High resolution neutron spectrometry with liquid scintillation detectors for fusion applications

Organic liquid scintillation detectors, e.g. NE213, EJ-301 or BC501A, are routinely used as high resolution neutron spectrometers in many nuclear experiments. The neutron energy spectrum can be reliably determined from the pulse height spectrum provided the response function of the detector is well determined, counting statistics is sufficient, a suitable unfolding method is applied and care is taken to ensure the gain stability of the system during the measurement. The Physikalisch-Technische Bundesanstalt (PTB) has many years of experience with the development, detailed characterization and use of liquid scintillation detectors. Recent work done at PTB in collaboration with ENEA and EFDA-JET concerning the use of liquid scintillation detectors as neutron diagnostic instruments in fusion experiments is discussed. An NE213 liquid scintillator system has been carefully characterized and successfully used in a series of measurements at the Joint European Torus (JET). We describe the improvements that were made to the system to meet the challenging measurement conditions at JET, as well as the processes used to calibrate and characterize the system. For the determination of the neutron light output function and for a comparison of experimentally determined response functions with those calculated with Monte Carlo techniques, measurements have been performed at the PTB facility in mono-energetic neutron reference fields and in fields with a broad energy distribution applying time of flight spectrometry. Selected examples of measured neutron spectra are discussed in terms of energy resolution and compared to the expected neutron spectra, both for measurements at the PTB accelerator and at JET. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.