| IAEA Conference on Fusion Energy | | Date Created: Nov 10, 2004, 08:02 AM |
 A report from the 20th IAEA Conference on Fusion Energy held last week at the small resort town of Vilamoura, Portugal.
My first observation is size. I've been attending these meetings for more 16 years, and the number of participants attending each meeting grows. I don't know the exact count, but there were well over 500 scientists from around the world. The larger numbers of
Europeans and Japanese scientists were particularly noticed. Several meetings encouraging further international collaborations in fusion research were held. With the growing success of the Chinese fusion program (their construction of the superconducting "EAST" tokamak) made interest in stronger Chinese-U.S.
collaboration very welcome. |
 My second observation was the quality of fusion-plasma "imagery". High-speed diagnostics and image processing were everywhere. Movies of plasma dyanamics and of realistic computer simulations of plasma dynamics made a big impression on me. Previously, I could only visualize the complex motion of magnetized plasma in my
mind. I would make line graphs of data measured at localized positions around a torus. Now, I could see the whole thing! Long, stretched-out flux tubes of hot plasma would be accelerated at high-speeds to the vacuum vessel walls of the magnetic containment experiment. These are laboratory equivalents to the coronal loops at the surface of our sun. When the first pictures from the SOHO and TRACE satellites appeared 10 years ago, I remember feeling the same way: it was like a child walking past a toy store, day after day, and finally earning the opportunity to walk inside and see everything with eye's open.
Third observation: the remarkable advancements in high-temperature plasma control tools. RF waves, beams, current-drive, external coils, passive and active feedback. Today's fusion device is covered with actuators. It seemed complicated to me, but it
worked!
Finally, I noted science and basic physics alive and well. Two talks were particularly impressive: Mike Zarnstorff and Stewart Prager. They spoke of quasi-symmetric stellarator and reversed field pinch experiments.
Figure at top: Frame from the neutron tomography images of the Joint European Torus (JET) experiment. Small puffs of tritium were injected at the edge of the plasma, and tomographic movies could trace the particle transport of the fusion fuel. Beautiful. |
| Nobel Prize in Physics to Theory of Quarks | | Date Created: Oct 05, 2004, 04:08 PM |
Very exciting.
I still remember my graduate student years (at MIT in the late 1970's and early 1980's) attending lectures about quantum field theory and QCD. I was introduced to an amazing and wonderful concept of "asymptotic freedom" and "quark confinement."Of course, as a graduate student, we were introduced to these subjects as a natural consequence of an SU(3) gauge theory, but this was just the math. Scientists around the country and in my classrooms were drawing beautiful pictures of pi mesons being stretched with lines of gluon force tied to the confined pairs of quarks.
Please take the time to read the tutorial on the Nobel web site: Information for the Public. As well as read the short official press release.
Congratulations to Profs. Gross, Politzer, and Wilczek! |
| Homework #2 | | Date Created: Sep 26, 2004, 03:56 PM |
Homework #2 is online at our class website. The secrets to solving these problems are: (1) understand conservation of momentum, (2) be aware that it is often easier to solve scattering problems in the frame of reference of one (or the other) particles. (For example, Prob. 5-1 should be solved in the rest-frame of the alpha particle), (3) be sure to read the textbook, and (4) use approximations. In the last problem, I expect your answer to be "qualitative" more than "quantitative."
As always, send email if you have questions. mauel@columbia.edu. |
| Research Conference (and Fusion Energy Alternatives) | | Date Created: Sep 25, 2004, 09:05 PM |
 Every Friday morning beginning at 9:15 am, the Department of Applied Physics and Applied Mathematics holds its "Research Conference". Here, faculty staff, and graduate students share their research progress, plans, and ideas. It's alot of fun, and one of the events that I most enjoy. This is the time when I can learn about the many new developments, projects, and discoveries made by members of our Department.
This past Friday, the Research Conference began with a talk by Prof. Chris Wiggins about bio-molecular networks associated with gene expression. The talk discussed the mathematical modeling used to understand and predict this very complicated process. Gene expression changes depending upon the cell's chemical environment. This is a fascinating and important area of research.
One comment by Prof. Wiggins was especially relevant to our class. Scientists are making great use of radiation to investigate the biochemistry of genes. Radiation can selectively destroy (or turn off or "knock out") genes, and the effects are now being studied from the point of view of cellular systems biology. The now routine use of DNA micro-array chips has accelerated the pace of this research. |
I was the second speaker, and I spoke about my research specialty in high-temperature plasma physics and fusion energy. I described my laboratory and computational studies of plasma "mixing" in an "artificial radiation belt." I described the world?s effort to build a large $6 billion experiment to investigate the behavior of strong self-heated (or ?burning?) plasma. This device would produce net power at the scale of a possible fusion power plant. Finally, I spoke about a new experiment, the Levitated Dipole Experiment that was completed this past summer at MIT.
During my talk, I had to explain the basic nuclear science of fusion power. Laboratory fusion involves nuclear reactions that release tremendous amounts of energy when light isotopes of hydrogen combine to form helium. A glass of water contains enough deuterium to be the energy equivalent of more than 250 glasses of oil! |
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To date, fusion power has been generated by the fusion of deuterium with tritium to form an alpha particle and a fast neutron. The cross-section for this fusion reaction is the largest (why?), and this makes it the easiest to produce in the laboratory. However, D-T fusion has two disadvantages. First, the neutron that carries away most of the energy (can you calculate how much?) is highly penetrating. As it passes through the materials that surround the hot plasma, the neutron causes activation. (Fortunately, these materials can be selected to nearly eliminate any long-lived radioactive material.) Secondly, tritium doesn?t exist naturally. With a half-life of about 12 years, it must be created.
The hoped-for plan for D-T fusion energy involves three nuclear reactions, and two of these are fission reactions. The D-T fusion reaction creates a fast neutron. This neutron most often splits a Li-6 nucleus into an alpha particle and a triton. But, we must make certain that there is enough tritium to replace that burned in the fusion reactor. Be-9 is also used in the material near the plasma. When a D-T neutron collides with Be-9, it fissions into two alpha particles and two more neutrons. Be-9 is a neutron multiplier. |
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The Levitated Dipole Experiment aims at a much more difficult fusion power cycle: one that does not require breeding of tritium. In this scheme, deuterium is combined with other deuterons and with the (natural) light isotope of helium, He-3, to form protons and alpha particles. This fusion cycle only involves fusion. As the reactions above illustrate, tritium is one of the (fusion) products, but if the plasma particles can be made to circulate from the hot core to the colder edge, there's a chance that the tritons can be pumped from the reactor before the create fast neutrons. If the tritium is stored for 12 years, it decays into He-3 (and an electron). The He-3 can then be injected back into the plasma where it can fuse with deutrerium to form He-4 and protons.
This fusion cycle avoids the need to breed tritons and reduces the damage and activation of the surrounding structure by reducing the intensity of neutron radiation. |
- General Info > Research Conference (and Fusion Energy Alternatives)
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| James Chadwick | | Date Created: Sep 19, 2004, 07:05 PM |
| On December 12, 1935, James Chadwick delivered his Nobel address after receiving his Nobel Prize in Physics for the discovery of the neutron. Chadwick's presentation address and short biography are available at the official historical site of the Nobel Prize. |
 I will discuss Chadwick's Nobel Lecture during our next class. It is a wonderful lecture that illustrates scientific discovery and the physics of radiation's passage through matter.
The lecture begins by comparing the interaction of the neutron with hydrogen and with nitrogen. Of course, Chadwick did not know what the neutron was and certainly not its mass. But, by measurint the maximum velocity that can be imparted to each gas, he was able to estimate the neutron's mass.
Next, he discusses the neutron's range. A neutron "can pass easily through a thickness of matter, e.g. 10 or even 20 cm of lead." If the neutron was charged, it's range would be much shorter. Thus, the neutron is a neutron particle.
Finally, Chadwick discusses beta decay, the elastic and inelastic interaction of neutrons with other nuclei, the deuteron, and nuclear structure. Having discovered the true constiutiants of the nucleus, physicists were finally able to describe the forces that hold the nucleus together and explain why the neutron is stable.
Remarkable. |
| Biomedical Engineering | | Date Created: Sep 19, 2004, 06:32 PM |
| I haven't written an entry into my blog for 10 days. I've visited four cities and spent more than enough time in airports, highways, and long technical meetings. |
| Fortunately, I made it back in time to attend at least a small part of the celebration in honor of Columbia's new Department of Biomedical Engineering. The BME Department hosted an excellent two day seminar covering history, cell and tissue engineering, neuroscience, computational biology and genomics, musculoskeletal and cardiovascular biomechanics. |
| Biomedical engineering was born from two important breakthroughs: non-invasive medical imagining and implantable biomechanical devices. For the past 50 years, the growth and success of interdisciplinary research that combines medicine and biology with engineering and applied science has been remarkable. Of course, this event was a celebration, but the enthusiasm for the future impact of research and developments in biomedical engineering, physics, mathematics, etc. was very evident at this wonderful celebration. |
| 137-Cs and the Movies | | Date Created: Sep 08, 2004, 08:08 AM |
This morning's New York Times put 137-Cs in the news when it highlighted the documentaries of Maryann De Leo, "Chernobyl Heart", which won the 2003 Academy Award for best documentary and of Rory Kennedy, who created "Indian Point: Imagining the Unimaginable" that reports opinions about what would happen if terrorists flew a plane into the Indian Point nuclear power plant just up the Hudson.
The Chernobyl accident was truly a horrible accident. The radiation sickness caused by the meltdown is heartbreaking and continues, and the whole mess seems all the more tragic because the accident was preventable. With the aftermath of 9/11 still in the minds of us New Yorkers, I too wonder what sort attack will be next directed to the United States. Since nuclear power can deliver so much more destruction and than chemical explosives (including jet fuel), it's not surprising that the potential for nuclear terror is appearing often in today's news. |
| I am a huge sympathizer with those calling for safety in the nuclear power industry, but I am also a solid supporter of nuclear power. With proper design, maintenance, and oversight, nuclear power can be made safe. Indeed, it has a track record that has already demonstrated proper safety methods. As the Times article mentioned, the fossil fuel alternatives (coal, oil, and gas) appear to be worst. They are changing our planet?s climate in ways that are difficult to predict, and they have their own set of well-known safety issues. |
| This brings us to 137-Cs. This isotope was discoverd in the 1930's by Glenn Seaborg. The Center for Desease Control (CDC) gives a safety brief about 137-Cs and notes the primary sources of the isotope in our environment are nuclear weapons testing in the 1950's and 1960's and nuclear fission reactor accidents like the Chernobyl accident. |
| 137-Cs decays to a meta-stable isomer of Barium-137m. 137m-Ba decays quickly by emitting an energetic gamma-ray, and this gamma-ray may cause biological damage if sufficiently intense. (What is the approximate energy of the gamma-ray?) |
The EPA discusses 137-Cs and reports the health effects to high exposures to Cesium-137. The disturbing questions revealed by those living around the Chernobyl accident concern birth defects to developing fetus and to future babies of parents exposed to high-levels of radiation. Not being an expert on the health effects of radiation, I feel obligated to admit to having no answers to these sorts of questions. We know that we can (and must) live safely with some radiation, but clearly, in order to reap the many benefits from nuclear science, we must also work tirelessly to eliminate accidental (or terrorists-inflicted) exposures to high levels of radiation.
What do you think?
p.s. A short report on the aftermath of Chernobyl appeared in a 2001 issue of Science. |
| Nuclear Science in Sept Issue of Physics Today | | Date Created: Sep 07, 2004, 01:41 PM |
| Physics Today is the monthly news magazine for physicists published by the American Institute of Physics. |
This month's issue has two interesting news articles.
First, medical physicists at the July meeting of the American Association of Physicists in Medicine, Duke University researchers reported the first 3D images of an inorganic test object using neutrons. Neutrons with energies between 1 and 10 MeV can penetrate humans and excite nuclei that later emmit characteristic gamma rays. One problem with this new technique is that an individual neutron causes more biological damage than an x-ray with the same energy. For the new diagnostic to work, researchers need to make the gamma detection system very highly sensitive.
Secondly, Physics Today reported the July US Court of Appeals ruling that DOE can not use the Yucca mountain site as a nuclear waste depository. The 1992 EPA rules state a safety standard at the time of peak risk. But, the Yucca Mountain depository can practically be declared safe for only 10,000 years. (This seems reasonable to me.) So, in the meanwhile, nuclear waste will continue to be stored in 100 smaller sites located within 39 states. |
| Clearly, during times like these, everyone needs to understand at least a little bit of nuclear science. |
- General Info > Nuclear Science in Sept Issue of Physics Today
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| Homework #1 | | Date Created: Sep 07, 2004, 08:25 AM |
| I just posted Homework #1 on our class website, http://www.columbia.edu/~mem4/ap4010/. Answers are due in two weeks (since class next week is canceled.) The main goal of this homework is to build understanding of the introductory material in Chapter 1 of Lilley's textbook. The first seven questions are straight from the book (and remember: the answers are in Appendix G.) Try to do the questions without looking at the answers. If your answer differs from that given in Appendix G, try to figure out your mistake and correct your answer. Four additional questions serve both to review the basics and to get your mind thinking like a physicist. |
| Mountain Hikes and Nuclear Astrophysics | | Date Created: Sep 05, 2004, 03:06 PM |
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I love mountain hikes. I can never stop feeling awe and wonder ascending by foot to a summit when the trees and rocks are suddenly brushed aside to reveal a clear view that seems to go on and on.
On friday, 9/3, I took a break from academic preparations and hiked with my family (wife, Allison, and two daughters, 4 and 11 years old) to the top of Mt. Hadley in the southern region of the grand Adirondack State Park in upstate New York. The day was clear, the weather fantastic, and the view from the summit spectacular. I was especially amazed at the long bare granite "sidewalks" that would sometimes extend 200 yards uninteruppted up the mountain side. The mountain was the site of devasting fires in the early 20th century that even burned the top soil. As a result, the weather and trail traffic has keep the trail bare. The white-grey rock combined with the young pioneer birch trees to give the whole trail the appearance of a beautiful cleanliness. |
What does a trip up a mountain have to do with nuclear science? Well, my daughters would discover small rocks with pea-sized chucks of "crystals". "Crystals! I found another crystal," my four-year-old would shout. This was a mountain that provided ample opportunity to explore the elements.
Nuclear astrophysics involves the study of the creation of the elements. In stars. It's a fascinating field and one with a long track record of success and one at the verge of more breakthroughs, especially with regards to understanding the formation of the early universe and the detailed dynamics within exploding stars.
We won't have time to discuss nucleosynthesis within our short introductory course, but we will discuss the deuteron. How lucky is the universe that the deuterium is a stable isotope! The nuclear force is sufficient to bind one neutron to one proton. With the production of deuterium, other nuclear reactions become possible. Deuterons combine with neutrons and other deuterons to form tritium; and with protons to form 3-Helium. Once these nuclei form, 4-Helium can be formed and so-on. By studying the ratios of various elements throughout the universe, nuclear astrophysicists check the consistency of modern the theories of particle physics and cosmology. |
 Some links:
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| Nuclear batteries! | | Date Created: Sep 02, 2004, 03:22 PM |
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| Just opened my issue of IEEE Spectrum, the professional magazine for electrical engineers. (See online version at http://www.spectrum.ieee.org/.) I found two articles inside: one on cold fusion (really) and the second on nuclear batteries. Both articles deserve at least some discussion in our class, but my reaction to the two articles were very, very different. Cold fusion often makes me cringe (and I have many interesting stories about my casual investigations into this and related phenomenon). As an addicted laptop and cell-phone user, the possibility of nuclear batteries was tremendously exciting. |
| The fundamental point of the articles is that the energy density that can be stored in the nucleus is so very much larger than can be possibly stored chemically in an equivalent weight of molecules and atoms. In nuclear power plants, the rate of energy release due to fission or fusion nuclear reactions is controlled and is large. In nuclear batteries, energy is released during the natural decay of radioactive materials. The energy release needs no control (other than through the selection of the material) and is generally very slow. |
| The authors describe an ingenious nuclear micro-generator that uses a beta-emitter to charge a MEMS cantilever connected to a piezoelectric crystal. Alternately charging and discharging the cantilever beam performs work on the piezoelectric crystal and generates power. A few microcuries of tritium provides an energy equivalent of 2400 Li-ion batteries of the same weight. Of course, energy density is just part of the picture. How much tritium would be required to provide the continuous power for my laptop (that has a 50 Watt-hour Li-ion battery that runs for 4 hours in normal use)? The answer from the article is: the needed 150 grams of chemical energy storage for the Li-ion battery can be replaced by 0.06 grams of tritium plus the mass of the MEMS devices needed for energy conversion.) |
| Welcome to my AP4010 Class Blog | | Date Created: Sep 01, 2004, 04:22 PM |
 This is a new idea for me: Create and maintain a web "blog" for our class AP4010 Introduction to Nuclear Science. Today's students and faculty are busy, balancing activities at multiple sites and keeping very full schedules. The idea of a "blog" is to have one on-line location for informal, up-to-date comments about our course, materials, homeworks, comments, answers, and corrections. The blog will not replace class handouts; it will not replace or serve as a substitute for our classroom discussions and lectures; and it will not replace any one-on-one conversations that you may wish to have with me about our course (or anything else about Columbia.)
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Like other blogs, I intend to write the material with a "first-person" point-of-view. Often, I will give some personal comments about what excites me about our lecture topics. I'll include links to supplemental materials. Since I love the historical context of the development of nuclear physics during the last century, I also intend to include links to relevant biographies, papers, and insights by some very remarkable scientists.
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Like other blogs, I want to make comments interactive. Interactive class "blogs" are not yet available at Columbia University (although this feature has been discussed!) I am not yet sure whether or not this feature will be helpful or not. For one thing: it is not private! We may get comments from medical physicists and students from around the world. Alternatively, you may email your comments to me mauel@columbia.edu. I'll post your contributions to the blog if two conditions are met: (1) you have to give me permission to share your question with others, and (2) your comments/questions must be judged by me to be relevant or interesting.
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I'm really looking forward to our first class next week. Until then, best wishes...
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