Multi-technical approach for the characterization of polychrome decorative surfaces at Spanish Mission Churches in Nueva Vizcaya (Chihuahua, Mexico)

An interdisciplinary and multi-institutional group of science and art conservation specialists has provided new insight into the painting materials used in the polychrome walls and wooden ceilings in four seventeenth century Spanish colonial churches of Nueva Vizcaya (Chihuahua, Mexico). A multi-analytical study of the decorative surfaces was performed in situ using spectroscopic approaches (XRF, FORS), False Colour Infrared Reflectography - IRFC, as well as micro sampling (ATR-FTIR, LM, GC/MS). A survey of natural resources and study (ATR-FTIR, LM) was carried out to elucidate the natural occurrence of a select number of materials in the surrounding areas of the churches. The present paper presents a multi-analytical study and characterization of green, red-orange and black colour pigments and binders selected from the decorative surfaces. The aim of this study is to highlight relationships between local materials and those from the original polychrome ceilings, in order to understand the material and technological influences that converged in the Spanish colonial architecture of northern Mexico

Monte Carlo modelling of a-Si EPID response: the effect of spectral variations with field size and position

Electronic portal imaging detectors (EPID) have initially been developed for imaging purposes but they also present a great potential for dosimetry. This is of special interest for intensity modulated radiation treatment (IMRT), where the complexity of the delivery makes quality assurance necessary. By comparing a predicted EPID image of an IMRT field with a measured image, it is possible to verify that the beam is properly delivered by the linear accelerator and that the dose is delivered to the correct location in the patient. This study focused on predicting the EPID image of IMRT fields in air with Monte Carlo methods. As IMRT treatments consist of a series of segments of various sizes which are not always delivered on the central axis, large spectral variations may be observed between the segments. The effect of these spectral variations on the EPID response was studied. A detailed description of the EPID was implemented in a Monte Carlo model. The EPID model was validated by comparing the EPID output factors for field sizes between 2x2 and 26x26 cm2 at the isocentre. The Monte Carlo simulations agreed with the measurements to within 0.5%. The effect of 1 spectral variations on the EPID response, with field size and position, was studied for three field sizes (2x2, 6x6 and 10x10 c