From Nanostructured Optics to Nuclear Safety: Physics Across the Scales

INTRODUCTION

The current issue of the Journal of Qassim University for Science (JQUS) features a diverse collection of contributions across chemistry, mathematics, biomedical science, and physics, exemplifying the multidisciplinary nature that has come to characterize the journal. Collectively, three articles hone in on a discipline that has anchored physical science for decades: How we understand matter under driven and structural perturbation at scales ranging from the nanometer to the atmospheric column. They convey, in unison with modern physics, the nuances of fundamental electronic structure, coupled with functional material design, applied to radiological safety. This editorial contextualizes these three contributions within broader science and provides a brief overview of the question that motivates each.

UNDERSTANDING MATTER UNDER DRIVEN AND STRUCTURAL PERTURBATION AT SCALES RANGING FROM THE NANOMETER TO THE ATMOSPHERIC COLUMN

One of the aforementioned articles reports the optical properties of laser-ablated polymeric/selenium–noble metal nanocomposites. Pulsed laser ablation in liquids has become a clean, additive-free route for manufacturing metal, semiconductors, and hybrid nanoparticles without the use of reducing agents or stabilizers, as required in the wet-chemical synthesis of these materials. The optical characteristics of a polymeric host, including a selenium–noble metal nanocomposite, can be manipulated by introducing new functionalities not exhibited by either constituent, such as shifted and broadened surface plasmon resonances, modified absorption edges, and altered refractive behavior arising from interfacial charge exchange between the semiconductor and the metal nanoparticles. Such systems are promising for optical limiting, photodetection, and other photonic applications that involve tailored composition and particle size distribution via ablation parameters — such as laser fluence, pulse duration, wavelength, and exposure time — since the polymer matrix simultaneously restricts particle growth while tuning the local dielectric environment. The contribution, which addresses this system in the current issue, complements a burgeoning chapter in which pulsed laser ablation serves as a platformed and scalable architecture of functional nanocomposites with optical properties that can be effectively engineered rather than simply bilaterally observed.^[1]

The second article honing in the sane area discussed charge transfer and core-hole screening in stoichiometric GaAs. The other extreme example involves the electronic structure of a technologically significant compound semiconductor. Gallium arsenide (GaAs) forms the basis of much modern optoelectronics technology, and the ability to interpret experiments involving charge exchange between constituent atoms is crucial for making rational predictions about performance. In particular, a knowledge of how different atomic environments influence the energy associated with the emission of “Auger” electrons – generated when atoms absorb energetic photons but instead of releasing emitted electrons, they share up their charge via interactions among the valence electrons - provides chemically sensitive markers against which one can measure changes caused by substitutional impurities.^[2] In practice, measuring such parameters requires subtracting a background that depends on the electrostatic charging induced in the samples due to differences between measured and true charges at individual atomic sites. This leads to a problem similar to the earlier binding-energy examples: Determining the relative strength of effects arising from the charge state before and after the interaction, compared with those resulting from screening of the electric field by the core hole left behind after absorption.^[3] To address these challenges, the paper presented in this issue models the effect of screening using results from a calculation based on a Dirac-Fock treatment incorporating relativistic effects necessary for the correct evaluation of properties of elements as heavy as gallium and arsenic.

Another article published in this issue regarding such interesting topic reports the radiological risk assessment of nuclear research reactor releases.^[4] From the very earliest days of our understanding of physics, we have sought to apply it for the good of mankind. This includes applications aimed at protecting public health against ionizing radiation. For example, even when operating normally, nuclear research reactors emit some radio nuclides into the atmosphere. Predicting where they will go, which depends on their ability to lift up (plume rise) and fall (deposition), is an important element of environmental radiological risk assessments. Plume rise can be driven by either buoyancy or momentum considerations. Its magnitude depends on several factors, including the characteristics of the stack itself, the velocity at which material exits the top of the stack, the presence of thermal buoyancy associated with a hot source, and meteorological conditions in general. Different methods of model development yield markedly different results for both ground-level concentrations and the resulting doses to nearby populations. The article contributes to the theme by evaluating radiological risk using different plume-rise models.^[5] It shows that consideration of different formulations of atmospheric dispersion impacts upon the degree of conservatism assumed within a given facility’s safety case.

A COMMON THREAD

While their subjects are quite disparate—photonic nanocomposites, core-level spectroscopy of a bulk semiconductor, atmospheric transport of radionuclides—the three studies do share a similar logical structure. Each report on a phenomenon with a distinctly microscopic/mesoscopic character—a particle-forming mechanism during laser ablation, the shielding of a core hole via valence electrons, the dynamics of a buoyant plume—and then describes how this phenomenon manifests itself at the macroscale as an optical spectrum, a spectroscopic shift, or some measure of radiation dose. It is both fascinating and instructive for scientists working across the breadth of applied physics to see how wide the diversity of phenomena is.

BEYOND PHYSICS: THE BROADER ISSUE

Of course, this issue contains much more than just these three contributions on physics — there is also good stuff from medicinal chemistry, biomedical science, microbiology, plant physiology, pharmacology, and even pure mathematics providing their related results and application.

FUTURE PERSPECTIVES

In conclusion, the topics featured in this issue offer many avenues for predicting further developments that may lead us towards interesting new results in these diverse fields. For instance, there appears to be potential for increased interplay between nanomaterial synthesis and in situ optical monitoring using laser-based techniques.^[6] There could also be greater emphasis on the use of Auger parameter analysis in electronic structure theories, now within a relativistic framework that covers a broader range of compound semiconductor systems, including those at interfaces important for next-generation device technologies. As ever, refinements and validations of atmospheric dispersion and plume-rise models against field measurement continue to play a significant role in radiological safety studies. Finally, we expect more cross-fertilization between computational model development and experimental verification across the disciplines highlighted here.^[7]

CONCLUSION

In addition to our broad range of interdisciplinary topics in previous issues, we have included 3 articles on physics. These articles are related to the engineered optical characteristics of nanocomposites, the theoretical analysis of core-level spectroscopy in semiconductor materials, and the evaluation of radiological risk associated with nuclear facilities. We thank all contributors, reviewers, and readers for their support toward the mission of our esteemed journal, Journal of Qassim University for Science (JQUS). We look forward to further progress of our journal in the coming times.