Prompt gamma ray activation analysis for determining chemical composition of 3D printing and casting materials used in biomedical applications.

Three-dimensional printing and casting materials were analyzed by prompt gamma-ray activation analysis (PGAA) to determine their suitability as human tissue surrogates for the fabrication of phantoms for medical imaging and radiation dosimetry applications. Measured elemental compositions and densities of five surrogate materials simulating soft tissue and bone were used to determine radiological properties (x-ray mass attenuation coefficient and electron stopping power). When compared with radiological properties of International Commission on Radiation Units and Measurements (ICRU) materials, it was determined that urethane rubber and PLA plastic yielded the best match for soft tissue, while silicone rubber and urethane resin best simulated the properties of bone.

Chopped Cold Neutron Beam Activation Analysis.

A linear fast neutron beam chopper has been deployed at a prompt gamma activation analysis instrument, enabling in-beam activation analysis of short-lived neutron capture products without the need for sample transfer. This article describes the design and operation of the chopper system and measurement results from test samples containing Se-77 and Yb-175m . The chopper timing was optimized for a specific isotope in each measurement, demonstrating an advantage of the programmable system.

Structural Properties of Kerogens with Different Maturities.

The thermogenic transformation of kerogen into hydrocarbons accompanies the development of a pore network within the kerogen that serves as gas storage locations both in pore space and surface area for adsorbed gas within the source rock. Therefore, the successful recovery of gas from these rocks depends on the accessible surface area, surface properties, and interconnectivity of the pore system. These parameters can be difficult to determine because of the nanoscale of the structures within the rock.

Spectroscopic Compton imaging of prompt gamma emission at the MeV energy range.

This work explores a novel tomographic approach to PGAA that is both quantitative and spatially resolved, adapted from a clinical "proton beam range finder" in which MeV gamma rays are imaged by coincidence measurements of Compton scattered gamma rays with multi-detector arrays. We performed preliminary measurements using a Compton camera made with CdZnTe detector arrays on a series of test samples with high-energy (> 1 MeV) gamma emission lines. 3D image reconstructions were performed on the 2.

Neutronic performance characteristics of different LEU fuels in a proposed NIST research reactor.

As a potential replacement for the National Bureau Standards Reactor (NBSR) at the U.S. National Institute of Standards and Technology (NIST), a conceptual design of a new reactor with a horizontally-split core has recently been studied using low-enriched uranium (LEU) silicide dispersion (USi/Al) fuel.

Natural alteration of Li alumino-silicate glass.

Understanding the chemical durability of neutron shielding materials is necessary when assessing their long-term service potential. In this study, the chemical durability of a Li enriched neutron shielding glass that has been exposed to natural, near-operational conditions is assessed by Prompt Gamma Activation Analysis (PGAA) and Neutron Depth Profiling (NDP). These non-destructive, nuclear analysis techniques are sensitive to Li, and PGAA is uniquely able to detect H in low quantities in solids.

On neutron activation analysis with γγ coincidence spectrometry.

A new γγ coincidence system has been set up at NIST. It is operated with a digital data finder supported by new software developed at NIST. The system is used to explore possible enhancements in instrumental neutron activation analysis (INAA) and study applicability to neutron capture prompt gamma activation analysis (PGAA).

Assessment of PGAA capability for low-level measurements of H in Ti alloys.

The accuracy of low-level hydrogen measurements with prompt gamma-ray activation analysis (PGAA) depends on identifying and accounting for all background H signals, including interfering signals. At the cold-neutron (CN)PGAA facility at the NIST Center for Neutron Research, the sources of background H signals were investigated in the context of titanium-based matrices containing low-levels of H (<300 mg H per kg Ti) with the measurements of prepared standards (mixtures of polyvinyl chloride and titanium oxide) and Ti alloy (Ti6Al4V) samples. The sensitivity ratio, defined as the ratio of the H signal to the Ti signal per unit mass ratio of H in Ti, was determined (1) with the measurements of prepared standards and (2) based on partial gamma-ray production cross sections and full-energy detection efficiencies.