Slow neutron spectroscopy and the grand atlas of the physical world

Abstract

On October 12, 1994, telephone communications from Stockholm ensured that I would have the privilege of giving a Nobel Lecture, for which I must thank all those involved in arranging for this great and surprising event of my life. But I had to go back some thirty to forty-five years, first in memory and then in the entropy of my files and library. The lecture was given on December 8, 1994 (and subsequently on several occasions). This written version covers the same ground, though sometimes in different order, with a little additional material from my preparations, which time prevented including in the spoken lecture. In August 1950, when I joined the Physics Division of the Chalk River Nuclear Laboratory, it was 18 years since the identification of the neutron as being emitted in some radioactive processes and 14 years since verification of the supposition that neutrons would exhibit wave-particle duality. A considerable body of theory was available in the open literature-which was still small enough so that one person could have read all that was then available. There had been significant measurements of total cross sections using neutron beams produced by cyclotrons. Self-sustaining reactors employing the neutron-induced fission of uranium had been demonstrated and full-scale models which emitted potent beams of both fast and slow neutrons had been constructed. Slow neutron beams from reactors were already in use at several laboratories (including Chalk River) for studies of crystals and other forms of matter. The works of E.O. Wollan and C.G. Shull at the Oak Ridge National Laboratory were particularly significant because they included the first studies of a number of phenomena and because they already presented values of scattering power for neutrons of a substantial number of elements. This history is discussed in the lecture of my senior colleague and co-winner of the 1994 Nobel Prize in Physics, Clifford Shull. To 1951, some studies had been made of the elastic scattering of monochromatic slow neutrons by specimens in the form of powdered crystals (the neutron analog of Debye-Scherrer patterns for X-rays), which led to improved crystallographic understanding of the substances involved. And there

Observation of Sub-Bragg Diffraction of Waves in Crystals

“…Frequency gaps called stopgaps, emerge for which waves cannot propagate inside crystals due to Bragg diffraction. Bragg diffraction is important for crystallography using X-ray diffraction [3] and neutron scattering [4]. Diffraction determines electronic conduction of semiconductors [1,2] and of graphene [5], and broad gaps are fundamental for acoustic properties of phononic crystals [6,7] and optical properties of photonic metamaterials [9, 10].…”

Introduction to the History of Semiconductors

“…Brockhouse published a review paper in 1995. 91 The optical phonon energy of 63 meV is something semiconductor people have to memorize.…”

Radiative neutron capture as a counting technique at pulsed spallation neutron sources: a review of current progress

“…Neutron scattering techniques are able to provide information on structure and dynamics of condensed matter. 'Where atoms are' and 'how atoms move' was the great achievement of Shull and Brockhouse using thermal neutron scattering [1][2][3][4]. Since that period these techniques were continuously refined and strengthened, extending the horizons of scientists working in different fields.…”