229Th

Thorium-229 is one of my favourite isotopes. With the lowest-energy first excited state of any known nucleus, it's the isotope of choice for interacting directly with things such as lasers, atoms and molecules, whose characteristic energies are much smaller than normal nuclear transition energies. One of the most promising practical uses of ²²⁹Th is in making a new time standard which is more accurate than existing atomic clocks. My friend and fellow blogger Rob Jackson has just published a paper on the chemical side of implanting ²²⁹Th in material for possible use in such a clock standard. He's blogged about it here.

IoP Schools Lectures

I've been shortlisted as a possible Schools Lecturer for the Institute of Physics next year. My pitch is about applications of nuclear physics to medicine. Any clever ideas of how to present this to school kids would be most welcome. Please comment!

Understanding the triple-alpha process

All nuclei heavier than lithium (atomic number 3) are made in stars. It's only pretty recently we've understood that and the confirmation that stars are giant nuclear reactors is one of the great stories of modern physics (which I will not tell here right now!) One of the stumbling blocks to realising that nuclear fusion happens in stars is that it seemed at first like there was no way helium nuclei could fuse to form anything, as they can't fuse with any single thing that's available in stars to make something stable.

The breakthrough was the realisation by Fred Hoyle that what must happen is that three helium nuclei must interact together to form carbon-12. This highly improbably process turns out to happen thanks to a resonance in carbon-12 just around the energy that is available when three helium nuclei meet inside stars. Without it, we would not be here. Some collaborators of mine have just published a really fantastic paper running simulations of this reaction and show how the alpha particles interact. It's available here and it takes the understanding of the process to a new microscopic level. Good work collaborators!

New isotopes

I reported not long ago that there's a new element known to science. Some recent news should be just as exciting as that, but somehow hasn't made the same splash. The news is that 45 new isotopes have been discovered. Discovering a new element means finding a nucleus with a number of protons never before seen, whereas discovering a new isotope means discovering a nucleus where both the number of protons and neutrons in combination have never been seen. In either case, they are nuclei seen for the first time in experiment, and they push our boundaries of knowledge and test our understanding of how nuclei are made.

The press release from the Japanese lab does a good job of explaining their experiment (smashing two known nuclei together and seeing what fragments you end up with). It's pretty exciting: They're getting really close to the r-process path: The route through the table of isotopes that happens in supernovae and is responsible for making much of the matter heavier then iron.

I suppose it makes a recent paper of mine less exciting. We only discovered two new isotopes ;-)

Detecting irradiated food

Quick Advert:

Tomorrow (Wednesday 19th May), a free public physics lecture is being given in Lecture Theatre M at the University of Surrey at 7pm. It's being given by Prof David Sanderson of SUERC - the Scottish Universities Environmental Research Centre, and it's about how to detect irradiated food, a technique which the SUERC group developed and is now a European standard.

I picked up a delivery today of some equipment that the speaker wants to use in the talk - and am intrigued!

No booking is required - just turn up to Lecture Theatre M for a 7pm start

What if everyone were a nucleus?

In a series of tweets this evening Jim Al-Khalili pointed out that there has been a small disagreement between him in his Atom series and Michael Mosley in the Story of Science. They each illustrated the ratio of occupied space to empty space in atoms by saying that if all the empty space were taken out of the entire human population then we would occupy a volume the size of an apple (Jim's calculation) or a sugarcube (Michael's calculation).

In either case, the analogy makes clear that atoms have a whole lot of empty space, but in terms of volume, there's a fair bit of difference between a sugarcube (around 1 cm³) and an apple (around 200 cm³). So who is right?

The population of the world is around 7 billion. The average mass of people is usually taken to be around 70kg so the mass of the human population is 7×10⁹×70 kg = 490 000 000 000 kg. Let's call that 5×10¹¹ kg. Now, if all the space were taken out of all these atoms, we would essentially be left with an enormous nucleus (as Jim says, a pulsar). The density of nuclear matter (i.e. of the inside of an enormous nucleus) is 0.16 nucleons per cubic femtometer. A nucleon weighs 1.7×10^-27 kg.

So: The number of nucleons in total is 5×10¹¹ / 1.7×10^-27 = 3×10³⁸ nucleons, giving a volume of 3×10³⁸/0.16 = 2×10³⁹ fm³ = 2 cm³.

Looks like I agree with Michael, more or less... unless I've guessed the size of a sugarcube wrongly. I mean, I haven't seen a sugarcube for years.

Nuclear Physics and the Election

I've not blogged at all about the forthcoming election. Nuclear physics is a pretty minor issue in the election, but not completely non-existent. The amount of overall science funding will be a factor in determining how much money will be spent on nuclear physics research, and the commitment to nuclear power (or otherwise) of the parties will be a factor in determining how much the UK is interested in keeping a knowledge base in nuclear science and engineering on a broader scale. These two facts are ironically approximately inversely correlated in the three main parties. I don't think I'd ever vote on a single issue alone, but there doesn't seem to be a completely obvious choice from a nuclear physics point of view. I think Martin Robbins' article in the Guardian sums things up pretty well, though, from an overall science perspective.