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We provide a worked example on how to obtain the total neutron scattering cross section of organic polymers at thermal neutron energies by means of the Average Functional Group Approximation. Within this framework, a polymer is rationalised as composed of hydrogen atoms belonging to specific functional groups,therefore taking into account the material-specific incoherent inelastic scattering contributions to the thermal cross section. Such simplified model allows the calculation of thermal neutron cross sections for a broad variety of materials of interest in neutron applications, e.g., sample containers and shielding components. We discuss in detail the case of ABS, often available as a 3D-printing material, whereby three polymers (acrylonitrile, butadiene, and styrene) can be combined in several mass percentages depending on the final application. Results are obtained using the NCrystal module already featuring the Average Functional Group Approximation.

The use of the Average Functional Group Approximation for self-shielding corrections at inelastic neutron spectrometers is discussed. By taking triptindane as a case study, we use the above-mentioned approximation to simulate a synthetic dynamic structure factor as measured on an indirect-geometry spectrometer, as well as the related total scattering cross section as a function of incident neutron energy and sample temperature, and the transmission spectra depending on the sample thickness. These quantities, obtained in a consistent way from the Average Functional Group Approximation, are used to calculate the energy-dependent self-shielding correction affecting the sample under investigation. The impact on the intensities of low-energy vibrational modes is discussed, showing that at typical experimental conditions the sample-dependent attenuation factor is about 15% higher compared to the correction at higher energies.

We present an experimental investigation of methylammonium lead tribromide single crystals in the orthorhombic, tetragonal, and cubic phases based on inelastic and deep inelastic neutron scattering experiments. We show how the average hydrogen nuclear kinetic energy, mainly affected by zero-point vibrational energies, shows differences larger compared to the changes simply related to temperature effects when moving from one phase to another. In particular, the Gaussian contribution to the average nuclear kinetic energy is larger in the tetragonal phase compared to the cubic and orthorhombic ones. Moreover, we find that the vibrational densities of states of MAPbBr3 single crystals in the orthorhombic phase are compatible with previously reported results on powder samples, and that the only vibrational modes that show slightly different frequencies compared to MAPbI3 are those in the energy range between 100 and 300 cm−1, related to librational/rotational modes. As these shifts are of about 10 cm−1 and do not affect any higher-energy vibrational mode, we conclude that the zero-point energies and average nuclear kinetic energies in the two-hybrid organic/inorganic perovskites are expected to be approximately the same within a harmonic framework. [ABSTRACT FROM AUTHOR]

Background: Boron‐containing compounds, such as 4‐borono‐phenylalanine (BPA) are used as drugs for cancer treatment in the framework of Boron Neutron Capture Therapy (BNCT). Neutron irradiation of boron‐rich compounds delivered to cancer cells triggers nuclear reactions that destroy cancer cells. Purpose: We provide a modeling of the thermal neutron cross section of BPA, a drug used in Boron Neutron Capture Therapy (BNCT), to quantify the competing contributions of boron absorption against hydrogen scattering, for optimizing BNCT by minimizing the latter. Methods: We perform the experimental determination of the total neutron scattering cross section of BPA at thermal and epithermal neutron energies using neutron transmission measurements. We isolate the contribution related to the incoherent scattering by hydrogen atoms as a function of the neutron energy by means of the Average Functional Group Approximation, and we calculate the probability for a neutron of being absorbed as a function of the neutron energy both for BPA and for its variants where either one or all four aromatic hydrogen atoms are substituted by 19F, and both for the samples with natural occurrence or enriched concentration of 10B. Results: While referring to the already available literature for in vivo use of fluorinated BPA, we show that fluorine‐rich variants of BPA increase the probability of neutrons being captured by the molecule. As the higher absorption efficiency of fluorinated BPA does not depend on whether the molecule is used in vivo or not, our results are promising for the higher efficiency of the boron neutron capture treatment. Conclusions: Our results suggest a new advantage using fluorinated compounds for BNCT, in their optimized interaction with neutrons, in addition to their already known capability to be used for monitoring and pharmacokinetics studies using 19F‐Nuclear Magnetic Resonance or in 18F‐Positron Emission Tomography. [ABSTRACT FROM AUTHOR]

Achieved spatial resolution of the PET systems is often limited by the parallax error due to the lack of information about the Depth of Interaction (DoI) inside the crystal of the incoming 511 keV annihilation photons. The smaller the diameter of the PET ring and the thicker the scintillator are, the more this error affects imaging performance. In this work, a DoI calculator suitable for monolithic scintillation crystals and based on the shape of the scintillation light distribution at the photodetector surface has been proposed. To test the estimator performance, a test PET module with a 50 \times 50 \times 20\; \mm monolithic LYSO crystal coupled to a 12 \times 12 SiPM array has been employed. In addition, for calibration and validation of the method, Geant4 simulations have been also used. The key result of the application of the proposed DoI estimator is obtaining a continuous DoI estimation with an average DoI resolution of about 5 mm in the 20 mm-thick crystal. Benefiting from the DoI estimation capabilities of the method, it has been also possible to achieve additional important goals, first of all reducing the parallax error. First, because the scintillation light collection varies as a function of the 3D position of the interaction of the annihilation photon inside the crystal, a method to correct this response variation via a proper 3D look-up-table is proposed. This has led to an improvement of about 35% in energy resolution. Moreover, a DoI-dependent position algorithm has been proposed, allowing an improvement of both planar (X-Y) position linearity and planar spatial resolution. This algorithm is specifically developed for the rows/columns multi-channel readout logic, that reduces the number of independent channels from {\rm N} \times {\rm N} to {\rm N} + {\rm N}$, where N is the number of SiPM photodetection elements (12 in our case) in each row and column. This development was performed in the framework of the MindView PET/MRI brain imaging project. [ABSTRACT FROM AUTHOR]

Aggregation states of amyloid beta peptides for amyloid beta A β 1 - 40 to A β 1 - 42 and A β p 3 - 42 are investigated through small angle neutron scattering (SANS). The knowledge of these small peptides and their aggregation state are of key importance for the comprehension of neurodegenerative diseases (e.g., Alzheimer's disease). The SANS technique allows to study the size and fractal nature of the monomers, oligomers and fibrils of the three different peptides. Results show that all the investigated peptides have monomers with a radius of gyration of the order of 10 Å, while the oligomers and fibrils display differences in size and aggregation ability, with A β p 3 - 42 showing larger oligomers. These properties are strictly related to the toxicity of the corresponding amyloid peptide and indeed to the development of the associated disease.