The measurement of the fusion neutron yield provides a direct relationship with fusion power and is hence an important measure of experimental performance. In pulsed neutron emission scenarios, such as those experienced in dense plasma focus devices, inertial confinement fusion and even in short-pulse tokamak experiments, considerations of the dynamic range for measurement of neutron fluence are essential to consider. Integrated fluence detection systems such as activation foils, CR39, bubble detectors are widely deployed for such fields, but have some practical drawbacks over integrated counting systems which allow for rapid retrieval of data. It may be advantageous to further develop highly sensitive, versatile devices, which can potentially operate over a large dynamic neutron fluence range, meeting the needs of a broad range of experimental scenarios. Here we explore, in a generalized parameter study, the use of activation materials that have been integrated within radiation detection technologies, together with algorithms to counter instrument paralysis effects.
Our paper surveys, using the FISPACT-II inventory code and various nuclear data libraries, the nuclear response of elemental materials to a range of pulsed fusion neutron fields. Through high-fidelity modelling of residual temporal emissions, and nuclear detector radiation transport models, we provide a general insight into their sensitivity and potential deployment as activation-based diagnostics for measuring these neutron fields.
We apply paralyzeable and non-paralyzable deadtime models to these systems at various incident neutron field intensities, and particularly in high neutron fluence scenarios, apply a backwards extrapolation, or adjoint, algorithm to estimate the pulse total neutron fluence, associated uncertainty and extend measurement capability across a larger dynamic range. Their suitability for short-pulse tokamak experiments at MAST-U and in inertial fusion experiments are discussed.