## Monday, 12 August 2019

### Happy 100th Birthday Margaret Burbridge!

Today, 12th August 2019, is the 100th birthday of Margaret Burbridge.  She is a British-American astrophysicist who is jointly responsible for the idea that stars are giant nuclear fusion reactors.  This started the whole field of nuclear astrophysics, and is canonical enough to be taught to undergraduates.  In fact, we (at Surrey) have a degree programme called Physics with Nuclear Astrophysics, which we wouldn't have if not for Prof (emeritus) Burbridge.  Happy Birthday!

The picture is from the Wikipedia article about her, and shows her in 1976 winning a Woman of the Year award.

## Thursday, 18 July 2019

### Thursday at #UNTF2019

#UNTF2019 continues today after yesterday's talks, poster session, and conference dinner, with two sessions in the morning, followed by the end of the conference and lunch.  Here's a summary of the first session's first two talks (with the third being designated for attendees-eyes only)

Toby Wright from Manchester started the morning with a comprehensive survey of all kinds of nuclear data being collected at the n_TOF (neutron time-of-flight) facility at CERN.  This includes things like neutron absorption cross sections and fission data, which provide useful input for applications - particularly nuclear reactors. Toby presented a lot of results of data, improving on older measurements and evaluations

The second talk had the title "Robots used to mitigate nuclear disasters", with a discussion of exactly that -- how robots can be made and used in nuclear disasters.  They need to be very radiation-resistant, for examples, which has consequences for the design.  Also, you can't go in and fix it if it has a small problem, so it has to be very reliable.  Ideally you'd like to communicate with it wirelessly, but nuclear reactors tend to be heavily shielded.  The environment (radiation aside) can be pretty hazardous; flooding, fallen masonry etc.  All-in-all, quite a challenge to the robot builder. We had
The talk covers robots used historically;  the "RadRobot", "RedBot", and "WorkHorse" used at Three Mile Island; At Chernobyl there is a museum dedicated to the robots used there, though full details of the ~60 robots used there have been lost.  The most succssful robot used there, "MoBot" was destroyed when a helicopter accidentally dropped it.  Some robots used, such as converted tanks and bulldozers, broke down very quickly due to the environmental hazards.   Some years after the initial disaster further more advanced robots were sent in to assess the continuing status of the ruined reactor;   The robots used at Three Mile Island and Chernobyl were built reactively after the disasters, while in Fukushima there were a number of robots built in advance to be used in case of problems (as well as to routinely monitor).  Unfortunately, they were not very usable in Fukushima because the robot projects had been defunded and the robots left in cupboards, lacking maintenance, and lacking expertise of the staff who had left or moved on to other projects.  Instead, "Packbots" and "Warrier" robots were bought off the shelf from the US and deployed.  They weren't radiation-hardened but were well-developed in other technological areas.  Many other robots were then deployed -- e.g. the "quince" which could go up stairs and over rubble, the "RaBot", a radiation-hardened robot which could handle very high radiation doses (10,000 Sv per hour).

The talk ended with a couple of robots designed for the future;  Honda's E2-DR and the Centauro from Italy.  We were treated to a video of the E2-DR which looks a little like it's trying to get back from a conference dinner after one too many drinks:

## Wednesday, 17 July 2019

### Conrerence photo from UNTF

Today, as #UNTF2019 continues, we had our conference photo.  Here it is.  If you click on it, it should come up larger. I'm the one nearest the top border of the image file.

## Tuesday, 16 July 2019

### Session 1 at #UNTF2019

It's a busy time conference-wise in the UK.  The week after next sees the world's largest periodic nuclear physics conference, INPC, taking place in Glasgow.  Next week I'll be at a conference organised here at Surrey on ab initio methods, designed to attract delegates attending INPC the following week.  That clashes with a workshop on octupole shapes in nuclei, taking place even more conveniently for INPC attendees, in Paisley.

This week there is a workshop at the University of York to celebrate the conferring of an honorary degree on Witek Nazarewicz, which would have been nice to attend, but I am staying in Surrey this week to attend our graduation ceremony (on Friday) and the Universities Nuclear Technology Forum (UNTF2019) today to Thursday.

The topics of #UNTF2019 cover a wide range of nuclear science and engineering, so I hope to learn a lot of things that are not so close to my own area.

Here is a live-blog summary of the first session:

First up is Sam Bennett (Manchester) who has performed new measurements on the capture of neutrons on C–13 in order to help understand how the long-lived radioactive contaminant C–14 is generated in graphite-moderated reactors.  The cross section for this reaction has been measured a few times historically, going back around 60 years, but there is inconsistency in the data.  Sam's work uses a method different to the past measurements -- irradiating a sample of carbon and using atomic mass spectroscopy to anaylse the results.  He discussed in some detail how to counter the problem of N–14 contamination in the samples.   The conclusion:  Good agreement with the most recent calculation which has been taken as the adopted value.

Second, Emma Braysher (Surrey/NPL), talks about the need to improve measurements of half-lives of long-lived isotopes for their use in things like radio-dating.  Surprising (to me) is that Uranium-238 has only had its mass measured once before (until very recently) and that the experimental uncertainty is a million years.  Emma talks about using mass spectroscopy to measure half-lives;  either one can use isotope dilution in which the isotope which one wants to measure is diluted with (preferably a stable) isotope of the same element as a reference and mass spectrometry is used to measure the ratio of the isotopes;  or one uses the in-growth method in which ones looks at the build-up over time of the daughter produces of the decay of the isotope in question.  The work presented showed the speaker's theoretical studied so far, with the experimental realisation the next stage in her project.

The third speaker is Rhiann Canavan (Surrey/NPL) who begins by asking what can be done with the large amount of U–238 waste from our standard nuclear reactors.  U–238 is not fissile, but is fertile so can be turned into a fissile material (in this case, isotopes of plutonium) by reaction with fast neutrons.  The fissile material can then be used as commercial fission reactor fuel.  The goal of Rhiann's work is to better understand the fast-breeding reactions which convert U–238 in to a fissile material and the resulting range of fission fragments.  In Orsay, near Paris, Rhiann and co-workers used an intense neutron source, LICORNE, to breed U–238 into fissile isotopes, and then a gamma-ray detector, NuBall, to look at the decay of the hot fission fragments.  A phenomenal amount of data is collected from the reactions, which then has to be painstakingly analysed, both for the fission decay products of interest, and also to avoid the background signal (e.g. from decay of germanium isotopes in the gamma-ray detector itself).  It's the first time I've seen a description of gamma-ray gating in spectroscopic analysis in terms of selecting coloured jelly-babies from a pile of sweets.

The final speaker is Thomas Fried (Lancaster).  As well as his affiliation to Lancaster Uni, Thomas works at Sellafield and is concerned with long-term decommissioning of the site.  This includes, in particular, older waste that has been processed for storage.  Some of it is known as "heat-generating sludge" and Thomas's project aims to develop a mechanism for assessing the properties (mechanical, thermodynamic) properties of the stored sludge.  The slide shows a schematic of the prototype mechanism.

I don't think I'll live-blog the whole thing, but I hope this gives you a flavour of the conference.  Next up: Coffee break :-D

## Tuesday, 2 July 2019

### Rutherford Medal Winner Prof Phil Walker

The Institute of Physics have just announced that the 2019 winner of their Rutherford Medal is Prof Phil Walker.

Phil is an emeritus professor here at the University of Surrey who straddles the experimental–theoretical divide and specialises in understanding metastable isomeric states in nuclei;  excited states that decay much more slowly that you'd expect for such an excitation.  The full citation is on the IoP's new story, as linked above.

Phil has been a good friend and colleague to me during my time at Surrey.  It was thanks to him that I got my first post-doctoral position here, joining the reaction-theory dominated theoretical group, though my specialty is in nuclear structure.  We have since worked together on various project together over the years, writing 14 co-authored papers together, which for me is one short of my record of 15 (with one of my two PhD co-supervisors, Irena Stone).  I've always found his way of thinking very clear, grasping the context of a problem and the bigger picture.  Hopefully I can up this figure of 14 with him.

My opinion may be biased, but I think his prize is very well deserved, and overdue. Cheers, Phil!

I attach to this post a rather blurry photo of Phil that I happen to have in my collection, from a meeting in Krakow a few years ago.

## Thursday, 27 June 2019

### Publishing proceedings in SciPost

In September, we (the Surrey nuclear theory group) are hosting the 24th European Few-Body Physics Conference.  One of my main roles on the local organising committee is to arrange publication of the proceedings, and I'm pleased to have organised this with the journal SciPost Proceedings.  Unlike most (all?) of the other regular journal options, SciPost proceedings are free to publish in and free to read.  The costs involved in the whole publication process are pretty modest, being the web–hosting of the papers, and the provision of a doi for each paper.  All other tasks, such as managing and implementing the refereeing and editing process is done, as usual, free of charge by academics, who are paid a full time salary to be academics.

Those low costs of running the journal are provided by sponsors, and I'm happy to see, from attending a presentation about Plan S last week, that the University of Surrey are sponsoring SciPost.  The amount paid by the University is minuscule compared to traditional journal subscription costs, and amounts to the cost of paying for a couple of Article Processing Charges to a regular journal.

I'm excited to go through the process of editing the proceedings (i say now, before the real work starts in earnest), and I'll report back here how it goes later in the year.

## Tuesday, 11 June 2019

### Advances in Time-Dependent Methods for Nuclear Structure and Dynamics

Together with some co-editors, I've started up a Research Topic in the journal Frontiers in Physics.  It's called Advances in Time-Dependent Methods for Nuclear Structure and Dynamics, which I hope is a reasonably self-descriptive title for the kinds of articles we are looking for for the special issue.

There's a little picture of me on the topic web page among the list of editors.  Fame at last.  If you want to submit an original research article, a review, or a perspective piece on future research areas, please get in touch.  We (the other editors and me) hope it will be a thorough snapshot of time-dependent methods being used today in nuclear physics research.

## Saturday, 8 June 2019

### Student placement in Beijing

 Marko, at the entrance to the nuclear physics building
I'm heading home from my last trip of the season to visit students on their MPhys Research Year placement.  This time it's been to Beijing where we have a student, Marko, working on some calculations of nuclear fission.  He is being hosted by Peking University, working in the group of Junchen Pei.  Usually on these trips, I am visiting a student working in an area not exactly the same as my own.  In this case, Marko, together with Pei, is building on some work that I did with a PhD student a few years ago, and it's exciting for me to see this work being continued.

I now have a relatively quiet summer (travel-wise, at least).  According to the rules for the MPhys Research Year, our students get visited twice by a member of academic staff, and I will make a second round of trips in September.

## Thursday, 23 May 2019

### Visiting students in Canberra

This year, we (University of Surrey Physics Department) have sent two of our undergraduate masters students out to the Australian National University in Canberra for a paid work placement in the nuclear physics department.  In the last few days I've been visiting them to find out what they've been up to, to check on progress, conduct an assessment and to make sure everything is generally okay.

The two students are working on reaction mechanisms, trying to understand the process of fusion better, particularly as fusion processes compete with reaction mechanism that lead to the combined nucleus, formed when two nuclei react, not sticking together.  This is especially important in understanding the reactions that lead to making new superheavy elements, where the competing processes dominate.

I'm happy to report that the students are enjoying life in Canberra and at ANU in particular, and I've enjoyed learning about the work they are doing.  I should be back for a second visit in September, which will coincide with a workshop taking place here (HIAS 2019).

Last night, as part of the visit, I took the students and two of the supervisory team out to dinner.   From left to right in the picture we are Prof Mahananda Dasgupta, Dr Ed Simpson, Stefan Parker-Steele, Wiktoria Wojtaczka, and me, Dr Paul Stevenson.

## Tuesday, 21 May 2019

### Re-writing nuclear physics textbooks

Following a Summer School in Pisa in 2017 with the ambitious title "Re-writing Nuclear Physics textbooks: Basic Nuclear Interactions and Their Link to Nuclear Processes in the Cosmos and on Earth" the notes from the lecturers have been written up and published in a special collection (a "focus point", so they call it) across several issues of the EPJplus journal.  They are freely available until 20th July 2019 here.  Seems like a useful resource to point students at and, indeed, to read oneself.

## Monday, 20 May 2019

### The early-universe lithium-beryllium wars

There's a spat playing out on the nucl-ex (nuclear experimental) part of the arXiv preprint server.  I have no special knowledge of what's going on, but the timeline of the papers on arXiv is:

1. Moshe Gai of UConn sent a paper to the arXiv "The Interaction of Neutrons With 7Be: Lack of Standard Nuclear Physics Solution to the "Primordial 7Li Problem"."  The paper describes an experiment to look at the capture of neutrons by beryllium–7 nuclei at energies similar to the conditions of the early universe, in order to try to understand if this reaction can account for the disagreement between the observed amount of lithium–7 in the universe compared to models of the big bang in which the lightest few elements were formed.  The paper appeared on 24th Dec 2018 and in the submission comments, Prof Gai says
Talk presented on behalf of the SARAF US-Israel, Switzerland Collaboration at Nuclear Physics in Astrophysics (NPA8), 18-23 June 2017, Catania, Italy, that was reviewed by two referees and accepted for publication in NPA6, EPJA, 2017
So it appears to be a paper written for and accepted for a conference proceedings, but that did not appear in the proceedings.  The preprint gives results from the experiment in a summarised list, promising that a full paper is planned for publication.

2. On 3rd April 2019 Dorothea Schumann submitted at "Comment to "The Interaction of Neutrons With 7Be: Lack of Standard Nuclear Physics Solution to the Primordial 7Li Problem", published by M. Gai in arXiv 1812.09914v1".  Dr Schumann is one of the authors listed as being in the collaboration on behalf of which the original Gai paper was claimed to be written and the comment is also coauthored by 5 other members of the original collaboration list.  The comment says that "The Hebrew University PI of this collaboration has dissociated himself together with his team from this experiment and from the collaboration in Fall 2016" though which members of the list given by Gai are from the Hebrew University is not obvious.

Moreover, the comment goes on to say that Gai had no permission from the collaboration to publish the experimental data, and that the cross sections given by Gai as deduced from the experimental data are unreliable for reasons that Dr Schumann will provide "on request".   The comment finished with the strongly worded statement
We  consider  unauthorized  release  of  questionable  data  an  intolerable  damage  of  the  scientific reputation  of  the  collaborators  personally,  the  involved  research  institutions  in  general  and  the trustworthiness of published data in the entire scientific field. We fully dissociate ourselves from any scientific content published by M. Gai on the project “The Interaction of Neutrons With 7Be: Lack of Standard Nuclear Physics Solution to the Primordial 7Li Problem" and request the paper currently posted on arXiv immediately to be retracted.
3. Today (why I am now noticing the conversation) Prof. Gai has posted, on the arXiv, "Gai Reply to Comment by Schumann et al. [arXiv:1904.03023]".  This is quite lengthy, but the gist of it is given in the abstract:
Statements included   in   the   comment   published   by   Schumann et al.(arXiv:1904.03023) are contradicted by documents that were communicated to one of the co-authors of the comment (Dr. Koester). These documents are reviewed but cannot be disclosed here due to copyright (they are available on request). A summary of the scientific dispute between the collaboration and Dr. Schumann,was submitted on September 24, 2018, to the Directorate Support of the Paul Scherrer Institute (PSI) and can be provided on request.
Here the disagreement is characterised as being between Schumann and "the collaboration".  Gai goes on to elaborate on his side of the story, though clearly there is more information that the authors have not disclosed (and I have not taken them up on their request, since I don't imagine that I am exactly going to arbitrate on this), but it's rather unfortunate that it is playing out in the arXiv.

I suppose next that either there will be a response on the arXiv from Dr. Schumann or another co-author, or perhaps better, that the institutes involved will convene a panel, if they haven't already, to adjudicate.

[N.B. I've used the titles Prof for Gai as per his institution' website, and Dr for Schumann as for hers.  Apologies to either if that is an incorrect title.]

## Friday, 17 May 2019

### Well hello neptunium-220

The discovery has been announced, in Physical Review Letters (here, but paywalled) of a new isotope of element number 93, Neptunium (Np).  It's Np–220, with 93 protons and 127 neutrons.

This isotope is a long way from the nearest stable isotope, as can be seen on this section of the nuclear chart, with proton number Z increasing along the vertical axis and neutron number N along the horizontal axis:

Np–220 is at the top left of the chart.  The stable isotopes are the black ones, with the nearest either involving losing many protons to go towards bismuth and lead, or to gain many neutrons to get towards the stable uranium isotopes.

It's possible to make these very far-from-stability isotopes by reacting together two lighter nuclei, in which the stable isotopes tend to have a N:Z ratio which is close to that of Np–220.  The actual reaction used was to fuse argon–40 with rhenium–185, making a very excited Np–225 nucleus, and then looking for decays in which 5 neutrons are emitted.

The experiments were performed in Lanzhou, China, and the resulting observation of alpha decay of Np–220 led to the conclusion that the extra stability conferred by the N=126 magic number survives into this far-from-stability region.

Thanks, as ever, to Ed Simpson, for providing the #1 online chart of the isotopes at http://people.physics.anu.edu.au/~ecs103/chart/index.php

## Wednesday, 24 April 2019

### My first video abstract

With my collaborator, Yoritaka Iwata, I have just published a paper in the New Journal Of Physics.  The paper is about conditions under which two nuclei can react in such a way that the final state of the reaction looks just like the initial state, despite a strong interaction taking place between all the nucleons involved.  If we're right, then our calculations might have implications for inert parts of stars' cores, or one day in nuclear fusion reaction.

This is the first time I've published in the New Journal of Physics.  They offer the possibility of having a video abstract with our paper, so I opened, probably for the first time, the iMovie software on my computer, made some animations, wrote a script and put it all together.  The final result is on the journal website.

## Wednesday, 17 April 2019

### Peter Butler FRS

The Royal Society has announced its newly-elected set of Fellows. There is a nuclear physicist amongst the cohort:  Prof. Peter Butler from the University of Liverpool has been made a fellow for his work on experimental nuclear physics.  In particular, they cite his work in reflection-asymmetric nuclei, and the leadership of prorgrammes at laboratories around the world such as at Jyväskylä and CERN.

Congratulations, Peter!

## Thursday, 4 April 2019

### Mathpix is pretty neat

Here's a neat piece of software I spotted via a re–tweet from @eddedmondson on Twitter:
It's called Mathpix and it lets you take screen captures of equations which it then turns into LaTeX code.  I thought I'd try it out with something quite stretching in the form of a slightly poorly scanned pdf of Max Planck's paper from 1900 Ueber das Gesetz der Energieverteilung im Normalspectrum.  Here is a screencap of the original equation:

As you can see, it's not perfectly scanned in, especially in the horizontal lines of the fractions.  Mathpix, though, did a fine job.  It said "We had trouble reading that.  Try zooming in for a better result." but the result was exactly right.  Its LaTeX result is

$E=\frac{8 \pi c h}{\lambda^{5}} \cdot \frac{1}{e^{\frac{c h}{k \lambda \vartheta}}-1}$

and its own graphical rendering comes out as

So pretty good really.

## Wednesday, 3 April 2019

### Welcome to O-11

The discovery of a new isotope was announced last week in Physical Review Letters (paper here, but it seems no open-access version exists, even on the arXiv).  Oxygen–11, aka 11O, has 8 protons (because it's oxygen) and 3 neutrons (to give it overall mass number 11).  That's a pretty extreme form of Oxygen, whose lightest stable isotope has 8 protons and 8 neutrons.

To make it, the experimenters from the NSCL (National Superconducting Cyclotron Laboratory at Michigan State University) started from a beam of stable oxygen–16 nuclei which they collided on a beryllium–9 (4 protons, 5 neutrons) target.  This bombarding produced a range of nuclei lighter than the oxygen–16 beam from which a magnetic separator was used to focus the oxygen–13 component of the debris into a secondary beam.  This was then sent to another beryllium–9 target.  Some of the reactions between the oxygen–13 and beryllium–9 nuclei caused two neutrons to be knocked out of the oxygen–13 to give oxygen–11.  Oxygen–11 quickly decays to carbon–9 (6 protons, 3 neutrons) and two protons.  These decay products were detected;  their coincident detection and the ability to reconstruct from the detection the properties of the parent oxygen–11 nuclei, repeated through thousands of events enabled the research team to confirm that indeed oxygen–11 had been produced.

Oxygen–11 is so unstable that it decays not by one of the three traditional radioactive decay mechanisms (alpha, beta, or gamma) but by losing two of its protons, and hence undergoing "two proton radioactivity".  This puts it on the borderline of actually existing as a nucleus at all.  The nucleus is so short-lived and unstable that it does not have a well-defined mass (or equivalently its ground state is not a stationary state of the nuclear Hamiltonian).  The experimental values of the observed mass of 11O is seen to have a spread of values ranging over about 3 MeV/c2.

The picture above is taken from Ed Simpson's excellent Colourful Nuclear Chart.  It currently has a blank space where oxygen–11 will no doubt soon go, just above nitrogen–10, and to the left of oxygen–12.  The black tramlines in the plot show the so–called magic numbers which are numbers of protons and/or neutrons which confer extra stability to the nucleus.  These cross each other at oxygen–10.  I doubt if oxygen–10 will really turn out to be noticeably stable compared to its neighbours.  There is already enough evidence that the magic numbers don't apply in light nuclei so far from stability.  I wonder if the odd stray oxygen–10 nucleus was made in the experiment at NSCL, in too little a quantity to get a good measurement of.

## Tuesday, 2 April 2019

### Nuclear Physics Meetings in 2020

 Bormio: Location of meetings in Jan and Feb 2020
Here is a post, which I will add to over the next 18 months or so, listing (mostly low-energy) nuclear physics meetings taking place in 2020 that I hear about.  Feel free to contact me or comment below with details of any that you think should be added

20/01–24/01: 58th Winter Meeting on Nuclear Physics, Bormio, Italy
It's blurb calls it a long-standing conference, and indeed at #58, it may hold a record for the most-held nuclear physics meeting.  The remit is very broad, including what might once have been called nuclear physics, but is now particle physics.  It is preceded by a one-day pre-conference school for students, covering the basics of the main physics areas dealt with in the conference.

Bormio is in the Italian Alps, and I understand that there is ample time in the programme for leisure activities, such as skiing. [website]

04/02–09/02: Vth Topical Workshop on Modern Aspects in Nuclear Structure, Bormio Italy
Subtitled "The many facets of nuclear structure" this workshop's aim is to explore topical issues in nuclear structure, bringing experimental and theoretical collaborators together.  It's part of a series taking place every two years.  This year, the meeting is preceeded by a one-day satellite meeting on 03/02 on Beta-decay studies: present and future campaigns [website]

24/02–28/02: Conference on Neutrino and Nuclear Physics (CNNP), Cape Town, South Africa
A conference for those working on the interaction between neutrinos and nuclei, whether it be for beta decay, reactor neutrino studies, dark matter searches, solar and supernova modelling and detector technologies.  Or anything else closely related.  This is the followup to a first CNNP meeting held in Catania in 2017 [website]

06/04–09/04: IoP Nuclear Physics Conferene, Edinburgh, Scotland
The annual UK Institute of Physics Nuclear Physics conference.

15/05–22/05: 13th International Spring Seminar on Nuclear Physics Perspectives and Challenges in Nuclear Structure after 70 Years of Shell Model, Ischia, Italy
A meeting organised by the theory group at the University of Naples, hosted on the island of Ischia.  The topics are fairly broad, covering anything in low-energy nuclear structure.  Should be good, and a lovely setting.  [website]

01/06–05/06: Nuclear Photonics 2020, Kurashiki, Japan
A conference on the emerging field of direct interaction and manipulation of nuclei with photons, coming about thanks to the new experimental sources of high-intensity lasers and monochromatic gamma rays.  Not sure there is a website yet.  Here is the first circular.

14/06–19/06: ARIS 2020, Avignon, France
ARIS stands for Advances on Radioactive Isotope Science (sic), and the conference series grew out of a combination of the earlier ENAM (Exotic Nuclei and Atomic Masses, I think) and RNB (Radioactive Nuclear Beams) conferences.  It's quite a general, large conference for work coming out of radioactive beam facilities -- i.e. most of the big nuclear physics labs.  At the time of writing they've sent out a save the date email, but there is not a website to link to yet.

29/06–03/07: DREB2020: Direct Reactions with Exotic Beams, Santiago de Compostella, Spain
A save-the-date email has been sent out for the latest in the series of DREB conferences.  The first circular, with more details, has been promised in Sep 2019

29/06–04/07: 10th Intl. Workshop on Quantum Phase Transitions in Nuclei and Many-body Systems, Dubrovnik, Croatia
"Quantum phase transitions" here means things like the change in shape or some other bulk property of a nucleus as a function of the number of particles with the emphasis being on the interpretation of such phenomena with the language and mathematics of phase transitions.  I enjoyed going to a couple of the earlier outings in this series, but don't really feel connected enough to the field to justify attending any more, interesting though it would be [website]

## Thursday, 28 March 2019

### Visiting a student at RIKEN

Part of my trip to Japan involves visiting a Surrey undergraduate MPhys student who is on his Research Year placement at the Radioactive Ion Beam Facility at RIKEN, just outside Tokyo.

The student, Richard, is working on the Rare-RI Ring[link to open access paper on the apparatus], a storage ring in which very unstable neutron-rich isotopes are injected, following their creation at the production target.  Here, by measuring their cyclotron frequency, their masses can be deduced.  Ultimately, good knowledge of these masses is important to understand the r-process of nucleosynthesis which takes place in (probably) colliding neutron stars and certain kinds of supernova.  Richard's task it to work on a replacement for one of the detectors which detects the precise location of the ion beam for one which perturbs the flight of the particle less as it makes the measurement, and hence increases the accuracy.

Here in the picture is Richard standing by the detector, where he is currently spending his days making measurements to characterise how it is working.

As well as his work, Richard has been enjoying getting to know Tokyo at the weekends.

## Tuesday, 26 March 2019

### JAEA Symposium at Tokai

I am in Japan this week, first at the 54th ASRC International Workshop "Nuclear Fission and Structure of Exotic Nuclei" which is partly based on the fact that the researchers here at JAEA (Japan Atomic Energy Agency) have a target made of Einsteinium-254.

I've given a talk on calculations to see what prospect there is for making the next unknown elements in the periodic table, and I've been interested to see that others are doing similar things.

This is my first time at JAEA in Tokai, and I was pleased that I managed to navigate here from Haneda Airport on Monday morning, though I waited at the wrong platform at Shinagawa station for a connecting train for a bit until I realised that I was probably at the wrong platform.

After this workshop ends today, I'm going to RIKEN, in Saitama prefecture just outside Tokyo, to visit an MPhys student from Surrey who is on placement there, and then home on Friday.

As ever, being at a conference has filled me with ideas and plans, and led to discussions for collaborations.  Now to see how much of that I can bring to fruition.

## Thursday, 14 March 2019

### Congratulations Katie Ley

Some congratulations are in order for The University of Surrey's Katie Ley, who won Gold Medal in Physics in the STEM for Britain Parliamentary Showcase this week:

Katie is a PhD student at Surrey, working in applied radiation physics.  Here is a recent paper of hers on thermoluminescent dosimetry.  It's behind a paywall, unfortunately, though at some point a freely-dowloadable version should appear on our university repository, and you should be able to find that from the journal website with Unpaywall.

## Friday, 8 March 2019

### Daphne Jackson at Surrey

What better day than International Women's Day 2019 to write a post about a nuclear physicist who was in the Physics Department here in Surrey some time before me, Daphne Jackson.

Daphne Jackson was the first female professor of Physics in the UK, here at Surrey — appointed in 1971, at the age of 34.  Initially she worked on the local Surrey specialty of nuclear reaction theory, before applying the theoretical work to nuclear medicine, in diagnosis and treatment.

She was a strong promoter of women in physics, particularly supporting those who had had a career break for family reasons from which the route back in to academic research used to be practically impossible (and is still very difficult).  In 1985 she started a fellowship scheme to enable women to return to research careers.  The scheme was continued after her untimely death in 1991 by the Daphne Jackson Trust, which continues today to help returners (both male and female) to academic research careers.

I attach to this post a couple of pictures I took this morning.  One is of a picture of Prof Jackson, which is hanging up in our Jackson Room.  I took the picture from the side to avoid reflections, hence the strange choice of angle.  The other picture is of a monograph that she wrote with Roger Barrett on fundamental nuclear physics in the mid 70s.  It's still referred to today:  Here is Google Scholar's take on citations in 2018-2019.

## Wednesday, 6 March 2019

### The zirconium-88 neutron caputre cross-section mystery

 Figure: The neutron capture cross section of measured nuclei.  The new measurement of zirconium-88 is the second-highest point.  From Shusterman et al., Nature 565, 328 (2019) doi: 10.1038/s41586-018-0838-z
Imagine you are a neutron,  newly–released from a fissioning nucleus in a reactor.  Your new–found freedom involves flying around in an environment full of other nuclei.  If you crash into one, it might grab you and keep you, converting the nucleus to the next-heaviest isotope.

Fortunately for you, you can see all these nuclei and they all look very small, and easy to avoid crashing into.  Except there are a few sneaky ones which can grab you as you fly past. According to a new paper published in Nature by Shusterman et al., zirconium–88 is one such nucleus, for reasons that are not at all clear.

The protons and neutrons in 88Zr define a nuclear density which extends up to a radius of a little over 5 fm (= 5 x 10–15m) which amounts to a cross–sectional area of ≈ π x (5 x 10–15)2 = 2 x 10–29 m2.  According to Shusterman et al., a 88Zr nucleus presents an effective cross–sectional area of  9 x 10-23 m2. That's around a million times larger than the extent of the matter that makes up the nucleus.  The effective radius of 88Zr for neutron capture is around 5 x 10–12m.  This is around the same radius as the innermost electrons circling round a zirconium atom.

So a neutron only needs to go in the vicinity of zirconium–88 for it to get captured.  This result is a surprise.  The predictions previous to the experimental work gave a predicted cross section around 4 orders of magnitude smaller.

The reason why 88Zr appears so large to neutrons is a mystery, then.  Presumably there is a strong resonance which makes the nucleus really likely to accept a neutron coming into it with just the right energy (the measurement is integrated over a range of energies).  But then, all nuclei have resonances like this.  Why is it so strong in 88Zr?  We don't know.

This result has consequences in modelling of stellar nucleosynthesis, where the absorption of neutrons is one of the key processes happening in novae and supernovae.  It also means that significant quantities of 88Zr in nuclear reactors — created during the fission process, for example — would be a reactor "poison", sucking up the slow neutrons which are the basis of the nuclear chain reaction.

A plot from the paper is shown here.  The large value for zirconium–88 is the second-largest measured ever.  The largest cross-section, in xenon–135 was measured in 1948.

## Friday, 1 March 2019

### Quantum Textbook Shelfie

Following a Twitter post from my colleague Jim Al–Khalili yesterday,
and a subsequent round of discussion of the books and which ones we had on our shelves, here is my shelfie of the quantum mechanics textbooks I have on the shelves in my office:

Physics textbooks are the sort of thing I coveted as an Undergraduate but couldn't afford, and now can afford but don't have, or don't make the time, to read.  I've more or less stopped acquiring physics books, though on the occasions that I go to second hand bookstores in college towns, I do sometimes fail to resist the temptation to buy one or two.

Of all the books in the picture here, it's the yellow one whose spine is hard to read – An Introduction to Quantum Physics by A. P. French & E. F. Taylor – that I've had the longest.  My brother bought it for me while I was still a sixth-form school student, who was hoping to go to university for further study (which I duly did).  It was a wonderful and thoughtful present, and I attempted to read it, though I'm not sure I really got very far.  Looking back, I recall what a struggle it was to learn most of undergraduate physics.  Now I can pick up an unseen area of UG physics relatively easily, despite a generally diminished brainpower.  Thinking like a physicist has, I suppose, seeped so far into my unconscious.

My copy of Pauling & Wilson's Introduction to Quantum Mechanics is a rare one that I saved up for and bought when an undergraduate student (most of the rest I bought later, second hand). Perhaps Pauling and Wilson is not the most suitable for a late-20th-century student, with its presentation unchanged since it was written in 1935. Shortly after I bought my copy, Pauling died, and I have a cut-out of his obituary from the Independent from 22nd August 1994, in the summer before my final year of undergraduate study.

Here's the obituary.  If you click on the picture it should come up in high enough resolution to read.

## Thursday, 28 February 2019

### Learning matplotlib

I've been doing some calculations today on the structure of some heavy transactinide nuclei.  This has involved running a code (ev8, from W. Ryssens et al, Comput. Phys. Commun. 187 175 (2015)) and manipulating the output data, which I would like to plot in the kind of sector plot that nuclear physicists use when plotting the potential energy surfaces of nuclei using Hill–Wheeler coordinates.

Here's an example of such a plot, which I've taken from the arxiv paper 1809.04406 (also by W. Ryssens et al., though the al is slightly different to the first paper above):

I have all the necessary data and have mapped it to the right sort of coordinates, but I am struggling to get matplotlib to encase it in the right circular sector.  So far, I've got it looking like this:

Any suggestions on how to mask this into a sector, would be most welcome.  I'd quite like to add a labelled axis along the gamma=60º line, too, if you have any ideas.  And add in those grey axis lines.  I can handle changing all the colours and font sizes that I need to do.

I should probably be posting this to stackexchange, right?

edit: This blog post might prove helpful, so I link to it for my future reference: http://blog.rtwilson.com/producing-polar-contour-plots-with-matplotlib/

## Monday, 18 February 2019

Google Scholar has again gone through a process of forgetting or purging a number of citations to my papers.  This time last week it said I had 1,589 citations to my work.  Today, 1,170 (both figures down from 2,130 in January last year).  Google Scholar is fairly opaque in how it does things, and I don't know what records it deleted and why, but it seems unfortunately very unreliable.   As a record of my papers, it's useful.  For citations?  It's becoming increasingly less so.  Anyone else noticed the same with them?

After noticing (some years ago) strangely fluctuating numbers coming from Google Scholar I started periodically recording the number of citations it reported for me on a spreadsheet.  Hence I can present the graph attached here.  The latest downward line is smaller than the one I noticed mid-way through last year, but still takes the number of citations back to that of around 5 years ago!

## Thursday, 14 February 2019

### Nuclear Spot The Difference #6 revisited

Regular readers of this blog will no doubt remember a previous spot-the-difference in which the understandable confusion between Art Malik and Jim Al-Khalili was explored.  With the recent acquisition of a beard, it has been claimed that nuclear physicist Jim now looks like comedian Alexei Sayle.  I present the following pictures to allow the reader to judge

 Sayle Al-Khalili

Here is Jim from his pre-nuclear days, singing "Ullo John, got a new motor?"

## Monday, 11 February 2019

### Relativity makes mercury liquid

The link between the theory of General Relativity and the orbit of the planet Mercury is pretty well-know.  What I learned recently is that it is a consequence of Special Relativity that the element mercury is liquid at room temperature.

In a paper by Krista G. Steenbergen, Elke Pahl, and Peter Schwerdtfeger (J. Phys. Chem. Lett. 8, 1407 (2018)) the authors perform calculations of bulk mercury using both relativistic and non-relativistic quantum mechanics, and show that the use of relativity lowers the melting point of mercury by 160 K.  The relativistic calculations give a melting point close to nature (within 10K).  They are sophisticated quantum mechanical calculations in which bulk many-body effects are taken into account.  You can't simulate melting and freezing by considering the interaction of two or three atoms, but need at least tens of them to get a realistic picture of bulk matter.  That's not easy to calculate, and the authors have made a convincing case that they have done so, and that the dominant effect in causing mercury's unusually low melting point comes from relativity.

The picture below is from the paper, showing the result of a simulation with a disordered liquid phase on the left, becoming an ordered solid on the right.

## Thursday, 31 January 2019

### Farewell to Kai

Last night I made a rare trip to the pub (okay, the same pub I went to last Saturday for dinner) where the Surrey nuclear theory group said goodbye to our postdoc Kai Wen, who is off to pastures new (Tsukuba University in Japan).  I took what young people call a "selfie", so I take the opportunity to post it here.  Best wishes for the future, Kai!

 L–R: me, my son Hamish, Kai, Pierre, Mehdi, Arnau

## Tuesday, 29 January 2019

### Raj K Gupta (1938–2019)

I read from various friends and colleagues on Facebook that Prof Raj K Gupta of Panjab University, Chandigarrh, has died.  I have read several touching stories about him on Facebook from physicists who knew him and worked closely with him over the years, and it is clear that he had a strong and positive impact on many younger physicists across India.

I worked with him (long-distance) via a collaborator, Suresh Patra, who came to Surrey for several month to work on giant resonances with me.  I then got involved a bit in a project on clustering and cluster radioactivity that Suresh worked on with Prof Gupta, it being the latter's specialty.  In the end, I published a few papers as co-author with Prof Gupta, as part of this collaboration, though I did not meet him until after this time, during a conference visit to New Delhi.  My research interests have evolved since that time, partly into heavy-ion fusion reactions, where I see his name regularly in publications about ioi-ion potentials in which he developed some important results.  Judging by those Facebook posts his scientific and personal legacy will both continue after his death.