Imaging of cultural heritage objects using neutron resonances

Abstract

Neutron resonances are the signature signals of a non-destructive elemental and isotopic analysis technique in archaeological sciences. We report on Neutron Resonance Transmission Analysis and its capabilities as a bulk elemental imaging technique to test the homogeneity of samples and to localize elements of interest in archaeological samples and museum objects. A high neutron flux is required for imaging in order to achieve reasonable spatial resolution and to keep measurement times within realistic limits. A modular system for neutron resonance transmission analysis has been designed and installed at the INES beamline of the ISIS spallation neutron source as a part of the ANCIENT CHARM project. The main component is a neutron position sensitive transmission detector which is based on a 10 × 10 array of 6Li-glass crystals mounted on a pitch of 2.5 mm, resulting in a 25 × 25 mm2 active area. Transmission spectra are obtained by a measurement of the flight time of epithermal neutrons passing through an object. The transmission dips observed in a time-of-flight spectrum can be used to identify and quantify specific nuclides. In this paper the technique is described together with the data reduction and analysis procedures. In addition, preliminary results obtained from measurements on cultural heritage samples are discussed

High resolution neutron resonance absorption imaging at a pulsed neutron beamline

“…The MCP detector used in our experiments is capable of neutron counting with simultaneous <100 /lm spatial and sub-/ls temporal resolution, enabling an order of magnitude improvement compared to previous measurements performed with a 1 Ox 1 0 pixel detector with 2x2 mm 2 pixels [6], [9].…”

“…Capture of the fine detail in these images is enabled by the high spatial resolution of our detection system. Previous measurements performed with a lOxlO detector only allowed a crude map of the silver distribution across the same belt mount [6]. The improved spatial resolution should enable high resolution non destructive elemental/isotopic mapping within objects containing elements and isotopes with relatively low resonance energies in the range 1-100 eV.…”

“…In this method the energy of the transmitted neutrons is measured by the neutron time of flight (TOF) providing the detector can both spatially and temporally resolve registered neutrons. The potential of neutron resonance absorption imaging (NRAI) was demonstrated by the previous measurements, where a number of museum artifacts were studied in terms of their constituent materials [4], [6], [9]. The depths of neutron absorption resonances can be translated into the quantitative amounts of specific elements in the sample, with the spatial resolution defined by the detector pixellation used in the experiments.…”

Orthodontic archwire composition and phase analyses by neutron spectroscopy

“…Moreover, many elements have overlapping peaks and some emitted X-rays may not escape the sample and be detected, reducing the accuracy in inhomogeneous samples 29) . Neutron Resonance Capture Analysis (NRCA) is a technique for the determination of elemental composition, making use of a pulsed beam of epithermal neutrons and a TOF system to recognize resonances of isotopes in the energy range of ~1 eV to ~10 keV 30,31) . For many metallic materials, the impinging epithermal neutrons are resonantly captured by the material's nuclei, showing intense peaks in the absorption cross section (probability of a neutron being absorbed by a nucleus).…”

Experimental demonstration of a compact epithermal neutron source based on a high power laser

“…Although fast neutrons are useful for many applications, such as imaging [6] and material testing for fusion reactor vessels [7], the arena of neutron science and applications mainly requires slow neutrons (with energies ranging from sub-meV to keV) which are provided at reactor [8] and accelerator [9] based facilities by moderating fast neutrons. In particular, sources of epithermal neutrons (eV-100keV) are of high interest for a wide range of applications, from material science [10][11][12] to nuclear waster transmutations [13] and healthcare [14,15]. However, the scale and operational costs involved in accelerator-based facilities not only limit their availability to the scientific community, but also hinder their wide promotion in the industrial, security and healthcare sectors.…”