TIME 0F FLIGHT (TOF) METHOD IN SANS TECHNIQUE

1. TIME 0F FLIGHT (TOF) METHOD IN SANS TECHNIQUE MBULE P.S1,MALINDISA C2, KOAO L.F1 Supervisor : Dr. KUKLIN A.L3 UNIVERSITY OF THE FREESTATE UNIVERSITY OF ZULULAND JOINT INSTITUTE OF NUCLEAR RESEARCH DUBNA, RUSSIA South African Student Summer Practice 2009 September

2. Laboratory Work

3. OUTLINE • Introduction • What is SANS • Neutrons sources • SANS Equipment • SANS Applications • Acknowledgement

4. Introduction • Time of flight (TOF)- Method used to measure the time that it takes for a particle, an object or stream to reach a detector while travelling over a known distance. • Small angle neutron scattering- Is a laboratory technique where radiation is elastically scattered by the sample and the resulting scattering pattern is analysed to provide information about the size, shape and the orientation of some components of the sample.

5. Why use neutrons? • Neutrons scatter from materials by interacting with the nucleus of an atom rather than the electron cloud. • The neutrons have a high penetrating probe • Neutrons have wavelengths similar to spacings, permitting diffraction measurements to be performed.

6. Sources of neutrons. • Nuclear Reactor A device in which nuclear chain reaction are initiated, controlled and sustained at a steady rate A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, leading to a self propagating number of these reactions. Fig 1: Possible nuclear fission chain reaction

7. Spallation neutron source • When a fast particle such as high-energy proton bombards a heavy atomic nucleus, neutrons are “spalled” in a nuclear reaction called spallation. • For every proton striking the nucleus, 20 to 30 neutrons are expelled. Fig 2: Schematic illustration of Spallation

8. Small angle neutron scattering YuMO spectrometer 1 -- reflectors, 2 -- active zone with moderator, 3 -- breaker (shutter), 4 -- changeable collimator with different beam-holes, 5 -- vacuum tube, 6 -- adjustable collimator determining the size and position of the direct beam, 7 -- thermostats, 8 -- sample container, 9 -- sample table, 10 -- standard vanadium scatterer, 11, 12 -- ``old'' and ``new'' detectors, 13 -- direct beam detector

9. In a typical experiment neutrons are scattered from an aqueous solution of a protein or complex. • Scattering occurs in a radically symmetric fashion and is measured on a 2D detector. Q= Scattering vector ki= incident wavevector Kf =scattered wavevector 𝜆= neutron wavelength 𝜃= scattering wavelength

10. Determination of Parameters The wavelength of incident beam is directly proportional to time.

11. Maxwell-Boltzmann Distribution for moderator energies of 4.22K, 77K, 200K and 300K

12. The flux of neutrons at different detector distance.

13. The flux of neutrons at different detector distance.

14. Objects and materials of SANS investigation • Biology • Protein • Viruses • Lipids aggregate • Chemistry • Polymers • Precipitates • Colloids • gels • Material engineering • Alloys • Ceramics • glasses

15. Acknowledgements • The members of the group would like to thank the following people: • Dr. Kuklin , Raul , Islamov and Maria for their patience and advices. • Dr.Noel and NRF for the opportunity given to us to participate in 2009 SA student summer practice. • All members of the JINR team for their warm hospitality.

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