Fig. 3-9 Transmission electron microscope images of Ni/Ti multi-layers polished using ion beam Sharp interfaces were observed by Ar+ ion irradiation at low energy and low angle. The thickness of each layer is 50 angstrom.

Fig. 3-10 A super-mirror guide tube first installed in the reactor pool of JRR-4 has succeeded in achieving a neutron intensity of 107 n/cm2/s at low background. Furthermore, it is being installed in the JRR-3 beam hall.

The super-mirror is the most important neutron control device utilized to transport, deflect, focus and polarize neutron beams which are generated by reactor or accelerator sources. A high performance super-mirror is required to consist of nearly a thousand layers with variable thickness and a minimum thickness of a few nano-meters, so that atomic scale control on multi-layer thickness has been required in the deposition process to keep sharp interfaces covering a whole multi-layer structure. We have succeeded in reducing the interface roughness of a Ni/Ti multi-layer by using an Ar+ ion polishing technique (Fig. 3-9). In the process of ion polishing, particles which are in a valley of the surface can be removed by recoil effects after ion bombardment. A super-mirror guide tube with a length of 10 m installed into a prompt gamma-ray analysis system at JRR-4 has made an increase of the neutron intensity by four times at a sample position, and it has made the system workable (Fig. 3-10). These kinds of advanced control devices using super-mirrors have been developed for beam lines at reactors or for a high intensity pulsed neutron source which is under planning.

Reference K. Soyama et al., Enhancement of Reflectivity of Multi-Layer Neutron Mirrors by Ion Polishing: Optimization of the Ion Beam Parameters, J. Phys. Chem. Sol., 60, 1587 (1999).

Select a topic in left column