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PHY313 - CEI544 The Mystery of Matter From Quarks to the Cosmos Spring 2005

PHY313 - CEI544 The Mystery of Matter From Quarks to the Cosmos Spring 2005. Peter Paul Office Physics D-143 www.physics.sunysb.edu PHY313.

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PHY313 - CEI544 The Mystery of Matter From Quarks to the Cosmos Spring 2005

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  1. PHY313 - CEI544The Mystery of MatterFrom Quarks to the CosmosSpring 2005 Peter Paul Office Physics D-143 www.physics.sunysb.edu PHY313 PHY313-CEI544 Spring-05

  2. We studied the nucleus. It is made up of a dense package of neutrons and protons, i.e. nucleons. The protons produce the positive charge Z that identifies the element, the N neutrons add to the mass number A = N+Z. Nucleons interact by the strong force, which is ~ 100 time stronger than the electromag-netic (EM) force. It has a range of only ~ 1 fm, about the same as the size of a nucleon. Yukawa invented the concept of the force being mediated by the exchange of specific particles, in this case pi mesons. These exchange particles are created out of nothing, as virtual particles that live for a time given by the Heisenberg Uncertainty Relation The nuclei derive their binding from the combined effect of all the nucleons inside the nucleus. The nucleons are packed together like water molecules in a liquid drop. Thus the volume (size) of the nucleus increases linearly with the number of nucleons, A, and the radius goes like the cube root of A: The binding energy increases as we add more nucleons, to a peak of 8.8 MeV/nucleon at the Fe (Iron) nucleus. As we add more protons the Coulomb repulsion between protons diminishes the binding of heavier nuclei. In nuclei past Pb (lead) the large Coulomb energy makes the nuclei prone to fission. After Thorium nuclei are not stable anymore. What have we learned last time I PHY313-CEI544 Spring-05

  3. Nuclei can transform themselves spontaneously by radioactive decay. Beta decay is the emission of a negative or positive electron and a neutrino. It changes a neutron into a proton or vice versa. It is mediated by the weak interaction and thus the half lives are quite long. Radioactive decay can be used for radioactive dating, by comparing the intensity left over after a given time to that predicted by the half life of the isotope. Positron emitters can be used for PET scanning of isotope distribution inside a human/animal body. To produce new isotopes or new elements one uses the fusion reaction. In this reaction two nuclei can be fused together, if they have sufficient energy to overcome their mutual Coulomb repulsion. This normally requires an accelerator. Neutrons, because they are not charged, can fuse with a nucleus at very low energy. What have we learned last time II PHY313-CEI544 Spring-05

  4. It was already realized before WW-II that the fission process can provide a huge source of energy. This energy is obtained without fossil fuel combustion. It does not produce CO2 which is the source for global warming. The challenges were at first considered technical: Produce a controlled fission reaction, in a safe vessel that contains all radioactivity. Then find a a way to deposit and safeguard the radioactive waste that has life times of tens of thousands of years. Soon, however, the challenges were more a matter of public acceptance and policy. The Nucleus as Energy Source: Fission First electricity producing reactor At INEEL in the U.S. 1951 Modern nuclear reactors PHY313-CEI544 Spring-05

  5. The fission process • The fission process for 235U: • This process releases 173 MeV directly, and overall about 202 MeV, per reaction. • It also produces 3 neutrons for each one that it used. • More precisely, the neutron excess for different nuclei is 235U  2.432 new neutrons 239Pu  2.874 new neutrons • These numbers are crucial for the production of a chain reaction. • http://lectureonline.cl.msu.edu/~mmp/applist/chain/chain.htm PHY313-CEI544 Spring-05

  6. Cross section area is a pictorial expression for the probability of a projectile interacting with a target nucleus. A Boron nucleus has a size RB~ 2.6 fm and a nucleon has a radius Rn ~ 1.2 fm Thus we expect A ~ (RB+Rn)2 = 14 x10-26 cm2 = 0.14 bn A cross section area of = 10-24 cm2 is called a barn (bn) because it is as easy for neutrons to hit as a barn door. In fact Boron has a neutron capture cross section at 0.1 eV of 3,800 bn = 35,000 times what one expects: Why?? It follows from the wave nature of the neutron that is important at low energies. If we take about Rn ~ the cross section can be A = 2400 bn Neutron cross sections PHY313-CEI544 Spring-05

  7. Neutron scattering as a function of neutron energy Neutron capture shows distinct resonances where the n is captures into excited nuclear states. Neutron reactions PHY313-CEI544 Spring-05

  8. Neutron multiplication factor If k =1 chain reaction is critical If k< 1 chain reaction is sub critical If k> 1 chain reaction is supercritical Explanation of factors in the equation:  = number of fission neutrons of any energy per initial thermal neutron absorbed in the fuel f = fraction of thermal secondary neutrons absorbed in the fuel p = number of neutrons that escape from being thermalized  = fast fission enhancement factor PL = neutron loss factor from volume These values are for pure isotopes. For natural uranium the 235U fraction is 0.72%; “weapons grade” uranium, the235U is enriched to at least 3% Typical values for a 3% enriched thermal-neutron reactor:  = 1.65 f = 0.71 P = 0.87  = 1.02 PL = 0.96 The values produce k = 1 For a chain reaction to build up k must be > 1. http://lectureonline.cl.msu.edu/~mmp/applist/chain/chain.htm. Multiplication factor for chain reactions PHY313-CEI544 Spring-05

  9. In the fission process neutrons are emitted with energies between 1 and 2 Me. They must be “moderated” down to thermal energies This is done in elastic collisions with so-called moderator material that surrounds the Uranium. The energy loss  = final average neutron energy/ initial neutron energy The lighter the scattering material is the more energy the light neutron is losing in the collision:  = 0.5 for hydrogen, 0.86 for Carbon, 0.99 for Uranium Thus light (H2O) and heavy (D2O) water are the best moderators. However, because of its propensity to absorb neutrons light water is not very good, D2O is in effect 100 time better, Graphite is next. Light and heavy water can also be used as a coolant, but not graphite. BNL heavy water- moderated HFBR research reactor: Neutron Moderation PHY313-CEI544 Spring-05

  10. n-capture on 238U can breed 239Pu, which is an even better fission energy source than 235U. Thus reactors produce their own fuel while they produce energy. Materials that absorb neutrons very effectively act either as poisons –stopping the reactor, or as control elements-keeping the power of the chain reaction in check http://library.thinkquest.org/17940/texts/java/Reaction.html Xenon-135 was an early poison that almost stopped the Pu production at the Hanford reactors in 11943 ~ 7 hours after its start. 135 Xe has a cross section of 2.65 barns for slow neutrons. Good control materials are 10B (cross section 3800 bn) and 113 Cd (20,000 bn). These materials serve in control rods that are inserted into or withdrawn from the core to absorb more or fewer neutrons. Plutonium Breeding, Xenon Poisoning & Control Material PHY313-CEI544 Spring-05

  11. The most widely used reactor types use water for cooling of the reactor core during the fission reaction. The water is either boiling or under pressure. In the BWR the steam heated in the reactor core directly drives the steam turbine which produces the Electricity. A typical reactor generates about 1000 MW of electricity. http://www.ida.liu.se/~her/npp/demo.html http://www.eia.doe.gov/cneaf/nuclear/page/at_a_glance/reactors/states.html Light-water reactors PHY313-CEI544 Spring-05

  12. The core of the reactor is an engineering marvel • But it is not physically complicated. It has few moving parts, mainly the control rods. • They cannot ever be allowed to get stuck in the pulled-out position or the reactor could not be controlled • The most critical parts are the cooling water pumps. If the cooling water stops the reactor will overheat and the fuel rods can melt. • Automatic safety precautions as fallbacks are incorporated into the reactor design, but these have not always been effective PHY313-CEI544 Spring-05

  13. Typically a reactor has about 280 fuel rods in a bundle. Typically fuel rods are changed when they become “poisoned” and replaced with new ones. The spent fuel can be re-processed and Pu can be extracted. A modern reactor has a thermal efficiency for the production of electricity of ~32%. Thus a 1000 MWe reactor needs to produce 3100 MW of heat. Uranium provides “burn-up” energy of ~ 40 GWd/ton at 3.75% enrichment 1 GWe-year requires 1.2 tons of 235U, or 32 tons of total Uranium (3.75% enrichment) Fuel is changes about 3 tomes/year This requires ~ 200 tons of natural uranium. Present world demand for Uranium is ~ 60,000 tons/years, corresponding to a power production of 300 GW-years. The price of ~$260/kg or $260,000/ton. Spent fuel can be re-processed, with 99.8% extraction of Uranium and Pu. The remainder needs to be stored somewhere to cool down thermally and in terms of radiation. Some facts about the fuel cycle Yukka Mountain Repository PHY313-CEI544 Spring-05

  14. Nuclear Reactors in the world PHY313-CEI544 Spring-05

  15. production from burning fossil Energy fuels produces CO2 which slowly accumulates in the upper atmosphere. CO2 transmits the sun‘s radiation to earth but absorbs the heat radiation emitted from earth and reflects it back. This leads to global warming. The emssion of CO2 could be significantly reduced by use of nucler enrgy production. Global warming has happened before in the Earth‘s history, but leads to serious climate changes Global warming PHY313-CEI544 Spring-05

  16. 3MI reactor unit 2 (~800 MW) had a serious accident on March 28, 1979 when the main cooling water pumps stopped working. The reactor fuel overheated and melted. Although the containment vessel was not breached the publics faith in nuclear power was badly shaken. The cause of the accident was human error, design deficiencies and component failures. Today the 3MI-II reactor is defueled and decommis- sioned. Total cost of accident ~ $1 Billion Time line: March 1979: Accident happened July 1980: 43,000 Ci of Krypton vented July 1980: First human entry into reactor building Oct 1985: Defueling begun Jan 1990: Defueling completed April 1991: Evaporation of 2.23 Million g of contaminated water begins August 1993: Water removal completed The Three-Mile Island Accident PHY313-CEI544 Spring-05

  17. Some commercial power statistics PHY313-CEI544 Spring-05

  18. World Growth of Nuclear Power PHY313-CEI544 Spring-05

  19. The U.S. Government is beginning a program to design the next generation nuclear reactors: Generation-IV program. This program is studying 6 reactor concepts with the goal of having designs ready for construction by 2030. It has dedicated the Idaho National Laboratory to this reactor development. The Japanese are also developing advanced concepts: The Reduced Moderation Light water Reactor: This reactor type leaves more energetic neutrons in the core that “burn away” heavy radioactive isotopes In addition there is development of Thorium fueled reactors which do not produce Pu and are thus proliferation-proof. Gas-Cooled Fast Reactor (GFR)features a fast-neutron-spectrum, helium-cooled reactor and closed fuel cycleINEEL contact: Kevan Weaver, weavkd@inel.gov Very-High-Temperature Reactor (VHTR)a graphite-moderated, helium-cooled reactor with a once-through uranium fuel cycleINEEL contact: Finis Southworth, fin@inel.gov Supercritical-Water-Cooled Reactor (SCWR)a high-temperature, high-pressure water-wooled reactor that operates above the thermodynamic critical point of waterINEEL contact: Jacopo Buongiorno, buonj@inel.gov Sodium-Cooled Fast Reactor (SFR)features a fast-spectrum, sodium-cooled reactor and closed fuel cycle for efficient management of actinides and conversion of fertile uraniumINEEL contact: John Ryskamp, jmr@inel.gov Lead-Cooled Fast Reactor (LFR)features a fast-soectrum lead of lead/bismuth eutectic liquid metal-cooled reactor and a closed fuel cycle for efficient conversion of fertile uranium and management of actinidesINEEL contact: Kevan Weaver, weavkd@inel.gov Molten Salt Reactor (MSR)produces fission power in a circulating molten salt fuel mixture with an epithermal-spectrum reactor and a full actinide recycle fuel cycle Next-Generation Reactors PHY313-CEI544 Spring-05

  20. Reduced-Moderation Water Reactor (RMWR) • As a candidate of advanced light-water reactors, JAERI is now developing RMWR. • RMWR has a possibility of a high conversion ratio of more than 1.0. • Gap spacing between each fuel rod is required to be only about 1 mm. • To attain the gap spacing of 1 mm, a tight-lattice core with triangular fuel rod arrangement can be needed. This requires very precise computer modeling drier separator core seed fuel control rod blanket fuel PHY313-CEI544 Spring-05

  21. For a bomb the neutrons are not very well contained; in addition one needs a rapid build-up of the chain reaction, before the material flies apart. For a nuclear bomb the uranium is highly enriched in 235U, between 60% and 90%. The minimum Uranium requirement is between 10 and 25 kg. For Pu bomb the minimum requirement is ~5 kg. If these “critical” amounts of material are in close proximity the nuclear reaction will explode. Two types of assembly: The gun-type where an explosive charge drives a sub-critical mass into a second sub-critical mass at high speed. A compression type where a spherical charge compresses the nuclear fuel from a low density to a high density where it becomes critical. Nuclear weapons Uranium fuel Pu fuel PHY313-CEI544 Spring-05

  22. Some archive pictures PHY313-CEI544 Spring-05

  23. Energy from Fusion in the Sun 4 1H + 2 e-  4He +2 n + 6  + 26.7 MeV energy per reaction at ~ 100 Million K temperature PHY313-CEI544 Spring-05

  24. The best fusion reaction is d + t   +n with an energy output of 17.6 MeV. D and T present the lowest Coulomb barrier to fusion, and thus the lowest temperature. But it requires ~ the temperature at the core of the sun, ~100 Million degrees. At this Temperature the electrons separate from the nuclei: a Plasma http://www.jet.efda.org/ In a thermonuclear bomb (hydrogen bomb, this temperature is produced through a fission explosion which then detonates the fusion reaction. For steady state operation the material needs to be held in a magnetic bottle Both the ions and the electrons in the plasma can be held by magnetic fields. Fusion energy in the Laboratory PHY313-CEI544 Spring-05

  25. Advantages and disadvantages of Fusion • Deuterium is available from sea water, about 10x 1012 tons. Tritium can be produced from Li through the reaction: • Sea water contains thousands of years supply of Li. • No long-lives radioactive material is created”: Tritium half life =32 years • Fusion reactors could be continuously loaded: no poisoning of fuel. • Fuel consumption extremely low because of huge energy production per kg of fuel. Disadvantage: The complexity of plasma confinement and heating has held back development for 40 years! http://fire.pppl.gov/fire_program.htm PHY313-CEI544 Spring-05

  26. 10 - 20 keV Is optimum ~ (plasma pressure)2 PHY313-CEI544 Spring-05 Need 10 atmospheres @ 10 keV

  27. Confinement of plasma particles by magnetic fields PHY313-CEI544 Spring-05

  28. Toroidal Magnetic Confinement “TOKAMAK” (Russian abbreviation for “toroidal chamber” with magnetic fields); includes an induced toroidal plasma current to form, heat and confine the plasma Charged particles have helical orbits in a magnetic field; they describe circular orbits perpendicular to the field with gyro-radius rl=v/Ω, where Ω=qB/mc PHY313-CEI544 Spring-05

  29. Product of fuel density, plasma lifetime and temperature is the “figure of merit”. PHY313-CEI544 Spring-05

  30. As the step to ignition ITER ready to be build Blanket Module421 modules Toroidal Field CoilNb3Sn, 18 coils Vacuum Vessel9 sectors Port Plug 6 heating 3 test blankets 2 limiters rem. diagnostics Poloidal Field CoilNb-Ti, 6 coils Central SolenoidNb3Sn, 6 modules Cryostat24 m high x 28 m dia. Divertor54 cassettes 500 MW of power in the plasma, plasma volume 840m3 PHY313-CEI544 Spring-05

  31. Cosmic Timeline for the Big Bang deuterons Quarks proton, neutrons He nuclei( particles) PHY313-CEI544 Spring-05

  32. Three minutes after the Big Bang the universe consisted of 75% Hydrogen, 25% 4He less than 0.01% of D, 3He and 7Li. The sun began to burn the available H into additional 4He, as we learned and heated itself up. Once there was sufficient 4He available the reaction 4He + 4He+ 4He  12 C + 8 MeV became efficient. It heated the sun up still further How are the light elements produced in stars PHY313-CEI544 Spring-05

  33. Energy from Fusion in the Sun 4 1H + 2 e-  4He +2 n + 6  + 26.7 MeV energy per reaction at ~ 100 Million K temperature PHY313-CEI544 Spring-05

  34. From Helium to Carbon • When the start has used up its hydrogen, the refraction stops and the star cools and contracts. If the star is heavy enough the contraction will produce enough heat near the core where the 4He has accumulated to start helium burning. • Because of gravity the heavier elements always accumulate in the core of the star. • The star now has 4 layers: at the center accumulates the Carbon, surrounded by a He fusion layer, surrounded by a hydrogen fusion layer, surrounded by a dilute inert layer of hydrogen PHY313-CEI544 Spring-05

  35. Once sufficient 12C is available it uses H nuclei to produce all the nuclei up to 16O in a reaction cycle. When sufficient 16O is available and the star has heated up muich more, the star breaks out of the CNO cycle by capture of a 4He or a proton. This forms all the nuclei up to 56Fe. In this process energy is produced to heat the star further because the binding energy/ nucleon is still increasing. Hans Bethe (Cornell) and Willy Fowler (Caltech) obtained Nobel Prizes for these discoveries The CNO Cycle PHY313-CEI544 Spring-05

  36. Relative Elemental Abundances of the Solar System .At least 4 processes generate heavier elements. PHY313-CEI544 Spring-05

  37. When a star has burned all its light fuel, it cools and contracts under the gravitatio- nal pressure. It then explodes. During the explosion huge numbers of neutrons are produced and captured rapidly by the exis- ting elements (r-process). Beta decay changes neutrons into protons and fills in the elements The new elements are blasted into space and are collected by newly formed stars. Binary stars which are very hot can also produce the heavy elements. Supernova explosion produces heavy elements PHY313-CEI544 Spring-05

  38. Location of the r-process in the nuclear mass table “Magic” neutron numbers ...+126 “Magic” proton numbers 2,8,20,28,50,82 N=Z Chart of the Nuclei Z The r-process works its way up the mass table on the neutron-rich side . There are other processes on the proton rich side N PHY313-CEI544 Spring-05

  39. Heavy elements are also created in a slow neutron capture process, called the “s” process. • The site for this process is in specific stage of stellar evolution, known as the Asymptotic Giant Branch(AGB) phase. • It occurs just before an old star expels its gaseous envelope into the surrounding interstellar space and sometime thereafter dies as a burnt-out, dim "white dwarf“ • They often produce beautiful nebulae like the "Dumbbell Nebula". • Our Sun will also end its active life this way, probably some 7 billion years from now. PHY313-CEI544 Spring-05

  40. Fifth Homework Set, due March 3, 2005 • Which two nuclei are used most often in nuclear fission reactors. How are these nuclei made to fission? • The most widely used reactor type is a lit-water reactor. What purposes does the water serve in the operation of the reactor? • What reaction does a fusion reactor use to produce energy and what are the principal advantages of a fusion reactor over a fission reactor that follow from using this reaction? • What is a nuclear chain reaction; how can it be started and can it be stopped? • How is the plasma in a fusion reactor kept away from the walls of the reactor vessel? What is the shape of the “bottle” that holds the plasma ? • What fuel does the sun burn to produce its power, and what is the “ash” left behind from the burning? pri PHY313-CEI544 Spring-05

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