Bob Golub

Norman Ramsey at the ILL

by Bob Golub, October 2022

If you look at the first chapter in Norman Ramsey’s book "Spectroscopy with Coherent Radiation" [1] you see immediately what an amazing productive life he had, covering a very broad range of activities. In view of this the comments below seem rather petty but nevertheless they represent my memories of interactions with Norman over many years.

Bob Golub was at the University of Sussex, England, when he came to the ILL in 1972 for the development of a Ultra Cold Neutron (UCN) source and for the search of an Electric Dipole Moment (EDM) of the neutron. In 1980 he moved to the Technical University Munich (T. U. M.), in Germany and continued his work at ILL where he constructed the first superthermal UCN source based on superfluid 4He and invented a new kind of neutron scattering method to study properties of the superfluid. He also co-invented the Neutron Resonance Spin Echo technique with Roland Gähler.

The neutron is made of three quarks with negative and positive fractional electric charges the sum of which is zero and, hence, the neutron is electrically neutral to the outside. However, if negative and positive charge distributions inside the particle do not coincide the neutron would exhibit a non zero - but incredibly small - Electric Dipole Moment (EDM). Current theories say that this can only occur if both parity symmetry (P) and time reversal symmetry (T) are violated, and this is also one of the necessary conditions to explain the observed matter anti-matter asymmetry of our Univers. That’s why, since Ramsey’s first EDM experiment, scientists are working so hard to try to observe the EDM of the neutron. <>

Most solide state physics spectrometers use hot to cold neutrons (temperature: 1500K to 2,5K, wavelength: 2,5Å to 20Å) but Ultra Cold Neutrons (temperatures 500Å) are much praised for particle physics due to their very special properties. E.g., as photons are reflected by mirrors, UCNs are reflected by material surfaces under any angle and cannot cross them. Thus they can be stored in bottles which gives scientists the possibility to measure their properties for a very long time. This bottle storage is todays best technique to measure the neutron lifetime (about 15 minutes), a crucial parameter to current particle physics theories and to explain the isotope abundance of the Universe.

The magnetic moment gives the magnetic strength and orientation of an object that produces a magnetic field. The neutron has a magnetic moment and hence behaves as a tiny compas sensitive to its magnetic environment. The accurate knowledge of the magnitude of this magnetic moment is crucial to the many solid state physics and fundamental physics experiments and techniques where neutron magnetism is involved.

The neutron is like a tiny compas the needle of which (the spin direction) rotates as a function of the magnetic field direction and intensity it crosses. Hence the spin of the neutron is not expected to rotate when it crosses a non-magnetic material. However, unlike other fundamental forces, the weak interaction which controls the interactions between the quarks inside the neutron is known to be chiral since 1957. In other words this force does not acts the same on neutrons with opposite spin directions. In 1998, Ramsey and collaborators observed this tiny effect for the first time in the isotope 117Sn and then in others isotopes. This offered physicists a new way for the study of parity violation.

It was initially assumed that an experiment conducted in a mirror should be the same one conducted in our world. Norman Ramsey was the first to check that at the particle level by searching for an Electric Dipole Moment (EDM) of the neutron which can only exist if that symmetry does not exist (parity violation).

My first contacts with Ramsey

In the 60’s I was a grad student in MIT’s Atomic Beams lab. The lab was under the nominal direction of J.R. Zacharias who had been, with Norman Ramsey, a student of I.I. Rabi (Nobel Prize in Physics winner in 1944) who pioneered atomic beam work in the USA. They both (Zacharias and Ramsey) went on to work on the Manhattan project and after the war were given chairs at MIT and Harvard respectively. Rabi was proud of being a rather abrasive character and was followed in this by Zacharias. Ramsey on the other hand was very personable. I learned the field from Ramsey’s encylopedic book: ”Molecular Beams[2] so I had great respect for him from the beginning of my career.

The only direct contact I had during those years was when Ramsey visited the Zacharias lab at MIT in the company of Ken Smith, a professor at the University of Sussex in the UK, whose group I later joined. On one occasion Ramsey gave a talk at Harvard on his neutron Electric Dipole Moment (nEDM) experiment which we had been analyzing carefully in our lab. He repeated several times that it was a wonderful experiment because it had no systematic errors which I knew to be false. Finally in the conclusion he again stated there were no systematic errors but then said "Oh yes there is just one" (known as the v cross E effect), which had been recently introduced to the field by Sandars and Lipworth [3]) which he continually down-played. Then as the result was just compatible with a null effect (zero EDM for the neutron) he did a kind of intellectual dance emphasizing the possibility that they were seeing a non-zero effect.

During the course of the years Zacharias had alluded several times to Ramsey’s alleged character defects. At the time I ascribed this to jealousy on Zacharias’ part as Ramsey seemed to be the more successful physicist, responsible for several significant innovations, including the Hydrogen maser, while Zacharias’ major successes were the Cesium beam atomic clock and as an advisor to the government and military. He was strongly involved in the decision to build the early warning radar network. There was a feeling of intense competition between the two, at least on Zacharias’ side.

The early nEDM project and others

After a 2 year post-doc at Brandeis university (1968) I joined Ken Smith’s group at Sussex University where there was an active beam experiment searching for a neutron EDM led by Mike Pendlebury. Our interests turned to Ultra-Cold Neutrons (UCN) and we developed a design for a UCN source that we eventually proposed to the ILL.
The director at the time (Rudolf Mössbauer) invited us to Grenoble to discuss the matter (probably 1972). When we arrived in Grenoble we were told that we would be joined by Norman Ramsey who was also interested in the neutron EDM. This led to the establishment of the "Sussex, Harvard, ILL collaboration" (later broadened to include the Rutherford laboratory), Ramsey’s neutron beam nEDM experiment being moved from Oak Ridge to ILL, and to the construction of the first UCN source at the ILL (with the strong technical and scientific support of Paul Ageron) and the construction of the original Sussex-ILL UCN apparatus to search for the nEDM.

Ramsey regularly visited the ILL and (less frequently) Sussex during the years of construction and measurement. He had a special grant that allowed him to support a grad student at ILL. The first was Geoff Greene (1975), who was a Harvard student whose PhD was the measurement of the neutron magnetic moment on an ILL neutron beam. Geoff remained as a postdoc and was joined by Blayne Heckel, another Harvard student whose PhD was the neutron spin rotation in the Forte apparatus (see below). After his PhD Blayne remained as a post-doc and started working on the UCN nEDM experiment. In 1983, Blayne was appointed as an assistant professor in Seattle (University of Washington) and joined Fortson’s group there. Steve Lamoreaux was his PhD student. After Steve’s PhD (Hg EDM) he went to ILL to work on the nEDM financed by Blayne’s grant. We have collaborated ever since.
All of them became prominent physicists.

Anecdotes of the early days

Some years after the establishment of our nEDM collaboration (probably in 1976) I had occasion to visit Harvard University. Norman proved to be a magnificent host arranging many interesting activities for me. One time we had lunch with Sheldon Glashow and Steven Weinberg. He also invited me to a dinner at an exclusive Harvard club (I forget the name). The rules were that every member had a key to the club’s building but no one could open the door for anyone else. Guests were allowed if accompanied by a member. As Norman was busy for the early part of the evening he arranged for me to meet another member on a street corner in Cambridge and we then walked to the club. Norman was to join us later. I don’t remember any of the conversation but toward the end of the dinner the famous philosophy professor fell out of his chair trying to make a pass at the young lady sitting next to him.
Norman was always a tremendous presence, being very tall and having a head of completely white hair.

One time there was a fancy dinner at some chateau near Grenoble (perhaps the Chateau de Sassenage). Ramsey and Mössbauer (then director of ILL) sat together and talked while every one else listened. My memory is that Ramsey was running circles around Mössbauer, who could not match Ramsey’s intellectual power.

Ramsey was almost always a supporter of the scientific case in any argument, regardless of the personalities involved. He was a strong supporter of any new innovations such as the superfluid Helium source of UCN developed by Mike Pendlebury and myself and once said we were in the ’year of cooling’ as we were discussing this in the same year as accelerator beam cooling was developed. After reading some papers from the Dubna group, which was more advanced in their development of a UCN experiment to search for an nEDM, I understood that the fact that a cylindrical magnetic shield is more efficient in the direction perpendicular to the axis of the shield meant that the axis of our cylindrical UCN storage chamber should be perpendicular to the shield axis. For some reason Ken Smith was vehemently opposed to this idea. When the subject was discussed at a meeting with Ramsey, he immediately supported the idea as "being best for the physics”.

Search for a neutron electric dipole moment (nEDM) at the ILL

Another example concerning the search for a neutron EDM (nEDM) at the ILL:
An analysis of the data based on taking weighted averages of the magnetometer data and subtracting from a weighted average of the nEDM data resulted in a non-zero result for the nEDM. Mike Pendlebury announced it at a conference. Steve Lamoreaux was suspicious and undertook his own data analysis which revealed strong correlations between the magnetometers and the electric field. The results of this analysis were consistent with a zero value nEDM. This resulted in some heated arguments as the discovery of a non-zero EDM would have been a considerable coup.
As soon as he saw Lamoreaux’s results Norman declared they were correct. He even took the unusual step, following a meeting where the issue had been strongly argued, of writing to every member of the collaboration, saying that he agreed with the correlation analysis and that it was the correct way to analyze the data. Technical details are discussed in the book "Ultra-Cold Neutrons" by Golub, Richardson and Lamoreaux [4].

Parity violating neutron spin rotation

Mario Forte, working in Italy, had built an apparatus to look for a parity violating neutron spin rotation on a neutron passing through solid matter. Ramsey was an avid supporter of the idea and arranged for Forte’s apparatus to be shipped to the ILL to be worked on by some of his students (G. Greene was a post-doc on that experiment named S43 and installed on the H142 guide tube). This initiated a line of research that is still active.
In addition to Geoff Greene’s comments on that experiment I remember there was an incident concerning the isotopically pure Tin samples. Oak Ridge claimed that the returned sample was natural tin and the pure isotope sample had somehow disappeared. Probably the samples had somehow got mixed together. At one stage Norman was worried that he would be asked to pay for the lost isotope but of course that was impossible. I do not know how the issue was resolved but he was not required to pay.

Norman’s company

It was always very pleasant and stimulating to be in Norman’s company. He had so many interests and experiences that he always had something new to relate. He had been on the committee to investigate the Kennedy assassination and worked on the Manhattan project. There is a photo of him standing next to the atomic bomb on the Pacific Island from where it was launched. As far as I remember he never discussed his work on the Manhattan project [5] but did tell us about the Kennedy assassination committee. He was convinced by the physical evidence that all the shots had been fired from the same position.

He had a booming voice [6]. Once a bunch of us went to a restaurant in Grenoble and it was snowing. I don’t remember the details but the result was that I offered to drive Norman and his then new wife back to their hotel, but I warned them that there was no back seat in my Citroen DS as I had removed it in order to transport some books. On the walk to my car we got separated and I heard Norman’s booming voice, coming from half a block away saying to his wife, ”I have perfect confidence in Bob, if he says there is no back seat then there is no back seat”.

One time we were all at some social event and the talk among the ladies had turned to fashion. Norman piped in with the statement (with a straight face) that he preferred the ”Sears Roebuck working man’s overall suit” because it had lots of pockets for tools.

The first ultra-cold neutron nEDM experiment

When we were constructing the first Ultra Cold Neutron nEDM experiment (UCN-nEDM) I would often complain that some material was incompatible with a good vacuum. The usual reply, I think from John Morse, was ”there is so much shit in there that a little more wouldn’t matter”. I eventually made a poster with this statement composed of cut out letters with different fonts, like a ransom note, and pasted it on the apparatus one night, as what I expected would be seen as a joke. The next morning everybody knew it was I who did it and Norman seemed particularly upset and remarked something like ’they should stick him (me) in there’.

There was also an incident when during a later run of the nEDM experiment one of our post-docs proposed an unorthodox method of data analysis which gave the result of a non-zero EDM of the neutron, a sensational result if correct. The only problem was that the observed value of the nEDM changed with time. The implications of the technique were that the noise in a signal could be reduced below the conventional limits set by the observation time so it was obviously (to me anyway) false. Nevertheless Norman remained an adamant supporter of this method until a search in the library revealed a physical explanation for the false results.

Some problems arose when the nEDM collaboration was preparing its first publication. Ramsey was strongly opposed to referring to the thesis of one of the Sussex grad students. In addition the first draft had neglected to give any reference to the proposers of the ’v cross E’ effect. When I suggested in a written comment, that we should refer to the original proposers of that effect he replied to the effect that ’I don’t know who Golub means. Should we refer to Maxwell or Einstein?’ knowing full well that nobody in the EDM field had been aware of this effect before the work of Sandars and Lipworth. While this seems like a minor event in the broad scheme of things I think it is worth mentioning.

Nobel prize winner

After receiving the Nobel prize Ramsey magnanimously used half the proceeds to buy HP programmable calculators (the most advanced and most expensive at the time) for all his former colleagues and co-workers.

It was common knowledge at the time that Ramsey had been awarded his Nobel for his decades long work on the nEDM, but, as a nEDM had not been discovered, it could not be cited as the reason for the prize, and the separated oscillating fields method had been chosen as a kind of surrogate. The fact that the Hydrogen maser, a much more significant achievement, had not been cited is consistent with this interpretation.

1- Norman Ramsey (1998) Spectroscopy with Coherent Radiation, World Scientific. DOI: 10.1142/3581
2- Ramsey, N. F., Molecular Beams, Oxford University Press (First edition 1956, Reprinted 1986).
3- Sandars P.G.H.and Lipworth E. (1964) Phys. Rev. Lett. 13, 718-20.
4- "Ultra-Cold Neutrons" by Golub, Richardson and Lamoreaux (1991) Ed. Taylor and Francis, p. 203.
5- "Norman had been demanded to participate in the Manhattan project in Los Alamos. This was probably the only topic he felt uncomfortable to talk about." (2022) Roland Gähler private communication.
6- "We invited him a few times for dinner in our house in Meylan - he filled the whole house with his deep sonorous voice. One evening he asked Katie for a needle and some dark thread. He had come to France with only one pair of trousers, and this got a hole when working at the ILL-EDM. He rejected help and he repaired it himself. Norman had grown up in a modest environment." (2022) Roland Gähler private communication.