The determination of the absolute response function of a deuterated benzene total energy detector to 6.13 MeV γ-rays

The γ-ray response function of a 0.4 l deuterated benzene liquid scintillation detector, used in the measurement of total neutron capture cross sections has been measured at 6.13 MeV and compared with spectra generated by the comprehensive Monte Carlo electron-gamma tracking code EGS-4. The experiment was performed in a nearly monoenergetic photon calibration field generated using the 19F(p, αγ)16O reaction by bombarding a thin CaF2/Ta target with protons from the Harwell 6 MV Van de Graaff accelerator. The absolute yield of photons was measured using a 101 cm3 HPGe γ-ray spectrometer whose efficiency had been previously determined using a combination of radionuclide and thermal neutron capture γ-ray sources. A secondary calibration, based on measurements with a standard 3 in.x3 in. NaI(Tl) scintillator, gave consistent results. A particularly open irradiation geometry was used so as to minimise the importance of scattered radiation and to enable the geometry to be accurately represented in the computer simulations. Satisfactory agreement between the experiment and the Monte Carlo simulations was only obtained when the transport of secondary radiations produced in the target assembly and other materials close to the detector were included in the calculation. The calculated spectra exhibit rather more fine structure when was actually observed. Subsidiary measurements however, made using intensity calibrated radionuclide sources, indicate that below 1.5 MeV agreement between the predicted and observed response is excellent. (orig.)