Advanced Certificate in Powder Diffraction on the Web Chapter 7 School of Crystallography, Birkbeck College, University of London

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Aims & Objectives

The aim of this chapter is to explain the "why and how" of powder neutron diffraction. This chapter continues on from the previous sections on both laboratory and synchrotron powder X-ray diffraction. You will find that much of the material in this section is of a descriptive nature.

Given the nature of powder neutron diffraction, this subject is best taught with reference to specific instruments, in contrast to the laboratory X-ray case, where reference to specific commercial manufactures was avoided whenever possible. However, it is important to distill from the material the general concepts involved rather specific details about certain neutron diffractometers referred to in the text.

Specific learning objectives for this section are given below:

• Following a short introduction to the subject, you will learn first about the properties of the neutron in order to understand the differences between neutron and X-ray powder diffraction. This then leads on to the subject of how to detect neutrons, and the characteristics of the samples used in powder neutron diffraction experiments.
• Neutrons are generated by two distinctly different types of source:

  Firstly, you will learn about the properties of neutrons produced by a nuclear reactor, how single wavelengths are produced by neutron monochromators, and how powder diffractometers are designed for either high-resolution or high-flux experiments at a reactor source. This is followed by a discussion on data acquisition, with special reference to calibration methods.

  In the second section, you will then learn about the properties of neutrons generated at a pulsed source. In order to exploit the nature of this source, you will learn about time-of-flight concepts, the characteristics of TOF powder diffractometers, and the differences between data collection at constant wavelength and at constant angle.

External Links

Given the nature of neutron scattering, there are potentially many hypertext links to information at the various national and international facilities. Links are given here for two specific sites to which reference is frequently made throughout this section. In addition, a further link is made to a source of links to world sites in general. For those less familiar with the properties of neutrons, a link to web site with scattering cross-sections is provided.

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