Bob Cywinski has already given three other talks over the years to the Club. He is now retired and spends much time abroad and feels that this may be his last public talk.
Bob started his talk by very briefly covering the basic physics of neutrons.
Atoms have a tiny central nucleus with electrons whizzing around outside it. The electrons are fundamental particles. However, the nucleus is made from collections of two smaller particles: protons and neutrons. They have very similar masses, but the proton has a positive charge whereas the neutron is not charged (hence the name neutron – neutral). The neutron helps keep the nucleus together. They were first discovered by James Chadwick in 1932 following observation by Bothe on bombarding beryllium with alpha particles.
Bob mentioned the DeBroglie wavelength expression for neutron waves much to the mystification of much of his audience; in order to show how neutrons can be used to jostle particles. Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material. A sample to be examined is placed in a beam of thermal or cold neutrons to obtain a diffraction pattern that provides information of the structure of the material. The technique is similar to X-ray diffraction but due to their different scattering properties, neutrons and X-rays provide complementary information: X-Rays are suited for superficial analysis, strong x-rays from synchrotron radiation are suited for shallow depths or thin specimens, while neutrons having high penetration depth are suited for bulk samples.
This means that steel castings can be examined to “see” their atomic structure and Bob had been involved with examining railway lines after a recent Reading rail crash as well as carriage wheels that proved to have been incorrectly designed.
From its start in 1940’s neutron radiography has been used increasingly in different areas of “science”. In the 1950’s it was physicist that used it; in 1960’s chemists became interested; in 1970’s biologists and engineers were using it and since 1990’s all branches of science are using it and it has tremendous social implications.
This radiography required a source of neutrons and these came from nuclear reactors. In 1990’s there was a fear of a “neutron drought” as reactors were closed down. Today spallation sources are used. Bob was much involved in trying to have such a facility constructed at Burn near Selby. It would have brought much research and jobs to the region for decades to come. The cost was about the same as staging an Olympic Games. Guess which one got the money?
Whilst the talk required concentration by the audience, it was lavishly illustrated by superb and wonderfully colourful illustrations and gave an insight into a major area of science that the writer of this blog was very ignorant of. As a Club, we are very lucky to have had Bob educate us in such a pleasing way.