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