1. B. N. Brockhouse, Proceedings of the Symposium on Inelastic Scattering of Neutrons, International Atomic Energy Agency, Vienna, 1961.
2. R. D. Lowde, Proceedings of the Meeting on Use of Slow Neutrons To Investigate the Solid State, Stockholm, 1957.
3. We are indebted to John Uglum for preparing these filters and studying their neutron energy characteristics.