Radioisotope Identification Research Articles

Growth and Characterization of Polycrystalline Lanthanide Halide Scintillators.

We are exploring a novel time- and cost-efficient approach to produce robust, large-volume polycrystalline lanthanide halide scintillators using a hot wall evaporation (HWE) technique. To date, we have fabricated LaBr3:Ce and LaCl3:Ce films (slabs) measuring up to 7 cm in diameter and 7+ mm in thickness (20 to 25 cm3 in volume) on quartz substrates. These polycrystalline scintillators exhibit very bright emissions approaching those exhibited by their melt-grown crystal counterparts. Scanning electron micrographs (SEMs) and X-ray diffraction analyses confirm polycrystalline growth with columnar structures, both of which help in light piping, thereby contributing to the observed high light yields. The new scintillators also exhibit good energy resolution for γ-rays over the tested range of 60 keV (241Am) to 662 keV (137Cs), although they have not yet reached that of the corresponding crystals. The measured response linearity over the same energy range is comparable for both our HWE synthesized films and melt-grown commercially-available reference crystals. Similar consistency in response is also observed in terms of their decay time and afterglow behaviors. The data collected so far demonstrate that our HWE technique permits the rapid creation of scintillators with desired structural and compositional characteristics, without the introduction of appreciable defects, and yields material performance equivalent to or approaching that of crystals. Consequently, the deposition parameters may be manipulated to tailor the physical and scintillation performance of the resulting structures, while achieving a cost per unit volume that is substantially lower than that of crystals. In turn, this promises to allow the use of these novel scintillation materials in such applications as SPECT, PET, room-temperature radioisotope identification and homeland security, where large volumes of materials in a wide variety of shapes and sizes are needed. This paper describes our growth and testing of polycrystalline LaBr3:Ce scintillators and provides comparative characterizations of their performance with crystals.

Microcolumnar and polycrystalline growth of LaBr 3:Ce scintillator

While a wide variety of new scintillators are now available, cerium-doped lanthanide halide scintillators have shown a strong potential toward fulfilling the needs of highly demanding applications such as radioisotope identification at room temperature, homeland security, quantitative molecular imaging for medical diagnostics, and disease staging and research. Despite their extraordinary advantages in terms of light yield and response uniformity over a wide energy range, issues related to reliable, large volume manufacturing of these high-light-yield materials in a rapid and economic manner has not been resolved or purposefully addressed. Here we report on synthesizing LaBr 3:Ce scintillator using a thermal evaporation technique, which offers the potential to synthesize large quantities of small-to-large volume, high-quality material in a time-efficient and cost-effective manner. To date we have successfully applied this method to form both microcolumnar films and thick polycrystalline slabs of LaBr 3:Ce, and have characterized their light yield, response linearity, decay time and afterglow.

Bright Semiconductor Scintillator for High Resolution X-Ray Imaging

We report on a novel approach to produce oxygen-doped zinc telluride (ZnTe:O), a remarkable group II-VI semiconductor scintillator, fabricated in the columnar-structured or polycrystalline forms needed to fulfill the needs of many demanding X-ray and -ray imaging applications. ZnTe:O has one of the highest conversion efficiencies among known scintillators, emission around 680 nm (which is ideally suited for CCD sensors), high density of 6.4 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , fast decay time of ~1μs with negligible afterglow, and orders of magnitude higher radiation resistance compared to commonly used scintillators. These properties allow the use of ZnTe:O in numerous applications, including X-ray imaging, nuclear medicine (particularly SPECT), room temperature radioisotope identification, and homeland security. Additionally, ZnTe:O offers distinct advantages for synchrotron-based high resolution imaging due to the absence of atomic absorption edges in the low energy range, which otherwise reduce resolution due to secondary X-ray formations. We have fabricated films of ZnTe:O using a vapor deposition technique that allows large-area structured scintillator fabrication in a time- and cost-efficient manner, and evaluated its performance for small-angle X-ray scattering (SAXS) at an Argonne National Laboratory synchrotron beamline. Details of the fabrication and characterization of the optical, scintillation and imaging properties of the ZnTe:O films are presented in this paper.

Linearization of Gamma Energy Spectra in Scintillator-Based Commercial Instruments

This paper presents a novel technique developed for linearizing the energy spectra of radiation detectors in commercial radioisotope identification devices. Based on few spectrum measurements with standard radio-nuclide sources, this method allows generation of individual nonlinear calibration functions at minimum expense in the routine instrument setup. Instead of fitting peak positions, the measured raw data are compared with simulated spectrum templates, and local gain factors providing the best correspondence are taken as reference points for the calibration function. This approach avoids the problem of fitting multiple peaks with intensity ratios influenced by absorbing layers and assures an accuracy of 1% in the energy range of 30 keV to 3 MeV.

Peak fitting and identification software library for high resolution gamma-ray spectra

A new gamma-ray spectral analysis software package is under development in our laboratory. It can be operated as a stand-alone program or called as a software library from Java, C, C++ and MATLAB TM environments. It provides an advanced graphical user interface for data acquisition, spectral analysis and radioisotope identification. The code uses a peak-fitting function that includes peak asymmetry, Compton continuum and flexible background terms. Peak fitting function parameters can be calibrated as functions of energy. Each parameter can be constrained to improve fitting of overlapping peaks. All of these features can be adjusted by the user. To assist with peak identification, the code can automatically measure half-lives of single or multiple overlapping peaks from a time series of spectra. It implements library-based peak identification, with options for restricting the search based on radioisotope half-lives and reaction types. The software also improves the reliability of isotope identification by utilizing Monte-Carlo simulation results.

Radio-Isotope Identification Algorithms for NaI γ Spectra

The performance of Radio-Isotope Identification (RIID) algorithms using NaI-based γ spectroscopy is increasingly important. For example, sensors at locations that screen for illicit nuclear material rely on isotope identification using NaI detectors to distinguish innocent nuisance alarms, arising from naturally occurring radioactive material, from alarms arising from threat isotopes. Recent data collections for RIID testing consist of repeat measurements for each of several measurement scenarios to test RIID algorithms. It is anticipated that vendors can modify their algorithms on the basis of performance on chosen measurement scenarios and then test modified algorithms on data for other measurement scenarios. It is therefore timely to review the current status of RIID algorithms on NaI detectors. This review describes γ spectra from NaI detectors, measurement issues and challenges, current RIID algorithms, data preprocessing steps, the role and current quality of synthetic spectra, and opportunities for improvements.

Augmenting real data with synthetic data: an application in assessing Radio‐Isotope identification algorithms

AbstractThe performance of Radio‐Isotope IDentification (RIID) algorithms using gamma spectroscopy is increasingly becoming important. For example, sensors at locations that screen for illicit nuclear material rely on isotope identification to resolve innocent nuisance alarms arising from naturally occurring radioactive material. Recent data collections for RIID testing consist of repeat measurements for each of several scenarios to test RIID algorithms. Efficient allocation of measurement resources requires an appropriate number of repeats for each scenario. To help allocate measurement resources in such data collections for RIID algorithm testing, we consider using only a few real repeats per scenario. In order to reduce uncertainty in the estimated RIID algorithm performance for each scenario, the potential merit of augmenting these real repeats with realistic synthetic repeats is also considered. Our results suggest that for the scenarios and algorithms considered, approximately 10 real repeats augmented with simulated repeats will result in an estimate having comparable uncertainty to the estimate based on using 60 real repeats. Published in 2009 by John Wiley &amp; Sons, Ltd.

Application of $^{6}{\rm LiI}({\rm Eu})$ Scintillators With Photodiode Readout for Neutron Counting in Mixed Gamma-Neutron Fields

This paper investigates the potential of 6LiI(Eu)/photodiode (PD) detector systems for application as neutron counters in radioisotope identification devices (RIID). Those are exposed to mixed neutron-gamma fields. An effective suppression of signals due to gamma interactions with the scintillator or the PD bulk material is of major importance since neutron alarms in RIID are triggered by a few single neutron counts; any gamma signal not rejected may generate a false neutron alarm. Measurements demonstrated that digital signal processing combined with simultaneous pulse height and pulse shape analysis can provide efficient neutron-gamma discrimination. The results were obtained with a compact, basic detector configuration and sampling rates of only 10 MS/s. Such systems can be realized with state-of-the-art miniaturized electronics.

Gamma radiation detectors for safeguards applications

The IAEA uses extensively a variety of gamma radiation detectors to verify nuclear material. These detectors are part of standardized spectrometry systems: germanium detectors for High-Resolution Gamma Spectrometry (HRGS); Cadmium Zinc Telluride (CZT) detectors for Room Temperature Gamma Spectrometry (RTGS); and NaI(Tl) detectors for Low Resolution Gamma Spectrometry (LRGS). HRGS with high-purity Germanium (HpGe) detectors cooled by liquid nitrogen is widely used in nuclear safeguards to verify the isotopic composition of plutonium or uranium in non-irradiated material. Alternative cooling systems have been evaluated and electrically cooled HpGe detectors show a potential added value, especially for unattended measurements. The spectrometric performance of CZT detectors, their robustness and simplicity are key to the successful verification of irradiated materials. Further development, such as limiting the charge trapping effects in CZT to provide improved sensitivity and energy resolution are discussed. NaI(Tl) detectors have many applications—specifically in hand-held radioisotope identification devices (RID) which are used to detect the presence of radioactive material where a lower resolution is sufficient, as they benefit from a generally higher sensitivity. The Agency is also continuously involved in the review and evaluation of new and emerging technologies in the field of radiation detection such as: Peltier-cooled CdTe detectors; semiconductor detectors operating at room temperature such as HgI 2 and GaAs; and, scintillator detectors using glass fibres or LaBr 3. A final conclusion, proposing recommendations for future action, is made.

Comparison of LaBr3:Ce and NAI(Tl) scintillators for radio-isotope identification devices

Lanthanum bromide (LaBr3:Ce) scintillators offer significantly better resolution (<3 percent at 662keV) relative to sodium iodide (NaI(Tl)) but contain internal radioactivity that contributes to spectral counts. LaBr3:Ce has recently become available commercially in sizes large enough for the hand-held radio-isotope identification device (RIID) market. To study its potential for RIIDs, a series of measurements were performed comparing a 1.5×1.5-in. LaBr3:Ce detector with an Exploranium GR-135 RIID, which contains a 1.5×2.2-in. NaI(Tl) detector. Measurements were taken for short time frames and included examples of naturally occurring radioactive material (NORM), typically found in cargo, and special nuclear materials. To facilitate direct comparison, spectra from the different detectors were analyzed with the same isotope identification software (ORTEC ScintiVision™). In general, the LaBr3:Ce detector was able to find more peaks and find them faster than the NaI(Tl) detector. To the same level of significance, the LaBr3:Ce detector was usually two to three times faster. The notable exception was for 40K-containing NORM where interfering internal activity due to 138La in the LaBr3:Ce detector exists and NaI(Tl) consistently outperformed LaBr3:Ce.

Comparison of a LaBr$_{3}$(Ce) Scintillation Detector With a Large Volume CdZnTe Detector

The performance of hand-held radioisotope identification devices (RIDs) is still hampered by the performance of the NaI(Tl) detectors, which are commonly used in such instruments. In this paper, we continue the search for better detector options. One of the largest single elements ever made, a coplanar CdZnTe (CZT) detector (30times15times12.1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> volume 5.45 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> designed by University of Michigan) is compared with a commercially available LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) detector (ominus1''times1'' volume 12.9 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .) Parameters that are relevant to the performance of isotope identification devices, such as resolution and efficiency as function of the gamma-ray energy, temperature shift, linearity and others are measured and compared. According to measurement results, it seems that for this application LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) detectors are a viable alternative to CZT detectors; even more so if one bears in mind that LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) became commercially available only recently and detectors with larger volumes are likely to appear in the near future

Determining activities of radionuclides from coincidence signatures

The spectral analysis of simultaneously observed photons in separate detectors may provide an invaluable tool for radioisotope identification applications. A general recursive method to determine the activity of an isotope from the observed coincidence signature rate is discussed. The method coherently accounts for effects of true coincidence summing within a single detector and detection efficiencies. A verification of the approach with computer simulations is also discussed.

Spectral gamma detectors for hand-held radioisotope identification devices (RIDs) for nuclear security applications

The in-situ identification of the isotope causing a radiation alarm at a border crossing is essential for a quick resolution of the case. Commonly, hand-held radioisotope identification devices (RIDs) are used to address this task. Although a number of such devices are commercially available, there is still a gap between the requirements of the users and what is actually available. Two components are essential for the optimal performance of such devices: i) The quality of the raw data-the gamma spectra, and ii) isotope identification software matching the specifics of a certain gamma detector. In this paper, we investigate new spectral gamma detectors for potential use in hand-held radioisotope identification devices. The standard NaI detector is compared with new scintillation and room temperature semiconductor detectors. The following spectral gamma detectors were included into the study: NaI(Tl), LaCl3(Ce), 6LiI(Eu), CdWO4, hemispheric and coplanar CdZnTe detectors. In the paper basic spectrometric properties are measured and compared in view of their use in RIDs

Application of neural networks for the analysis of gamma-ray spectra measured with a Ge spectrometer

The analysis of gamma-ray spectra to identify lines and their intensities usually requires expert knowledge and time-consuming calculations with complex fitting functions. A neural network algorithm can be applied to a gamma-ray spectral analysis owing to its excellent pattern recognition characteristics. However, a gamma-ray spectrum typically having 4096 channels is too large as a typical input data size for a neural network. We show that by applying a suitable peak search procedure, gamma-ray data can be reduced to peak energy data, which can be easily managed as input by neural networks. The method was applied to the analysis of gamma-ray spectra composed of mixed radioisotopes and the spectra of uranium ores. Radioisotope identification was successfully achieved.

A new approach to automatic radiation spectrum analysis

The application of adaptive methods to the solution of the automatic radioisotope identification problem using the energy spectrum is described. The identification is carried out by means of neural networks, which allow the use of relatively reduced computational structures, while keeping high pattern recognition capability. In this context, it has been found that one of these simple structures, once adequately trained, is quite suitable to identify a given isotope present in a mixture of elements as well as the relative proportions of each identified substance. Preliminary results are presented, and are deemed good enough to consider these adaptive structures as powerful and simple tools in the automatic spectrum analysis. >

IDENT, a radioisotope identification subroutine for use with the gamma-ray spectrum analysis program SAMPO

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