A journey into inner space by Professor Bob Cywinski -3rd April 2017

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.