A Powdered Simulant of Triacetone Triperoxide (TATP) for Safe Testing of X-ray Transmission Screening Equipment.

Explosives detection systems (EDS) based on X-ray are used at airports to screen baggage for the presence of explosives. Once EDS are installed in airports, however, it can be challenging to test the EDS equipment and verify that it continues to perform at the highest level, because of the impracticality of introducing bulk explosives into civil aviation airports. The problem is particularly acute for sensitive homemade explosives, such as triacetone triperoxide (TATP). This paper describes our work to develop a safe, accurate and stable simulant for TATP for EDS based on X-ray transmission. Bulk quantities of TATP were synthesised and characterised especially for this project, and we describe the unique challenges and safety considerations of collecting this data. Our calculations show that the expanded measurement uncertainty with a coverage factor of k = 2 is 5.7% for bulk density and 1.0% for Zeff at 24 months.

Development of Inert, Polymer-Bonded Simulants for Explosives Detection Systems Based on Transmission X-ray.

Explosives detection systems (EDS) based on X-ray are used at airports to screen baggage for the presence of explosives. In Europe and the United States, EDS equipment is tested extensively by specialist test centres prior to approval for operational use in airports. Once EDS are installed in airports, however, it can be challenging to test the EDS equipment and verify that it continues to perform at the highest level, because of the impracticality of introducing bulk explosives into civil aviation airports. We have developed inert, non-toxic polymer-bonded simulants and validated them against real explosives using EDS equipment. The accuracy of our simulants is within 1% of the target bulk density, and within 2% of the target effective atomic number, and the materials have a stability of at least 4 years, with an uncertainty of 0.5%. The simulants generate alarms in almost 100% of cases on a wide range of commercial EDS models, and we consider the simulants fit for purpose for use during testing of EDS equipment at airports.

Carbon dioxide activation and reaction induced by electron transfer at an oxide-metal interface.

A model system has been created to shuttle electrons through a metal-insulator-metal (MIM) structure to induce the formation of a CO2 anion radical from adsorbed gas-phase carbon dioxide that subsequently reacts to form an oxalate species. The process is completely reversible, and thus allows the elementary steps involved to be studied at the atomic level. The oxalate species at the MIM interface have been identified locally by scanning tunneling microscopy, chemically by IR spectroscopy, and their formation verified by density functional calculations.

Non-covalent interactions in supramolecular assemblies investigated with electron spectroscopies.

A new view: A picture of the different non-covalent interactions relevant for the self-assembly of organic layers and their spectroscopic fingerprints is provided (see figure). In particular, state-of-the-art spectroscopic measurements are performed for supramolecular assemblies, comparing the electronic structure of single-component layers with that of binary organic layers.

Spectroscopic fingerprints of amine and imide functional groups in self-assembled monolayers.

The electronic structures of naphthalene tetracarboxylic diimide (NTCDI) and 1,4-bis(4,6-diamino-1,3,5-triazin-2-yl)benzene (BDG) monolayer assemblies grown on Au(111) are investigated by photoemission spectroscopy, X-ray absorption, and density functional theory. The different spectroscopic features in the absorption and core-level photoemission spectra are understood in terms of contributions from different core and molecular levels at N- and O-atom sites. This study provides clear spectroscopic fingerprints for amine and imide functional end groups, which drive the self-organization process in a number of planar, pi-conjugated molecular structures.