Increasing the oxidation power of TCNQ by coordination of B(C6F5)3

The oxidation power of the cyanocarbon TCNQ (tetracyano-quinodimethane) can be significantly increased to approximately E = +0.9 V vs. Cp2Fe by coordination of up to four equivalents of the strong fluorinated Lewis acid B(C6F5)3, resulting in a highly reactive but easy-to-use oxidation system. Thianthrene and tris(4-bromophenyl)amine were oxidized to the corresponding radical cations. Dianionic [TCNQ·4 B(C6F5)3]2− was formed upon reduction with two equivalents of ferrocene or decamethylcobaltocene. [TCNQ·4 B(C6F5)3]− and [TCNQ·4 B(C6F5)3]2− are rare cases of redox-active weakly-coordinating anions

Performance comparison of small-pixel CdZnTe radiation detectors with gold contacts formed by sputter and electroless deposition

Recent improvements in the growth of wide-bandgap semiconductors, such as cadmium zinc telluride (CdZnTe or CZT), has enabled spectroscopic X/γ-ray imaging detectors to be developed. These detectors have applications covering homeland security, industrial analysis, space science and medical imaging. At the Rutherford Appleton Laboratory (RAL) a promising range of spectroscopic, position sensitive, small-pixel Cd(Zn)Te detectors have been developed. The challenge now is to improve the quality of metal contacts on CdZnTe in order to meet the demanding energy and spatial resolution requirements of these applications. The choice of metal deposition method and fabrication process are of fundamental importance. Presented is a comparison of two CdZnTe detectors with contacts formed by sputter and electroless deposition. The detectors were fabricated with a 74 × 74 array of 200 μm pixels on a 250 μm pitch and bump-bonded to the HEXITEC ASIC. The X/γ-ray emissions from an 241Am source were measured to form energy spectra for comparison. It was found that the detector with contacts formed by electroless deposition produced the best uniformity and energy resolution; the best pixel produced a FWHM of 560 eV at 59.54 keV and 50% of pixels produced a FWHM better than 1.7 keV . This compared with a FWHM of 1.5 keV for the best pixel and 50% of pixels better than 4.4 keV for the detector with sputtered contacts

Improvement of Electron Field Emission in Patterned Carbon Nanotubes by High Temperature Hydrogen Plasma Treatment

In this paper, we report a significant improvement of electron field emission property in patterned carbon nanotubes films by using a high temperature (650 °C) hydrogen plasma treatment. This treatment was found to greatly increase the emission current, emission uniformity and stability. The mechanism study showed that these enhanced properties are attributed to the lowering of the potential barrier and the creation of geometrical features through the removal of amorphous carbon, catalyst particles and the saturation of dangling bonds after such a hydrogen plasma treatment

Unravelling the corrosion processes at steel/bentonite nterfaces in in situ tests

Microscopic and spectroscopic analyses were conducted on steel/bentonite interface samples removed from four in situ experiments that were carried out in three underground research laboratories at different temperatures and under different hydraulic and geochemical conditions. The results provide valuable information about the corrosion processes occurring in high-level radioactive waste repositories. Systematic patterns can be deduced from the results, irrespective of carbon steel grade, type of bentonite and its degree of compaction, geochemical environment or experimental setup. Thus, a clear dependence of the corrosion rates on temperature and exposure period, as well as on the availability of H2O and O2 provided by the surrounding bentonite buffer, is observed. Furthermore, Fe(II) ions released by corrosion interact with the structural Fe in the clay. Recent developments highlight the usefulness of reactive transport modelling in understanding the coupled corrosion and Fe–clay interaction processes

Assessing the suitability of three proxy sources for the development of detectors of special nuclear materials

Numerous techniques and equipment have been developed to provide a capability for the detection of special nuclear materials (SNM), but due to the necessary security measures surrounding these materials alternate, or proxy, neutron sources are often utilised in their stead. In this paper we report the neutron and gamma pulse shape discrimination response of plastic scintillator to mixed neutron/gamma beams produced from two radionuclide neutron sources, and also from an SNM source of weapons-grade plutonium. We discuss the suitability of using radionuclide sources, with appropriate shielding configurations as proxy sources for SNM.A 3σnth-γ discrimination level has been achieved for an SNM source at a low-level energy threshold of ~220 keVee when a shielding configuration of 5 cm of lead was implemented. Varying amounts of lead and high-density polyethylene (HDPE) shielding were also investigated with the 3σ limit being reached by ~240 keVee.This work shows that an AmBe neutron source serves as an appropriate SNM proxy achieving a comparable value for figure of merit above ~1 MeVee. For energies below 1 MeVee down to ~100 keVee a closer approximation of the expected FoM for SNM can be attained when using 252Cf as a proxy source or by utilising an 'enhanced' AmBe source with the addition of a further low energy γ ray source

Neutral Dissociation of Hydrogen Following Photoexcitation of HCl at the Chlorine K Edge

Time-of-flight mass spectroscopy was used to study the relaxation dynamics of HCl following photoexcitation in the vicinity of the Cl K edge (~2.8 keV) using monochromatic synchrotron radiation. At the lowest resonant excitation to the 6ơ* antibonding orbital, almost half of the excited molecules decay by emission of a neutral H atom, mostly in coincidence with a highly charged Cln1 ion. The present work demonstrates that neutral-atom emission can be a significant decay channel for excited states with very short lifetimes (1 fs). [S1050-2947(98)03604-X