All posts by Rob Jackson

Chemistry/Forensics Academic (Reader), researcher in Computational Solid State Chemistry; blogger, trombone player, CAMRA member.

The development of nuclear clocks: a new time standard

Currently, time standards (i.e. the way a unit of time is defined) are set by ‘atomic clocks’. These rely on using electromagnetic waves to excite electronic transitions in an atom. The atom chosen is caesium, Cs. But electronic transitions define the chemistry of the elements, and can therefore be subject to external influences. This leads to atomic clocks being constructed in very complicated ways so as to minimise these effects.  Nuclear transitions, i.e. transitions between the energy levels within an atomic nucleus, have the potential of offering greater stability, and considerably improved accuracy (potentially up to 6 orders of magnitude).

Electronic transitions in atoms correspond to a range of energies (and therefore frequencies). For example, for the simplest atom, hydrogen, there are transitions in the infra-red, visible and ultra-violet regions of the spectrum, but all can be probed by laboratory spectroscopic equipment. The issue with nuclear transitions is that, at least potentially, the energies involved can be much higher, making the transitions less straightforward to probe using available sources of electromagnetic radiation. At the very least, a laser will be required, and even then, the energies involved may not all be accessible.

The discovery that made the development of nuclear clocks a real possibility was that the isotope 229Th has a low lying state with a transition energy of 7.6 eV. Although this is in the vacuum ultraviolet region, it is easily accessible by laser spectroscopic methods. This isotope of thorium is rare; it results from the alpha decay of 233U, which is in itself not universally abundant. Not only is it rare, but it is expensive ($50M per gram!). It’s not available for mail order from a chemicals catalogue, for example, and relatively few laboratories in the world have supplies available.

So, how might the clock be constructed, and why is ii of interest to a materials modeller like myself? Well, the thorium nucleus must be embedded in suitable crystal lattice, so once a suitable material is identified, the question arises as to where the nucleus will substitute. One of the groups interested in developing nuclear clocks identified me as someone who could help with this question. The background to their research is given here. They had already identified LiCAF (LiCaAlF6) as a suitable host (it is transparent with a high band gap), so where would a thorium nucleus substitute in the lattice, and if it didn’t have the same charge as the ion it was replacing, how would the charge be compensated? These details are outside the scope of this posting, but can be summarised by saying that the thorium is expected to substitute at a calcium site, and the charge compensated is achieved by two additional fluorine atoms occupying interstitial sites in the lattice. You can read all about it here (contact me if you would like a PDF of the published paper).

So, where are we with nuclear clock development? With collaborators from the USA and Brazil, we will grow LiCAF crystals with 229Th nuclei embedded in them. Once this has been done, testing and ultimately device construction can commence. I will publish further posts as we progress with this exciting project!

The long wait for the Labour leadership election

In an earlier blog post I bemoaned the length of time being taken for the Labour leadership campaign. And now we are nearly at the end of July, and still it goes on! The candidates have now canvassed support, and CLPs and Unions have made their preferences. So what is still to be done? Rather than delay another month, it would be far better to have the election in early August. The sooner our new leader is in place, the sooner we can move on and provide a credible opposition to the ConDems. The continuing delay is nothing but harmful and frustrating!

European Conference on Defects in Insulating Materials, 2010

I recently attended one of my regular conferences, the European Conference on Defects in Insulating Materials, which was held in Pecs, Hungary from 11-16 July. For me, this conference was really excellent, with all my current research collaborators attending, providing an unparalleled opportunity for networking, and planning future projects. Earlier in the year I defended scientific conferences against criticisms, and this conference was an excellent example of how conferences can be really effective. In a series of future blog postings, I will describe some of the topics covered at the conference, and how they link with my current research interests.

All quiet on the blogging front!

I haven’t posted to my blog for some time, I realise. This won’t do, but why the silence? After the election there was plenty to write about. Since then I’ve been bogged down by a combination of exam marking and administration, preparing a talk for a conference last week, and a kind of resigned feeling of despair at the actions of the ConDem government, culminating in the awful budget last week. Now the students have packed their bags, we have a rare ‘research window’, and time to post some entries. Watch this space for more soon!

The World Cup Final and Conferences

The last 3 World Cup Finals, and the one that will happen this year. have all coincided with a conference that I attend regularly, the European Conference on Defects in Insulating Materials. So, in my mind the 2 events are associated with each other. I have watched the final in 3 different conference locations, always with my Brazilian research collaborator, which has added ‘spice’ to the occasion! In 1998, when France beat Brazil, we were in Keele, while 2002 found us in Wroclaw, Poland. On that occasion, Brazil beat Germany, so that was OK! 2006 was perhaps most eventful. We were in Milan, and the final was between France and Italy! To be in an Italian city as the drama unfolded was something else. When Italy won, my Brazilian friend memorably remembered his Italian roots, and went native while the rest of us tried to go to bed and sleep in preparation for the conference.
So, what of 2010? We’ll be in Pecs, Hungary, in some unsuspecting bar, watching who? It would indeed be poetic if it was England against Brazil, but that seems unlikely if we play like we did against Japan recently! But who knows?

The abolition of ID cards

Our new ConDem Home Secretary, Theresa May, today announced the abolition of the ID card scheme. I seem to be one of the few people among those I know, both socially and via the web, that regrets this.

For some reason unknown to me, many people equated ID cards with an invasion of civil liberties. But they are not seen that way in the many countries that have them!

For me, an ID card would have been very useful for my travels, which sometimes take me to more ‘exotic’ locations, and where having a second form of photo ID would be useful. Even in the USA I have been asked for this, including, somewhat scarily, twice at immigration! On these occasions all I could do was show my work ID card and hope for the best.

No-one has mentioned the practical advantages of an ID card scheme, and I’m sorry that I won’t now have one. I’ll have to look into applying for a driving licence with a photo ID, as this seems the only alternative.

Learning to play the ukulele!

OK, I’m a musician. An experienced trombone player and a very amateur pianist. But I’ve never played a guitar or an orchestral stringed instrument like the violin. Then my admiration for the music of George Formby sparked an interest in the ukulele, and my dear wife Angela has just bought me one as an anniversary present. So I’m going to learn to play it, and blog my progress, which will make a change from my usual posts on chemistry and politics! More when I’ve tuned it!