A simple method for the analysis of neutron resonance capture spectra

Neutron resonance capture analysis NRCA is a method used to determine the bulk composition of various kinds of objects and materials. It is based on analyzing direct capture resonance peaks. However, the analysis is complicated by scattering followed by capture effects in the object itself. These effects depend on the object's shape and size. In this paper the new Delft elemental analysis program DEAP is presented which can automatically and quickly analyze multiple NRCA spectra in a practical and simple way, yielding the elemental bulk composition of an object, largely independent of its shape and size. The DEAP method is demonstrated with data obtained with a Roman bronze water tap excavated in Nijmegen The Netherlands. DEAP will also be used in the framework of the Ancient Charm project as data analysis program for neutron resonance capture imaging NRCI experiments. NRCI provides three-dimensional visualization and quantification of the internal structure of archaeological objects by performing scanning measurements with narrowly collimated neutron beams on archaeological objects in computed tomography based experimental setups. The large amounts hundreds to thousands of spectra produced during a NRCI experiment can automatically and quickly be analyzed by DEAP .© 2009 American Institute of Physics. DOI: 10.1063/1.3094010 Neutron resonance capture analysis NRCA is based on the existence of resonances in neutron capture cross sections in the epithermal energy range for almost all nuclei. As these resonances are characteristic for each element, their observa- tion and quantitative analysis provide information about the occurrence and concentration of the elements in an object. NRCA has been developed at the GELINA pulsed neu- tron facility of the European Commission EC Joint Re- search Centre, Institute of Reference Materials and Measure- ments IRMM in Geel Belgium, starting in 2000 as a joint project between that institute and Delft University of Tech- nology The Netherlands. It has been applied in a series of experiments on archaeological bronzes.1-6 The elemental composition of such artifacts, including trace elements, may be helpful in the determination not only of its origin and that of its raw materials e.g., metal ore, but also of the way they were produced, thus helping to learn more about trade routes and production methods in prehistoric times. In addition in- formation about the authenticity of objects can, under suit- able conditions, be obtained as has been shown for a series of Etruscan statuettes.3 NRCA can be applied to detect most of the medium and heavy weight elements as these are characterized by neutron resonance energies suitable for analysis roughly in the range of 1 eV- 10 keV. Energy information for resonances in the neutron capture process is obtained by means of time-of- flight TOF measurement over a well defined neutron-path length. Most of the lighter elements and some nuclides with or close to double magic numbers have neutron resonances at energies too high to be conveniently measured with the TOF method. NRCA provides bulk elemental composition be- cause of the large penetration depth of neutrons in dense high Z materials, as opposed to x-ray fluorescence tech- niques and particle induced x-ray emission that yield infor- mation about the composition of the "skin" of an object as x-rays are strongly absorbed in high Z materials. Since bulk