Effects of Instrumental Energy Resolution on the Measured MSD as Obtained by Elastic Incoherent Neutron Scattering Data

In the present paper we compare the mean square displacement (MSD) values obtained on dry and hydrated (H2O andD2O) lysozyme samples by using two spectrometers, IN13 and IN10 at the Institute Laue Langevin (Grenoble, France), working at the energy resolution value of 8μeV , corresponding to an elastic time resolution of 516 ps, and at the energy resolution value of 1μeV , corresponding to an elastic time resolution of 4136 ps. In particular the comparison is performed when only vibrational motions occur, i.e. when the system MSD can be considered almost constant⟨r2⟩(t) → ⟨r2⟩V . Such a condition is approximately satisfied in the low temperature range up to T = 40 K. The analysis furnish values that agree very well with data reported in literature while comparison between the measured MSDs shows the role played by the instrumental energy resolution.