The focusing of a cold neutron beam by multiple biconcave lenses
has recently been proposed as a practical means of extending the
lower limit of Q in conventional, long flight-path small-angle neutron
scattering (SANS) instruments. To test the feasibility of this
approach, we have carried out extensive measurements on one of the
30 m SANS instruments at NIST of the focusing characteristics of a
set of 28 biconcave MgF2
lenses. The focused beam profile has been
measured over several orders of magnitude using high resolution
neutron auto-radiography. The focusing lens configuration
outperforms the pinhole collimation at Qmin lower than 0.004 Å-1. At
Qmin = 0.001 Å-1, the intensity gain of the lens configuration over the
pinhole collimation is greater than one order of magnitude.