The neutron cross section of barite-enriched concrete for radioprotection shielding in the range 1 meV–1 keV

Abstract

We present a characterization of a series of barite-enriched concrete samples at the atomic scale using neutron-based techniques. In particular, neutron transmission measurements provide the macroscopic cross section (also known as neutron removal cross section) as a function of the incident neutron energy in the range 1 meV-1 keV. In this range, where fewer experimental investigations are available in the literature, the cross section is dominated by the scattering events from hydrogen, as opposed to the fast-neutron region (MeV-energy neutrons) where capture events by Ba are more important. Moreover, below 1 eV, the cross section depends on the molecular or crystal structure of the components. For each sample, the amounts of barium and hydrogen are provided by neutron resonance capture analysis and deep inelastic neutron scattering, respectively. We find that the amounts of barium and hydrogen are correlated, with a lower amount of hydrogen in the samples with more barium, likely because of the absence of some calcium-silicon-hydrate structures, whose formation is inhibited by the presence of barite. Moreover, we quantify the non-negligible contribution to the neutron macroscopic cross section arising from water molecules loosely bound in concrete. This contribution makes the shielding performance of concrete dependent upon the humidity and temperature conditions affecting the installation. Our results provide additional guidelines for radioprotection workers to determine the optimal concentration of barite in mixed gamma/neutron radiation environments.

Glass Transition in Rice Pasta as Observed by Combined Neutron Scattering and Time-Domain NMR

“…For the treatment of neutron transmission data, a bespoke VesuvioTransmission algorithm, implemented in the MantidPlot computational environment, was employed [29,31,32,34]. In the case of high-resolution neutron diffraction data recorded on VESUVIO, the VesuvioD-iffractionReduction algorithm, a part of the MantidPlot environment, was used [28,59].…”

“…With the sample composition Moreover, the clearly observed increase in the magnitudes of the plateau regions of the transmission curves with the increasing temperature signifies a systematic decrease of the sample scattering power with temperature. The scattering power is defined as a product of the sample number density, its thickness, and the total free scattering neutron cross-section weighted by the sample composition [29,31,32,34]. With the sample composition being constant over the entire temperature range under investigation, as evidenced by the NCS data analysis (see Figure 5), the only plausible explanation for such a systematic trend in sample scattering power is that the average sample number density decreases with increasing temperature.…”

“…In order to get additional insight into the vibrational structure of the rice pasta sample under investigation, one has to take into account that neutron transmission data always exhibit much more marked dependence on the atom-projected vibrational densities of states (apVDOSes) in the low incident neutron energy region [26,29,31,32,[34][35][36]. To this end, the neutron transmission data have been integrated into the incident neutron energy window, in which the temperature changes are most apparent, i.e., between 2.6 and 10 meV.…”

“…Traditionally, the core technique employed at VESUVIO has been neutron Compton scattering (NCS) [19][20][21][22][23]. Due to the recent upgrades in the instrumentation, sample environment, and software [19,20,24,[26][27][28][29][30], VESUVIO has become a very versatile tool, enabling concurrent measurements using techniques such as NCS, energy-dependent neutron transmission [29,[31][32][33][34][35][36][37][38][39], neutron diffraction [30,40,41], and gamma spectroscopy [24,[42][43][44][45]. The aforementioned techniques, especially when applied concurrently, enable the investigation of a plethora of physical and chemical properties of condensed matter systems.…”

“…The initial part of the transmission curve, corresponding to the incident neutron energies in the range 1 meV to 1 eV, is shaped by a wide range of different types of excitations, from local to the long-range ones [29,36,49]. Moreover, owing to the capability of VESUVIO to detect the second part of the transmission curve, corresponding to the incident neutron energies above a few eV, the regime of the Impulse Approximation (IA) is reached, where each neutron transmission curve reaches a plateau with the magnitude of transmission determined solely by the product of the sample thickness, its number density, and the total free scattering cross-section weighted by the sample stoichiometry [21,22,29,31,[34][35][36]39,49]. This last unique feature of VESUVIO enables measurements of changes of density in different regions of phase diagrams of condensed matter systems and molecules, particularly important in the context of the glass transition.…”