Investigation of frequency spectrum of light water to generate thermal scattering law

Standard thermal neutron scattering cross-section libraries of light water generated using the LEAPR module of the NJOY code treat the cross-sections as an analytical function of the density of states, i.e. the frequency spectrum. Hence, an accurate estimation of the frequency spectrum is necessary to generate reliable thermal scattering cross-sections, as long as one chooses to use LEAPR. In this paper the experimental frequency spectrum of light water measured at several temperatures and pressures, using high resolution time-of-flight inelastic spectrometers, namely the IN4c and the IN6 at the Institut Laue-Langevin, Grenoble, France is presented. Within the scope of the experimental limitations of our measurements, an effort has been made to provide qualitative comparisons of the experimentally obtained frequency spectrum with that derived from the classical molecular dynamics simulations. The thermal scattering law present in the JEFF-3.1.1 library and a very recent test library developed at Centro Atomico Bariloche, Argentina, named as CAB library were chosen for our comparison. A study of the dependence of pressure and temperature on the experimental frequency spectrum was also carried out, majorly to predict the sensitivity of thermal scattering law to pressure.