Nuclear Spot The Difference #10

 I wonder if readers have noticed the similarity between footballer & sex-symbol George Best and nuclear wunderkind and Nature-botherer Liam Gaffney?

Best

Gaffney

Bell Burnell Diversity PhD studentship at Surrey

My department are offering a fully-funded PhD studentship to candidates from under-represented groups.  It is loosely tied to the IoP Bell Burnell Scholarship, and we would seek to submit an application to the IoP for the successful candidate, though the university guarantees funding even if the IoP bid is unsuccessful

More details are here.

I did post this on Twitter already, trying to see if anyone there might be interested in applying for the studentship with me.  I got one angry (or "disgusted") respondent who does not like this kind of scheme.  The point is that the word "under-represented" means less represented than you would expect if there were not a long-standing systemic bias against particular classes of people.  Those who don't fall in the "under-represented" category already have plenty of opportunity to get into they system, as seen by their over-representation. 

This studentship is unusual (compared with any other studentships that have been used to fund students I've taken in the past) in that it even international students are eligible, which is usually not the case for government-funded places.

A proper Zoom backdrop, finally

 We have been having some work done at home, to have our loft changed into a bedroom and an office for home working.  We have had a bookshelf built in to one of the rooms, and it has just been populated by books, so finally I can take a photo and have proper background to my Zoom calls, which I understand is supposed to be a full bookcase

Online teaching & Maple Calculator

 It's the middle of the semester, and it's my busiest semester, in which I teach two full 15-credit final year modules – i.e. I am teaching half of a student's full time effort, and with the extra preparation of online lectures, online tutorials, videos of answers to problems, more time on online discussion, as well as all the non-teaching parts of my job, I am finding myself working after the family has gone to bed most days.  Not a position I ever try to get myself in, but I'm more or less resigned to it for the rest of semester.

For most of my lectures and problem solution walk-throughs I'm using a video of me writing on a tablet device, accompanied by my voice.  It works tolerably well, though not without glitches. I'm getting increasing adept at re-opening the whiteboard app when part of my writing hand accidently touches a part of the screen and closes it.  At the same time, my usage of mild swear words has never been higher, and no doubt the students will also be saying crivvens whenever they need to express some slight horror.

Some of the problem solutions I've been working through involve sticking in actual real-life numbers into calcualtions.  These are calculations a bit too complicated to do mentally, and I rarely find myself in need of doing such calcualtions so that I don't have an old-fashioned calculator to hand.  I have, of course, a computer, and also a smart phone, and usually I end up using the calcualtor function on my smart phone.  As I wrote an equation on my tablet a couple of weeks ago, I did find myself musing that it would be nice if there were an app to recognise the equation and do the sums for you.  Lo and behold, of course there is. One of the courses I am teaching right now involves the use of the programming language Maple and there is a app written by the Maple people called Maple Calculator.  It has exactly this function; you can take a picture of some mathematics with a camera, it will recognise it (hopefully) and then evaluate it for you.

Here is an example of it working out a calculation for a kinematics problem in special relativity:

I tried to make sure that I wrote the equation very neatly, and indeed it seemed to recognise it okay.  The answer, though, is not what I was expecting.  The actual answer is around 1.73.  It took me a little while to understand why...

Open Access Royal Society (one week only)

While we wait for all academic publishing to be properly open access, Royal Society Publishing have kindly opened up their pretty extensive archive for free for the next week.  See here. 

They do not have an extensive amount of nuclear physics stuff, but they are currently my publishing BFF because they published my student's article on Terrell rotations earlier this year, whcih I may have metioned here before.  More than once. In fact, more than twice.  Well, modesty prohibits me from linking to the paper again, but that's okay because there are lots of other articles of interest, dating back, of course, many centuties.  

If anyone has any favourite articles from Proceedings of the Royal Society, or the Philosophical Transactions, please do share in the comments. 

Here's a snapshot of some sketches by William Herschel, from Philosophical Transactions, vol 74, p233 (1784)

 

Lattice calculations of nuclear vibrations

  I just received a notification that the penultimate article in the special topic in Frontiers In Physics that I am co-editing has appeared.  It's called "Nuclear Collective Dynamics in Transport Model with the Lattice Hamiltonian Method" and it deals with a method in which the motion of a nucleus is described in terms of the the evolution of the Wigner function (the nuclear density Fourier-transformed to the momentum representation).  By including collisions between nucleons in the formalism, the authors describe the width of giant resonances rather well, as shown in the picture above (fig 7 from the paper).

 That leaves just one more paper to appear, and also means that I should get on with writing the editorial in time to make a free e-book of the Special Topic.

Roger Penrose, Nobel Laureate 2020

Roger Penrose was announced this morning as the winner of half of the 2020 Nobel Prize in Physics, with the other half being shared equally between Andrea Ghez and Reinhard Genzel.  I will leave others to explain about the physics behind the prize award, since it is not really my area of expertise, but I wanted to post to mention the ways Penrose and his work has cropped up in my life

As a physics-interested schoolboy, I used to read through popular science books.  Probably the first one I read, to the best of my memory, was Stephen Hawking's A Brief History of Time, which I got for Christmas the year it came out and was something of a must-read book for more or less anyone, though there was a kind of joke that few people finished it.  I did finish it, and though I probably didn't understand it all, I found it at least readable and understood the words and got a sense always of the ideas being communicated, even if perhaps I didn't always gain a deep understanding. 

Another one I read, while I was in the lower sixth (what we used to call Year 12) and applying to University, was Penrose's The Emperor's New Mind.  I lent my copy to a girl I fancied and never got it back.  I later learned that the rule of lending books to anyone was that you just go out and buy yourself another copy straight away.  Anyway, I had finished the book, though I'm not sure I can remember too much of it in great detail now.  It did make quite an impression on me at the time, though I think it was "harder" than Stephen Hawking's book and no doubt there was lots I didn't understand.  I liked it for its broad sweep, combining ideas from physics to advanced mathematics, Turing machines, and on to somewhat more speculative stuff (which I didn't distinguish at the time, I suppose) to do with consciousness.  

In December of 1991, when I was in the lower sixth and up in Oxford for an interview to read Physics and Philosophy I noticed that Penrose was giving a lecture for prospective students in Mathematics.  In my interview for my place in college when asked if I had any questions I said I'd seen the advert for the talk and I asked if it would be okay if I went along to it.  I'm not sure what they thought of my question - I guess I had no idea at the time that it would be perfectly fine for anyone to turn up and they wouldn't exactly be checking to see if I was really a prospective mathematics student.  Anyway, I went along, and enjoyed the talk very much.  Penrose talked about the famous Penrose tiles.  I remember particularly a demonstration of how for certain near-symmetries you could make the symmetry almost perfect - as near to perfect as you liked, except not quite actual perfection - and he showed this by having two identical overhead projector slides with a 5-fold Penrose tiling, which he overlaid, and you could see the bands made in the thin regions where the pattern didn't quite repeat.  

I don't think I have seen Penrose in person since then, 29 years ago, but I did get a copy of his huge "The Road To Reality" book as a 30th birthday present a bit later (in 2004).  That's been sitting on my office shelves unread, I have to admit.  I'm sure, as a practicing theoretical physicist, that I ought to be able to read and understand it, but even to me, opening it up it does look intimidating.

The other Penrose anecdote I have is that I found out at some point (perhaps the advent of wikipedia) that I share a birthday with several famous physicists, two of whom won Nobel prizes long ago).  Now I can fill in another cell in this table:

Physicist	Date of Birth	Year of Nobel Prize
E.O. Lawrence	08/08/1901	1939
P.A.M. Dirac	08/08/1902	1933
R. Penrose	08/08/1931	2020
P. D. Stevenson (me!)	08/08/1974	-

The final Penrose-related thing links with my research:  Earlier this year I co-published a paper with a bachelor's student based on his Final Year Project on the visual appearance of objects moving very fast (at an appreciable fraction of the speed of light).  This is a new look at something which are either called  Terrell Rotations, after the author who first got his name attached to it, or as the Penrose-Terrell effect, since Penrose independently submitted a paper on the same topic, published in the same year as Terrell.  Even more properly, it can be called the Lampa-Terrell-Penrose effect, since Lampa published it first, in a paper that wasn't so widely known.

Here's a picture of Penrose, which he sent to the Nobel Committee from his house in Oxford this morning

Science books of the year

 I saw yesterday that the Royal Society published their shortlist for their science books of the year.  There are 6 in the shortlist: The World According to Physics by Jim Al-Khalili, The Body by Bill Bryson, The Great Pretender by Susannah Cahalan, Explaining Humans by Camilla Peng, The Double X Economy by Linda Scott, and Transcendence by Gaia Vince.

Unusually, since I don't read a lot of popular science, I've actually read two of the books:  Transcendence and The World According to Physics.  They are both excellent, and would be worthy winners.  I got Transcendence for Christmas last year, and found its arguments compelling that humans' achievements are part and parcel of the way humans work together; the network of ideas, activities, language and culture evolve together with biological humans and have created a kind of super-organism.  Mind-blowing, well-researched and full of interesting anecdotes, I found myself wanting to tell people things I'd read in it as I was going through.  

The World According to Physics is right up my own subject area, so though I would expect to enjoy it, I wouldn't necesasrily prioritise adding a popular explanation of something I think I know well to my reading list, but I'm glad I did read it:  Sure, I knew most of the stuff already, but it was infused with such a joy for the wonder of the Universe, and our way of explaining it through physics, that I rekindled my own sense of awe at what I sometimes let lapse as part of my day-to-day activities.  I did even learn a few things, thanks to the inclusion of lots of very up-to-date and speculative ideas (which were flagged as such).  I should add that I read a draft of the book and gave some comments, and the author did hand me a copy once it was published.  Jim is my colleague at the Unviersity of Surrey.  No payment was received for this review ;-)

arxiv-vanity

 The document format pdf is pretty good when you want to make nice-looking output for printing for your scientific paper.  It's not always so handy when you want to read something on e.g. your phone screen, though, where you have to do a combination of zooming in and scrolling around to be able to read a paper.

A nicely-formated html version of a scientific paper, on the other hand, should be able to render nicely on a wider range of screens, and these days reading from screen has largely superseded reading from paper for me.  I read on Twitter about an arxiv-to-html translator called arxiv-vanity.  You give it an arxiv URL and it returns a nice readble web-page version of the paper you are interested in.  

I tried it on the recent whitepaper / review I was involved in writing on fission theory and the results are impressive.  Perhaps arxiv will fold it into its own offering soon.  

Update on the time-dependent methods special topic

 I last posted an update back in June about the Special Topic in Frontiers in Physics that I am co-editing.   Then, a new article on solitons in nuclear reactions had just been published.  This was actually followed a few days later with another paper, and then there has been a fallow period while the last few papers go through refereing, proofing, and publication.  Today, the next of those was published. so let me briefly mention the two new papers since June:

Marc Verriere and David Regnier have written a review on the time-dependent Generator Coordinate Method.  In fact, they discuss a number of related models which all share the character of mixing multiple Slater determinant wave functions to represent complex nuclear phenomena (reactions, fission) in which there is a significan change over time of the quantum state, and for which a time-dependent method is appropriate.  It's a nice contribution the Special Topic, covering one of the current hot methods in nuclear theory.  I can say this since I have a PhD student working on something that can be termed time-dependent Generator Coordinate Method, though it is not quite the same as the methods presented by Verriere and Regnier.  

 The other paper, published today, is written by a University of Surrey undergradute student who took a year-long research placement at Peking University in Beijing, China.  He used time-depedent Hartree-Fock (TDHF) to look at the part of the fission pathway near scission where the TDHF method is applicable, and to study how different parameterisation of the nuclear force give different predictions for the pathway to fission.  It's a short piece of original research, which complements nicely the mix of other research and review articles in the Special Topic.  I worked on this project with Marko and his host supervisor, and am co-author on the paper.  I took the liberty of using a picture from this paper as an accompaniment to this blog post.

Once the two remamining papers appear,  on spontaneous fission and collective dynamics with a transport model, have appeared, the whole Special Topic will be avaiable as a free e-book, in pdf and epub format, so get your Kindles ready.

Deep Summer in Bishop's Stortford

 

It's a strange time right now, of course, with the Covid-19 pandemic ongoing.  I've been taking summer holiday in the form of working a couple of days per week and having more days off than on.  This week, I'm on holiday, and we have made a trip to visit my parents, following both our households isolating for an extended period.  I don't have a car, which is usually no problem, but we didn't fancy travelling by public transport right now, and fortunately my parents came to pick us up and bring us all up to their house, while my mother-in-law lent us her car, too, so that we could have the two-cars needed for the 6 of us.

So ... we have been carrying on the lifestyle of staying in and isolating from other people with the exception of my parents, at their house. It's nice spending so much time with them.  They've lived in this house for more than twenty years, and this two-week visit is the longest time I have continuously been here.  With 4 kids to play with and look after, there is no shortage of things to do, and my parents have (unlike us at home) subscriptions to the likes of Disney+ and Netflix.  

While I've been working just enough to keep up with MSc, PhD and undergraduate summer project students, a paper I worked on as part of a large supergroup of theorists to map out the next steps in understanding nuclear fission from a microscopic point of view was published.  It's a comprehensive (86 page!) paper bringing together expertise from a lot of different people to try to figure out how to move towards a unified theory of fission, a process which consists of many stages, operating a different timescales, with different degrees of freedom coming into play;  this calls out for a different range of approximations for each stage, and an understanding of how to link them together ideally with a single framework.  The paper is an attempt to put down all our ideas on how to proceed here.  I contributed what I could to those parts I felt sufficiently expert in, and the whole paper was put together by Prof Dobaczewski from the University of York.  It's available now, via its doi: 10.1088/1361-6471/abab4f, though it has not yet been assigned a page or article number.  Because there are UK-based co-authors, it is fully open-access, as is the case with all J Phys G papers with UK authors.

At the top is a picture of me photobombing my 8 month old son Kit, outside at my parents' house. 

A paper in IoP SciNotes on generating ion-ion potentials

I have had a paper published today in (new) journal IoP SciNotes.  It's on how to use the existing Sky3D code (written by a collaboration including me) with some small modifications to be able to do something it was not particularly designed for:  Generating the interaction potential between two nuclei.  The paper is referred to as P. D. Stevenson, IOP SciNotes 1, 025201 (2020).

This new journal, SciNotes, is supposed to be for research outputs which are perhaps not worthy of a full paper, but things that should nevertheless be out there.  Seemed like an appropriate place to document how to make a (very minor) tweak to a published code to do something new with it.  Here's a picture of the potential between two oxygen–16 nuclei made for the paper.

The method, by the way, uses an approximation called the Frozen Hartree-Fock approximation.  It may or may not be a brilliant approximation depending on your needs.  There are some references in the paper / note for further discussion of this points. 

This is the first single-author paper that is not a conference proceeding that I have published since 2003, I think.

Margaret Burbridge Symposium

I received an email advertising a symposium celebrating the life and work of the late Eleanor Margaret Burbridge, pioneer of nuclear astrophysics.  The invitation to attend (online) is open, and I copy the email below with details of the event next week.  The image is a stylish representation of Prof Burbridge, from the linked-to website below:

Dear Colleagues,

 

Please join us on July 8th 2020 from 1:00-3:00 EDT for an online symposium to honor the late pioneer Eleanor Margaret Burbidge. The event will celebrate her life and science through short talks from her colleagues and collaborators as well as researchers who have benefited from her trailblazing and scientific insights.

 

Speakers include:

 

George Fuller  -  University California, San Diego

Anneila Sargent  -  California Institute of Technology 

Virginia Trimble  -  University California, Irvine

Fred Hamann  -  University California, Riverside

Vesa Junkkarinen  -  University California, San Diego

Amanda Karakas  -  Monash University

Artemis Spyrou  -  Michigan State University

Anna Frebel  -  Massachusetts Institute of Technology

Nicole Vassh  -  University of Notre Dame

 

The JINA-CEE website https://www.jinaweb.org/events/celebration-margaret-burbidge

can be consulted for any updates and viewing a commissioned illustration.

 

We encourage you to please share this email invitation with any colleagues, friends, or institutions that might be interested as the event is open to all.

 

We hope to see you there,

 

The Organizing Committee:

Frank Timmes, Arizona State University

Nicole Vassh, University of Notre Dame

Nuclear soliton review

The latest article in the special topic I am co-editing in Frontiers in Physics appeared today.  It is called "Solitons in Nuclear Time-Dependent Density Functional Theory" and is by Yoritaka Iwata, from Kansei University, Osaka.

It follows on from some of his previous work (including a paper in New Journal of Physics I co-authored with him), combining a review of why one might expect soliton behaviour in nuclei, some existing results, and a new more thorough exploration of relevant parameter space.

The basis of the idea is that the time-dependent density functional theory which describes nuclear systems appears as a non-linear Schrödinger equation which formally is equivalent to the canonical equation with which solitons are described.  Depending, then, on details of the nuclear interaction, and on the boundary conditions – the specific nuclear interaction being explored – one may find soliton solutions.

One particular confounding factor with the existence of solitons in nuclear reactions is the relative speed of the waves which equilibrate the charge and those which move matter.  If neutrons and protons are exchanged too quickly in reactions, then solitons are not possible.  This is something highlighted in Iwata's previous papers, and a hot topic in understanding heavy-ion reactions, with a recent paper in Physical Review Letters studying the same thing from a more nuclear physics (rather than mathematical/solitonic) perspective. 

Here's a picture from the paper (their Figure 4) showing a collisions around the boundary where charge equilibration is important:

The Surrey Alumnus and The Spy

Some nights, as I go to bed, if I am not falling asleep as my head hits the pillow, I pick up a book on the history of MI5, the British security service.  It's enjoyable bedtime reading, and a mighty tome which I am about 3/4 of the way through.  The book proceeds chronologically, and I'm currently around the 1970s.  This was perhaps a quieter time for spying than the days of the Profumo scandal or the Cambridge Five, at least in terms of international intrigue involving the Soviets, but I've just come across a spy that I had not heard of, that has some local interest to me.

Though I was an undergraduate at an Oxford college, I was never recruited as a spy, and if anyone tried, I totally misread it.  Now I have been at the University of Surrey for 20 years, it turns out that one of the ex-undergraduates here, from the earliest days of the University in the late '60s became a spy.  Michael John Smith studied electronic engineering at Surrey, and came to MI5s attention as someone who got involved in the activities of the Communist Party of Great Britain (CPGP).  He worked, after graduation, as an electronic engineer at EMI where he had clearance to work on technology contracts for Britain's nuclear bomb.  Apparently his security clearance was granted thanks to a mix-up in his rather common name, and the fact that there was another Michael John Smith enrolled in the Surrey branch of the CPGB.  He duly worked on radar fuses for Britain's free-falling nuclear bomb, and was able to pass documents on to the KGB.  Eventually, the clerical error at the security service was spotted, and his clearance was revoked.  His Soviet handlers had made sure he stopped taking the Morning Star, and switch to the Telegraph, join a local tennis club, and stop association with the CPGB;  still, they were suspicious that so soon after this preparation he was able to pass them such secrets, and they thought that the information about the radar-activated fuses, complete with details of the frequency used, and hence how to jam them, might have been fake plants from the British.  Not so. 

Eventually, Smith was arrested, and sentenced to 25 years in 1993, reduced to 20 on appeal.  I wonder where he is now.  Retired, and living round the corner from me, perhaps.  

The image at the top is from Britain's free-fall nuclear bomb WE.177, now at the Imperial War Museum North (presumably without the warhead inside).

Cycling near the speed of light in Nature

As mentioned in my last post, a paper written by a BSc project student and me has just appeared in Proc Roy Soc A, and was due to be mentioned in Nature.  Duly the Nature "research highlight" has appeared.

Here's a video the student made for the project (but which we did not include in the paper)

A paper on relativity, and a book on instantons: The week in Lockdown Guildford.

I've lost count of which week of lockdown it is, but I do know that it's Week 13 in the University calendar, which means two more weeks of semester to go and then it is the long vacation - or "the summer semester" depending how you reckon it.  I have two MSc projects to supervise over summer, so I have some direct teaching to do, as well as plenty of preparation for my autumn semester modules. 

This week I have been marking Final Year Project reports from various students on our BSc programmes, covering various different topics.  It's been interesting to see what they have been up to in their projects, and as marking goes, they are enjoyably varied – more so than 50 exam scripts answering the same questions, though the similarity in that case has its own benefits. 

This week also sees the publication (here) of a work done in a Final Year Project last year, by a student (Evan Cryer-Jenkins) working with me on a topic in Special Relativity - namely on the visual appearance of fast-moving objects.  There are well known optical distortion effects that arise in Special Relativity thanks to a combination of length contraction, and the finite speed of light meaning that light has to leave different parts of an extended object at different times in order to arrive at ones eye at the same time.  Evan, in this project looked at how such a distortion would appear to a two-eyed observer (or to two spatially-separated cameras) and how the two different images would not be able to be focused to a single image.  In a way it's similar to looking at an object through a glass of water - each eye will see a fixed shape distorted in to two different shapes because of the different optical path taken to reach each eye.  We also looked at what one might be able to infer (the distance and speed of the object) from the absolute and relative distortions.

We submitted the paper not much less than a year ago.  The first referee reports came back giving us hope for acceptance if we made a few changes, and responded to the referees' points.  The journal (Proceedings of the Royal Society) told us that a resubmission would be treated as a new submission, and so the published version is listed as being submitted in October.  They are also quite on the slow side at doing things at that journal, not helped by the Coronavirus situation.  Anyway - the paper was published this week.  The same day, a journalist from Nature got in touch asking about the paper in order to run a story on it.  That never happens to my nuclear physics research.

I also got, in the post, the fruits of my labour commenting on a book proposal for Cambridge University Press.  This was a book on instantons which can be used to describe quantum tunnelling processes.  I harbour a desire to use the technique to understand tunnelling in nuclear fission.  If, after some effort at understanding the book, and further effort with implementing the calculations, running the code, processing and understanding the output, I may be able to write that up and see it published for all to see.  I won't expect a journalist to get in touch with me, though.  Perhaps I should think more often of writing for such a general journal as Proc Roy Soc A.

The picture shows me reading the book about instantons.  Well, pretending to read, but activating the PhotoBooth app on my computer to take the picture.

A master list of research seminars

Having previously posted about some online seminar series of interest to nuclear physicists, I have since come across the site https://researchseminars.org/, which contains a big list of research seminars that can be watched live online.  They are hosted by institutes around the world, so you can almost keep watching them 24h a day.  I see that the nuclear reaction seminar series are included there already.  There is a lot of maths and quite a bit of physics, as well as a smaller selection of computer science and biology (at least as I type this post.  Hopefully it will become more inclusive as time goes on).  There's a search and filtering facility, or you can just browse and try something that sounds interesting.  Big mapping class groups fail the Tits alternative, for example.

Not on the list are the UK nuclear physics lockdown seminars, which are perhaps not supposed to be opened to the world community.  I enjoyed hearing about an ex-Surrey undergraduate student's PhD work yesterday when he gave a seminar.  Here's a picture of the seminar just getting ready to start.

David Rowe 1936 – 2020

I learnt from a tweet today from one of his past post-docs that David Rowe died yesterday.  David was a theoretician who worked mainly on nuclear physics, famous for, amongst other things, his application of group theoretical methods in the latter part of his career and on the equations of motion approach to many-body physics earlier on.  I very much enjoyed his first book, covering many-body physics in general and covering in detail the equations of motion approach, and when it came to leaving my office for the last day before lock-down,  I decided that the one book I would fit into my bag would be his book Fundamentals of Nuclear Models, co-written with John Wood. 

David was British-Canadian, with dual nationality, following moving to Canada after study at Cambridge and Oxford, and a research position at the UKAEA with Tony Lane.  He spent the bulk of his career at the University of Toronto and though he retired in 1998, his interest and activities in nuclear theory did not wane.  Indeed, he published a paper in this month's edition of Physical Review C (on a quantized algebraic version of the Bohr-Mottelson Unified Model)

Nuclear Physics Meetings in 2021

Here is my annual post of (low-energy, mostly) nuclear physics meetings taking place around the world.  This is for 2021 and includes some meetings postponed from 2020

18/07–23/07: 14th Nucleus-Nucleus Collisions Conference, Whistler BC, Canada
A conference on collisions between nuclei at a wide range of energies, from superheavy-element fusion to quark-gluon plasma.  I have never been to one of these, but I'm certainly interested in this area, particularly in heavy-ion reactions around the fusion barrier.  I dare say Whistler is a nice place to visit. [website]

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...

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 (https://reactionseminar.github.io/schedule), which are on Tuesday and Thursdays.   It's almost like being at a conference...

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)

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. 

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.

Online seminars during the coronavirus epidemic

My 3yo son, realising that many things are cancelled at the moment, asked me this morning "is working from home cancelled?"  Alas not.  As it looks like we'll all be working from home for at least a couple of months, various schemes seem to have popped up to start research seminars that are given over the newly dominant teleconferencing platform, Zoom.  

The nuclear reaction theory community has started a series of seminars, detailed on https://reactionseminar.github.io. I wasn't aware of it when the first seminar was given, but I plan to attend future seminars.  One will be given by my Surrey colleague Natasha Timofeyuk.  I'm not aware of a similar initiative by the nuclear structure theory community (structure + reactions is a traditional way of dividing up low-energy theoretical nuclear physics, though I sit in both camps).  I would certainly join one if it started, though I'm not quite keen enough to start such a project by myself.

Based at CERN there is a series called Seminar on Precision Physics and Fundamental Symmetries which includes nuclear physics, but is broader than that.  There will be two seminars per week (Tuesday and Thursday at times to suit the speaker) starting today: https://indico.cern.ch/category/12183/.

If anyone knows of any more, please advertise them in the comments below.

That's my son who asked the question in the picture, during one of our daily permitted excursions for exercise.  It was at the weekend when the weather was very cold, and a streak of hailstone is caught in the picture too.

edit: Thanks to JINA-CEE for responding to me tweeting this blogpost.  They point out their online seminars in nuclear astrophysics.  See https://www.jinaweb.org/events and look for the events tagged "IReNA online seminar"

Li-6 as a probe of giant monopole resonances

A new paper appeared on the arXiv this morning (in nucl-ex, cross-posted to nucl-th) titled Reexamination of 6Li scattering as a Probe to Investigate the Isoscalar Giant Resonances in Nuclei.  The Isoscalar Giant Resonances are excitations of nuclei in which the protons and neutrons move together en masse, in phase.  

The two main isoscalar giant resonances, and the two examined in the paper, are the monopole and quadrupole versions.  The Isoscalar Giant Monopole Resonance (ISGMR) is sometimes called the breathing mode, since it can be loosely imagined as a kind of inflating and deflating of the nucleus, though there is no air being pushed inside or breathed out to cause the motion.  The breathing mode is set off when particular kind of particle is sent scattering of the nucleus in such a way that no angular momentum is imparted.  In this case, a nucleus which started off as spherical will retain its spherical shape as it breathes in and out.

The other one of interest here is the Isoscalar Giant Quadrupole Resonance (ISGQR) which gets excited when two units of angular momentum are  transferred to the nucleus by the excitation.  This gives a different shape for the excitation in which the nucleus is squeezed in one direction while expanding in the orthogonal plane -- imagine the Earth squeezing down along the poles and expanding along the equatorial plane as a result, and then bouncing back as it tries to restore its equilibrium shape.

A key interest in making these excitations is that they probe rather generic properties of nuclear matter.  By squeezing a nucleus you can immediately probe the matter all the way through it and try to understand how "stiff" it is - how hard it is to compress.  The answer here has to come from the underlying forces between the nucleons, and we can learn all about that force by exciting these resonances.  

The traditional particle of choice for striking on nuclei to form the ISGMR is the alpha particle.  This works well because alphas only excite isoscalar excitations (those in which the protons and neutrons behave in the same way, unlike isovector excitations in which they act out of phase, and which can strongly mask isoscalar excitations).  A difficulty, though, is that the scattered alpha particles, which have to be observed to deduce how they interacted with the nucleus, have to be measured at very small scattering angles.  In other words, these measured alpha particles are very close to the beam line which is full of alpha particles which did not interact, or even worse, with stray alphas that scatter out of the beam line but not due to the interaction being targetted.   

The paper, then, uses lithium-6 (3 protons, 3 neutrons) to scatter off the target nucleus and cause the excitation.  The benefit here is that Li-6 breaks up easily into an alpha particle and a deuteron, and the interaction with the target nucleus will often cause this to happen.  One can then look for the alpha particles coming off, which are no longer contaminated by beam alphas (since the beam is now lithium).  The cost is a more complicated analysis of the scattering process and the possibility of different excitations of the target nucleus.  From the paper, though, the results seem very nice.  Here is a plot of the excitation of carbon-12, showing the tiny error bars:

 There is some structure to the peak.  Even ignoring what is happening below ~13 Mev, there appears to be one main peak and at further peaks in the shoulders - at least one prominent one in the higher-energy side.  This could be due to all sorts of things, but with carbon-12 not being spherical (it is oblate deformed, like the Earth) then there should a strong coupling to the ISGQR when the ISGMR is excited, and that is likely what dominates the structure.

Working from home

Today is day one of working from home for me.  The University stopped its face-to-face teaching at the end of last week, and now although the University is still open, there is little justification for going in.  I have contemplated walking in – it's about 15 minute walk for me – and chances are I could get in to my office and shut the door without bumping in to anyone, but for now I'm attempting home working.  

The hardest parts are (1) having my partner and 3 youngest children here and (2) there not being as good a desk or other working space as I have at work.  (1) is hard because I have to resist the temptation to spend the whole day helping with childcare, but at least being here I can help for little bits during the day in short breaks which I couldn't do if I was in the office.  It's just hard to strike the right balance.  I am still full-time at work and have the various associated obligations that go with that.  With a bit of time and practice, I'm sure I'll get there.  For (2) I might need to invest in a better office-type chair to sit in, or to clear some space at the dining-room table.  Our house is in a kind of chaotic state thanks to having builders in building an extension (started last September, end date hopefully another 3 months).  There's only a partial roof on our house, and the dining room in particular is the dumping-place for everything that had to be moved somewhere.  Still, the environment is not too bad for working.

The University have just launched a new VPN program for us to use.  It's unfortunate that their planned roll-out and replacement of the old VPN co-incided with the Coronavirus pandemic, but there you go.  In fact, the VPN only has some minor use for me for accessing those of the University websites which are only available on campus (some management/teaching ones are, some aren't).  The most useful aid to home-working, which the VPN doesn't do as standard is to run a SOCKS5 proxy so that I can make all my web-browsing happen through a machine at work.  It doesn't actually help me access some work-based websites because it doesn't change the DNS to resolve internal-only addresses, but it lets me access journals and other professional websites from a University IP address - something the split tunnel VPN doesn't do.  

Here are some brief instructions for setting up a SOCKS5 proxy from a Unix-based machine (e.g. linux or Mac OSX):

• Use Firefox and install the Proxy Toggle add-on.  Set up its preferences to look like this:

• Open a terminal and type ssh -N -D 1337 -q myname@machine.my.uni.edu except that you should replace myname@machine.my.uni.edu by a machine at your University that you can ssh into.

• Turn on proxy browsing in your Firefox by clicking on the icon that's been added to the toolbar.  It should look like this:

 

when the SOCKS5 proxy is not active and this:

when it is active.

When you are done, you can quit the ssh command with ctrl-c and switch the proxy back to the off position. 

Coronavirus 20th March

Today is the last day that the University is operating roughly as normal, at least in terms of teaching undergraduates.  We've been teaching as normal this week, and from next week everything is to be done remotely.  For me, this is relatively easy, as this is my light teaching semester, when I only have project supervision to do.  Today is also the last day my middle two children are at school (oldest already been off since beginning of week and youngest is only a few months old, so no school for him anyway).

I'm all set up with a University-issue headset, and I've done my first meeting with the Zoom teleconferencing software, so I feel more or less able to go with working from home.  The difficult thing will be getting anything done while in the same house as my family, with young children.  We'll just have to see how that goes. 

My parents made it home from Spain in a mad dash last weekend.  They had gone their for a 1-month holiday on the car ferry via Bilbao.  They drove back over the period of 2 days getting through France just before the borders within Europe were generally shut (though they might still have let people through to return to their homes, I think).  It's a relief that they are at home.

The FaceBook group I set up in the nearby roads has had lots of people join it.  For now no-one has requested help with things like getting groceries, but I expect that will change if things carry on like they do, with more and more people being asked to self-isolate at home. 

Nuclear Fission Dynamics in our Frontiers special topic

The next article published in our special topic on advances in time-dependent methods in nuclear structure and reactions in Frotiers in Physics is "Nuclear Fission Dynamics: Past, Present, Needs, and Future" by Aurel Bulgac, Jin Shi, and Ionel Stetcu.  The reference is Front. Phys. 8, 63 (2020) doi:10.3389/fphy.2020.00063.

It's a broad-ranging discussion of how the process of fission works from a microsopic point of view (microscopic meaning at the level of individual nucleons and their quantum wave functions).  The take home message is that the adiabatic approximation that is frequently applied does not work for the last stages of fission where the rearragement of the nuclear shape is too fast for the nucleus to continuously relax into the ground state associated with its instantaneous shape.  

There are lots of nice figures included which makes it easy for me to include one in the blog post.  This is part of their Figure 7 showing a typical density plot of the point in the fission process in which the nucleus (in this case fermium-258) splits into two.  One sees the importance of not assuming spatial symmetry, which is an approximation often made.

Coronavirus 15th March

Here are some photos from my nearby branch of Waitrose:

They show where the pasta usually is, where the toilet rolls usually are, and where the baby wipes normally would be.  Panic buying has hit Guildford.  It's a bit dispiriting to see, and to realise that at the first sign of a social difficulty, in the form of the effects of people having to self-isolate because of the Coronavirus, is that people go and take more from the supermarkets than they need, thus depriving others.  There were a couple of things on my shopping list that I couldn't get (Lemsip, baby wipes (and I actually have a baby that needs wiping)) but I'll manage without, and will probably be able to pick them up when they are re-stocked.  But still, a bit sad.

It's Monday tomorrow, and my flexible working arrangement mean that I work compressed hours, which involves me staying at home on Mondays to spend time with my #1 son.  As a bonus, my #2 daughter's school has just (at 23:15) emailed to say it will be closed tomorrow because a staff member has developed symptoms consistent with Coronavirus infection.  Aside from looking after kids, my other plan is to make and distribute leaflets to all the houses in my block to set up a network where people who need help shopping (for example) because they are self-isolating get the help.  Hopefully it will not much be needed, but it would be awful if it were needed and it wasn't there.

On the plus-side, Waitrose had loads of half kilo "Essential" tiramisu, and on special offer too:

Affected by Coronavirus

The World Health Organisation has declared that the incidence of the coronavirus is enough to count as a pandemic, and the UK is one of the countries affected.  The University of Surrey has just announced that next week will be our last week of regular teaching activities.  After that we will be switching to all-online teaching and examining activities.  The campus is not yet planning to shut down, so going in to work is supposed to carry on as normal for now.

Had the coronavirus pandemic not come about, I would have just return a couple of days ago from a meeting in Beijing, but that was cancelled several weeks ago.  Yesterday the Institute of Physics announced the cancellation of all their meetings coming up, which includes the annual Nuclear Physics Conference which they sponsor.  I was due to talk in that, but it's not going ahead.  Before that, is a meeting in Jyväskylä, Finland, which is now almost certain to be changed in some way (cancelled, moved, or performed online).  It's all rather dramatic.  But of course, these small aspects of my work are nothing compared with the consequences of the disease.

On a more personal level, this year very unusually my family was going to come with me on my work trips.  Unusually because my partner is on maternity leave and this gives her the time to travel with me, as well as meaning I can carry on sharing the care of our children when I get home from work even when travelling.  With the Edinburgh conference cancelled it looks like we will be losing quite a bit of money on the travel costs (unless we go anyway, I guess), and the same may well happen yet to a meeting we are all supposed to be going to in Japan in May.  My parents are in Spain for a month-long holiday.  Where they are, all bars, cafes and restaurants have just been shut down, so it is well that they are in a self-catered apartment.  But worrying for them (and me), as their age makes them more at danger from the virus.  They have yet to learn whether the ferry they have booked to get them home will still be running.

Oh, and tomorrow night's school quiz run by my daughter's school Parent-Teacher-Association has been cancelled.  Gah!

Next papers in our Frontiers In Physics Special Topic

I posted earlier in the month about the first papers to appear in the special topic on time-dependent methods in nuclear physics in Frontiers in Physics that I am co-editing with some colleagues.  Here are a summary of the next four, which have all appeared since then:

• Far Off Equilibrium Dynamics in Clusters and Molecules (doi: 10.3389/fphy.2020.00027) by Phuong Mai Dinh, Marc Vincendon, Jordan Heraud, Eric Suraud, and Paul-Gerhard Reinhard, describes techniques and results from non-nuclear systems such as small metal clusters, atoms, and molecules.  The techniques are compared with analagous methods in nuclear physics, and the differences discussed, such as the need to deal with electron emission, and the interaction with laser fields, as well as the different interactions involved in the density functionals.  The plot shown here (from Fig 1 in the paper) shows the response in the dipole moment of a cluster of five sodium atoms to an excitation by a laser pulse.  The excitation and deexcitation is seen over a period of about 20 fs (though I dare say the compitational simulation takes some orders of magnitude to reproduce what nature does in real time).

• Predictions of New Neutron-Rich Isotopes at N=126 in the Multinucleon Transfer Reaction 136Xe + 194Ir (doi:10.3389/fphy.2020.00038) by Xiang Jiang and Nan Wang uses the time-dependent Hartree-Fock method to provide a microscopic description of nuclear reactions of the xenon and iridium isotopes mentioned in the title, to look at some non-central reactions in which the reacting nuclei transfer some neutrons form one of the nuclei to the other during their reaction time, and then are left in excited states of another pair of isotopes following the transfer of neutrons.  A semiclassical approach (the GRAZING model) is then used to give a statistical de-excitation of the excited fragments to see what final set of isotopes are likely.  The purpose is to see if this kind of reaction can be used to study as-yet-unseen isotopes in current experimental facilities.  The results are that the proposed reaction should have a cross section large enough to produce new isotopes in presently feasible reactions, for isotopes around N=126 and Z~74.  The figure shows snapshots of the time-dependent part of the simulation of the two reacting xenon and iridium nuclei.

 

• Quasifission Dynamics in Microscopic Theories (doi:10.3389/fphy.2020.00040) by Kyle Godbey and A. S. Umar discusses the microscopic picture of what happens when you try to make the kind of fusion reactions to discover new superheavy nuclei.  The two nuclei you are trying to fuse together might, depending on the exact details of how they impact on each other, might briefly fuse before falling apart again ("fusion-fission") or they might graze each other with the transfer of a few nucleons (neutrons, mainly - the mechanism discussed in the paper above by Xiang Jiang and Nan

Wang) or they might stick together without really fusing to an equilibriated compound nucleus and split apart into two fission fragments from a kind of molecular state.  This is quasifission and is discussed here for the purposes of understanding it as a kind of hindrance to forming new superheavy nuclei.  The authors show how to identify quasifission in mass-angle distribution measurements and map out the landscape of the briefly-made (super)heavy system, as shown in the figure showing how the entrance and exit channels are constituted in terms of the shapes of the combined system.

• Fusion Dynamics of Low-Energy Heavy-Ion Collisions for Production of Superheavy Nuclei (doi: 10.3389/fphy.2020.00014) by Xiao Jun Bao is a mini-review surveying the literature for the various components of the mechanisms by which superheavy nuclei are formed, or fail to form (such as by the quasifission process discussed above by Godbey and Umar).  Aside from covering a broad survey of different theoretical methods, the paper highlights the uncertainty in the probability for a reaction to form a compound nucleus - an excited nucleus made from the colliding fragments which has lost the memory of what the intial fragments were.  That uncertainty, then, points to the need for more work in this area.  There is one figure in the paper, which neatly shows the possible reactions mechanisms for two colliding heavy nuclei.

Acceleration is a vector

I had a meeting in the ATI (Advanced Technology Institute) earlier today, and as I stole along the walkways leading up to the second floor where my meeting was, I noticed the interesting pattern of the wear on the wooden flooring.  Here's a picture taken from the second floor, looking down at the walkway on the first floor.

What strikes me about it is that at the bottom, there is relatively little wear on the wood, while the corner shows considerable wear.  Probably with little exception everyone that walks along the unworn section also walks along the worn section, and each part has been thus been subject to the same footfall.  It is turning the corner, then, that causes the damage to the surface, and not walking in a straigh line.  While there may be a lot more going on in terms of gait factors, it seems to me that this is a nice pictorial example of the fact that force is proportional to acceleration, and acceleration is a vector.  When someone is travelling in a straight line at constant speed they are not acceleration, but to turn a corner, even at constant speed, requires acceleration, and hence a force, which wears away the surface of the walkway.  

While we have an Advanced Technology Institute on campus, we do not yet have a Retarded Technology Institute. 

Mahir Hussein memorial workshop

I have just seen advertised a workshop called "7th IEA International workshop on Clustering aspects in nuclei and reactions" to be held in São Paulo in September.  The workshop is being dedicated to Mahir Hussein, who died last year.  

Mahir was a nuclear reaction theorist whose work overlapped with much of the work that the Surrey theory group has specialised in.  He visited the group at least once, and gave jobs to some graduating Surrey PhD students over the years.  Though spending most of his research career in Brazil, he was originally from Baghdad in Iraq, and he graduated from Baghdad University in the 1960s.

Workshop details are here.  I've added it to my 2020 list of conferences and workshops.

Death and serious injury from dark matter

A few years ago, I wrote a blog post about a paper published on the subject of dark matter as a potential cancer-causing agent.  Today, a related paper was published on the potential of "macros" -- dark matter object of macroscopic size (or weight) that could cause death or serious injury in humans, in the form a bullet-like wounds.  The apparent absence of such dark matter deaths is then used to put limits on the actual occurrence of such forms of dark matter.  

The paper is published open access in Physics Letters B, here.