Prompt Gamma Activation Analysis at the Budapest Research Reactor

Introduction of the prompt γ-ray neutron activation analysis system at CARR and the first pilot experiment on boron-containing high-temperature alloys

A prompt γ-ray neutron activation analysis system has recently been developed at China advanced research reactor (CARR), the 60 MW research reactor in China Institute of Atomic Energy (CIAE). The system is set at the cold neutron beam guide with a thermal equivalent neutron flux at the sample position of 1.0 × 109 n·cm-2·s-1 with the power of 30 MW, and it is mainly composed of a neutron beam collimator, a sample chamber, a beam stopper, neutron and γ-ray shieldings and a detection system. The detection system can realize three modes of measurement: single, Compton suppression, and pair modes. The detection efficiency was calibrated up to 11 MeV using a set of radionuclides and the (n, γ) reactions of N and Cl. Boron, one of the most important elements in high-temperature alloy material studies, was analyzed in this work, as the first pilot experiment of the CARR-PGNAA system. The analytical sensitivity of 2000 cps/mg-B was obtained. The results verified the feasibility of the CARR-PGNAA system to measure boron in high-temperature alloys, and laid a foundation for the accurate quantification of boron in the next step.

A comparison of machine learning methods to classify radioactive elements using prompt-gamma-ray neutron activation data

The detection of illicit radiological materials is critical to establishing a robust second line of defence in nuclear security. Neutron-capture prompt-gamma activation analysis (PGAA) can be used to detect multiple radioactive materials across the entire Periodic Table. However, long detection times and a high rate of false positives pose a significant hindrance in the deployment of PGAA-based systems to identify the presence of illicit substances in nuclear forensics. In the present work, six different machine-learning algorithms were developed to classify radioactive elements based on the PGAA energy spectra. The model performance was evaluated using standard classification metrics and trend curves with an emphasis on comparing the effectiveness of algorithms that are best suited for classifying imbalanced datasets. We analyse the classification performance based on Precision, Recall, F1-score, Specificity, Confusion matrix, ROC-AUC curves, and Geometric Mean Score (GMS) measures. The tree-based algorithms (Decision Trees, Random Forest and AdaBoost) have consistently outperformed Support Vector Machine and K-Nearest Neighbours. Based on the results presented, AdaBoost is the preferred classifier to analyse data containing PGAA spectral information due to the high recall and minimal false negatives reported in the minority class.

Position-Sensitive Bulk and Surface Element Analysis of Decorated Porcelain Artifacts

Non-destructive characterization of decorated porcelain artifacts requires the joint use of surface-analytical methods for the decorative surface pattern and methods of high penetration depth for bulk-representative chemical composition. In this research, we used position-sensitive X-ray Fluorescence Spectrometry (XRF) and Prompt-gamma activation analysis (PGAA) for these purposes, assisted by 3D structured-light optical scanning and dual-energy X-ray radiography. The proper combination of the near-surface and bulk element composition data can shed light on raw material use and manufacturing technology of ceramics.

Experimental determination and simulation of neutron and gamma flux parameters in horizontal channel for Prompt Gamma Neutron activation analysis implementation at Es-Salam research reactor

Since 2004, the k₀-standardization method has been applied and evaluated in three experimental channels at Es-Salam research reactor of the Algerian Centre de Recherche Nucléaire de Birine (CRNB). The NAA laboratory at CRNB is well involved in the implementation of the Prompt Gamma Neutron Activation Analysis to extend the field of analyses to some additional elements to the NAA method. In the frame work of the PGNAA research project, several works have been carried out in the present study including the experimental and simulation characterization of neutron and gamma flux parameters of the horizontal channel. The absolute and relative neutron fluxes of the studied channel have been determined by using a set of monitors including Al, Au, Cu, Fe and Zr. Furthermore, measurements of gamma and thermal neutron doses have been achieved using LiF: Mg, Ti (TLD 600 and TLD 700) detectors. The gamma dose rate at the experimental channel center position was found to be 0.6 Gy/min·MW. The experimental results obtained in this study have been used as input information for simulations and design of neutron facilities and radiation shielding, which are successfully established by SCALE code. The results were compared in terms of spectral detail and precision and a good agreement has been revealed. The value of the thermal neutron flux was found to be (6.29 ± 0.25) E+08 n/cm².s which allows the implementation of PGNAA at the Es-Salam research reactor.

Analytical Techniques for the Preservation of Cultural Heritage: Frontiers in Knowledge and Application

Chemistry is considered as the heart of preservation science. The archaeological objects are an organic-inorganic system and need comprehensive techniques to investigate the different materials with a high resolution and accuracy. The characterization process of archaeological materials is a useful guide to develop the right strategy for the conservation and intervention of the objects. In analytical chemistry practice, there are many techniques to employ the characterization process of the artworks: molecular, elemental, imaging, surface, thermal, separation, nuclear, dating, electrochemical, and miscellaneous techniques. It highlights the potential of chemical investigations to present reliable information to the conservators and art historians.

Neutrons for Cultural Heritage-Techniques, Sensors, and Detection

Advances in research in Cultural Heritage see increasing application of a multidisciplinary approach and the combined use of physical and chemical characterization of artefacts that can be used to define their structure and their state of conservation, also providing valuable information in selecting the most suitable microclimatic conditions for the exhibition environment. This approach provides a platform for a synergic collaboration amongst researchers, restorers, conservators, and archaeologists. Existing state-of-the-art technologies for neutron-based methods are currently being applied to the study of objects of historical and cultural interest in several neutron-beam facilities around the world. Such techniques are non-invasive and non-destructive and are, therefore, ideal to provide structural information about artefacts, such as their composition, presence of alterations due to the environmental conditions, inclusions, structure of the bulk, manufacturing techniques, and elemental composition, which provide an overall fingerprint of the object's characteristics, thanks to the nature of the interaction of neutrons with matter. Here, we present an overview of the main neutron methods for the characterization of materials of interest in Cultural Heritage and we provide a brief introduction to the sensors and detectors that are used in this framework. We conclude with some case studies underlining the impact of these applications in different archaeological and historical contexts.

Measuring neutron capture rates on ILL-produced unstable isotopes (147Pm, 171Tm and 204Tl, and plans for 79Se and 163Ho) for nucleosynthesis studies

Neutron capture cross sections are among the main inputs for nucleosynthesis network calculations. Although well known for the majority of the stable isotopes, this quantity is still unknown for most of the unstable isotopes of interest. A recent collaboration between ILL, PSI, U. Sevilla and IFIC aims at producing the isotopes of interest at ILL, preparing suitable targets at PSI, and measuring their capture cross sections at facilities such as n_TOF/CERN, LiLiT and the Budapest Research Reactor (BRR). This work is focused on the description of the different beams and techniques and shows some highlights of the preliminary results of the capture measurements on 171Tm, 147Pm and 204Tl, along with the future plans for 79Se and 163Ho.

Novel method to study neutron capture of 235U and 238U simultaneously at keV energies

The neutron capture cross sections of the main uranium isotopes, (235)U and (238)U, were measured simultaneously for keV energies, for the first time by combining activation technique and atom counting of the reaction products using accelerator mass spectrometry. New data, with a precision of 3%-5%, were obtained from mg-sized natural uranium samples for neutron energies with an equivalent Maxwell-Boltzmann distribution of kT ∼ 25 keV and for a broad energy distribution peaking at 426 keV. The cross-section ratio of (235)U(n,γ)/(238)U(n,γ) can be deduced in accelerator mass spectrometry directly from the atom ratio of the reaction products (236)U/(239)U, independent of any fluence normalization. Our results confirm the values at the lower band of existing data. They serve as important anchor points to resolve present discrepancies in nuclear data libraries as well as for the normalization of cross-section data used in the nuclear astrophysics community for s-process studies.