Friday, 27 June 2014

Nuclear women in Bulgaria

One thing that my partner pointed out to me about the group of people attending this workshop in Bulgaria is that there are a lot of women present.  I guess it is true.  I had a look through the delegate list at the back of the booklet, and counted 27 male and 16 female attendees.  I don't know if that really counts as a lot, but it must say something about most physics gatherings she has been in that the group assembled here seemed out of the ordinary.  Good for Bulgaria!  The number of female nuclear theorists with permanent positions in Bulgaria (pop 7m, GDP USD0.1t) who are attending this small workshop is around the same as the number of nuclear theorists of both sexes in the entirety of the UK (pop 70m, GDP USD1.5t) with permanent positions.  

Anyway... A conference update:  I have generally enjoyed all the talks, but particularly I enjoyed learning a neat mathematical trick from Nikolay Minkov to do with factorising the Schrödinger equation in a way I will save describing further until I have successfully got mathjax working in Blogger.  I liked Xavier Viñas's work on attempting to write down a nuclear energy density functional based on a matching of a polynomial form of the density functional to give a realistic equations of state, with small additions to give good results for more or less all finite nuclei.  This is the sort of spirit in which energy density functionals should probably be used, rather than what I tend to do, starting from the Skyrme interaction.  It was nice to hear about a new facility being set up in Yerevan, in a talk by Roza Avetisyan.  A cyclotron mainly for medical isotope generation is being set up, with a beam line for nuclear physics experiments which will be a good place to train students in the arts of nuclear techniques, and some interesting ideas of reactions to look at were presented.

Yesterday saw our excursion day.  It was quite a long day, running from 9:15 to 19:15,  taking in a reconstituted Roman hill fort near Samokov, then lunch, then a tour round the Rila Monastery.  Alba, my 8mo daughter did an admirable job of coping with the long coach journey, the being carried round the sites, and the cabbage-rich lunch.  She continued to be a more or less welcome diversion to the other attendees, never getting to the stage of screaming constantly in a confined coach for hours on end, which would no doubt have changed other people's ideas about having babies as accompanying people at conferences...

The picture is a view from the hill fort.  Mostly, of course, it's just a tree.  You can see a bit of reconstructed wall, and some indication from the plain below of how high up we were.  The funicular was broken for the journey up, by the way, and pushing the pram up the path was hard work.  Special thanks to Rajdeep Chatterjee from Roorkee for helping here!

Monday, 23 June 2014

Rila, again

Like last year and the year before, I'm at the Nuclear Theory Workshop, organised by the group in Sofia, and held in a rustic hotel in the Rila Mountains.  It's day one, and I was scheduled to speak in the first session, like last year.  My talk followed talks by Andrzej Góźdź, and his student Aleksandra Pędrak (from Lublin, Poland) concerning collective Hamiltonians, and one by Attila Krasznahorkay (Debrecen, Hungary) on resonance states in calcium isotopes.  I enjoyed all the talks, and with Attila's experimental talk being relevant to things I can calculate, I got a few ideas of things to do.

My talk was a kind of advert for our recently-published computer code, Sky3D, with some details of the kind of physics problems one can solve with it -- quite a wide range from nuclear structure and dynamics -- and some technical details of implementation and usage.  I got a reasonable amount of interest out of the talk and a fair few questions.  Hopefully, having published the code, we'll get plenty of people interested in running it.  It's good to have given the talk on the first day, partly because now I can relax more and enjoy the other talks, and chatting to people, rather than tinkering with my talk, but also because there is now plenty of time for me to sit down with people and infect their computers with my code install my code on their computers.

This year, I brought travelling companions, as seen in the picture.  Eagle-eyed regular readers may notice that the mountains in the background haven't changed much, but the climbing frames in the playground have had a lick of paint.  My daughter Alba, in the picture, is a little young for the climbing frame, but she has already proved to be the star of the conference.  Her first plane journey went well,  It was on a pretty busy plane, and we had two seats in a group of three.  Our fellow passenger, seeing that he was sitting next to a family with an 8 month old baby graciously begged the stewardess to be allowed to sit elsewhere so as to give us a little more space.  We certainly didn't mind...

Friday, 20 June 2014

Where did the isospin sign convention come from?

Perhaps a reader may be able to help with this conundrum, which came to my attention on Tuesday following a seminar at Surrey from Mike Bentley, from York, which was all about isospin.

In 1932, Werner Heisenberg introduced the concept of isospin [1].  At least, that's what we call it these days, though it was Wigner, in a 1937 paper [2], who first referred to Heisenberg's idea as isotopic spin, which we've since shortened to isospin.

Heisenberg's idea was that protons and neutrons are really very similar objects - both about the same mass, and having a close link via beta decay in which a neutron can turn into a proton and an electron.  Together neutrons and protons constitute atomic nuclei, and can be termed nucleons.  Heisenberg wondered if it would be possible to conceive a theory where one dealt with just nucleons, but had some way of distinguishing them as either protons or neutrons.  He said (excuse my translation)

Each particle in the nucleus would be characterised in five dimensions:  The three spatial coordinates (x,y,z), the spin in the z-direction, and through a fifth number, ρξ, for which the values of +1 and -1 are possible.  ρξ = +1 would mean that the particle were a neutron, ρξ = -1 that it were a proton.

The whole concept can just be considered a mathematical convenience;  now one can write equations in a higher-dimensional space, but without having to have a notation with 'p' and 'n' subscripts everywhere for proton and neutron states.  However, it also helps notate an apparent underlying symmetry;  that protons and neutrons nearly behave as mirror particles.  The purpose of my post is not about anything as deep as that, but rather about the choice of +1 for neutrons and -1 for protons.   It is just an arbitrary choice, but it's the one originally made by Heisenberg, and repeated by Wigner shortly after.

If I look more or less in any modern textbook, or the Wikipedia article on isospin, one finds the opposite sign definition.  Here I quote from the textbook Nuclear and Particle Physics, by Burcham and Jobes, which I bought while an Undergradute (so you may argue it is not "modern"):

Heisenberg introduced an internal degree of freedom, the isospin I, in complete analogy with the ordinary intrinsic spin s.  The two orientations of the isospin I (I=½) in a notional isospin space, namely I= +½ and I= -½, would correspond with the proton and neutron respectively

The factor of ½ difference I understand, but where did the sign flip come from?  Anyone know?  In Mike's talk on Tuesday, he used the Heisenberg convention, and this is the norm for nuclear physicists, but particle physicists use the opposite sign, as the textbook does.



[1] Über den Bau der Atomkerne. I., W. Heisenberg, Zeitschrift für Physik 77, 1 (1932)

Thursday, 19 June 2014

Unexpected Liverpool

I'm in Liverpool today, thanks to various tedious reasons to do with getting a passport for my daughter to be able to come with me on a conference trip to Bulgaria next week.  Her application had been sitting in the Liverpool passport office for a few weeks without being processed, and it worked out that the only practical way of ensuring that it was in my hands in time for the trip was to come up here today.   I came up last night and stayed in a hotel overnight, so as to be able to go to the passport office when it opened at 8am.  Fortunately, it all seemed to go okay there, and I should be able to pick the passport up this afternoon.

Being in such a fine city as Liverpool means that I can go to its wonderful Central Library - refurbished at a time when such spaces are being closed down elsewhere.  I got there a little before 9, and there were a group of people waiting outside for it to open.  Once inside, I wandered round it a bit, went to its cafe for a cup of coffee then settled in to one of the reading rooms in the old part of the library.  The picture attached to the post is taken from where I sat to work.  

It's heartening to see that not only are there parts of the country where community facilities are retained, but that the library is so well-used, with what seems to be to be quite a cross-section of people;  people engaging in scholarship, like me, and what appear to be college-age students;  people coming to study the Financial Times; many people sat at the computers; tourists walking round with cameras; people coming to indulge a hobby;  a group of disabled women come to hang out in the cafe together; and who knows for what other reasons (I didn't actually interrogate anyone about their reasons for coming).  

It might seem an unnecessary extravagance to some to pay for libraries these days.  I would have been fine without it, as I'd have been able to get in to one of Liverpool's University libraries, but with poverty getting worse, society more divided, and study-space at home at a premium for many, I am very happy to see such a wonderful library thriving, and paid for by me and the rest of the taxpayers.

Wednesday, 11 June 2014

Research for its own sake

Reading the Independent on Sunday (on Sunday), I came across an article headed "Universities are 'not just for getting a job'".  In some ways it was a bit of a non-story; a story about the opinion of someone who had made the remark.  I was pleased to see that the person saying it was the Vice Chancellor of my own institution, who is also the chair of the Vice-Chancellors' supergroup Universities UK.

The headline seems a rather uncontroversial statement (to me, at least), but the idea of charging students large tuition fees was predicated on the fact that University students earn more money, on average, than those not going to University, and so charging them high fees is therefore justified.  I never much liked that argument.  I mean, we have a graduated income tax to account for that time of thing, and it always smacked of the politics of envy.  We should fund from taxation anything we think is worth having in a society.  The last couple of governments seem to have decided that we do want people to be educated up to sixth form level, but that's enough, and anything else is a kind of personal luxury.  What I don't like most of all about it, though, is the assumption that Universities only exist for people to serve their own financial self-interest.   What of the people who want to go because there is so much to know?  How do we account for the fact that this desire to push the boundaries of knowledge is part of what makes us human?  

I may be doing a subject which has a lot of positive financial benefits, but I also want to live in a society where we have Professors of Medieval Poetry, just because such a society enriches us in ways beyond money.

I'm glad my vice-chancellor thinks so too. 

Thursday, 5 June 2014

Video test post

As the title suggests, I'm making this post to see how to include videos most easily within Blogger-hosted blogs.  This one is uploaded via Blogger's tool.  It doesn't do anything in preview mode, hence I am publishing it.  

It's a simulation of a nuclear fusion reaction between Oxygen-16 and Zirconium-64

video


If anyone has a good guide to including videos in web-pages, in a Blogger-compatible way, I'd welcome some pointers.  I can host the videos elsewhere and edit the blog posts in pure html mode, if it helps you make suggestions.

Monday, 2 June 2014

Conference of the week: ARIS2014

[ARIS 2014 logo]
I'm at home this week, but many people I know from the nuclear physics community are at ARIS2014, in Tokyo.  In fact, there are enough people there that if you follow the twitter hashtag #ARIS2014 you can keep up with nuclear physics news (so people at ARIS, please tweet news!)