A new thermal triple-axis spectrometer at the research reactor FRJ-2

Abstract

A high intensity triple-axis spectrometer is described, which has been commissioned only a year before the final shut-down of the FRJ-2 reactor in May 2006. It was designed both as an instrument for quasi-elastic scattering with polarisation analysis on an area detector, and as a triple-axis spectrometer with polarization analysis for measurements of magnetic and nuclear inelastic scattering. The instrument features two exchangeable monochromators (Cu [200] and PG [002]), which enable both horizontal and vertical focusing. High monochromatic neutron current densities at the sample position of up to 4 × 10⁷cm^− 2 s^− 1 (for pyrolytic graphite at 34 meV) and energies of up to 117 meV (with copper) have been achieved at the FRJ-2 (thermal flux density: 3 × 10¹⁴cm^− 2 s^− 1). The utilization of ³He filters both as polarizer and analyzer will enable polarization analysis for high-energy neutrons. The spectrometer is presently being prepared for installation at the new Chinese research reactor CARR at the China Institute of Atomic Energy in Fang Shan near Beijing.

Keywords:

• Neutrons
• Triple-axis spectrometer
• Focusing monochromators
• Magnetic scattering
• ³He filters

Acknowledgements

One of us (H.C.) is particularly grateful to A. Kollmar⁺ and H. Grimm for invaluable scientific advice with triple axis spectroscopy. Indispensable technical assistance by R. Heinrichs, M. Heinzler, M. Klefeld, F. Lexis, M. Paulzen, J. Schmitz, G. Schaffrath, A. Sparbrodt and G. Stollwerk during design, construction and commissioning of the instrument is greatly acknowledged.