*The passing of Hugo Rietveld, on the 50th anniversary of Rietveld
Refinement and the 100th anniversary of Powder Diffraction*

It is our sad duty to report the death of Hugo Rietveld at the age of 84
after a short illness. He leaves behind his wife, a son and two daughters
to whom we extend our heartfelt sympathy on behalf of the more than one
thousand members of the Rietveld Mailing List.

Hugo was born on the 7 March 1932 in The Hague and migrated to Western
Australia with his family, where in 1957 he enrolled at the University of
WA at the same time as Brian O’Connor and Syd Hall.  He obtained his Ph.D.
under the supervision of Ted Maslen who had studied under Dorothy Hodgkin
at Oxford. Hugo pioneered single crystal neutron diffraction at Lucas
Heights Sydney with Terry Sabine, and their first paper was published in
Nature in 1961.

Clews C J B, Maslen E N, Rietveld H M and Sabine T M (1961) Nature 192 154
“X-Ray and Neutron Diffraction Examination of p-Diphenylbenzene"

Hugo's experience with manual data collection and refinement convinced him
of the need to computerise such tasks, and at Lucas Heights and the UWA he
programmed two of the first IBM-1620 mainframes
<http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP1620.html> in
Fortran-II. After obtaining his Ph.D. in 1964 with Dorothy Hodgkin as
external examiner, (she had received the Nobel Prize for her work on
penicillin and vitamin B12), he joined the neutron diffraction group of the
Reactor Centrum Nederland in Petten and his interest turned to powder
diffraction because large single crystals were not available for the
inorganic materials of interest.

The young group at Petten including Bert Loopstra, Bob van Laar and Hugo
Rietveld first addressed the problem of overlapping powder reflections by
using a relatively long neutron wavelength (2.6 Å) with a pyrolytic
graphite filter. This spread out the long d-spacing peaks, allowing more of
them to be resolved, and is still a good solution for the magnetic
structures in which they were interested. However, for structure refinement
many peaks were still unresolved, and the shorter d-spacings needed for
high atomic resolution could not even be seen.

In a 1966 paper, Hugo already used intensities from overlapping Bragg
peaks. Along with others with the same problem, he then tried to fit
multiple peaks to overlapping regions, but with limited success. As well, a
neutron powder pattern took a whole week to collect, and the local
computer <https://ub.fnwi.uva.nl/computermuseum//X1.php> was less powerful
than the IBM-1620 - and programmed in Algol.  It was there and then that the
brilliantly simple but profound idea arose of refining the crystal
structure together with the parameters describing the peak positions and
profiles all together, as published in the famous 1969 paper.

Rietveld H M (1969) Journal of Applied Crystallography 22 65-71
“A profile refinement method for nuclear and magnetic structures”

Hugo distributed his Algol refinement program
widely, but very few papers were initially published using the method.
Discouraged by the limited funding available for neutron diffraction, he
successfully applied to become head of the library department at Petten.

One of us (AH), who had also completed his Ph.D. at Lucas Heights in 1970
and who had moved to Harwell, encountered the same problems with neutron
diffraction for structural transitions. On the advice of George Bacon, AH
visited Hugo in 1971 and brought back Hugo's new Fortran-II version of the
profile refinement program. A Harwell version
modified to model the anisotropic vibrations preceding structural
transitions, was very successful, both at Harwell and with Brian Fender's
students at Oxford, in particular Tony Cheetham and Bob von Dreele.

In 1973, when the UK joined the EEC and AH moved to ILL in Grenoble,
another Oxford student (WIFD) performed his first neutron powder
experiments on AH's new D1A high resolution diffractometer, where a powder
pattern took only one day to collect, and later only one hour. Again this
work was very successful, and the number of papers using what Terry Sabine,
in 1978, christened the "Rietveld Method" exploded, supported by new
computer programs including those of the early Oxford-Grenoble champions
Bob von Dreele and Juan Rodriguez-Carvajal. Yet it was not until 1977 that
R.A. Young and colleagues applied the method to X-ray powder diffraction,
leading to further rapid growth in the number of publications. Thousands of
X-ray publications using Rietveld Refinement are now published every year.

Perhaps the greatest acknowledgement of Hugo’s work was his receipt of the
1995 Aminoff Prize, awarded by the Royal Swedish Academy of Sciences, Two
of us (AH and WIFD), along with Juan Rodriguez-Carvajal and Ivar Olovsson,
were there to witness Hugo, accompanied by his wife and children, receive
his accolade from the King of Sweden with typical modesty, delight and
genuine astonishment at the pervasive influence of his Method across the
sciences around the world. And beyond the world - in December 2012 he was
thrilled to receive an e-mail from David Blake of the CheMin team of the
Mars Science Laboratory rover, Curiosity, who wrote saying that *he did not
think they could have convinced NASA to send an X-ray powder diffractometer
to Mars without the Rietveld Method*.

After almost 50 years, the Rietveld Method has returned to its origins in
the Netherlands, with the third of us (LvE) completing a fast new high
resolution neutron powder diffractometer (PEARL) on the Delft reactor. Hugo
Rietveld lived to see that, and last year was the guest of honour at the
opening of this new diffractometer. He, who had been honoured throughout
the world for his achievement, was honoured in his own country by a new
generation working with neutron powder diffraction and Rietveld Refinement.

Having achieved all of that, and with a loving family and friends, he will
surely rest in peace.
Alan Hewat (AH), Bill David (WIFD) and Lambert van Eijck (LvE) July 2017
*   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE *
<alan.he...@neutronoptics.com> +33.476.98.41.68
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