Thursday, 13 October 2011
Bananas!
There's a nice article on the BBC News website talking about the Banana Equivalent Dose as a measure of radiation. It's a kind of nice idea, since it's motivated by the desire to point out that everyday objects are radioactive. Bananas are more radioactive than most things since they are high in potassium, which has a radioactive primordial isotope, Potassium-40 (K-40). K-40 is also responsible for the last item in the table in the BBC article - sleeping with someone is equivalent to half a banana's worth of radiation dose, because your bed partner is partly made of potassium, as are you. Around 5000 radioactive potassium decays occur every second in a typical adult.
Monday, 3 October 2011
Spot the difference
With due deference to Private Eye, and Peter Coles's Astronomy Look-a-likes, I must say that I have been struck (as pointed out by Kate Lancaster), by the similarity between neutron discoverer James Chadwick, and Old Vic artistic Director Kevin Spacey:
Spacey
Chadwick
Spacey
Chadwick
Saturday, 1 October 2011
On the train through K-25
I'm in Oak Ridge, Tennessee. It's an important place in the history of nuclear physics, being built in the second world war for the Manhattan Project. One of the main jobs that Oak Ridge had was to separate the two main isotopes of Uranium that are found in Uranium ore, Uranium-235 and Uranium-238. U-235 is the one that is needed for nuclear reactors and bombs, but makes up a little under 1% of natural Uranium. For fission in either bombs or a reactor, a much higher concentration of U-235 is needed - the Little Boy bomb that was dropped on Hiroshima consisted of two lumps of enriched Uranium, which were pushed together by a chemical explosion in the bomb to create one lump exceeding critical mass. The average enrichment of those lumps of Uranium was around 80% U-235.
Three different enrichment techniques were developed at Oak Ridge: Gaseous diffusion, electromagnetic separation, and liquid diffusion, with gaseous diffusion taking place at the K-25 plant. The Uranium ore, which came from mines in the Belgian Congo, and bought by the US on the open market, was processed into Uranium Hexaflouride, which is is gaseous at about 55°C. The plant works by repeatedly allowing the gas (containing both isotopes of Uranium) to diffuse through a porous membrane, with the lighter U-235 finding it easier to do so, and so being more concentrated after diffusion. To get high concentrations, the process must be repeated many times, and a huge cascade of diffusing membranes was built, making the plant building enormous.
The picture on the right shows the main building. Each arm of the "U" is half a mile long, and it was reportedly the biggest building under a single roof at the time of completion.
The building is now part-way through being demolished, but today I took a train journey through the site, and saw some of what was left. The Secret City Scenic Excursion Train is a volunteer-run railway that does occasional trips over about a 7 mile distance and back, starting from the edge of the old K-25 plant, through the plant, and then on through some East Tennessee countryside, before getting to the junction with a freight line it's not allowed to use. It's been in existence for coming up for 10 years, so just young enough that it wasn't here when I lived in Oak Ridge, and I was glad I found out about it while I'm over visiting. It would be even better to have really got to look inside the K-25 plant while it was still operational. During decommissioning, the plan had been to preserve the top of the U-shaped building, but it turned out to be too corroded and contaminated to make it viable. A shame...
Three different enrichment techniques were developed at Oak Ridge: Gaseous diffusion, electromagnetic separation, and liquid diffusion, with gaseous diffusion taking place at the K-25 plant. The Uranium ore, which came from mines in the Belgian Congo, and bought by the US on the open market, was processed into Uranium Hexaflouride, which is is gaseous at about 55°C. The plant works by repeatedly allowing the gas (containing both isotopes of Uranium) to diffuse through a porous membrane, with the lighter U-235 finding it easier to do so, and so being more concentrated after diffusion. To get high concentrations, the process must be repeated many times, and a huge cascade of diffusing membranes was built, making the plant building enormous.
The building is now part-way through being demolished, but today I took a train journey through the site, and saw some of what was left. The Secret City Scenic Excursion Train is a volunteer-run railway that does occasional trips over about a 7 mile distance and back, starting from the edge of the old K-25 plant, through the plant, and then on through some East Tennessee countryside, before getting to the junction with a freight line it's not allowed to use. It's been in existence for coming up for 10 years, so just young enough that it wasn't here when I lived in Oak Ridge, and I was glad I found out about it while I'm over visiting. It would be even better to have really got to look inside the K-25 plant while it was still operational. During decommissioning, the plan had been to preserve the top of the U-shaped building, but it turned out to be too corroded and contaminated to make it viable. A shame...
Thursday, 16 June 2011
IoP lecture on Fukushima
If I lived nearer Warrington, I'd definitely attend this talk by HM Chief Inspector Nuclear Installations, Dr Mike Weightman.
What's special about Thorium-229?
As a UK academic, a combination of government and university policies push me towards publishing in particular journals, at least for a fraction of my research. One of the top journals that they (and indeed I) would like me to publish in is Physical Review Letters, as it is a highly respected and highly read journal. It publishes articles across all areas of physics, and with nuclear physics being only a part of all physics activity, and a somewhat small one at that, there are often no nuclear physics articles in an edition of the journal. This makes it somewhere that I don't always look for the latest nuclear physics research, but partly for the reasons stated above, I do look every now and then.
As I type this, there are indeed no articles on nuclear physics in the latest complete edition. If I look back to the last issue, then there are a couple of articles in the Nuclear Physics section. What interests me more from a nuclear physics point of view, though, is the article listed next - in the atomic physics section. The article is entitled "Wigner Crystals of 229Th for Optical Excitation of the Nuclear Isomer".
Thorium-229 (229Th) is a special isotope. Of all know nuclides, it has the lowest-lying excited state above the ground state, at only around 7eV. That's around 10,000 times less energy than it usually takes to make a nucleus excite into an excited state. It's comparable to the sort of energy an atom needs to excite an electron. The strange thing is that nuclei, being so much smaller than atoms usually require much shorter wavelengths - and hence higher energies - of light to cause excitations. What this means is that sooner or later we will be able to directly excite and control nuclei with light pulses in the same way that we can do with atoms. The scope for applications is immense, from UV lasers, to more accurate atomic clocks, to stable quantum computers. Nuclei are so much better isolated from their environment than atoms that devices relying on quantum effects are easier to make.
If the history of the development of fields that were at the cutting edge of smallness (e.g. as atomic physics once was) into practical applications is anything to go by, Thorium-229 will be the start of a technological leap in the forthcoming years. Watch that isotope!
As I type this, there are indeed no articles on nuclear physics in the latest complete edition. If I look back to the last issue, then there are a couple of articles in the Nuclear Physics section. What interests me more from a nuclear physics point of view, though, is the article listed next - in the atomic physics section. The article is entitled "Wigner Crystals of 229Th for Optical Excitation of the Nuclear Isomer".
Thorium-229 (229Th) is a special isotope. Of all know nuclides, it has the lowest-lying excited state above the ground state, at only around 7eV. That's around 10,000 times less energy than it usually takes to make a nucleus excite into an excited state. It's comparable to the sort of energy an atom needs to excite an electron. The strange thing is that nuclei, being so much smaller than atoms usually require much shorter wavelengths - and hence higher energies - of light to cause excitations. What this means is that sooner or later we will be able to directly excite and control nuclei with light pulses in the same way that we can do with atoms. The scope for applications is immense, from UV lasers, to more accurate atomic clocks, to stable quantum computers. Nuclei are so much better isolated from their environment than atoms that devices relying on quantum effects are easier to make.
If the history of the development of fields that were at the cutting edge of smallness (e.g. as atomic physics once was) into practical applications is anything to go by, Thorium-229 will be the start of a technological leap in the forthcoming years. Watch that isotope!
Wednesday, 27 April 2011
Chernobyl on Radio 4
Last night, there was a rather good program on Radio 4 about the legacy of the Chernobyl accident. As usual, the BBC makes an effort to provide a "balanced" view, even if it means putting mainstream views against outsider views on the same basis. This program, though, pits evidence-based view against non-evidence-based, and the program is definitely worth a listen. Well done BBC, this time. You can listen again here for the next 6 days.
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.
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.
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