Thursday, 30 April 2020

New Royal Society Fellows

I see a list of newly-elected members of the Royal Society has appeared.  I carefully checked, but did not see my name there.  Oh well.  Searching on the word 'nuclear' brought up a link of Nobel laureate Donna Strickland's work to nuclear fusion, and the words 'Nuclear Magentic Resonance'.  Next year, then...

Tuesday, 21 April 2020

UK Lockdown seminars

The UK nuclear physics community has just announced its own series of lockdown seminars to deal with the present situation where were are all working from home.  The idea is to include the sort of people who different nuclear groups from around the UK were planning to have to speak before all live events were cancelled.  The webpage for the initiative is here

The first seminar is 3pm BST this Friday, with Alessandro Pastore from York, and there are three seminars every week - on Mondays, Wednesdays, and Fridays.  This fits in well with the nuclear reaction seminar series I'm already (mostly) watching (, which are on Tuesday and Thursdays.   It's almost like being at a conference...

Wednesday, 8 April 2020

HIAS Proceedings Online

Way back in ancient times (i.e. before Covid-19), academics used to go and meet up with each other to talk about science and stand around awkwardly in coffee breaks.  Such a thing happened to me last September when I was in Canberra, Australia.  I attended the HIAS conference at the Australian National University (ANU) in Canberra.  HIAS stands for Heavy Ion Accelerator Symposium and it is a regular meeting to showcase the kind of science they can do at their own on-site accelerator facility, though speakers are invited from competing and complementary facilities around the world.  They ask the participants to write up their presentations for the conference proceedings.  I duly did this, and the collected proceedings have been published today in the EPJ Web of Conferences vol 232.

As a (rather large) figure to accompany the post, here is Figure 1 from the first paper in the proceedings.  The paper is an overview of the kind of work they do at the ANU accelerator, written by Andrew Stuchbery.

My own contribution is about what heavy-ion reactions can tell you about the surface energy of nuclei (not much): P. D. Stevenson, EPJ Web of Conferences 232, 03005 (2020)

Thursday, 2 April 2020

A rare pair of mirror nuclei

Yesterday a paper appeared in Nature which describes on the second case of a pair of "mirror nuclei" (which differ from each other by having the number of protons and neutrons swapped) in which the ground states have different spin.

The pair in question is strontium-73 (Z=38, N=35) and bromine-73 (Z=35, N=38) which have been measured to have spin-parity assignments of 5/2 and 1/2 respectively. The states of mirror nuclei are pretty close to identical, thanks to the isospin symmetry of the nuclear force:  To a good approximation the nuclear force looks the same between pairs of protons, pairs of neutrons and neutron-proton pairs.  There are a couple of ways in which differences appear in mirror nuclei - e.g. because there is also the Coulomb force in play which acts between protons but not neutrons, and these small differences can sometimes cause an effect like the one seen in the Sr-Br pair.  In this case, the small differences are enough to give a different ground state as there seems to be a very low-lying state close to the ground state in these nuclei and the small differences happen to be enough to swap the order of these levels in the two nuclei.  

The figure to the right is part of one of the figures in the supplementary material on the paper.  It's a section in the nuclear chart of isotopes in which the line of N=Z nuclei appears as a vertical line in the middle, and nuclei close to this line are shown - the ones for which mirror pairs are known to exist.  The two pairs coloured in black with little cracks in, are the two cases in which the mirror ground state symmetry is broken.  The other case which was previously known is 16F/16N.  In that case the fluorine isotope has its last proton unbound, and it only exists as a nucleus thanks to the Coulomb barrier.  The nitrogen valence proton is not unbound and this significant difference is enough to cause the difference in the ground states.  The same effect is not in play in the Sr-Br case. 

Wednesday, 1 April 2020

My first remote PAC

My working from home today consisted of participating in the Jyväskylä accelerator laboratory Programme Advisory Committee (PAC) where were review proposals for beamtime and then make recommendations to the laboratory for how to allocate resources requested in the proposals.  The hosts in Finland graciously moved the start time of the meeting to 10:15am Finnish time, so 8:15am UK time, and we had a good meeting, in terms of getting through the agenda with the same diligence as when we all attend the meeting in Jyväskylä in person.  We missed the peripheral, but still nice, and still important parts of the meeting.  The full social exchange, the visiting another country and interacting with it and people there outside the meeting, the chatting to colleagues working in the physics department at the University there during the breaks in the meeting, the nice meal afterwards... But the meeting did work well, and we saved our carbon emissions.  I also had less time away from my family.  Indeed since we are in our extended lock-in, my 3yo son even decided to spend some of the meeting sitting on my lap.  I hope, though, on balance, to be able to have the next meeting in person.