Characterization and response comparison of various liquid scintillation detectors
D. Schmidt B. Asselineau R Böttger H Klein L Lebreton S Neumann R Nolte G Pichenot
International Workshop on Neutron Field Spectrometry in science, technology and radiation protection, Pise 2000
Six liquid scintillation detectors, different in size (diameter d=2", length between l=1" and l=4") and scintillator type (NE213, BICRON501A), were investigated using quasi-mono-energetic neutrons of the DD reaction in the energy range between 1.2 MeV and 14 MeV. Time-of-flight (TOF) technique was applied including a TOF monitor for fluence normalization and a well specified reference detector (d=4", l=1") for fluence comparison. For neutron energies below 8 MeV, appropriate windows in the TOF spectra were set in the region of neutron continuum stemming from the deuteron breakup.
Response functions for monoenergetic neutrons were extracted from the measurement and compared with calculations using the NRESP code. Individual proton light output (LO) functions relative to the electron light output were determined being different to each other up to about ±20%. The energy-dependent resolution was parametrized individually for each detector.
The fluence ratios for monoenergetic neutrons of the detectors studied in comparison with the reference detector deviate by less than 2%. The reference detector was calibrated with a proton recoil telescope previously. Using a standard LO function, the fluence ratios deviate the more from those values derived with the individual LO functions, the larger the differences in shape of the individual and standard LO functions are.
Neutron detection efficiencies can be calculated reliably using the individual LO functions, because the interaction of neutrons with the hydrogen nuclei in the scintillator and with the housing material are adequately described. Small systematic corrections (energy- and threshold-dependent) of the calculated efficiencies may be necessary if measured and calculated response functions deviate at low amplitudes. Such deviations occur due to incorrect 12C(n,n¢3alpha) cross sections in the calculations and/or incorrect LO functions for alpha particles.
The influences of different LO functions on efficiency calculations and on unfolding procedures are discussed.
This work was done in collaboration with PTB ( Physikalisch-Technische Bundesanstalt, Braunschweig, Germany).