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Inelastic Neutron Scattering

My INS experiments are performed in the Institut Laue-Langevin (ILL), Grenoble, France. Neutrons at the ILL are produced from a high-flux reactor. The two instruments used to probe the endofullerenes are IN4C and IN5. They are both time-of-flight (TOF) spectrometers. IN4C uses thermal neutrons, which are neutrons in the wavelength range of 1.1A and 3A, while the IN5 uses cold neutrons, which are in the range of 4A to 8A. The wavelength of the neutron is inversely proportional to its energy.

Introduction to Neutron Science:

Inelastic neutron scattering spectroscopy is a very powerful technique in probing dihydrogen endofullerenes. Unlike other photon spectroscopies, neutrons are able to induce transitions between ortho and para-H2 species. This is useful in probing the entire energy levels of endofullerenes. Furthermore, hydrogen has the largest scattering cross section among all atoms.

h2c60_1.6a_1.8k_full_spectrum.jpg

Inelastic neutron scattering is a powerful spectrocopic technique capable of probing the molecular dynamics of dihydrogen endofullerenes. Unlike other photon spectroscopies, neutrons are able to induce transitions between ortho- and para-H2 species. This is useful in probing the entire energy levels of endofullerenes. Furthermore, hydrogen has the largest scattering cross section among all atoms.

There are three main features in the neutron scattering spectrum, neutron energy gain (NEG) lines, neutron energy loss (NEL) lines and the elastic line. The elastic line is situated at the 0 energy value of the spectrum, while the neutron energy gain and loss lines are situated in the negative and positive energy region of the spectrum respectively. NEG denotes the neutron gains in energy after scattering with scatterer, inducing a downward transition in the energy level diagram. Conversely, NEL denotes that the scatterer gains energy from incident neutron. Higher energy neutrons allows for higher range of energy transitions to occur in the NEL side of the spectrum. However, the resolution is lowered if high energy neutrons are used. Hence, high energy neutrons are used for probing the full energy level of the system, while cold neutrons are favoured for high resolution spectroscopy.

IN4:

IN4 schematicsIN4

IN5:

IN5 schematicsIN5