We have synthesized and characterized the first example of an atomically precise 2D film of radioactive atoms.(1,2) Our data indicate that radioactive iodine-125 atoms form well-ordered monolayers on gold/mica substrates that are stable under ambient conditions and amenable to study by high resolution microscopy and surface analysis techniques. We first observe nuclear transmutation of I-125 to Te-125 at the individual atom level and support our elemental assignments with theory. The fact that the radioactive decay occurs via electron capture with low recoil energy renders these films robust with respect to autoradiolysis that plagues many alpha and beta emitter constructs.
Scanning tunneling microscope data from a 2-D radioactive film showing individual atoms of both iodine-125 and the nuclear transmutation product, tellurium.
Despite the importance of radioactive decay in a wide range of technologies there is currently no other known air-stable 2D radiation sources. The reduced dimensionally of these surface-bound films provides the ability to study high energy nuclear processes safely and enables the microscopic details of radiation chemistry, biological degradation and material damage to be quantified. Most significantly, our results indicate that interaction of I-125 with the metallic surface produces more than five times the expected flux of electrons that accompany the high energy gamma/X-ray emission and are peaked in the 0-20 eV range. These lower energy electrons are the most important species in radiation induced chemistry and biological damage due to their high damage cross sections and short range. I-125 is commonly used in medical imaging, radiation therapy and biological assays and the iodine-gold surface chemistry described here is transferable to biocompatible gold nanoparticles. Therefore, our electron emission results offer the intriguing prospect of using metal nanoparticle supported radioisotopes for the enhanced, targeted electron dosing of tumor cells with short range, chemically active low energy electrons; a goal which we are actively pursuing. We envisage a new field that combines nanoscience with radioisotopes enabling understanding of many aspects of radiochemistry, physics and biology, as well as offering new constructs for in vivo radioisotope delivery for cancer therapy. Furthermore, a microscopic picture of how radioactive atoms can be assembled on surfaces/nanoparticles, how they decay, and how the resulting radiation affects their local molecular environment will provide fundamental knowledge about both materials and biological damage, uncover new non-equilibrium chemistries, fuel the discovery of methods for constructing nanoscale radioactive materials, and enable new technologies.