Focusing and imaging of cold neutrons with a permanent magnetic lens.

This paper reports imaging of objects with slow neutrons, specifically very cold neutrons and cold neutrons, at Institut Laue Langevin, using novel, permanent magnet (NdFeB) compound refractive lenses (MCRL) with a large 2.5 cm bore diameter. The MCRL focuses and images spin-up neutrons and defocuses spin-down neutrons via a large, radial magnetic field gradient.

Characteristics of the thick, compound refractive lens.

A compound refractive lens (CRL), consisting of a series of N closely spaced lens elements each of which contributes a small fraction of the total focusing, can be used to focus x rays or neutrons. The thickness of a CRL can be comparable to its focal length, whereupon a thick-lens analysis must be performed. In contrast with the conventional optical lens, where the ray inside the lens follows a straight line, the ray inside the CRL is continually changing direction because of the multiple refracting surfaces.