Focusing cold neutrons with multiple biconcave lenses for small-angle neutron scattering

The focusing of a cold neutron beam by multiple biconcave lenses has recent ly been proposed as a practical means of extending the lower limit of Q in conventional, long flight-path small-angle neutron scattering (SANS) instru ments. To test the feasibility of this approach, we have carried out extens ive measurements on one of the 30 m SANS instruments at NIST of the focusin g characteristics of a set of 28 biconcave MgF2 lenses. The focused beam pr ofile has been measured over several orders of magnitude using high resolut ion neutron auto-radiography. The focusing lens configuration outperforms t he pinhole collimation at Q(min) lower than 0.004 Angstrom(-1). At Q(min) = 0.001 Angstrom(-1), the intensity gain of the lens configuration over the pinhole collimation is greater than one order of magnitude.