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.

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.

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:

Congratulations to the winners in the physics category

Bronze - Amalia Thomas
Silver - Lorenzo Zanisi
Gold - Katie Ley#STEM4BRIT19 pic.twitter.com/jmmTPPNmmz

— STEM for Britain (@STEM4Brit) March 13, 2019

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.

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.

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.  

Plenty to ponder about this result.  

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. 

Quantum Textbook Shelfie

Following a Twitter post from my colleague Jim Al–Khalili yesterday,

Quantum physicists, what are you favourite quantum textbooks? Mine are: 1.Schiff, 2.Messiah, 3.Merzbacher, 4.Bohm and, of course, the very first one ever written: Dirac.

— Jim Al-Khalili (@jimalkhalili) February 28, 2019

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.