NCTS (South)


DATE2011-11-17

TIME15:10

PLACE物理二館 一樓會議室(49101)

FIELDOther

SPEAKER Dr. Wai Tung Hal Lee - Bragg Institute, Australia Nuclear Science and Technology Organisation (ANSTO)

TITLEPolarised 3He based Neutron Polarisers and Analysers for Magnetism Research at the Australian Research Reactor OPAL

ABSTRACTPolarized neutron scattering techniques allow us to study magnetic materials with details down to the atomic level. It has found applications in the study of magnetic structures such as spin density wave and the associated magnetic excitations. It is instrumental in the R&D of magnetic multilayers and nano-patterned surface magnetic structures for spintronics. To produce polarised neutrons and analyse the neutron polarization, a technique called polarised 3He based neutron polariser and polarization analyser [1] have in recent years become a matured technology for neutron scattering works. A joint project of the Australian Nuclear Science and Technology Organisation (ANSTO) and the Institute Laue Langevin (ILL) is underway to provide 6 OPAL neutron scattering instruments with polarized 3He based neutron polariser and polarization analyser. The instruments include thermal triple-axis spectrometer Taipan, Taipan’s cold-neutron counterpart Sika, cold neutron time-of-flight spectrometer Pelican, SANS Quokka, diffractometer Wombat, and reflectometer Platypus. The project will produce a 3He gas polarizing station that uses the Metastable Exchange Optical Pumping method [2], silicon-window polarised 3He cells for polarizing the incident neutron beam on several instruments and for analysing the scattered neutrons on Platypus and Quokka, wide-angle analyser “Pastis” cells for Wombat and Pelican. At present, the polarizing station is undergoing commissioning, the equipment for use on instruments are being built and tested for 3He polarisation lifetime, and infrastructural changes are being incorporated on ANSTO instruments. This presentation will first provide examples on the use of polarized neutron techniques to study magnetism. Different polarized neutron techniques and the two leading 3He polarizing methods will be explained and compared. The latest status of the polarizing station and test results of the instrument components will be presented. And finally, examples illustrating the use and the methodology for using this technique for neutron scattering will be given. References [1] F. Tasset, et. al., Physica B 180 & 181, 896 (1992). [2] G. K. Walters, et. al., Phys. Rev. Lett. 8, 429 (1962).