Rutherford in Manchester . by J E Geake . Manchester College of science and technology . it is now 50 years since Rutherford , working in Manchester , conceived the idea that the atom had a small concentrated nucleus , and from this idea sprang the whole of our present-day knowledge of atomic structure and our exploitation of its consequences . this great landmark in physics was celebrated by holding the Rutherford international jubilee conference early in September . it was appropriate that the conference should be held at Manchester University because , although Rutherford did valuable work at Cambridge and at McGill , it was his Manchester period which produced the most important results , and the discoveries with which his name is mainly associated . it was also appropriate that there were two parts to the conference - a commemorative session in which some of the surviving members of Rutherford &apos;s Manchester team took us back by their reminiscences to those great days of the past , and also a full-scale conference setting out the present state of our knowledge of the nucleus . to keep up with a rapidly-changing subject such as this , one must not spend too long looking backwards . of those closely associated with Rutherford in Manchester , Marsden , Darwin , Chadwick , Andrade and Niels Bohr were all present , and it was greatly regretted that William Kay , Rutherford &apos;s laboratory steward and personal assistant , to whom he acknowledged a great debt , did not live to be present at these celebrations ; he died in Manchester only a few months ago . the main commemorative session of the conference consisted of the reminiscences of Sir E Marsden , Sir Charles Darwin and Professor Andrade , and this was followed by a ceremony at which honorary degrees were bestowed . during the week , delegates saw something of the local Derbyshire scenery , visited Jodrell Bank and A.E.I at Trafford Park , were received by the Lord Mayor at a lavish reception in Manchester &apos;s impressive Victorian Gothic town hall , and rounded off the week at a special concert given by Sir John Barbirolli and the Hall&amp;eacute; orchestra - the source of another of Manchester &apos;s claims to renown . concurrently with the conference an exhibition of things associated with Rutherford was held - photographs , letters , models and , most interesting of all , some of his actual apparatus , including the piece said to have been his pet - the superb piece of glass-blowing by Baumbach which made possible the spectral identification of a-particles as helium . the letters on view gave some interesting glimpses into the organization and economics behind the scene . there was Schuster &apos;s letter offering to hand his chair over to Rutherford ( then at McGill ) , Rutherford &apos;s answer making careful enquiries about the financial arrangements for research , and Schuster &apos;s detailed reply saying how he spent his annual grant for teaching and research ( all &amp;pound;450 of it ! ) and by how much it was safe to overspend without getting into trouble . Rutherford was satisfied , and came in 1907 , and thus began the work in Tom Tiddler &apos;s field , which was how Rutherford referred to one of the most celebrated research groups in the history of physics . Rutherford owed a considerable debt to Schuster for handing over to him a well organized and relatively well equipped laboratory and teaching department . while the glory of discovering the nucleus falls to Rutherford , it was entirely owing to Schuster that the work was done in Manchester . as early as 1906 Rutherford , then at McGill , had realized , from the observation that an a-particle beam was spread out slightly by passing through a mica sheet , that there must be surprisingly large electric fields within atoms , but it was not until 1911 that the idea of the nucleus was finally conceived . a trivial defect in an a-beam tube , which was cured empirically by inserting brass washers to confine the beam , suggested that a-particles were reflected by metals . Rutherford suggested to Marsden , a second-year student ( in those days undergraduates were given small research projects as part of their training ) , that he should follow this up . after some initial difficulties , because the available a-particle sources were too weak , Marsden eventually obtained a stronger source and did the experiment which is seen in retrospect to be one of the most profitable ever carried out . he directed a beam of a-particles at metal foils , and observed the range of angles at which they came off . the result was staggering ; although most of the particles were only deflected slightly , a few were turned through large angles , and a very few came almost back along their tracks . as Rutherford said later , it was as if one fired 15 in shells at tissue paper , and found that occasionally they bounced back ! Marsden told Rutherford what he had observed , Rutherford questioned him about the experiment to convince himself that it was all right , and that was all for several weeks , until a Sunday evening in the autumn of 1911 . Rutherford had invited several of his research workers to supper in his house at Withington , as he often did , and while they were chatting after supper Rutherford suddenly came out with his first ideas about the atomic nucleus ; before they went home he asked one of them , Darwin , to check his hasty derivation of the scattering law to be expected when a-particles were deflected by point nuclei . they even discussed , on that first evening , the idea that , if the nucleus were not quite a point , departures from the law at close approach could yield information about nuclear structure . although Rutherford did not live to see powerful enough scattering experiments performed , this is now the basis of modern methods of investigating the structure of nuclei and nucleons . in the months that followed Geiger and Marsden carried out more sophisticated scattering experiments than the one which had revealed the effect , and actually measured the angular distribution of the scattered a-particles . the results confirmed Rutherford &apos;s scattering law and therefore the validity of the assumptions he had made in deriving it , and led in 1913 to a group of three papers which laid the foundations of nuclear physics . the commemorative session of the conference produced reminiscences about several of Rutherford &apos;s group in Manchester ; of Moseley whom Sir Charles Darwin ( who worked with him ) described as the hardest-working person he had ever known , and who was an expert in finding a meal in Manchester at 3 a.m ; of Niels Bohr who was a very comforting theoretician with great skill in bridging the gap between startlingly new theoretical concepts and classical ideas ; of Robinson , a keen music-hall addict - and indeed of the music-hall origin of the correct intonation to Rutherford &apos;s nickname of Papa . while these reminiscences of the physics of 50 years ago were appropriate and entertaining , it was right that most of the time at the conference should be concerned with the physics of the present . there were nearly 200 contributed papers , and for those who want a detailed picture of the present state of nuclear physics these papers will shortly be published as a 750-page volume . the conference sessions , however , consisted of the presentation of invited papers , each intended to summarize a different aspect of the subject . thirty years ago Rutherford said , it is my personal conviction that if we knew more about the nucleus , we should find it much simpler than we suppose . I am always a believer in simplicity being a simple fellow myself . the subject at present seems a long way from this simplicity ; parts of the conference seemed to be in a foreign language , and at one point there were so many rival theories that they were referred to by reference numbers . perhaps we need another Rutherford . the main topics reviewed included nuclear forces , nuclear structure , and the interactions with outside particles from which most of the evidence for nuclear properties is obtained . there was also a paper on the limitations and possibilities of the instruments for nuclear investigation , and another , rather off the main line , on cosmological dating by nuclear methods . it has long been understood that the attractive forces between nucleons ( the neutrons and protons which comprise nuclei ) were somehow concerned with the interchange of a particle ( the p-meson or pion ) between them . there has also been evidence that sometimes two pions are in transit between the interacting nucleons at the same time , and the possibility of this occurrence modifies the force to be expected ; although the theory of this process is still an unsolved problem , models describing the resulting behaviour have been proposed . what has only recently been confirmed - in fact it was announced at this conference - is that occasionally three pions at a time are involved . these three pions may actually be joined together transiently as a compound particle during the interchange process ; indeed , theoreticians have been invoking a compound particle of this type for some time . there now seems to be evidence for its existence . a nuclear model which has been surprisingly long-lived and successful is the shell model , which was first proposed 25 years ago . this assumes nucleons to occupy energy levels , obey quantum-number selection rules , and group themselves into closed shells in a manner analogous to the electrons outside the nucleus . this theory was given a new lease of life by adding the concept of nucleon spin , which undergoes coupling with the nucleon orbital motion . the presence of any nucleons in addition to the numbers which comprise closed shells will tend to distort the otherwise spherical shape , but these distortions were ignored in the approximate treatment of the problem . if there are only a few nucleons more ( or less ) than complete shells the mean distortion is indeed small , but the theory has been extended to include vibrations about this mean shape . with larger numbers of extra nucleons , mid-way between the numbers comprising complete shells , the nucleus is much more distorted , and rotational modes become important . with these larger numbers of extra nucleons it is no longer practicable to treat them singly and only their collective behaviour is considered . the way nucleons are arranged in a nucleus , and especially in the surface regions of heavy nuclei , is another topic of current interest . some workers consider that nucleons tend to be found singly or in pairs in the nuclear surface , while others believe that there is more than a random chance of their being found in groups of four , although the grouping may be of a very transitory nature , the particles perhaps remaining associated for 10-22 of a second or so . indeed , it is known that if a single particle , say a neutron , hits a nucleus it may result in the ejection of an a-particle ( an assembly of 2 protons and 2 neutrons ) . however there was a vigorous argument at one session of the conference as to whether this a-particle existed in the nuclear surface and was knocked out by the neutron , or whether the incident neutron simply collected three more particles and itself became part of the resulting a-particle . the evidence seems to be in favour of the former idea - that the four particles were already associated before ejection . soon after Rutherford came to Manchester he and Geiger , using Geiger &apos;s new a-particle counting techniques , were able to make the first measurements of the half-lives of radioactive elements . nearly 20 years later , when Aston measured the relative abundances of the isotopes in lead ( the end-points of radioactive decay series ) from a lead-uranium ore , Rutherford realized that this , combined with his half-life measurements , could yield estimates both of the age of the earth ( i.e the time since solidification ) and of the time since the actual formation of the heavy elements . Rutherford &apos;s results increased the estimated time-scale for the earth &apos;s development by a factor of more than 10 over the currently accepted estimates due to Kelvin , and this advance produced the newspaper headline doomsday postponed . apart from Rutherford &apos;s assumption that the amount of 235U initially formed was at the most equal to that of 238U , modern cosmochronologists would agree with him . it is now believed that 235U was produced initially in greater abundance than 238U , and this , plus minor changes in the accepted values of other constants , pushes the estimated time since the formation of the heavy elements ( loosely called the age of the galaxy ) up from Rutherford &apos;s estimate of 3.4 x 109 years to about 20 x 109 years . 