Focusing Cold Neutrons with Multiple Biconcave Lenses

for Small-Angle Neutron Scattering

Sung-Min Choi, John. G. Barker, and Charles. J. Glinka

NIST Center for Neutron Research

National Institute of Standards and Technology, Gaithersburg, MD 20899

Y. T. Cheng

NeuTek, Darnestown, MD 20878

P. L. Gammel

Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974

The focusing of a cold neutron beam by multiple biconcave lenses has recently been proposed by scientists at Lucent Technologies 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 conventional 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.