Tuesday, 19 April 2011

Nuclear Physics in Japan

I've been unreasonably quiet lately. Unreasonable for all sorts of reasons, but not least of which is that there has been, and is, a prominent news story related to nuclear physics issues that demands comment. I write, of course, of the damaged nuclear power plant in Fukushima Prefecture, Japan, which has released radioactive material into the environment following (non-nuclear) explosions at it, in turn caused by the power outage from the recent earthquake and tsunami.

In some ways, I feel a little unqualified to talk about it. My research expertise in theoretical nuclear physics reminds me of this tweet that I saw re-tweeted by @snim2. It says that "Asking a computer scientist to fix your computer is like asking a physicist to fix your car." In all honesty, I probably know a little more about nuclear reactors than a genuine layperson. Still, I will refer readers interested in detailed commentary on the Fukushima reactors to my colleagues, who have written sensibly on the matter in a series of articles and blogposts, including my own institution's Paddy Regan, my colleague on the Institute of Physics South Central Branch, Alby Reid and fellow nuclear researcher, at Oak Ridge National Lab, Kelly Chips.

I will only add to the Fukushima discussion reinforcement of something that has been said by many others, namely the irresponsible nature of much of the news reporting. A rather badly written article appeared a couple of days ago on the BBC News website, and has prompted me to comment. It's title marks it clearly as being about the nuclear power plant and ongoing problems there. The first paragraph, the second paragraph and the third are all about the nuclear power plant. The fourth paragraph states "Nearly 14,000 people died and another 14,000 are still unaccounted for." Now, the third paragraph does blame the earthquake and tsunami for the damage to the power plant, but one could easily read this statement as saying that the nuclear incident caused those deaths. I know it's not true, the journalist surely knows it's not true, and many readers will know it, but it comes across in a very misleading way. Very sloppy journalism, in my opinion. Mind you, the BBC News website is written in the style of a tabloid paper with the prose infantalised to single-sentence paragraphs that you could rather imagine reading one per page below a picture in a children's story book. I should know better than to go there for news.

Well, rant over. The real purpose of this post is to celebrate Japan's contribution to more basic nuclear physics research - i.e. the understanding of what atomic nuclei are and how they work, rather than nuclear applications. I do this, sitting at a desk in a research institute just outside Tokyo called RIKEN. RIKEN was founded in 1917 (initially as a private company) and has a long history of pioneering scientific research in many areas. If I stick to nuclear physics though, I can mention Yoshio Nishina, who made one of the first breakthroughs in quantum field theory, which has become part of the language of fundamental nuclear physics. The division of RIKEN which I'm visiting is called the Nishina centre in his honour. There is Sin-Itiro Tomonaga, who worked on nuclear physics in Nishina's group, and won his Nobel prize for work with Richard Feynman on Quantum Electrodynamics. Most prominent of all, though, as far as nuclear physics is concerned, is Hideki Yukawa.

Yukawa worked on the problem of nuclear forces. How is it that protons and neutrons can stick together to form a nucleus? It cannot be due to electric forces, as neutrons are neutral and protons positively charged. An electric force could only stick positive and negatively charged particles together. There must be some kind of independent nuclear force. Yukawa was the first to make a real breakthrough in to what it might be. He proposed that the nuclear force worked by the exchange of particles between the nucleons (collective term for protons and neutrons), and developed the theory to work out some of their properties, including a prediction for their mass (around 200 times heavier than an electron) and their charge (the same magnitude as the electron, but coming in both positive and negative charge versions). He predicted, too, that in sufficiently energetic reactions, a meson should be able to be freed from a nucleus. At the time (1934), no experimental facility would be able to create them, but Yukawa predicted that they should be observable in cosmic rays. As it turns out, most of the mesons from Yukawa's theory will decay in the atmosphere to a particle newly discovered in 1937, we now call a muon, but Yukawa's particles, by now christened mesons, were discovered in 1947. Yukawa won the Nobel prize in 1949 for his prediction and the meson-exchange view has been vindicated ever since, though we now know it to be a manifestation and approximation of an underlying theory, mesons themselves being composite particles, made of quarks.

Since Yukawa's time, Japan has remained prominent in nuclear physics research. I cannot risk lauding all of the activity going on today, since I will surely unintentially miss some world-class activity by a sin of omission, but I will deliberately mention, since I am here, that RIKEN hosts one of the leading nuclear physics experimental facilities: RIBF - the Radioactive Ion Beam Factory. It has been instrumental in recent years in the discover of new elements, and quite remarkably has added many new isotopes to our knowledge of the Universe. I mean that quite literally - knowledge of these isotopes is necessary to understand how heavy elements are created in stars.

I'm glad I made the trip to Japan. The ongoing aftershocks are a little disconcerting, but I understand the risks well enough to know that my radiation dose rate on the flight over (~5 µSv/h) is far higher than that here at RIKEN (~0.14 µSv/h). The average background in UK is about the same as here in RIKEN. I've no idea what it is in Guildford, though. Would be interesting to find out.