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.
Magnetic Imaging: a New Tool for UK National Nuclear Security
Combating illicit trafficking of Special Nuclear Material may require the ability to image through electromagnetic shields. This is the case when the trafficking involves cargo containers. Thus, suitable detection techniques are required to penetrate a ferromagnetic enclosure. The present study considers techniques that employ an electromagnetic based principle of detection. It is generally assumed that a ferromagnetic metallic enclosure will effectively act as a Faraday cage to electromagnetic radiation and therefore screen any form of interrogating electromagnetic radiation from penetrating, thus denying the detection of any eventual hidden material. In contrast, we demonstrate that it is actually possible to capture magnetic images of a conductive object through a set of metallic ferromagnetic enclosures. This validates electromagnetic interrogation techniques as a potential detection tool for National Nuclear Security applications.
Three-dimensional time and frequency-domain theory of femtosecond x-ray pulse generation through Thomson scattering
060703-1 The generation of high intensity, ultrashort x-ray pulses enables exciting new experimental capabilities, such as femtosecond pump-probe experiments used to temporally resolve material structural dynamics on atomic time scales. Thomson backscattering of a high intensity laser pulse with a bright relativistic electron bunch is a promising method for producing such high-brightness x-ray pulses in the 10–100 keV range within a compact facility. While a variety of methods for producing subpicosecond x-ray bursts by Thomson scattering exist, including compression of the electron bunch to subpicosecond bunch lengths and/or colliding a subpicosecond laser pulse in a side-on geometry to minimize the interaction time, a promising alternative approach to achieving this goal while maintaining ultrahigh brightness is the production of a time-correlated (or chirped) x-ray pulse in conjunction with pulse slicing or compression. We present the results of a complete analysis of this process using a recently developed 3D time and frequency-domain code for analyzing the spatial, temporal, and spectral properties an x-ray beam produced by relativistic Thomson scattering. Based on the relativistic differential cross section, this code has the capability to calculate time and space dependent spectra of the x-ray photons produced from linear Thomson scattering for both bandwidth-limited and chirped incident laser pulses. Spectral broadening of the scattered x-ray pulse resulting from the incident laser bandwidth, laser focus, and the transverse and longitudinal phase space of the electron beam were examined. Simulations of chirped x-ray pulse production using both a chirped electron beam and a chirped laser pulse are presented. Required electron beam and laser parameters are summarized by investigating the effects of beam emittance, energy spread, and laser bandwidth on the scattered x-ray spectrum. It is shown that sufficient temporal correlation in the scattered x-ray spectrum to produce sub-100 fs temporal slice resolution can be produced from state-of-the-art, high-brightness electron beams without the need to perform longitudinal compression on the electron bunch.