Extension of the Calibration of an NE-213 Liquid Scintillator Based Pulse Height Response Spectrometer up to 18 MeV Neutron Energy and Leakage Spectrum Measurements on Bismuth at 8 MeV and 18 MeV Neutron Energies

Monoenergetic neutrons were produced at the Van de Graaf accelerator of the EC-JRC-Institute for Reference Materials and Measurements (IRMM, Geel, Belgium). An air-jet cooled D2-gas target (1.2 bar, Ed = 448 keV) was bombarded with Ed =4976 keV deuterons to produce neutrons up to En = 8 MeV energy via the D(d,n)3He reaction. Higher energy neutrons up to En = 18 MeV were produced via the T(d,n)4He reaction by bombarding a TiT target with Ed =1968 keV deuterons. Pulse height spectra were measured at different neutron energies from En = 8 MeV up to En = 18 MeV with the NE-213 liquid scintillator based Pulse Height Response Spectrometer (PHRS) of UD-IEP. The energy calibration of the PHRS system has been extended up to En = 18 MeV. Pulse height spectra induced by gamma photons have been simulated by the GRESP7 code. Neutron induced pulse height spectra have been simulated by the NRESP7 and MCNP-POLIMI codes. Comparison of the results of measurements and simulations enables the improvement of the parameter set of the function used by us to describe the light output dependence of the resolution of the PHRS system at light outputs of L > 2 light units. Also, it has been shown that the derivation method for unfolding neutron spectra from measured pulse height spectra performs well when relative measurements are done up to En = 18 MeV neutron energy. For matrix unfolding purposes, the NRESP7 code has to be preferred to calculate the pulse height response matrix of the PHRS system. Leakage spectra of neutrons behind bismuth slabs of different thicknesses have been measured with the PHRS system by using monoenergetic neutrons. The maximum slab thickness was d = 14 cm. Simulations of the measurements have been carried out with the MCNP-4c code. The necessary nuclear cross sections were taken from the from the ENDF/B-VII and JEFF-3.1 data libraries. For both libraries, the agreement of measured and simulated neutron spectra is good for the 5 MeV = En smaller than or equal to 18 MeV neutron energy region. However, for both libraries, the observed differences between measured and simulated neutron spectra are beyond statistical uncertainty for the En < 5 MeV region. Further experimental check of cross section data of the two libraries for bismuth is recommended for the En < 5 MeV region.

FENYVESI A.;  OLAH L.;  VALASTYAN I.;  CSIKAI J.;  PLOMPEN Arjan;  JAIME TORNIN R.;  LOEVESTAM Nils Evald Goeran;  SEMKOVA Valentina; 

2011-11-14

Organisation for Economic Co-operation and Development (OECD) - Nuclear Energy Agency (NEA)

JRC61876