Genoveva Burca

New insights into alloy compositions: studying Renaissance bronze statuettes by combined neutron imaging and neutron diffraction techniques

Until recently the inside parts of hollow cast Renaissance bronze statuettes were concealed, yet they hold important information on the production techniques used in the manufacture of these fine works of art. For that specific reason the inside of the sculptures have been made visible using a neutron imaging technique (tomography) at the Paul-Scherrer Institut, Villigen, Switzerland. This method allowed us to study the internal structure of a bronze sculpture and provided an indication of different material compositions. Since sample taking is not advised on these precious works of art, different non-destructive methods had to be investigated to obtain more specific information on the compositions of the inner parts. This research focuses on analyzing pre-determined small volumes selected from neutron tomographies. With this approach it has become possible to study the material compositions and crystalline structures of these statuettes with a millimetre-sized gauge volume placed at any selected point within the object, using time-of-flight neutron diffraction in the setup of ENGIN-X at the ISIS facility at the Rutherford Appleton Laboratory, UK. Analysis of a Renaissance statuette from the Rijksmuseum, a Striding Nobleman, gives evidence of the different copper alloy compositions of superficial and internal parts but also shows small amounts of ferrite present which until recently was not reported for Renaissance bronzes. The alloy is magnetic due to the ferrite, and strong rare-earth magnets were used to establish whether or not other Renaissance bronzes and brasses contain ferritic iron. A combined application of neutron techniques leads to a better understanding of the production techniques and will, in general, help to advance the analytical studies of these marvelous objects.

Materials analysis opportunities on the new neutron imaging facility IMAT@ISIS

A new neutron imaging and diffraction facility, called IMAT, is currently being commissioned at the ISIS pulsed neutron spallation source. IMAT will take advantage of neutron time-of-flight measurement techniques for flexible neutron energy selection and effective energy discrimination. The instrument will be completed and commissioned within the next few months, after neutrons have been recently delivered to the sample area. From 2016 IMAT will enable white-beam neutron radiography and tomography as well as energy-dependent neutron imaging. The facility will offer a spatial resolution down to 50 microns for a field of view of up to 400 cm2. IMAT will be operated as a user facility for material science applications and will be open for developments of time-of-flight imaging methods.

Modelling of an imaging beamline at the ISIS pulsed neutron source

A combined neutron imaging and neutron diffraction facility, IMAT, is currently being built at the pulsed neutron spallation source ISIS in the U.K. A supermirror neutron guide is required to combine imaging and diffraction modes at the sample position in order to obtain suitable time of flight resolutions for energy selective imaging and diffraction experiments. IMAT will make use of a straight neutron guide and we consider here the optimization of the supermirror guide dimensions and characterisation of the resulting beam characteristics, including the homogeneity of the flux distribution in space and energy and the average and peak neutron fluxes. These investigations take into account some main design criteria: to maximise the neutron flux, to minimise geometrical artefacts in the open beam image at the sample position and to obtain a good energy resolution whilst retaining a large neutron bandwidth. All of these are desirable beam characteristics for the proposed imaging and diffraction analysis modes of IMAT.

Design and Characterisation of Metallic Glassy Alloys of High Neutron Shielding Capability

This paper reports the design, making and characterisation of a series of Fe-based bulk metallic glass alloys with the aim of achieving the combined properties of high neutron absorption capability and sufficient glass forming ability. Synchrotron X-ray diffraction and pair distribution function methods were used to characterise the crystalline or amorphous states of the samples. Neutron transmission and macroscopic attenuation coefficients of the designed alloys were measured using energy resolved neutron imaging method and the very recently developed microchannel plate detector. The study found that the newly designed alloy (Fe48Cr15Mo14C15B6Gd2 with a glass forming ability of Ø5.8 mm) has the highest neutron absorption capability among all Fe-based bulk metallic glasses so far reported. It is a promising material for neutron shielding applications.

Characterization of γ-ray background at IMAT beamline of ISIS Spallation Neutron Source

TThe environmental γ -ray background on the IMAT beamline at ISIS Spallation Neutron Source, Target Station 2, is characterized via γ spectroscopy. The measurements include gamma exposure at the imaging detector position, along with the gamma background inside the beamline. Present results are discussed and compared with previous measurements recorded at INES and VESUVIO beamlines operating at Target Station 1. They provide new outcome for expanding and optimizing the PGAA experimental capability at the ISIS neutron source for the investigation of materials, engineering components and cultural heritage objects at the ISIS neutron source.

Time-of-Flight Neutron Imaging on IMAT@ISIS: A New User Facility for Materials Science

The cold neutron imaging and diffraction instrument IMAT at the second target station of the pulsed neutron source ISIS is currently being commissioned and prepared for user operation. IMAT will enable white-beam neutron radiography and tomography. One of the benefits of operating on a pulsed source is to determine the neutron energy via a time of flight measurement, thus enabling energy-selective and energy-dispersive neutron imaging, for maximizing image contrasts between given materials and for mapping structure and microstructure properties. We survey the hardware and software components for data collection and image analysis on IMAT, and provide a step-by-step procedure for operating the instrument for energy-dispersive imaging using a two-phase metal test object as an example.