Thursday, 28 July 2016

Nuclear Structure Day 3

This morning's run
It's more than half way through the Nuclear Structure 2016 conference.  Thanks to Kelly's comment on my previous post, I indeed took a run straight down Walnut Street to the river so that I could run along the "Greenway" path that runs alongside it.  I was a bit worried by the very steep hill I ran down to get to the bridge across the main road and then the stairs down to get to the riverside.  It meant that there would be a lot of uphill on the return run, and of course so there was.  I ended up running 2km, so no great shakes, but I certainly felt like I got a lot of exercise while doing it.  

There have been a lot of good talks at this conference.  I particularly enjoyed Gaute Hagen's talk yesterday which showed some recent results from his group's calculations using the coupled cluster method to calculate the properties of the doubly-magic 48Ca nucleus.  They use interactions from chiral effective field theory which one can think of as a fairly fundamental way of describing the nucleon-nucleon (NN) interaction (though it turns out that they are still a little uncontrolled so that there are many such interactions they can choose from) and the whole method falls under the name ab initio, meaning really that they use free NN interactions rather than in-medium interactions to produce the structure of nuclei.  I think there is still some work to make NN interactions sufficiently fundamental to justify the ab initio moniker. But okay, they are heroic calculations that were justifiably published in Nature Physics.  It was good, I think, that they made some effort to get the radius of their nuclei right.  The radius always seems to take second place to binding energy when people are trying to reproduce the properties of nuclei with their theories.  There are strong links between the neutron-proton radius difference and e.g. the expected properties of neutron stars, linked via the equation of state of nuclear matter.  Anyway, the result Gaute presented suggest that the neutron skin is on the lower end of what is usually predicted, which is certainly an interesting result, and I (and many others) await the CREX experiment which is planned to make the best ever measurement of the neutron radius.  The proton radius is relatively easy to measure via electron scattering.

charge radii
The radii of nuclei in this region show really interesting behaviour, as shown by Kei Minamisono in the talk before Gaute's, and by Ronald Garcia-Ruiz's talk immediately after Gaute's.  The second picture here shows a snapshot I took during Kei's talk.  If you click on it you get a slightly bigger version.  The points show the charge radius – so the proton distribution, basically.  The black triangles (second line from top) are for calcium, in which there are always 20 protons.  The radius, between neutron number 20 and 28, shows a kind of inverted parabola with odd-even staggering.  Very few theories can reproduce this.  Then there is a strong linear increase after the N=28 magic number.  Add one proton for scandium, or subtract one for potassium and the details don't just mirror calcium shifted up or down a bit, but look quite different.  There are rich structure effects going on in here that I don' think we fully understand.  Certainly there are approaches (such as density functional theory) which have reproducing radii well within their remit, but simply don't get the details right.

Lee Evitts
Yesterday also saw a Surrey PhD student (who spends all his time actually working at the TRIUMF lab in Canada despite formally being enrolled at Surrey) who is also a graduate of our MPhys programme, Lee Evitts, give a talk to the couple of hundred delegates present.  He did a good job, talking about his results of spin-zero excited states in nickel isotopes, and what they tell us about the nature of those nuclei.  In particular he was looking at electromagnetic transitions between spin-zero states, which are very peculiar as they cannot proceed by the emission of a gamma–ray photon, which is the usual way that electromagnetic transitions proceed.  This makes the experiments harder as the probes tend to be messier.  Lee's experiment used proton scattering off of the nuclei to let the associated Coulomb field cause the transition to take place.

Tuesday, 26 July 2016

The old stomping ground

I am at the Nuclear Structure 2016  conference in Knoxville, TN for this week.  This is part of a series of conferences that moves around the US, organised by a different National Laboratory each time.  This time is the turn of Oak Ridge National Laboratory (ORNL).  A previous time that it was organised by ORNL was one of the first conferences I went to as a young researcher.  The conference website this time gives a history of the biannual conference back to 2008.  A quick search (for the conference proceedings) reveals that I was at the 1998 conference in Gatlinburg, which is a nearby resort town in the Smoky Mountains.  Back then I lived here in East Tennessee.

I usual consider the part of nuclear physics I do to be nuclear structure (the properties of individual nuclei), as opposed to nuclear reactions (how they interact with each other).  So this conference series is sort of my main area, but actually I've increasingly moved to the border between structure and reactions, and I never feel like I am completely at home at most conferences any more.  Not that there is anything wrong with being away from home.  

Well, one of the pictures attached to the post shows a slide from a talk given by Jolie Cizewski from Rutgers University.  I took a picture of it because of the prominent featuring of a list of University of Surrey collaborators, most of whom are our MPhys students, which Prof. Cizewski has been kind enough to host during their research years.  The other picture shows I run I went on at around 6 am this morning.  There's a bit of a heatwave here this week, but running before dawn was pretty acceptable (and there were a few of us out).  After a long time of not doing too much running, I'm trying to get back into doing more of it to improve physical and mental health.  This was not a terribly long run on the scale of things (1.5km) but it's a start.  If my jet lag keeps me getting up early, hopefully I'll be going a bit further while I am here.

Wednesday, 20 July 2016

Ghost Rider

I don't think I can construe this as a nuclear physics post, but I notice that Alan Vega, of the bad Suicide died this week, and so I present a Suicide song, covered by REM:

Monday, 4 July 2016

2016 Rutherford Medal

It was announced at the end of last week that the 2016 Rutherford Medal of the Institute of Physics was awarded to Professor John Simpson, of Daresbury Laboratory.  The award cites his contributions to the understanding of atomic nuclei, particularly in the high-angular-momentum regime, and through his leadership in associated detector development.  

The picture attached to the post features John, though if you don't know what he looks like, you're hardly going to find him in it.  It's a picture take from before my time in nuclear physics, at Daresbury Laboratory, before nuclear accelerator facility was closed down.  John is wearing a white top, to the left of the centre of the detector, as the camera is looking at it.

Congratulations, John!

Friday, 1 July 2016

Mid–year book post

Around the new year, I made a post pointing out that I had discovered a list, from 2006, of all the books I had read that year.  Back then, for various reasons, I used to read a lot more than I have come to in recent years.  I used to never be without a book about my person so that if I got a chance to read (on a train journey, say) I'd always have my latest read to hand.  There have been times lately when I have found myself on a journey only to realise that I don't have a book with me.  That never used to happen, and this year I've been trying to find the time to keep up a better reading rate.

As a half-year status report, I list the books that I've read so far this year.  I don't have any mini-reviews prepared, but I might try to retrospectively fit some in.  If you are desperate to know what I think of any of them, feel free to ask in comments and I will take your interest as a prompt to write something.  Anyway, for the record -- and I'll report back at year end -- here is what I have read thus far:

Seymour, an Introduction – J. D. Salinger
American Gods – Neil Gaiman
Raffles – E. W. Hornung
Moby Dick – Herman Melville
The Buried Giant – Kazuo Ishiguro
The Secret Garden – Frances Hodgson Burnett
Gone Girl – Gillian Flynn
Oliver Twist – Charles Dickens
A Little Life – Hanya Yanagihara
Everyone Brave is Forgiven – Chris Cleave
Night Blind (still reading) РRagnar Jónasson