Neutron-based computed microtomography: Pliobates cataloniae and Barberapithecus huerzeleri as a test-case study.

OBJECTIVES: High-resolution imaging of fossils with X-ray computed microtomography (µCT) has become a very powerful tool in paleontological research. However, fossilized bone, embedding matrix, and dental tissues do not always provide a distinct structural signal with X-rays. We demonstrate the benefits of high-resolution neutron radiation in three different specimens showing problematic contrasts with X-ray µCT. MATERIALS AND METHODS: We compare neutron with X-ray µCT scans of fossils from two Miocene catarrhines from the Vallès-Penedès Basin: the cranium (IPS58443.1, holotype) of the putative stem hominoid Pliobates cataloniae, to discriminate between bone and matrix; and two lower molars (IPS1724n,o, holotype) of Barberapithecus huerzeleri, to discriminate among dental tissues. RESULTS: X-ray µCT scans of these specimens fail to retrieve any contrast between matrix/bone and enamel/dentine, whereas neutron µCT scans deliver high-contrast images, enabling a proper evaluation of the specimens' internal anatomy. DISCUSSION: Low bone/matrix intensity difference with X-ray µCT scans in IPS58443.1 is due to the extreme similarity in chemical composition between the matrix and the fossilized tissues, and the presence of high-density elements. In IPS1724, it is attributable to the convergence of enamel and dentine compositions during fossilization. On the contrary, neutron radiation returns very different contrasts for different isotopes of the same element and easily penetrates most metals. Neutron-based µCT scans therefore enable a correct definition of the bone/sediment and enamel/dentine interfaces, and hence a better segmentation of the images stack. We conclude that neutron radiation represents a successful alternative for high-resolution µCT of small-sized fossils that are problematic with X-rays.

Neutron microtomography-based virtual extraction and analysis of a cercopithecoid partial cranium (STS 1039) embedded in a breccia fragment from sterkfontein member 4 (South Africa).

The Plio-Pleistocene karstic sedimentary deposits of Sterkfontein Cave, South Africa, yielded numerous fossil primate specimens embedded in blocks of indurated breccia, including the partial cercopithecoid cranium labelled STS 1039. Because the surrounding matrix masks most of its morphology, the specimen remains taxonomically undetermined. While the use of X-ray microtomography did not allow extracting any structural information about the specimen, we experimented a new investigative technique based on neutron microtomography. Using this innovative approach, we successfully virtually extracted, reconstructed in 3D and quantitatively assessed the preserved dentognathic structural morphology of STS 1039, including details of its postcanine maxillary dentition. Following comparative analyses with a number of Plio-Pleistocene and extant cercopithecoid taxa, we tentatively propose a taxonomic attribution to the taxon Cercopithecoides williamsi. Our experience highlights the remarkable potential of this novel imaging method to extract diagnostic information and to identify the fossil remains embedded in hard breccia from the South African hominin-bearing cave sites.

Kinks in experimental diffusion profiles of a dissolving semi-crystalline polymer explained by a concentration-dependent diffusion coefficient.

The dissolution of polyethylene oxide (PEO) tablets in water has been followed in situ by neutron radiography. When in contact with water, the crystalline phase of semi-crystalline PEO melts once a certain water content is attained. Polymer concentration profiles obtained from the neutron transmission images exhibited a pronounced kink which corresponds to a sharp front in the images and which is related to the melting transition. Sharp diffusion fronts and phase transitions are often linked to non-Fickian behaviour. However, by considering the time evolution of the complete concentration profiles in detail it is shown that the dissolution process can be explained using Fickian diffusion equations with a concentration-dependent diffusion coefficient.

New Neutron Imaging Facility NIFFLER at Very Low Power Reactor VR-1.

The paper describes the construction of the neutron imaging facility at the very low-power research reactor VR-1. The training reactor VR-1 is operated by the Czech Technical University in Prague, Czech Republic. It is mainly used for the education of students in the field of nuclear engineering as well as for the training of professionals. Neutron imaging is the new field of VR-1 reactor utilisation currently under development. Extremely low reactor power at the level of 100 W brought many challenges that were necessary to overcome to build and commission a sustainable neutron radiography facility. The paper describes the reactor's neutron flux verification and the basic concept and design of the neutron imaging instrumentation. The first experimental results were mainly dedicated to testing the detection system for different radial beam port configurations, different L/D ratios, and different exposure times. Preliminary results of neutron radiography and tomography measurements at VR-1 clearly showed the potential of using neutron imaging in low-power reactors such as the VR-1 reactor.

The Complex, Unique, and Powerful Imaging Instrument for Dynamics (CUPI2D) at the Spallation Neutron Source (invited).

The Oak Ridge National Laboratory is planning to build the Second Target Station (STS) at the Spallation Neutron Source (SNS). STS will host a suite of novel instruments that complement the First Target Station's beamline capabilities by offering an increased flux for cold neutrons and a broader wavelength bandwidth. A novel neutron imaging beamline, named the Complex, Unique, and Powerful Imaging Instrument for Dynamics (CUPI2D), is among the first eight instruments that will be commissioned at STS as part of the construction project. CUPI2D is designed for a broad range of neutron imaging scientific applications, such as energy storage and conversion (batteries and fuel cells), materials science and engineering (additive manufacturing, superalloys, and archaeometry), nuclear materials (novel cladding materials, nuclear fuel, and moderators), cementitious materials, biology/medical/dental applications (regenerative medicine and cancer), and life sciences (plant-soil interactions and nutrient dynamics). The innovation of this instrument lies in the utilization of a high flux of wavelength-separated cold neutrons to perform real time in situ neutron grating interferometry and Bragg edge imaging-with a wavelength resolution of δλ/λ ≈ 0.3%-simultaneously when required, across a broad range of length and time scales. This manuscript briefly describes the science enabled at CUPI2D based on its unique capabilities. The preliminary beamline performance, a design concept, and future development requirements are also presented.

Boron-Based Neutron Scintillator Screens for Neutron Imaging.

In digital neutron imaging, the neutron scintillator screen is a limiting factor of spatial resolution and neutron capture efficiency and must be improved to enhance the capabilities of digital neutron imaging systems. Commonly used neutron scintillators are based on 6LiF and gadolinium oxysulfide neutron converters. This work explores boron-based neutron scintillators because 10B has a neutron absorption cross-section four times greater than 6Li, less energetic daughter products than Gd and 6Li, and lower γ-ray sensitivity than Gd. These factors all suggest that, although borated neutron scintillators may not produce as much light as 6Li-based screens, they may offer improved neutron statistics and spatial resolution. This work conducts a parametric study to determine the effects of various boron neutron converters, scintillator and converter particle sizes, converter-to-scintillator mix ratio, substrate materials, and sensor construction on image quality. The best performing boron-based scintillator screens demonstrated an improvement in neutron detection efficiency when compared with a common 6LiF/ZnS scintillator, with a 125% increase in thermal neutron detection efficiency and 67% increase in epithermal neutron detection efficiency. The spatial resolution of high-resolution borated scintillators was measured, and the neutron tomography of a test object was successfully performed using some of the boron-based screens that exhibited the highest spatial resolution. For some applications, boron-based scintillators can be utilized to increase the performance of a digital neutron imaging system by reducing acquisition times and improving neutron statistics.

Evidence for increased hominid diversity in the Early to Middle Pleistocene of Indonesia.

Since the first discovery of Pithecanthropus (Homo) erectus by E. Dubois at Trinil in 1891, over 200 hominid dentognathic remains have been collected from the Early to Middle Pleistocene deposits of Java, Indonesia, forming the largest palaeoanthropological collection in South East Asia. Most of these fossils are currently attributed to H. erectus. However, because of the substantial morphological and metric variation in the Indonesian assemblage, some robust specimens, such as the partial mandibles Sangiran 5 and Sangiran 6a, were formerly variably allocated to other taxa (Meganthropus palaeojavanicus, Pithecanthropus dubius, Pongo sp.). To resolve the taxonomic uncertainty surrounding these and other contentious Indonesian hominid specimens, we used occlusal fingerprint analysis (OFA) to reconstruct their chewing kinematics; we also used various morphometric approaches based on microtomography to examine the internal dental structures. Our results confirm the presence of Meganthropus as a Pleistocene Indonesian hominid distinct from Pongo, Gigantopithecus and Homo, and further reveal that Dubois's H. erectus paratype molars from 1891 are not hominin (human lineage), but instead are more likely to belong to Meganthropus.

What did the "Unossified zone" of the non-mammalian therapsid braincase house?

Most nonmammalian synapsids possess a mid-dorsal depression in the brain cavity known as the "unossified zone." It remains obscure which structures this zone contained, and, as candidates, the vermis of the cerebellum, the superior sagittal sinus, a junction of several blood vessels, the pineal gland or other midbrain structures were considered. Neutron tomography of a skull of Diictodon feliceps (Therapsida, Anomodontia) revealed some clear impressions of canals in this region of the brain cavity. Furthermore, the prootic sinus probably ran on the internal surface of the pila antotica and had a similar course in anomodonts as it has been proposed for cynodonts and Mesozoic mammals. Comparisons with the vascular systems of nonmammalian synapsids and mammals suggest that the unossified zone is best interpreted as a terminal chamber of the anterior segment of the medial head vein, which housed the junction of the superior sagittal sinus and the transverse sinuses. Consequently, the system of cranial vessels in Diictodon reveals a partial division of the medial head vein system into an anterior and a posterior segment at an early stage of synapsid evolution, which is consistent with the well-known common pattern of early ontogenetic development in amniotes. J. Morphol., 2017. © 2017 Wiley Periodicals, Inc.

Energy-selective neutron radiography and tomography at FRM.

At the reactor FRM at Technical University of Munich energy-selective neutron radiography and tomography experiments were performed. For an energy separation of the neutrons from the primary beam a mechanical velocity selector was used. The radiography images show a different contrast of the investigated elements for neutron energies below and above their Bragg-cutoff energy. A comparison between the standard and energy-selective neutron tomography is presented. In spite of a reduction of the neutron intensity due to the velocity selector technique a realistic experimental time in order of some hours for the tomography experiment was achieved.