Date Published: March 01, 2018
Publisher: International Union of Crystallography
Author(s): Bob van Laar, Henk Schenk.
Around 1965 at the Reactor Centre Netherlands at Petten, Loopstra, van Laar and Rietveld developed ‘profile refinement’. Although Loopstra had the idea, van Laar worked it out mathematically and Rietveld wrote the computer program, the essential contributions of the first two are forgotten when using ‘Rietveld refinement’.
In the 1950s the Dutch government decided to set up a nuclear reactor centre in Petten, the Reactor Centre Netherlands, RCN. The construction started and some scientific co-workers were hired and sent abroad to learn how to work with the future equipment. On the list of future activities were neutron scattering and neutron diffraction, the latter being the focus of this article.
The neutron physics group at RCN Petten originally consisted of one person only, Bert Loopstra, who got his training in crystallography with Carolina H. MacGillavry in Amsterdam and worked among others on scattering factors (Berghuis et al., 1955 ▸). Loopstra was hired in 1955 by the group constructing RCN and sent to Kjeller, Norway, to practice neutron scattering work. In the same period Jaap Goedkoop, the scientific Director of RCN, was also in Kjeller (Goedkoop & Loopstra, 1959 ▸). Among others Loopstra used neutron powder diffraction in Kjeller to locate the hydrogen atoms in CaH2 (Bergsma & Loopstra, 1962 ▸).
After Rietveld had settled into his new environment Loopstra explained his ideas for addressing the problem of overlapping peaks by using the complete observed profile of the powder pattern. van Laar described to him how the powder pattern depends on collimation and scattering angle, and contributed his formulae for calculating the magnetic contribution, unfamiliar to classical crystallographers.
Using Google Scholar to search for the citations to Rietveld’s 1967 and 1969 papers we found until 1973 only papers from the RCN and their relations in Kjeller, Munich and at PSI Switzerland. These concerned mainly magnetic structure refinements.
One of the most important ideas in powder diffraction is cited thousands of times as the description of a computer program. It would perhaps be more appropriate to cite instead the earlier Loopstra & Rietveld (1969 ▸) paper as the scientific basis and applications of the profile refinement method; it currently has only 0.9% the number of citations of the Rietveld (1969 ▸) paper. Rietveld left science before the importance of the work he had done with Loopstra and van Laar was recognized. Even later, profile refinement was confined to the relatively small community of neutron scatterers, before becoming a specialist technique in X-ray powder diffraction. It was only really adopted by the wider crystallographic community 20 years later, after the original small group at Petten had all left science.
(i) In his book in Dutch ‘De Republiek der Kerngeleerden’ (The Republic of Nuclear Scientists), about all science at the RCN, the Dutch scientific historian C. D. Andriesse (2000 ▸) concluded about the profile method: