Next Wednesday, Prof Wade Allison will be at the University of Surrey giving an evening Institute of Physics lecture based on his book "Radiation and Reason".
The talk is at 7pm in lecture theatre M, and is free to attend. Please turn up for a 7pm start, if you wish to come. I will summarise what he says here afterwards.
Here is a facebook event page for it, if you wish to register interest, but there's no obligation to.
Wednesday, 17 November 2010
Wednesday, 3 November 2010
Nuclei in Semiconductors
Semiconductors are substances who electronic structure is such that they are neither good electrical conductors nor insulators, but whose conduction properties may be altered by various means, chemical and physical to produce materials which can do all sorts of amazing things. Things like transistors, and all the technology that comes from them, things like solar cells, things like cheap LED lighting, like lasers for BlueRay players - like a lot of the neat things that get developed by my colleagues in the Advanced Technology Institute here at the University of Surrey.
Usually, people interested in semiconductor materials are not terribly concerned with the nuclei that hold the electrons in place, except that the nuclei have to be the right element, say Silicon, in order to have the right number of electrons and so the right electron structure. It's not always the case, though. One cutting edge of semiconductor research involves using quantum "spins" to make quantum computers. Spin is a kind of quantum angular momentum - to do with things rotating - though in the quantum world things don't have to rotate to have angular momentum. In spin-based semiconductor research (or "spintronics"), one tries to manipulate the orientation of a spinning electron to store information, rather than by presence or absence of a charge. This is one of the promising ways of creating a quantum computer.
Once one starts to deal with electron spins, however, the nuclei can start becoming interested. Silicon is element number 14, with 14 protons in each nucleus, and 14 electrons around a neutral silicon atom. Silicon comes in three naturally occurring isotopes, though: Si-28 with 24 protons and 24 neutrons but also Si-29 and Si-30 with one and two extra neutrons respectively. Si-28 and Si-30 have no nuclear spin, so they don't interfere with spin-based quantum computers, but Si-29 (like all odd-numbered isotopes) has a non-zero nuclear spin, and their presence in naturally occurring silicon causes the quantum computer states to decay, or "decohere". The solution? Make isotopically-enriched silicon, without the natural Si-29. It turns out not to be that easy to either make a sample sufficiently isotopically pure, or even get rid of other contaminants, as a paper published last week, cited below, shows. Surprising sometimes where nuclear physics issues pop up.
Witzel, W., Carroll, M., Morello, A., Cywiński, L., & Das Sarma, S. (2010). Electron Spin Decoherence in Isotope-Enriched Silicon Physical Review Letters, 105 (18) DOI: 10.1103/PhysRevLett.105.187602
Usually, people interested in semiconductor materials are not terribly concerned with the nuclei that hold the electrons in place, except that the nuclei have to be the right element, say Silicon, in order to have the right number of electrons and so the right electron structure. It's not always the case, though. One cutting edge of semiconductor research involves using quantum "spins" to make quantum computers. Spin is a kind of quantum angular momentum - to do with things rotating - though in the quantum world things don't have to rotate to have angular momentum. In spin-based semiconductor research (or "spintronics"), one tries to manipulate the orientation of a spinning electron to store information, rather than by presence or absence of a charge. This is one of the promising ways of creating a quantum computer.
Once one starts to deal with electron spins, however, the nuclei can start becoming interested. Silicon is element number 14, with 14 protons in each nucleus, and 14 electrons around a neutral silicon atom. Silicon comes in three naturally occurring isotopes, though: Si-28 with 24 protons and 24 neutrons but also Si-29 and Si-30 with one and two extra neutrons respectively. Si-28 and Si-30 have no nuclear spin, so they don't interfere with spin-based quantum computers, but Si-29 (like all odd-numbered isotopes) has a non-zero nuclear spin, and their presence in naturally occurring silicon causes the quantum computer states to decay, or "decohere". The solution? Make isotopically-enriched silicon, without the natural Si-29. It turns out not to be that easy to either make a sample sufficiently isotopically pure, or even get rid of other contaminants, as a paper published last week, cited below, shows. Surprising sometimes where nuclear physics issues pop up.
Witzel, W., Carroll, M., Morello, A., Cywiński, L., & Das Sarma, S. (2010). Electron Spin Decoherence in Isotope-Enriched Silicon Physical Review Letters, 105 (18) DOI: 10.1103/PhysRevLett.105.187602
Thursday, 30 September 2010
Nuclear archaeology
Nuclear Physics can help in the world of archaelogy, helping to understand artefacts created long before humankind knew anything about atomic nuclei. I heard a story on Radio 4's Today programme yesterday about the discovery of the skeleton of a bronze age teenage boy near Stonehenge who came from the Mediterranean.
The story mentioned "geochemical" analysis, but the main interviewee mentioned nothing about the nuclei behind the story. What they really discovered was that the isotope ratios of both Oxygen and Strontium isotopes were more characteristic of someone growing up in a Mediterranean environment than a British one.
Heavy oxygen isotopes in water molecules tend to fall more readily as rain when a cloud is cooling, and when it gets colder and colder it tends to be more and more depleted in heavy oxygen. The ratio of Oxygen-18 to Oxygen-16 can be used therefore as a reasonable guide to temperature (and it is used, for example, in measuring the historical temperature of the earth by looking in ice cores from Greenland).
By looking at the oxygen isotope ratio in tooth enamel, which is grown during childhood, evidence of the climate one experienced while growing up can be found.
The other clue comes from the presence of Strontium. Strontium occurs all over the world in ores, but its occurrence, like with all elements varies across the world as a result of chance geological events. Strontium makes its way into the local food chain and then substitutes for calcium in bones, it being in the same chemical group of the periodic table. Looking at the strontium isotopes can then be correlated with where one grew up. This all adds up to the ability to determine where a boy from 1550 BC grew up!
More details can be found on the British Geological Survey's website.
The story mentioned "geochemical" analysis, but the main interviewee mentioned nothing about the nuclei behind the story. What they really discovered was that the isotope ratios of both Oxygen and Strontium isotopes were more characteristic of someone growing up in a Mediterranean environment than a British one.
Heavy oxygen isotopes in water molecules tend to fall more readily as rain when a cloud is cooling, and when it gets colder and colder it tends to be more and more depleted in heavy oxygen. The ratio of Oxygen-18 to Oxygen-16 can be used therefore as a reasonable guide to temperature (and it is used, for example, in measuring the historical temperature of the earth by looking in ice cores from Greenland).
By looking at the oxygen isotope ratio in tooth enamel, which is grown during childhood, evidence of the climate one experienced while growing up can be found.
The other clue comes from the presence of Strontium. Strontium occurs all over the world in ores, but its occurrence, like with all elements varies across the world as a result of chance geological events. Strontium makes its way into the local food chain and then substitutes for calcium in bones, it being in the same chemical group of the periodic table. Looking at the strontium isotopes can then be correlated with where one grew up. This all adds up to the ability to determine where a boy from 1550 BC grew up!
More details can be found on the British Geological Survey's website.
Tuesday, 24 August 2010
NIF video
To follow up the previous post about the NIF, I notice in a tweet from @lasers_llnl that they have a pretty cool-looking 3D movie of the facility online. Must make some 3D glasses...
Tuesday, 17 August 2010
The Conference Excursion
I'm back from California now, and enjoyed the Nuclear Structure 2010 conference. I'll probably blog about more of the talks - I particularly enjoyed George Dracoulis' on Tantalum-180 - but not this evening. Instead, I want to talk about the conference excursion.
For those that don't have the pleasure of going to scientific conferences, let me explain the conference excursion. Not every conference has one, but often one afternoon of a week-long conference will involve taking a trip somewhere of interest near to the conference venue. It doesn't have to be somewhere of relevance to the conference topic. It could be a local place of historical interest, or something like that. The excursion is partly an excuse to socialise with the other people at the conference, which is an important part of the purpose of getting all the attendees together at a conference. Indeed physicists sometimes need help in socialising, and these events can lead to useful discussions and collaborations. Of course the excursions are also partly for fun.
The excursion at Nuclear Structure 2010 certainly counts as a physics excursion, and also a fun one. We went to NIF: the National Ignition Facility, based at Lawrence Livermore National Laboratory not too far from San Francisco. The facility is being built to make small pellets of Hydrogen-2 and Hydrogen-3 nuclei fuse together to give off energy, just as they might do in a future fusion reactor and just as they actually do in thermonuclear weapons.
The US has a stockpile of thermonuclear weapons (the phrase used to describe hydrogen bombs, which work by fusing hydrogen isotopes together as opposed to nuclear fission bombs used in anger in WW2), but it has agreed that it will no longer test them in either atmospheric or underground explosions. However, it would like to understand that they are being well-maintained and still functional - something that I suppose it not obvious when you have a rather hi-tech device which you have built and then left on the shelf for many years. The way around the test-ban is to build a kind of controlled thermonuclear bomb, and that is what the NIF is. They certainly make no secret that the driving purpose of the facility is weapon "stewardship" but given that the weapons already exist and will continue to do so, it seems that they have managed to build something that allows quite a bit of interesting basic physics research to take place, piggybacked onto the weapons programme.
To get to see the facility, alien attendees at the conference had to get security-checked months in advance, and thankfully I passed the tests (though I don't know what I was being tested for). So last Wednesday, I boarded a bus in Berkeley, showing my passport before I even got on, and we drove to the lab. We stopped at the security gate for a while, and were escorted to the badge office to get our temporary badges. The whole procedure was generally taking so long that I feared we would have an hour-long trip to the security office and a 10-minute tour of the facility. We were all enjoying joking about it, though, which I was also nervous wouldn't endear us to the facility people... but all was well.
The building in which NIF sits is a rather ugly warehouse-looking place, but inside it is impressively hi-tech. I've been to a few facilities (as a mere theoretical physicist, I don't actually see inside labs all that often) and I think it's fair to say that I've never seen one so sparkling, shiny, sophisticated and hi-tech. The fusion will take place by having a tiny capsule of H-2 and H-3 that you could hold in your fingertips, placed at the focus of a couple of hundred laser beams - the most powerful in the world, which will collapse the capsule causing compression and heating and then nuclear fusion. They haven't started fusion runs yet, but have fired the lasers at non-fusion pellets and everything looks good so far.
The current set up is such that the pellet is placed very carefully in a big spherical chamber into which the lasers are beamed. They will be able to make one explosion every four hours or so when it is all up and running. If they want to actually get fusion energy out of this, they said that they need a rate of 10 Hz - i.e. 10 explosions per second. That seems quite ambitions to me, but I expect that they will learn some important things about the hydrodynamics of fusing hydrogen plasma, which is really what is needed. Certainly the nuclear physics reactions are well enough understood.
After the tour, and I wish I could show you pictures but cameras were verboten, we were treated to cookies and a talk about the basic science that might come out - about matter at the extremes of density - and the promise that the majority of the experiments would be unclassified. Then it was time to head back to the bus, and back to Berkeley. Back from the borders of the sunny desert to the perennially cloudy Bay Area...
For those that don't have the pleasure of going to scientific conferences, let me explain the conference excursion. Not every conference has one, but often one afternoon of a week-long conference will involve taking a trip somewhere of interest near to the conference venue. It doesn't have to be somewhere of relevance to the conference topic. It could be a local place of historical interest, or something like that. The excursion is partly an excuse to socialise with the other people at the conference, which is an important part of the purpose of getting all the attendees together at a conference. Indeed physicists sometimes need help in socialising, and these events can lead to useful discussions and collaborations. Of course the excursions are also partly for fun.
The excursion at Nuclear Structure 2010 certainly counts as a physics excursion, and also a fun one. We went to NIF: the National Ignition Facility, based at Lawrence Livermore National Laboratory not too far from San Francisco. The facility is being built to make small pellets of Hydrogen-2 and Hydrogen-3 nuclei fuse together to give off energy, just as they might do in a future fusion reactor and just as they actually do in thermonuclear weapons.
The US has a stockpile of thermonuclear weapons (the phrase used to describe hydrogen bombs, which work by fusing hydrogen isotopes together as opposed to nuclear fission bombs used in anger in WW2), but it has agreed that it will no longer test them in either atmospheric or underground explosions. However, it would like to understand that they are being well-maintained and still functional - something that I suppose it not obvious when you have a rather hi-tech device which you have built and then left on the shelf for many years. The way around the test-ban is to build a kind of controlled thermonuclear bomb, and that is what the NIF is. They certainly make no secret that the driving purpose of the facility is weapon "stewardship" but given that the weapons already exist and will continue to do so, it seems that they have managed to build something that allows quite a bit of interesting basic physics research to take place, piggybacked onto the weapons programme.
To get to see the facility, alien attendees at the conference had to get security-checked months in advance, and thankfully I passed the tests (though I don't know what I was being tested for). So last Wednesday, I boarded a bus in Berkeley, showing my passport before I even got on, and we drove to the lab. We stopped at the security gate for a while, and were escorted to the badge office to get our temporary badges. The whole procedure was generally taking so long that I feared we would have an hour-long trip to the security office and a 10-minute tour of the facility. We were all enjoying joking about it, though, which I was also nervous wouldn't endear us to the facility people... but all was well.
The building in which NIF sits is a rather ugly warehouse-looking place, but inside it is impressively hi-tech. I've been to a few facilities (as a mere theoretical physicist, I don't actually see inside labs all that often) and I think it's fair to say that I've never seen one so sparkling, shiny, sophisticated and hi-tech. The fusion will take place by having a tiny capsule of H-2 and H-3 that you could hold in your fingertips, placed at the focus of a couple of hundred laser beams - the most powerful in the world, which will collapse the capsule causing compression and heating and then nuclear fusion. They haven't started fusion runs yet, but have fired the lasers at non-fusion pellets and everything looks good so far.
The current set up is such that the pellet is placed very carefully in a big spherical chamber into which the lasers are beamed. They will be able to make one explosion every four hours or so when it is all up and running. If they want to actually get fusion energy out of this, they said that they need a rate of 10 Hz - i.e. 10 explosions per second. That seems quite ambitions to me, but I expect that they will learn some important things about the hydrodynamics of fusing hydrogen plasma, which is really what is needed. Certainly the nuclear physics reactions are well enough understood.
After the tour, and I wish I could show you pictures but cameras were verboten, we were treated to cookies and a talk about the basic science that might come out - about matter at the extremes of density - and the promise that the majority of the experiments would be unclassified. Then it was time to head back to the bus, and back to Berkeley. Back from the borders of the sunny desert to the perennially cloudy Bay Area...
Wednesday, 11 August 2010
Superheavy in Berkeley
I'm in Berkeley, California, attending the Nuclear Structure 2010 conference. There have been a few talks on superheavy elements (roughly those heavier than found on the earth, so heavier than Uranium). This is hardly any wonder since Berkeley is home of the Lawrence Berkeley National Laboratory, where superheavy element creation was pioneered.
Krzysztof Rykaczewski presented a talk about the recently-announed discovery of element 117. Like all superheavy nuclei, it is made by reacting together two lighter nuclei: In this case Calcium-48 (20 protons, 28 neutrons) and Berkelium-249 (97 protons, 152 neutrons). This is the most obvious choice, since Calcium-48 is the most neutron rich stable light nucleus that there is and then one needs to match with the right number of protons in the other nucleus to make the one you're interested in. The tough thing about this is that Berkelium has a half life of around 320 days and is itself a superheavy nucleus that has to first be made in a lab. They made it at Oak Ridge, Tennessee, where they placed (also superheavy, or at least transuranic) Americium (element 95, widely used in household smoke detectors) and Curium (element 96) samples in a nuclear reactor for 250 days, where they absorbed neutrons and underwent beta decay until heavier elements had been created, including the Berkelium, which was separated by chemical means.
They made a total of 22mg of Bk-249 which they then turned into a target which they shipped to Russia (which turns out to require quite a bit of paperwork) to the nuclear physics lab at Dubna. Here they installed the Berkelium target onto which the Ca-48 beam impinged. They had a total of 3g of Ca-48 to work with. It's not as rare as Berkelium, but it's pretty rare, and Russia have it all. They ran the experiment for several months, and in that time made a positive identification of the isotopes of Z=117 with N=176 and N=177. When there has been independent verification of the discovery, the group will be invited to name the new element.
As my Institute of Physics Branch colleague Alby notes, the same group are now in a position to name element 114.
The paper announcing the element, in Physical Review Letters, is available (to subscribers). Details below:
Oganessian, Y., Abdullin, F., Bailey, P., Benker, D., Bennett, M., Dmitriev, S., Ezold, J., Hamilton, J., Henderson, R., Itkis, M., Lobanov, Y., Mezentsev, A., Moody, K., Nelson, S., Polyakov, A., Porter, C., Ramayya, A., Riley, F., Roberto, J., Ryabinin, M., Rykaczewski, K., Sagaidak, R., Shaughnessy, D., Shirokovsky, I., Stoyer, M., Subbotin, V., Sudowe, R., Sukhov, A., Tsyganov, Y., Utyonkov, V., Voinov, A., Vostokin, G., & Wilk, P. (2010). Synthesis of a New Element with Atomic Number Z=117 Physical Review Letters, 104 (14) DOI: 10.1103/PhysRevLett.104.142502
Krzysztof Rykaczewski presented a talk about the recently-announed discovery of element 117. Like all superheavy nuclei, it is made by reacting together two lighter nuclei: In this case Calcium-48 (20 protons, 28 neutrons) and Berkelium-249 (97 protons, 152 neutrons). This is the most obvious choice, since Calcium-48 is the most neutron rich stable light nucleus that there is and then one needs to match with the right number of protons in the other nucleus to make the one you're interested in. The tough thing about this is that Berkelium has a half life of around 320 days and is itself a superheavy nucleus that has to first be made in a lab. They made it at Oak Ridge, Tennessee, where they placed (also superheavy, or at least transuranic) Americium (element 95, widely used in household smoke detectors) and Curium (element 96) samples in a nuclear reactor for 250 days, where they absorbed neutrons and underwent beta decay until heavier elements had been created, including the Berkelium, which was separated by chemical means.
They made a total of 22mg of Bk-249 which they then turned into a target which they shipped to Russia (which turns out to require quite a bit of paperwork) to the nuclear physics lab at Dubna. Here they installed the Berkelium target onto which the Ca-48 beam impinged. They had a total of 3g of Ca-48 to work with. It's not as rare as Berkelium, but it's pretty rare, and Russia have it all. They ran the experiment for several months, and in that time made a positive identification of the isotopes of Z=117 with N=176 and N=177. When there has been independent verification of the discovery, the group will be invited to name the new element.
As my Institute of Physics Branch colleague Alby notes, the same group are now in a position to name element 114.
The paper announcing the element, in Physical Review Letters, is available (to subscribers). Details below:
Oganessian, Y., Abdullin, F., Bailey, P., Benker, D., Bennett, M., Dmitriev, S., Ezold, J., Hamilton, J., Henderson, R., Itkis, M., Lobanov, Y., Mezentsev, A., Moody, K., Nelson, S., Polyakov, A., Porter, C., Ramayya, A., Riley, F., Roberto, J., Ryabinin, M., Rykaczewski, K., Sagaidak, R., Shaughnessy, D., Shirokovsky, I., Stoyer, M., Subbotin, V., Sudowe, R., Sukhov, A., Tsyganov, Y., Utyonkov, V., Voinov, A., Vostokin, G., & Wilk, P. (2010). Synthesis of a New Element with Atomic Number Z=117 Physical Review Letters, 104 (14) DOI: 10.1103/PhysRevLett.104.142502
Wednesday, 28 July 2010
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.
Saturday, 12 June 2010
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!
Thursday, 10 June 2010
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!
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 ;-)
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 ;-)
Tuesday, 18 May 2010
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
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
Sunday, 9 May 2010
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.
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.
Wednesday, 5 May 2010
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.
Tuesday, 20 April 2010
Edinburgh
Well, to follow up the last post, I did go to the hat shop, and now have a nice grey trilby and a black bowler. I also did attend Jim Al-Khalili's talk, where he pointed out some of the sexy things about nuclear physics - the things that excite people - like the fact that looking up at the night sky means looking at nuclear reactions. He also said that no matter what you do in nuclear physics, you should be able to talk passionately and with enthusiasm about what you do.
I think that's right. You don't have to be creating new elements or looking at stellar nuclear reactions - if you're doing it, it should have a purpose that you should be able to enthuse people about. And of course, this goes for all scientists, generally. I wonder how many scientists would be able to do that to any member of the public. I like to think that I'm a little more practiced at it, but my recent encounter on I'm a scientist reminds me that it's not always so easy. Must make more effort to try - otherwise, why am I doing it?
In other conference news, I chaired a session earlier today featuring talks by current PhD students, and I am happy to report that they all gave decent talks and were clearly interested in what they are doing. Probably the best was the talk about laser spectroscopy, in which some pretty clever experiments were described which used atomic transitions to understand the properties of nuclei. Electrons in atoms get slightly affected by the fact that different nuclei have different sizes and shapes, and one can actually measure nuclei by looking at atomic (electron) transitions. A very nice talk by Frances Charlwood of Manchester showed how her group have been figuring out the size and shape changes in manganese isotopes, and showing how the sizes show distinctive changes when you reach the N=28 (28 neutrons) magic (extra-stable) number, yet the nuclear mass does not. It's a bit of a puzzle, and must be telling us something about nuclear structure - just trying to think what it is...
I think that's right. You don't have to be creating new elements or looking at stellar nuclear reactions - if you're doing it, it should have a purpose that you should be able to enthuse people about. And of course, this goes for all scientists, generally. I wonder how many scientists would be able to do that to any member of the public. I like to think that I'm a little more practiced at it, but my recent encounter on I'm a scientist reminds me that it's not always so easy. Must make more effort to try - otherwise, why am I doing it?
In other conference news, I chaired a session earlier today featuring talks by current PhD students, and I am happy to report that they all gave decent talks and were clearly interested in what they are doing. Probably the best was the talk about laser spectroscopy, in which some pretty clever experiments were described which used atomic transitions to understand the properties of nuclei. Electrons in atoms get slightly affected by the fact that different nuclei have different sizes and shapes, and one can actually measure nuclei by looking at atomic (electron) transitions. A very nice talk by Frances Charlwood of Manchester showed how her group have been figuring out the size and shape changes in manganese isotopes, and showing how the sizes show distinctive changes when you reach the N=28 (28 neutrons) magic (extra-stable) number, yet the nuclear mass does not. It's a bit of a puzzle, and must be telling us something about nuclear structure - just trying to think what it is...
Sunday, 18 April 2010
In Edinburgh
I'm in Edinburgh for the annual Institute of Physics Nuclear Physics Conference. It's partly an excuse for everyone in the UK nuclear physics community to get together and chew the fat, to discuss latest research, to discuss funding issues and to drink wine. Or beer. I've mostly drunk beer so far. I made the excellent decision to book a seat on a train far in advance. In fact, three seats since my partner and daughter are here too. The train was completely packed, not helped by the lack of flights currently. I was impressed with how well my two-year-old coped with the long journey, though I have learnt that other passengers get somewhat irate when they see you use a nit-comb on your child in public, and tell you that you shouldn't be out spreading lice.
So, the conference has a fun-packed schedule of talks. I'm looking forward to Jim Al-Khalili's talk entitled Is Nuclear Physics Research Sexy? (presumably the answer is simply "yes") and a finding out what some of the students in groups around the country are up to in the parallel sessions. And everything else, of course. But I might find time during my stay to go to Fabhatrix, an excellent hat shop on Grassmarket. When I say might, I think I mean will.
So, the conference has a fun-packed schedule of talks. I'm looking forward to Jim Al-Khalili's talk entitled Is Nuclear Physics Research Sexy? (presumably the answer is simply "yes") and a finding out what some of the students in groups around the country are up to in the parallel sessions. And everything else, of course. But I might find time during my stay to go to Fabhatrix, an excellent hat shop on Grassmarket. When I say might, I think I mean will.
Friday, 16 April 2010
Nuclear Power Quiz
From CNN, a nuclear power quiz. I got 9 / 10 :-)
http://edition.cnn.com/2010/TECH/03/31/nuclear.power.quiz/index.html
http://edition.cnn.com/2010/TECH/03/31/nuclear.power.quiz/index.html
Wednesday, 14 April 2010
New element!
A paper, just published in Physical Review Letters, has announced the first observation of element 117. This element, which will only be named when confirmed by an independent experiment and ratified by IUPAC, has been observed in an collaborative experiment between groups in Russia and the USA. The experiment took an isotope of Calcium and an isotope of an already rather heavy synthetic nucleus Berkelium, and produced two different isotopes of element 117. These isotopes decayed by a combination of alpha decay and fission, with a chain of decays that left a trail from which element 117 could be deduced. The observation gives further evidence that there may be more long-lived elements in the region.
There is no element 117 on Earth, but it is possible that it is produced in supernovae. Better understanding of the superheavy elements created in the lab helps us understand element formation in the stars, as well as the way in which protons and neutrons interact to give stable nuclei.
There is no element 117 on Earth, but it is possible that it is produced in supernovae. Better understanding of the superheavy elements created in the lab helps us understand element formation in the stars, as well as the way in which protons and neutrons interact to give stable nuclei.
Friday, 2 April 2010
The Antihypertriton
So, part of the reason to write this blog is to talk about some of the interesting isotopes out there - some of the uses they get put to, some of the reasons why they're of interest to physicists, or astronomers, or geologists, or oncologists, or radiologists, or engineers, or ... well, you get the idea. So let's kick off with a specific nucleus.
Each isotope is defined by the number of protons and neutrons it contains. The number of protons tells you what element the nucleus is (1=Hydrogen, 2=Helium and so on. This number is also called the atomic number) and the number of neutrons specifies which isotope of that element you are dealing with. I thought I would write about nuclei with atomic numbers going up as high as around 120, and down as low as zero (and I thought that zero would be a neat trick, talking about neutron clusters with no protons present), but I was a little shortsighted in how low you can go in atomic number.
In an article just published in the journal Science, the STAR collaboration - a team of scientists from around the world working at the Relativistic Heavy Ion Collider (RHIC - think LHC but smashing heavy gold nuclei together rather than single protons) at Brookhaven Lab in New York State, USA - have reported observation of a really exotic nucleus with atomic number -1, so it has an antiproton instead of a proton, and with a particle that doesn't usual feature in nuclei called an antihyperon. This kind of "antinucleus" doesn't make up normal matter. Nature has provided us with a whole set of particles (protons, neutrons and so on) along with a complete mirror image set, known as antiparticles. Their behaviour seems to be pretty much the same as regular matter, yet most of what we see is made of regular matter, and it's not clear why. It's thought that the big bang created basically the same amount of matter and antimatter, but that some process led to matter being more dominant now. We can't go back and observe the big bang, but by colliding two heavy nuclei together, we can get a small scale version of the high density and energy that occurred just after the big bang, and see what happens. This occurrence of the antihypertriton seems to concur with the expectation that matter and antimatter behave exactly the same - but its nice to have experimental evidence that the big bang should have behaved that way, and it's pretty cool to be able to write about a nucleus so exotic that no-one has seen one on the Earth before.
The LHC may get all the press attention, but they haven't seen an antihypertriton yet :-)
Each isotope is defined by the number of protons and neutrons it contains. The number of protons tells you what element the nucleus is (1=Hydrogen, 2=Helium and so on. This number is also called the atomic number) and the number of neutrons specifies which isotope of that element you are dealing with. I thought I would write about nuclei with atomic numbers going up as high as around 120, and down as low as zero (and I thought that zero would be a neat trick, talking about neutron clusters with no protons present), but I was a little shortsighted in how low you can go in atomic number.
In an article just published in the journal Science, the STAR collaboration - a team of scientists from around the world working at the Relativistic Heavy Ion Collider (RHIC - think LHC but smashing heavy gold nuclei together rather than single protons) at Brookhaven Lab in New York State, USA - have reported observation of a really exotic nucleus with atomic number -1, so it has an antiproton instead of a proton, and with a particle that doesn't usual feature in nuclei called an antihyperon. This kind of "antinucleus" doesn't make up normal matter. Nature has provided us with a whole set of particles (protons, neutrons and so on) along with a complete mirror image set, known as antiparticles. Their behaviour seems to be pretty much the same as regular matter, yet most of what we see is made of regular matter, and it's not clear why. It's thought that the big bang created basically the same amount of matter and antimatter, but that some process led to matter being more dominant now. We can't go back and observe the big bang, but by colliding two heavy nuclei together, we can get a small scale version of the high density and energy that occurred just after the big bang, and see what happens. This occurrence of the antihypertriton seems to concur with the expectation that matter and antimatter behave exactly the same - but its nice to have experimental evidence that the big bang should have behaved that way, and it's pretty cool to be able to write about a nucleus so exotic that no-one has seen one on the Earth before.
The LHC may get all the press attention, but they haven't seen an antihypertriton yet :-)
Thursday, 25 March 2010
Voted off
Well, I got voted off of I'm A Scientist. Never mind! It was good fun trying to answer all the questions, and chatting to school kids about science. And hats.
This post serves to provide something for anyone who still didn't get a chance to ask me questions in the competition to ask me, now that I'm out. Please feel free to comment with questions!
This post serves to provide something for anyone who still didn't get a chance to ask me questions in the competition to ask me, now that I'm out. Please feel free to comment with questions!
Wednesday, 24 March 2010
Survived the first eviction
Well, I survived the first eviction. Woo! I feel a bit bad for Sarah, though. What she does is really interesting, but I think computer science is a harder sell than disease-curing biosciences, or gee-whizzy space stuff. I hope she prompted some of the kids to think about things like computer science as proper science. She pointed them to Project Euler, too, and maybe some of the more keen ones will get started with the problems there. Which reminds me, I should try some more of them too. My solved problems page is looking a little weak.
Saturday, 20 March 2010
Get me out of here?
We're half way through I'm a Scientist Get Me Out of Here. From Monday, the students will start voting us off. Eek! Hopefully I won't be gone on the first day. They've just fixed the website so that you can see all the questions that we've been asked and what answers we've given. Mine are here. It's sort of a shame, but completely reasonable, that people not in the competition can't comment. Feel free to comment here though :-)
Monday, 15 March 2010
I'm A Scientist Get Me Out Of Here
The two-week run of I'm A Scientist Get Me Out Of Here started today, and I've had quite a few questions from the kids taking part so far. Have a look at the lithium zone on their site to see what questions I, and the other scientists, have been asked. It's been pretty interesting to find out what sort of things the student are interested in. Everything from "was it really hard work to get where you are now?" to "do you harm animals in your work?" (quick answers: kinda and no)
Tuesday, 2 March 2010
The new alchemists
One of the cool things doing nuclear physics is that it has realised the old alchemists' dream of turning lead into gold - or indeed any element into any other. While one of my colleagues has genuinely turned lead into gold, some of the most exciting work in nuclear physics comes from trying to make new elements.
The chemical elements start with element 1 - Hydrogen - with one proton in the nucleus, then on to element 2 - Helium - with two protons and so on. The heaviest element that you can dig out of the earth (in trace amounts) is Plutonium, with 94 protons. Beyond lead (element 82) all known nuclei are unstable against decay into lighter nuclei with characteristic lifetimes ranging from tiny fractions of a second to many trillions of years. As one gets, though, to heavier and heavier elements, the lifetimes get shorter and any nuclei heavier then plutonium that might have existed on the Earth have long decayed. This doesn't stop us trying to make new elements in the laboratory, though, to better understand the forces between neutrons and protons, and to try to understand what isotopes may have been made in nuclear reactions in stars.
These "superheavy" elements are made by colliding two lighter nuclei together and hoping that they fuse together. One then looks for the alpha particles that come from the decay and the resulting residual nucleus which one can hopefully identify as a known nucleus. Indirectly, by studying the decay chain, one gets a "genetic fingerprint" for the original superheavy nucleus. Recently, however, a group based at the GSI facility in Germany has actually measured a superheavy nucleus' mass directly, rather than by inferring it from the decay. By trapping it in a magnetic field and observing how fast it oscillates round the trap, one can determine its mass very accurately. Knowing the mass is important, as it is a measure of the stability of the nucleus. This helps us point to the possibility that there is a more stable region of superheavy nuclei inaccessible to experiment as yet, but containing nuclei long lived enough to make an appreciable amount of material from.
The work is published in Nature, and the IoP's Physics World blog has already reported it. It's perhaps not as earth-shattering, but before the Nature paper appeared, a PhD student of mine, and myself submitted a theoretical paper on the likely appearance of especially superheavy nuclei with very large numbers of neutrons. Fingers crossed the referees will return with positive comments!
The chemical elements start with element 1 - Hydrogen - with one proton in the nucleus, then on to element 2 - Helium - with two protons and so on. The heaviest element that you can dig out of the earth (in trace amounts) is Plutonium, with 94 protons. Beyond lead (element 82) all known nuclei are unstable against decay into lighter nuclei with characteristic lifetimes ranging from tiny fractions of a second to many trillions of years. As one gets, though, to heavier and heavier elements, the lifetimes get shorter and any nuclei heavier then plutonium that might have existed on the Earth have long decayed. This doesn't stop us trying to make new elements in the laboratory, though, to better understand the forces between neutrons and protons, and to try to understand what isotopes may have been made in nuclear reactions in stars.
These "superheavy" elements are made by colliding two lighter nuclei together and hoping that they fuse together. One then looks for the alpha particles that come from the decay and the resulting residual nucleus which one can hopefully identify as a known nucleus. Indirectly, by studying the decay chain, one gets a "genetic fingerprint" for the original superheavy nucleus. Recently, however, a group based at the GSI facility in Germany has actually measured a superheavy nucleus' mass directly, rather than by inferring it from the decay. By trapping it in a magnetic field and observing how fast it oscillates round the trap, one can determine its mass very accurately. Knowing the mass is important, as it is a measure of the stability of the nucleus. This helps us point to the possibility that there is a more stable region of superheavy nuclei inaccessible to experiment as yet, but containing nuclei long lived enough to make an appreciable amount of material from.
The work is published in Nature, and the IoP's Physics World blog has already reported it. It's perhaps not as earth-shattering, but before the Nature paper appeared, a PhD student of mine, and myself submitted a theoretical paper on the likely appearance of especially superheavy nuclei with very large numbers of neutrons. Fingers crossed the referees will return with positive comments!
Thursday, 25 February 2010
I'm a scientist, get me out of here!
I'm rather excited, as I've been picked for the next installment of "I'm a Scientist, Get Me Out of Here!"
I'll have to try to enthuse various groups of school kids about what I do, and in a better way than my competitors. Should be lots of fun, if a little daunting. Details of the competition are here. I'm up against a range of other scientists, doing lots of interesting sounding things. Now I have to think of all the reasons that nuclear physics is really interesting...
I'll have to try to enthuse various groups of school kids about what I do, and in a better way than my competitors. Should be lots of fun, if a little daunting. Details of the competition are here. I'm up against a range of other scientists, doing lots of interesting sounding things. Now I have to think of all the reasons that nuclear physics is really interesting...
Sunday, 21 February 2010
TTFN, BBFH
Nuclear Physics is not an isolated subject, but influences, and is influenced by other areas of physics, other scientific subjects, and wider society. One of the strongest and closest scientific links is in astrophysics, since stars are nothing but giant nuclear reactors. This realisation - that all elements heavier than lithium were created in the stars - does not go back to the days when the chemical elements were identified as such, or when it was realised that the elements are made of atoms with tiny nuclei at the centre. They were both pre-requisites for astrophysicists to finally understand what powers stars, namely nuclear fusion. The bulk of the puzzle was not solved until the 1950s (and indeed the entire picture is still not known) when a seminal work by Burbidge, Burbidge, Fowler and Hoyle was published which laid bare most of the nuclear reactions that occur in stars, converting lighter elements to heavier, and responsible for all the heavy elements in our bodies ("we are all stardust.") Last month, one of the co-authors of the famous paper died. Though he wouldn't have called himself a nuclear physicist, he helped define the field.
Sunday, 14 February 2010
Celebrity Nuclear Physicist
Since this is a nuclear physics blog, I think it's definitely on-topic to mention that Jim Al-Khalili, theoretical nuclear physicist and colleague of mine at the University of Surrey, was the guest on Desert Island Discs this morning. If you missed it, you can still listen for the next twelve days. He talks a bit about his personal life, and a bit about science, but the most controversial thing he said was that no good music came from the 1980s. I've pointed out this basic error in his thinking before, so I don't know why he would repeat it on Radio 4 ;-)
Monday, 1 February 2010
Labour's ambitions
A recent article in Policy Review by David Lammy makes uncomfortable reading for the future of Science funding in particular, and UK universities in general.
I don't think it's a misinterpretation of the article to conclude that the minister's position is that
I wish it were a misinterpretation, though.
I don't think it's a misinterpretation of the article to conclude that the minister's position is that
- Britain's position in the world is declining. The standard of its universities is linked to its position in the world. Its universities are currently disproportionately good and should be less good.
- Expensive-to-run courses (specifically "medicine, engineering and the natural sciences") will be cut by many universities, because they need too much money to run, and no-one wants to fund them, including the government.
- The ambition of most universities is too lofty - to be universal in what subjects they offer, and doing blue-skies research that does not directly attract private funding is not commensurate with the government ambition for UK universities.
I wish it were a misinterpretation, though.
Monday, 25 January 2010
Missing the "subcritical" point
The Ion Report warned that further cuts in STFC's support for nuclear physics could make it "subcritical." According to a report in today's Research Day (needs a subscription) Lord Drayson said that this point was dismissed because international collaborations are independent of each other and "withdrawing from some does not adversely affect the others."
That is missing the point of what the Ion report said. Without the critical mass in size of UK community, we are not able to provide the broad student training, to run summer schools, the national conference, the vibrant MSc and specialist undergraduate programmes or the specialist training and advice to industry, to law, to journalists and the media. Without adequate funding, people are lost, and along with them the bright PhDs who go off to work in nuclear engineering and industry. Yes, the projects STFC have pulled out of will largely continue, albeit without some UK expertise, but the survival of the nuclear physics community in the UK, which is small by international standards, but packs quite a punch, risks falling apart, and with it, all the added value that it brings to our moderately ambitious country.
That is missing the point of what the Ion report said. Without the critical mass in size of UK community, we are not able to provide the broad student training, to run summer schools, the national conference, the vibrant MSc and specialist undergraduate programmes or the specialist training and advice to industry, to law, to journalists and the media. Without adequate funding, people are lost, and along with them the bright PhDs who go off to work in nuclear engineering and industry. Yes, the projects STFC have pulled out of will largely continue, albeit without some UK expertise, but the survival of the nuclear physics community in the UK, which is small by international standards, but packs quite a punch, risks falling apart, and with it, all the added value that it brings to our moderately ambitious country.
Thursday, 14 January 2010
Doomsday update
Sometimes, when people ask what I do and I tell them that I'm a nuclear physicist, they look a bit amazed and ask me if I make weapons. It's not terribly surprising since, of all the many uses that nuclear physics has been used to, weapons are the one that has made most impact on culture. Though there are lots of other interesting (and more positive uses) of nuclear physics, weapons will probably always be the most iconic one, and by association, I will have to get used to being vaguely associated with them.
I sort of feel that I came to nuclear physics too late to really be associated with weapons, and I sometimes forget what a powerful influence the threat of nuclear war and nuclear weapons had on the generation before mine. I even spent my first postdoc in Oak Ridge National Laboratory in Tennessee, which was built for the atom bomb project, and visited the museums... but I've never really felt too associated with weapons, though I find the history fascinating. One of the almost romantic hangovers from the cold war era is the Doomsday clock. It was set up by a group of nuclear scientists worried about the problems of the weapons that they created. It perpetually points at a time close to midnight to represent the danger the world is under from threats so serious (originally and particularly nuclear war) that it could spell "doomsday". The clock still exists, and today it was moved back one minute to be 6 minutes from midnight, reflecting an improvement in the global situation, as judged by the Bulletin of the Atomic Scientists. I guess that's good news... and the announcement, which mentions climate change in conjunction with nuclear proliferation, suggests that the era of nuclear war as the primary (perceived) threat to civilisation is over, and we have a new enemy.
I sort of feel that I came to nuclear physics too late to really be associated with weapons, and I sometimes forget what a powerful influence the threat of nuclear war and nuclear weapons had on the generation before mine. I even spent my first postdoc in Oak Ridge National Laboratory in Tennessee, which was built for the atom bomb project, and visited the museums... but I've never really felt too associated with weapons, though I find the history fascinating. One of the almost romantic hangovers from the cold war era is the Doomsday clock. It was set up by a group of nuclear scientists worried about the problems of the weapons that they created. It perpetually points at a time close to midnight to represent the danger the world is under from threats so serious (originally and particularly nuclear war) that it could spell "doomsday". The clock still exists, and today it was moved back one minute to be 6 minutes from midnight, reflecting an improvement in the global situation, as judged by the Bulletin of the Atomic Scientists. I guess that's good news... and the announcement, which mentions climate change in conjunction with nuclear proliferation, suggests that the era of nuclear war as the primary (perceived) threat to civilisation is over, and we have a new enemy.
Thursday, 7 January 2010
Funding cuts - update
So, as mentioned before Christmas, nuclear physicists were awaiting news of potential funding cuts that would come as a result of a shortage of money at the funding counil, STFC. We were worried that, of all the areas STFC fund, nuclear physics would face disproportionately higher cuts. We were right. I could have (perhaps should have) been blogging about this daily - it's too late to do a complete summary now, but my colleague Niels at Manchester has set up an excellent website summarising much of the information about the cuts and the response to it, and I suggest looking there for more comprehensive information.
This afternoon, I happened to look at a Twitter feed not long after STFC tweeted that their director of science programs had just had an op-ed published in New Scientist. It was something that deserved comment - and it's got it. Take a look (my comment is by user "drpdstevenson" since I logged in with my AIM credentials)
This afternoon, I happened to look at a Twitter feed not long after STFC tweeted that their director of science programs had just had an op-ed published in New Scientist. It was something that deserved comment - and it's got it. Take a look (my comment is by user "drpdstevenson" since I logged in with my AIM credentials)
Subscribe to:
Posts (Atom)