuel assemblies. The absolute 137Cs count rate and the 154Eu/137Cs, 134Cs/137Cs, 106Ru/137Cs, and 144Ce/137Cs isotopic ratios were extracted; these values were used to construct corresponding model functions (which describe each measured quantity’s behavior over various combinations of burnup, cooling time, and initial enrichment) and then were used to determine those same quantities in each measured spent fuel assembly. The results obtained in comparison with the operator declared values, as well as the methodology developed, are discussed in detail in the paper.

Neutron measurements with lanthanum–bromide scintillation detectors—A first approach

In this paper we report on the measurement of γ-rays using a 2in.×2in. LaBr3:Ce scintillation detector. The γ-rays were emitted in the spontaneous fission of 252Cf and detected in coincidence with fission fragments. After presenting some of the properties of the detector, we show how well γ-rays produced in different reactions may easily be distinguished by their characteristic time-of-flight. Then we focus on the analysis of γ-rays from inelastically scattered neutrons in the scintillation crystal and demonstrate how this information may be used for neutron spectroscopy. We determine the neutron detection efficiency and compare it to the result of calculations based on existing reaction cross-sections. Finally, we discuss the detection performance in relation to other detector systems commonly used for neutron monitoring.

Analytical Method to Calibrate Cylindrical LaBr<sub>3</sub>(Ce) Scintillation Detector

A new analytical method of efficiency calibration is proposed for cylindrical lanthanum bromide (LaBr3:Ce) scintillation detectors. The cerium-doped lanthanum halide crystals have gained special interest due to their high density and atomic number, which results in excellent scintillation properties and higher detection efficiencies in comparison to NaI(Tl). The comparisons with the experimental and Monte Carlo method data reported in the literature indicate that the present method is useful in the efficiency calibration of the cylindrical lanthanum bromide scintillation detectors.

Analytical expression to calculate total and full-energy peak efficiencies for cylindrical phoswich and lanthanum bromide scintillation detectors

Abstract An analytical expression for the total and full-energy peak efficiencies for cylindrical phoswich and lanthanum bromide (LaBr 3 :Ce) scintillation detectors is derived. This approach depends on the accurate analytical calculation of two important factors; the path length d , the photon traverses within the active volume of a gamma detector, and the geometrical solid angle Ω , subtended by the source to the detector at the point of entrance. In addition, the attenuation of photons by the detector housing materials is also treated by calculating the photon path length through these materials. The comparisons with the experimental and Monte Carlo method data reported in the literature indicate that the present method is useful in the efficiency calibration of the cylindrical phoswich and lanthanum bromide scintillation detectors.

High energy gamma-ray spectroscopy with LaBr 3 scintillation detectors

Lanthanum bromide scintillation detectors produce very high light outputs (∼60,000 ph/MeV) within a very short decay time (typically ∼20 ns) which means that high instantaneous currents can be generated in the photocathode and dynode chain of the photomultiplier tube (PMT) used for the scintillation readout. The net result is that signal saturation can occur long before the recommended PMT biasing conditions can be reached. In search of an optimized light readout system for LaBr 3, we have tested and compared two different PMT configurations for detection of gamma-rays up to 15 MeV. This range was chosen as being appropriate for gamma-ray remote sensing and medium energy nuclear physics applications. The experiments were conducted at two facilities: the Laboratori Nazionali del Sud (LNS) in Catania, Italy [1] and the High Intensity Gamma-ray Source (HIγS) at Triangle University Nuclear Laboratory, in Durham, North Carolina, USA [2]. The PMT configurations we have tested are (1) a standard dynode chain operated under-biased; (2) a 4-stage reduced chain operated at nominal inter-dynode bias. The results are that shortening the number of active stages, as in configuration (2), has advantages in preserving energy resolution and avoiding PMT saturation over a large energy range. However, the use of an under-biased PMT, configuration (1), can still be considered a satisfactory solution, at least in the case of PMTs manufactured by Photonis. The results of this study will be used in support of the Mercury Gamma-ray and Neutron Spectrometer (MGNS) on board of BepiColombo, the joint ESA/JAXA mission to Mercury, scheduled for launch in 2014.

Pulsed Neutron Facility for Research in Illicit Trafficking and Nuclear Safeguards

The Joint Research Centre has taken into operation a new experimental facility designed for research in the fields of illicit trafficking and nuclear safeguards. The research projects currently undertaken include detection of shielded contraband materials (drugs, explosives, nuclear materials), and mass determination of small fissile materials in shielded containers. The facility, called the Pulsed Neutron Interrogation Test Assembly (PUNITA), incorporates a pulsed 14-MeV D-T neutron generator and a large graphite mantle surrounding a sample cavity. The sealed generator emits neutrons in 10-microsecond pulses. After a slowing-down time of approximately 300 mus, an average thermal neutron lifetime of approximately one millisecond is achieved in the graphite moderator and the sample cavity. By pulsing the neutron generator with a frequency between 10 to 150 Hz, a sample may be interrogated first by fast neutrons, and a few hundred microseconds later by a pure thermal neutron flux. For the detection of materials such as explosives the facility employs gamma detectors for characteristic prompt gamma rays from inelastic scattering by fast neutrons, and from thermal neutron capture. The gamma detectors include HPGe detectors and lanthanum bromide scintillation detectors. This new type of scintillation detector is particularly suited for the detection of activation gamma rays in the MeV range. For the purpose of fissile material assay (nuclear safeguards) the PUNITA facility employs 96 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He proportional counters located on the outside of the graphite liner and embedded in cadmium covered polyethylene modules. The paper reports about the design and characterization of the new research facility as well as the different experimental configurations employed for the research activities in the fields of illicit trafficking and nuclear safeguards.