Advanced active interrogation sources for remote detection of special nuclear material
AWE has recently commenced a research programme to develop techniques for the remote detection of illicitly trafficked, special nuclear material. Three techniques that are being investigated as part of this programme utilise an active interrogation source to stimulate a radiation signature within SNM. A photonuclear technique and nuclear resonance fluorescence require an active gamma source while a technique stimulating fission with low energy neutrons requires a low energy neutron source. The potential for consolidation of the photonuclear and neutron technique is discussed. Conceptual designs of intense, pulsed, ion beam diodes to generate suitable sources of 6-7MeV gamma photons for the photonuclear technique and ≪100keV neutron sources for the active neutron technique are presented. The sources required for remote detection via the 60keV neutron or photofission techniques are contrasted with the source requirements for nuclear resonance fluorescence.
A resonant system for electromagnetic induction imaging of concealed conductive targets
The possibility of revealing the presence and identifying the nature of electrically conductive targets is of central interest in many fields, including security, medicine, industry, archaeology and geophysics. In many applications, these targets are electromagnetically shielded by other external materials and thus cannot be directly accessed and detected. Hence, material interrogation techniques are required that allow penetration through the shielding materials, in order for the targets to be identified. Electromagnetic interrogation techniques represent a powerful solution to this challenge, as they enable penetration through conductive shields. Two resonant electromagnetic induction imaging (EII) methods, based on the use of LCR circuits, were developed in this research work. These proof-of-principle EII methods were based, respectively, on position-resolved-measurements of resonant frequency and Q-factor shifts, which occurred as a consequence of eddy current induction inside the conductive targets to be detected. The proposed techniques were applied to 2D imaging of conductive targets (having conductivities σ ranging from 0.54 to 59.77 MSm-1), both unshielded and shielded by an aluminium shield (1.5-mm-thick). The experimental results achieved in the first part of this work highlighted a limitation in the LCR resonant circuits used for EII investigations, linked to the Q-factor low absolute 5 values (between 7 and 23). Therefore, investigations were conducted, leading to the implementation of an improved version of the EII system, based on active bandpass filters. The sensitivity of the novel EII system was found to be larger by a factor of 3.5 compared to the previously used LCR-based system, when both systems were used for imaging copper. Additionally, the new system allowed achieving images with higher contrast. The research work reported in this thesis led to establishing a proof-of-principle method for EII of conductive samples, also in the interesting scenario where the samples were shielded by conductive shields preventing them from being directly accessed.
Continuous calibration of a vacuum ultraviolet system from 65 to 125 nm by a cascade arc and comparison with the calibrated line radiation of a hollow cathode.
A high-power stationary helium cascade arc has been developed as a standard source for continuum radiation in the VUV spectral range from 65 to 125 nm. The calibration of the VUV system response was based on the calculated and measured continuum radiation of a 2-mmphi pure He arc. Diagnostics of the arc plasma in partial thermal equilibrium yielded the electron density and the temperature that were inserted in the calculations of the continuous radiation. The results were compared with the helium, argon, and krypton radiation lines of a high-current hollow cathode lamp. This lamp was built according to the construction drawings of a hollow cathode, which was calibrated by means of the electron synchrotron radiation at the Physikalisch Technische Bundesanstalt Berlin.