Abstract
We report the results of inelastic neutron scattering measurements on bulk water and ice using the direct geometry SEQUOIA chopper spectrometer at the Spallation Neutron Source (USA), with incident energy Ei= 6 eV. In this set up the measurements allow to access the Deep Inelastic Neutron Scattering regime. The scattering is centred at the proton recoil energy given by the impulse approximation, and the shape of the recoil peak conveys information on the proton momentum distribution in the system. The comparison with the performance of inverse geometry instruments, such as VESUVIO at the ISIS source (UK), shows that complementary information can be accessed by the use of direct and inverse geometry instruments. Analysis of the neutron Compton profiles shows that the proton kinetic energy in ice at 271 K is larger than in room temperature liquid water, in agreement with previous measurements on VESUVIO.
Highlights
Recent developments of the Deep Inelastic Neutron Scattering (DINS) technique for the measurement of atomic momentum distributions in materials provide an insight into the local environment of light and intermediate-weight elements [1,2,3,4,5,6,7,8,9,10] in a variety of settings
We have superimposed three lines representing the expected proton recoil excitation with a recoil width equal to σH = 5 ̊A−1, corresponding to ωR = 2q2/(2M ), ω = [ 2q2/(2M ) ± 2qσH /M ], respectively, where M is the proton mass
The measurements presented here allowed an assessment of the performance of SEQUOIA for DINS measurements of proton momentum distribution
Summary
Recent developments of the Deep Inelastic Neutron Scattering (DINS) technique for the measurement of atomic momentum distributions in materials provide an insight into the local environment of light (proton, deuteron, helium, lithium) and intermediate-weight (oxygen, fluorine, sodium, etc.) elements [1,2,3,4,5,6,7,8,9,10] in a variety of settings.
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