Neutron diffraction

Neutron diffraction is the application of neutron scattering to the determination of atomic/ magnetic structure of a material. The technique is similar to XRD but the different type of radiation gives complementary radiation. It is of different types and overcomes the demerit of XRD. It has a lot of applications such as structure determination, locating light atoms, magnetic properties study, study of atomic vibration and other excitations.

1. NEUTRON DIFFRACTION Presented by- Nirmal Urma Jayashree Sa Rajashree khatua

2. Contents- Introduction XRD Neutron Diffraction Principle Instrumentation Working Application Future

3. Introduction- A phenomena that occurs when a wave encounters an obstacle When collimated beam of waves strikes pair of parallel lattice planes in a crystal, each atom acts as a scattering center The secondary waves from the diffraction interfere with each other to produce diffracted images Three types of diffraction techniques - XRD - Neutron diffraction - E lectron diffraction

4. XRD- XRD is a common analytical technique used for the study of crystal structures and atomic spacing. It is used to identify the degree of crystallinity of a material which provides information on unit cell dimension. This technique is based on the principle of interference. XRD has size limitation. It is much more accurate for measuring large crystalline structures rather than small ones. It does not interact strongly with lighter elements. It is relatively low in sensitivity. It cannot explain the magnetic properties.

5. Why neutrons? - W ave length comparable with inter atomic spacing - K inetic energy is comparable with the interaction energy in solid Isotopic sensitivity allows contrast variation Neutrons has both wave and particle properties Penetrating => bulk properties are measured - Neutron possesses spin

6. Neutron diffraction- Neutron diffraction is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material. It can be equally well applied to study crystalline solid, gases, liquids or amorphous materials. The technique is similar to X-ray diffraction but the different type of radiation gives complementary information. As neutrons have high penetration depth are suited for the analysis of bulk samples.

7. XRD vs NEUTRON DIFFRACTION NEUTRON DIFFRACTION Neighbours and isotopes can be discriminated Light elements can be detected Magnetic structures can be investigated Lower absorption XRD Neighbours and isotopes cannot be discriminated Light elements hard to detect Magnetic properties cannot be investigated Strong absorption

8. Different modes in neutron scattering- Nuclear scattering- It involves the interaction of a neutron with the nucleus of the atom , so scattering is isotopic 2. Magnetic scattering- It involves the interaction of a neutron with the extended atomic electron distribution, so the form factor is more like that seen for XRD and it revels the microscopic magnetic structure of material The magnetic scattering length is comparable to the nuclear scattering length, i.e the magnetic and nuclear signals have comparable strengths.

9. Importance- Nuclear neutron scattering: - Elastic scattering diffraction-crystal structure - Inelastic scattering excitations-phonons Magnetic neutron scattering: - Elastic scattering diffraction- spin structure -Inelastic scattering Excitations- magnons

10. Principle- When a monochromatic radiation fall on sample, the diffraction from a B ragg plane results in the form of a cone ( Debye Scherer cone) with angle 2 θ . The diffracted beam is shaped using suitable optical devices. The intensity profile is recorded in the detector.

11. Instrumentation- Neutron source- produce neutrons Monochromator Diffractometer or spectrometer -allows neutron to interact with sample - sorts out discrete wave length by monochromator Detector- detectors pick up neutrons scattered from sample Analysis methods to determine material properties Brain power to interpret results

12. Working- This techniques requires a source of neutron. Neutrons usually produced in a nuclear reactor or spallation source. The source of neutron passed through the monochromator , the monochromatized beam is subjected to fall on diffractometer. Filters are also used to select desired neutron wavelength. The sample is placed within a neutron beam and the angles at which the neutrons are deflected or scattered by the material are recorded to generate a “diffraction pattern” from which structural information can be extracted.

13. Application- Used for determination of structure Locating light atoms Heavy atoms that absorb x-ray strongly Similar atomic no/ isotopes Magnetic properties Single crystal study analysis Inelastic scattering used for study of atomic vibration and other excitations

14. Future of neutron diffraction- Neutron diffraction is now a tried-and tested technique in strong demand by researchers investigating the structure of material. Neutron diffraction is also being used to develop technologies for electrical energy storage : researchers are investigating the light elements present in compounds suitable for ion exchange systems. As the technique advances and wider ranges of temperature and pressure are incorporated , the research condition will improve, opening the doors for new investigation.