7-5

Neutron Focusing with a Magnetic Lens


Fig. 7-10 Photograph of a superconducting sextupole magnet for neutron focusing

A sextupole superconducting magnet is shown as installed in the cryostat


This picture.(18.6KB)

Fig. 7-11 Experimental apparatus to characterize the neutron magnetic lens

Monoenergetic, spin-polarized neutrons are delivered to the magnetic lens through a slit. The image of the focused neutrons is observed with a two-dimensional detector placed in the focal plane.


Fig. 7-12 Neutron beam profile observed with a two-dimensional detector in the focal plane

The neutron beam density has clearly been increased on the magnet axis.


Neutrons are a valuable probe for the study of materials science and bioscience for two major reasons. They penetrate material easily, since they have no electric charge, and they scatter strongly from light elements such as hydrogen atoms by means of nuclear interactions. High-flux neutron beams for materials research are available at research reactors and accelerator-based facilities, but the scope of their research is currently limited by their relatively low intensity.
In collaboration with RIKEN, we are developing a magnetic neutron lens to increase effective beam intensities within the research program "Development and Application of Neutron Optics," supported by the Special Coordination Fund for Promoting the Ministry of Education of the Japanese Government. The magnetic lens is a sextupole magnet in which six magnetic poles are placed around an annular aperture. The neutrons are refracted along the gradient of magnetic field strength and focused onto the magnet axis through the interaction between neutron magnetic dipole moments and the sextupole magnetic field. We have successfully developed a strong magnetic lens with an aperture as large as 50 mm by employing a superconducting sextupole magnet (Fig. 7-10). We have confirmed that the magnetic lens has sufficient power to focus the cold neutron beam from the research reactor JRR-3, as shown in Figs. 7-11 and 7-12.


Reference
H. M. Shimizu et al., Neutron Optics and a Superconducting Magnetic Lens for Small-Angle Neutron Scattering with Focusing Geometry, Nucl. Instrum. Methods Phys. Res., Sect. A, 529, 5 (2004).

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