Monday, 14 January 2019

del-squared-cactus

A quick post today as I take a break in marking computing assignments.

I saw on Twitter a post about not recognising Greek letters in physics equations:

and a response from someone who teaches physics

Looking through many of the responses, it seems that it is a common problem among physics students to not have learnt or be able to pick up from context the names of the symbols used in physics equations if they are Greek letters (or other unfamiliar symbols presumably).

I think I do try to teach the names of the symbols I use when I use them, but maybe I don't.  Maybe I just say them out loud as I read or write them down and hope that's enough, but it seems from the Twitter responses above that it's probably not.  Would be interested to hear anyone's experiences on the matter.

Thursday, 10 January 2019

Pear-shaped fission

Over the Christmas break I noticed that a paper appeared in Nature giving an explanation of why fission fragments tend to favour particular daughter nuclei over others which might naively be expected to dominate.

When a heavy nucleus, like Plutonium–240, with 94 protons and 146 neutrons, fissions, it splits up into two lighter nuclei.  Different daughter nuclei can be produced in different fission events, but there is a distribution which centres on a light fragment with around 54 protons and 85 neutrons, and a heavier one taking the rest of the nucleons.  The reasons why particular daughter products are favoured are to do with how the slow process of the parent nucleus stretching before forming two nascent fragments and finally splitting is energetically possible.  It has been a bit of a puzzle why ~54 protons should be more favoured than 50.  50 is a "magic number" for protons;  an especially stable configuration which you might expect to be a preferred end product when looking at energetically possible outcomes.  

The paper by Scamps and Simenel calculate that the key reason that 50 is bypassed is that octupole shapes (pear shapes) are favoured at around proton number 54, and these are the gateway shapes formed as the nucleus fissions and the neck of the fissioning nucleus splits to give the narrow end of the "pear" in the daughter nuclei.  This effect is more important than the final stability of a 50–proton nucleus.  

The paper is in Nature, which is behind a firewall, so I'm not sure that it is available to a general audience.  With the unpaywall browser plugin, I see that there is a "bronze open access" version available here.  The first description of what bronze open access means is that it is an potentially fleeting open access status without the backing of a perpetual license that some publishers are implementing.  This somewhat critical description is something I found in ... Nature.

The kind of calculations performed in this paper are very close to what I do, so I'm (a) pleased to see that it gets published in Nature (b) pleased they cite work done by my PhD student a few years ago and (c) annoyed that I didn't followup with my student's work after he left to work for Sainsbury's by making this same analysis that got published in Nature.   The attached picture is a snapshot from a movie they provided in the article as supplementary material.

ResearchBlogging.org Guillaume Scamps and Cédric Simenel (2018). Impact of pear-shaped fission fragments on mass-asymmetric fission in actinides Nature, 564 : 10.1038/s41586-018-0780-0

Thursday, 3 January 2019

Two new isotopes: Boron-20 and Boron-21

I noticed a new paper appear on the arXiv this morning, announcing the discovery of two new isotopes;  boron–20 and boron–21.  Boron has atomic number 5, so each boron nucleus has 5 protons.  There are two stable isotopes; boron-10 with 5 neutron and boron-11 with 6 neutron.  Boron–20 and –21 have 15 and 16 neutrons respectively.  That large asymmetry between the number of neutron and protons makes the isotopes unstable.  They are so unstable that the last neutrons do not even stick on to the nucleus for long and they decay by emitting one or two neutrons.  The live long enough to be identified as a resonance state in experiment, which is exactly what happened in the experiment that led to their discovery. 

Figure from arXiv:1901.00455
The experiment took place at the Radioactive Isotope Beam Facility (RIBF) at RIKEN Nishina Center, in Japan.  A beam of calcium–48 ions was fired at a beryllium target at very high energy, causing some of calcium nuclei to have a number of their protons and neutrons ripped off to give lighter isotopes of various sorts.  From this cocktail of fragments, the experimenters extracted nitrogen–22 and carbon–22 which were then directed onto a second target (of carbon) where some reactions knocked protons out of the nitrogen–22 and carbon–22 nuclei to form the previously-unknown boron isotopes. The snapshot taken from the paper in the arXiv shows the reactions taking place.  The plot is a section of the Segrè chart in which isotopes are shown with increasing proton number in the y-direction and increasing neutron number in the x-direction.  The arrows show the proton knockout reactions leading to the boron isotopes.  The red line marks out the neutron drip-line, separating those nuclei which are stable with respect to losing a neutron, and those which are not.  

Though the paper just appeared on the arXiv today, it was published in Physical Review Letters on 27th December.  Odd to put it on the arXiv only after it has been published elsewhere, but at least it means it reaches a wider audience (including me!), albeit belatedly.  Unfortunately the arXiv is not as widely adopted in nuclear physics as astro or high energy physics.

Tuesday, 1 January 2019

PhD in theoretical nuclear physics -> fitness trainer

One thing that some students ask when it comes to signing up for PhD study is what is the job market like afterwards?  One thing is for sure – a PhD does not mean that the only thing you can do is to go further and deeper into academia in the specialty area of your PhD research.  Here's one example of a previous PhD student of mine.  After her PhD in theoeretical nuclear physics (leading to publications here, here, here, here, here, here, here, here, and here) Emma went to work on climate science, where she devloped a successful career.  Most recently she has started a new business as a fitness trainer for children.  Here's a video featuring her for her company Kidz Impact.  I note that the link to nuclear physics is still present: "Kidz Impact and Teen Impact are trading names of Strong Force Limited"

Monday, 31 December 2018

Books of 2018

Since signing up with Goodreads, it has become easier to present a list of the books I have read during a year.  I seem to have missed posting this the last couple of years (since 2015).  Thanks, too, to Goodreads, I seem to be able to copy and paste a list of the books, with little pictures, hyperlinks, and the date I finished the book.  For many of them, I've written a review on Goodreads, which you might be able to find if you follow the book title link

Strong Poison (Lord Peter Wimsey, #6)



Dec 30, 2018 


Relativity and Common Sense: A New Approach to Einstein



Dec 24, 2018 


Home Fire



Dec 14, 2018 


We Have Always Lived in the Castle



Nov 20, 2018 


Armadale



Nov 04, 2018 


A Legacy of Spies



Oct 27, 2018 


Finding April



Oct 24, 2018 


The Shortest History of Germany



Oct 11, 2018 


Lincoln in the Bardo



Sep 21, 2018 


A Matter of Choices: Memoirs of a Female Physicist



Sep 16, 2018 


Home: A Time Traveller's Tales from Britain's Prehistory



Sep 10, 2018 


Kent Dialect



Aug 31, 2018 


Don Camillo And The Devil



Aug 30, 2018 


Why I'm No Longer Talking to White People About Race



Aug 21, 2018 


Kim



Aug 09, 2018 


The Last Wild



Aug 08, 2018 


Learn German with Stories: Karneval in K�ln - 10 Short Stories for Beginners



Jul 31, 2018 


Radiation Diaries: Cancer, Memory and Fragments of a Life in Words



Jul 23, 2018 


The Young Atheist's Handbook: Lessons for Living a Good Life Without God



Jul 03, 2018 


The Old Curiosity Shop



Jun 08, 2018 


Autumn



May 17, 2018 


Peter Pan & Wendy



May 09, 2018 


Deerbrook



May 03, 2018 


The Book of Wonders



Apr 23, 2018 


Walks with Walser



Apr 18, 2018 


Ivanhoe



Mar 27, 2018 


Girl in a Band: A Memoir



Mar 16, 2018 


What's Next?: Even Scientists Can’t Predict the Future – or Can They?



Mar 09, 2018 


How Not To Be a Boy



Feb 15, 2018 


The Story of the Lost Child (The Neapolitan Novels, #4)



Feb 14, 2018 


Black Sheep



Feb 13, 2018 


In the Heart of the Sea: The Epic True Story That Inspired Moby-Dick



Jan 31, 2018 


Walking



Jan 27, 2018 


The Epic of Lofoten



Jan 25, 2018 



Sunday, 30 December 2018

Roy Glauber 1925–2018

I saw (initially from Peter Woit's blog) that Roy Glauber died a few days ago.  Glauber's name is known to nuclear physicists for his approximate treatment of scattering theory which can be applied to nuclear collisions at high energies.  It was an ingredient in some of the seminal work from the nuclear theory group in Surrey when we became the go-to people for the reaction theory needed to understand the reaction of halo nuclei, and the extraction of their sizes. I say "we" – this was slightly before my time at the group.  Here is a paper by Jim Al-Khalili and Jeff Tostevin from 1996 on the subject of nuclear sizes, making use of Glauber theory. 

Nuclear Physics was a relatively small part of Glauber's work.  His biggest thing, at least the thing that got him the Nobel Prize, was his foundational work on quantum optics.  The picture attached to this post is Glauber at the Nobel Prize Ceremony in 2005, courtesy of Wikipedia.

Friday, 28 December 2018

2019 Nuclear Physics Meetings


There was a spate of emails leading up to Christmas from conference and workshop organisers sending reminders or announcements about their conferences.  I thought I would assemble the details, along with some other relevant meetings coming up in low-energy nuclear physics here.  It will help me decide which I might attend.  I'll add more 2019 meetings as I hear about them.

25/02–27/02: ENSAR2 NUSPRASEN Workshop, GSI, Germany
Very much a workshop by the sounds of it, with an aim to stimulate cooperation between laboratories working on superheavy element synthesis research.  The blurb says "It is the opportunity to dwell on topics which are not usually treated in regular conferences or collaboration meetings" [website]

25/03–26/03: Workshop AGATA@LNL for stable beams, Padua, Italy
The first of two meetings in Padua on this list.  This one primarily for those interested in undertaking gamma ray spectroscopy experiments in Legnaro.  If I go to any meetings on this date, it'll be the next one in the list.  [website]

25/03–27/03: 54th ASRC International Workshop "Nuclear Fission and Structure of Exotic Nuclei", Tokai, Japan
From the website: "The meeting will mainly be devoted to new experimental and theoretical achievements in fission, super-heavy nuclei, nuclear reaction and structure of exotic nuclei. Especially, our group is driving a dedicated program using the rare target material, einsteinium-254, for which new results and new proposals will be discussed."  I've set some calculations with einsteinium–254 going to see whether I might find anything interesting enough to talk about.  If so, I'll tell the organisers and see if they'd like to hear my talk.  [website]

13/05–17/05: NSD2019 Nuclear Structure and Dynamics, Venice, Italy
This is one of a series of conferences hosted by one of a number of University-based research groups somewhere around the Adriatic.  I went to a very enjoyable one in Dubrovnik some years ago, and this is a nice medium-sized general low-energy nuclear physics conference that always has lots of talks on-topic for me.  Though I don't think I'll be going to this one. [website]

19/05–24/05: PLATAN 2019, Mainz, Germany
I didn't put the whole title of this one in the bold header line, because its name is "Merger of the Poznan Meeting on Lasers and Trapping Devices in Atomic Nuclei Research and the International Conference on Laser Probing".  I've been tangentially involved in work related to laser trapping and excitation of nuclei in the form of calculations of isotope shifts, but it's not something I've done much of lately, and I don't expect to attend this one.  [website]

27/05–31/05: 7th Workshop on Level Density and Gamma Ray Strength, Oslo, Norway
I've been to one of these before, in 2015.  The lab in Oslo have a technique (named after them) to measure the quantities used to name this workshop.  I can calculate them, or at least closely related things, and it's not crazy to think of going.  And Oslo is lovely.  [website]

20/05–21/05: TNP19 Theoretical Nuclear Physics in Padova, Padua, Italy
The subtitle is "a meeting in honor of Prof. Andrea Vitturi" and the meeting is organised due to his retirement.  I suppose the attendees will be largely drawn from his collaborators, and those whose research overlaps strongly.  Vitturi has done a lot of work on giant resonances (among many other things), which is relevant to me.  [website]

23/06–29/06: International Workshop on Nuclear Theory #38, Rila Mountains, Bulgaria
The annual workshop organised by the theoretical nuclear physics group in Sofia.  I've been to this a few times and always like to come.  I had to stop when I took over running the MPhys Research Year programme at Surrey, as this meeting is always during our exam board meeting and my attendance became more or less compulsory.   [website]

01/07–05/07: ANPC African Nuclear Physics Conference, Kruger National Park, South Africa
I heard about this when attending COMEX6 in Cape Town in October.  It's a broad conference of fundamental and applied nuclear physics which I'm sure I'd enjoy, and it's in a lovely location.  I've used their website photo on this post above.  I can't really justify going, though.  [website]

29/07–02/08: INPC2019, Glasgow, Scotland
As the conference flyer says, "INPC is the biggest conference in the world for fundamental nuclear physics".  And it's in the UK this year, so the chances of me going are very high.  And it's in one of the UK nicest cities, so that helps too.  I like INPC, with its very broad coverage of nuclear physics areas.  I end up going to a combination of sessions which are right up my street, and others which broaden my horizons.  [website]

25/08–30/08: 6th International Conference on the Chemistry and Physics of the Transactinide Elements (TAN 19), Wilhelmshaven, Germany
I haven't been to editions 1-5 in this series.  I don't expect I an add this to my list of conferences to attend, though fusion reactions (leading to superheavy nuclei) is one thing I work on.  [website]

01/09–07/09:  XXXVI Mazurian Lakes Conference, Piaski, Poland
Every year there is a large nuclear physics conference in Poland – either the Zakopane conference or the Mazurian lakes conference.  I've never been to either.  Maybe one year, but not this, since it clashes with the next conference, which I am co-organising.  [website]

02/09–06/09: 24th European conference on few-body problems in physics, Guildford, UK
Well, I'm a local organiser of this, so I will definitely attend, though more for the scientific interest than because I am any kind of expert with few-body systems.  Mostly I deal with nuclei made of many (rather than few) particles which means particular kinds of approximation in theoretical study, while "few-body" implies a different method of solution.  [website]

09/09–13/09: HIAS2019 Heavy Ion Accelerator Symposium, Canberra, Australia
A long way away from me, in Canberra, but this annual meeting all about heavy-ion reactions of the sort that can be performed at the Canberra accelerator is very relevant to me through my time-dependent Hartree-Fock work.  This year, I (as coordinator of the Surrey MPhys Research Year) have placed two students for research work in Canberra, and I will have to visit them roughly at that time of year, so it wouldn't be crazy to make my visit coincide with the symposium.

15/09–20/09: Nuclear Physics in Astrophysics IX, Frankfurt, Germany
I've been involved with work on nuclear physics for neutron stars, actually going back to my PhD a long time ago which included calculating properties of predicted neutron stars from a particular form of the nuclear interaction.  While I've also done follow-up things more recently, I don't think I will be able to present anything sufficiently interesting and on-topic here.  Of course, attending conferences is more about learning new things than telling everyone else your latest results, but without the latter, it's harder to justify attending.  [website]