Frame overlap Bragg edge imaging.

Neutron Bragg edge imaging enables spatially resolved studies of crystalline features through the exploitation and analysis of Bragg edges in the transmission spectra recorded in each pixel of an imaging detector. Studies with high spectral resolutions, as is required e.g. for high-resolution strain mapping, and with large wavelength ranges have been largely reserved to pulsed neutron sources. This is due to the fact, that the efficiency for high wavelength resolution measurements is significantly higher at short pulse sources. At continuous sources a large fraction of the available neutrons must be sacrificed in order to achieve high wavelength resolution for a relevant bandwidth e.g. through a chopper system. Here we introduce a pulse overlap transmission imaging technique, which is suited to increase the available flux of high wavelength resolution time-of-flight neutron Bragg edge imaging at continuous neutron sources about an order of magnitude. Proof-of-principle measurements utilizing a chopper with a fourfold repeated random slit distribution of eight slits were performed at a thermal neutron beamline. It is demonstrated, that disentanglement of the overlapping pulses is achieved with the correlation theorem for signal processing. Thus, the Bragg edge pattern can be reconstructed from the strongly overlapping Bragg edge spectra recorded and the results demonstrate the feasibility of the technique.

Implementation and assessment of the black body bias correction in quantitative neutron imaging.

We describe in this paper the experimental procedure, the data treatment and the quantification of the black body correction: an experimental approach to compensate for scattering and systematic biases in quantitative neutron imaging based on experimental data. The correction algorithm is based on two steps; estimation of the scattering component and correction using an enhanced normalization formula. The method incorporates correction terms into the image normalization procedure, which usually only includes open beam and dark current images (open beam correction). Our aim is to show its efficiency and reproducibility: we detail the data treatment procedures and quantitatively investigate the effect of the correction. Its implementation is included within the open source CT reconstruction software MuhRec. The performance of the proposed algorithm is demonstrated using simulated and experimental CT datasets acquired at the ICON and NEUTRA beamlines at the Paul Scherrer Institut.

Development of neutron imaging quantitative data treatment to assess conservation products in cultural heritage.

Distribution, penetration depth and amount of new mineralogical phases formed after the interaction between an inorganic treatment and a matrix are key factors for the evaluation of the conservation treatment behaviour. Nowadays, the conventional analytical methodologies, such as vibrational spectroscopies, scanning electron microscopy and X-ray diffraction, provide only qualitative and spot information. Here, we report, for the first time, the proof of concept of a methodology based on neutron imaging able to achieve quantitative data useful to assess the formation of calcium oxalate in a porous carbonatic stone treated with ammonium oxalate. Starting from the neutron attenuation coefficient of Noto stone-treated specimens, the concentrations of newly formed calcium oxalate and the diffusion coefficient have been calculated for both sound and decayed substrates. These outcomes have been also used for a comparative study between different treatment modalities. Graphical abstract Horizontal slice at 300 mm depth and CaOx molar density profile by NEUTRA output.

Rotation axis demultiplexer enabling simultaneous computed tomography of multiple samples.

This paper describes a device that allows for simultaneous tomographic imaging of samples on three independent rotational axes. This rotation axis demultiplexer (POLYTOM) is equipped with anti-backlash gears and placed on a standard sample rotation stage thus allowing for the transformation of the input rotation axis onto two additional parallel vertical axes. Consequently, three times the number of samples can be investigated within a given time period, thereby reducing the acquisition time of multiple sample tomographic investigations by a factor of three. The results of our pilot experiments using neutron tomographic imaging are presented. We foresee that the device will be of particular use for tomographic imaging of elongated samples at low-flux (e.g. neutron) sources; however, its use for the more widespread types of imaging techniques (e.g. X-rays) is not ruled out. The highlights of this new device for the purpose of the (neutron) computed tomography are: •Anti-backlash transformation of the input rotation onto two additional rotational axes.•Reduction of the acquisition time of the multiple sample tomographic investigations by a factor of three.•Low-cost.