Enhancement of low-energy electron emission in 2D radioactive films

Abstract

High-energy radiation has been utilized for decades, however, the role of low-energy electrons created during irradiation has only recently begun to be appreciated Nuclear decay is one of the most extreme processes and is central to a range of fields including energy, medicine, imaging, labelling, archaeology and sensing. Radiation in the form of alpha particles, beta particles and gamma rays have fundamentally different interactions with matter and therefore exhibit different mean-free paths (∼1 μm, 1 mm and 1 cm, respectively). These forms of primary radiation deposit their energy over the course of their trajectory by ionizing their surroundings and producing non-thermal secondary electrons. Only very recently has the ability of low-energy secondary electrons to induce chemical reactions and biological damage begun to be appreciated 1 , because they have energies below the typical ionization threshold of organic matter. For example, low-energy electrons (3-20 eV) have been shown to be effective at causing DNA cleavage 2,4,7 . This ability stems from their high cross-section for breaking chemical bonds, and as a consequence they have a very short meanfree path of ∼1-10 nm in solution 8,9 . Furthermore, hot electrons that are not captured by surrounding molecules become thermalized as solvated electrons which are known to be chemically and biological active [9][10][11][12] . To harness these unique properties, the design of radioactive materials that increase and localize the flux of short-range lowenergy electrons to target sites is crucial for their application in targeted cancer therapies that minimize damage to healthy cells. Thus far, it has not been possible to design atomically precise radioactive materials that maximize these effects due to self-destruction arising from nuclear recoil, Coulomb explosion and self-irradiation [13][14][15][16] . We report a straightforward method for synthesizing monolayer films of radioactive 125 I atoms on gold-coated mica substrates under ambient conditions, and characterize their composition and their electron emission. Despite being synthesized from radioactive 125 I (> 99.9% purity) they are robust with respect to self-destruction, and provide well-defined, intense planar sources of secondary electrons. 125I decays by electron capture (EC) of a core shell electron to produce a nuclear excited state of 125 Te (Figure 1a), the majority of which eject another core

Single‐Crystalline Ultrathin Nickel Nanosheets Array from In Situ Topotactic Reduction for Active and Stable Electrocatalysis

“…Two-dimensional (2D) crystals with atomic thickness have attracted extensive attention because of the dramatically increased surface/volume ratio and unique electronic structures. [1][2][3][4][5][6][7][8][9] Thus,t hey have been considered as promising materials in electronics, [10][11][12][13][14] optics, [15,16] magnetics, [17,18] and catalysis. [19,20] Active and stable metal-based 2D crystals have shown ag reat potential as efficient electrocatalysts.…”

Quantitative electron spectroscopy of 125I over an extended energy range

“…Samples with a third of a monolayer of 125 I on a Au(111) surface were prepared following the procedure described by [11]. Au(111) surfaces were obtained by flame annealing Au samples from Arrandee Metal GMBH, Germany just before the 125 I deposition.…”

“…[8,9,10]. Recent experimental work on Auger emission after decay of 125 I, using an electrostatic analyser, [11] indicates an enhancement of the very-low energy electron yield. A summary of results for the KLL and LMM Auger electrons was given elsewhere [12].…”

Low-energy electron therapy

“…Such new sources could also help in specifying any modification of these basic mechanisms that may be needed for understanding the action of LEEs in cells. Now, writing in Nature Materials, Alex Pronschinske et al 3 describe the construction of such a source of LEEs and characterize its properties.…”

“…Pronschinske and co-workers synthesized a two-dimensional source of LEEs from a one-atom-thick layer of the radioisotope 125 I deposited on a gold film 3 . The working principle of the source is simple.…”