Papers and Exams

Papers and Exams

Delivery systems Papers and exams Centrifuge enrichment Iran’s centrifuges Proliferation Orbits • I’ve graded everything but the water tower assignment (will return that on Thursday). • I spent a lot of time making comments on your papers. I really found them to be quite good! The large number of comments are not to express unhappiness, but to give you constructive criticism for future improvements. • What about grades? I tend to not give many perfect scores, but to go along with that I tend to regard the A/B threshold as being in the low 80% range on my grading scale (and the B/C threshold as in the low 70% range). Delivery systems Last assignments Centrifuge enrichment Iran’s centrifuges Proliferation • Writing assignment due March 11: a briefing paper to the President Orbits of the USA on a topic where some physics knowledge is required (see next slide). • It is better to pick a specific subtopic with specific proposed actions. This is not a philosophy class but Physics for Future Presidents, so emphasize information relevant to the problem and solution. It’s good to show passion for a solution, but passion without solid information is not well matched to this class. • You are encouraged to email me about your proposed topic; I can give you a few suggestions and ideas. • Exam on Tuesday, March 19 at 7 pm. Exam will be open laptop or tablet, where you email to me your exam answers; otherwise, similar style to midterm exam. If you do not have a laptop or tablet, email me. Delivery systems Final paper due March 11 Centrifuge enrichment Iran’s centrifuges Proliferation Orbits 8–12 page briefing paper, double-spaced, with citations. Submit through SafeAssign. I’ll set the SafeAssign deadline to be March 13 at 11 pm::: • Abstract (roughly half a page, summarizing your paper; use italic font) • Statement of problem • Relevant information (the quality of the sources you use will be part of your grade) • Proposed action, including discussion of costs and benefits • Arguments against your proposed action, and your counter-arguments • Conclusion 235 Delivery systems Gun-type U bomb Centrifuge enrichment Relatively easy to make a bomb; industrial-scale effort required to Iran’s centrifuges enhance the isotopic concentration of 235U from 0.7% to > 40%. Proliferation ∼ Orbits 239 Delivery systems Implosion-type Pu bomb Centrifuge 239 238 enrichment Easier to get Pu (neutrons in a reactor on the common isotope U, Iran’s centrifuges followed by chemical separation. Harder to produce implosion using Proliferation conventional explosives. Orbits Delivery systems Little Boy and Fat Man Centrifuge Hiroshima: Little Boy, 15 kt. Nagasaki: Fan Man, 21 kt. enrichment Iran’s centrifuges Proliferation Orbits USSR: copy of Fat Man tested on Aug. 29, 1949 before indigenous designs allowed. Delivery systems Modern example: W80 Centrifuge enrichment • B61: developed by Los Alamos 1961–1968 (airplane-dropped Iran’s centrifuges bomb; up to 340 kt). Proliferation Orbits • Smaller version sought for cruise missles; W80 developed by Los Alamos 1976–1982. • 290 pounds, dial-a-yield from 5–150 kt, 31” long, 12” diameter. Delivery systems The Cold War Centrifuge enrichment Iran’s centrifuges Proliferation • At their peak around 1985, the US and USSR each had about Orbits 20,000–30,000 nuclear weapons. • Nuclear testing: a total of about 2000 tests worldwide, including about 500 above-ground. • Both the US and the USSR developed a triad of weapons delivery systems: bombers, intercontinental ballistic missiles (∼30 minutes “door-to-door delivery”), and missile-launching submarines. Other nations have one or two parts of such a triad. • Strategic weapons: destroy big targets in the interior of the opposing country (missile launch sites, command and control centers, and cities as a last resort). First strike; “use them or lose them.” • Tactical weapons: destroy troop concentrations, command centers, etc. on the battlefield. Delivery systems Nuclear weapons tests Centrifuge enrichment From Wikipedia: Iran’s centrifuges Proliferation Orbits Delivery systems Nevada test site Centrifuge enrichment Iran’s centrifuges Proliferation Orbits Test “Buster-Jangle Dog,” Nevada Test Site, 1951. Craters at the Nevada Test Site. Delivery systems Perfecting nuclear weapons Centrifuge enrichment Iran’s centrifuges Proliferation • The WWII bombs were very conservative in design. Orbits • Weapons testing allowed various tricks to be perfected. • Improved conventional high exposives that won’t go off in accidents (e.g., aircraft crash and fire). • Levitated implosion cores (to drive a nail, do you push with a hammer, or swing it?) • Small accelerators as neutron initiators. • 235U or 239Pu triggers with 238U fission boosts. • Improved radiation heating of Li-based fusion cores. • Permissive Action Links (PALs) of increasing sophistication, so that only a specific, secret electrical signal sequence will arm a bomb. • A danger: are US weapons too “tweaky” to be robust to ageing? Will they rust in peace? Codeword: stockpile stewardship. New generation of robust, simpler weapons? Delivery systems MIRVs Centrifuge enrichment MIRV bus: multiple independent re-entry ve- Iran’s centrifuges hicle (on a missle). CEP (circular error prob- Proliferation able) is 30 m for Tomahawk (cruise missile), Orbits 80–100 m for LG-118A (land-based missile; 8 warheads; decommissioned 2005!), 90–120 m for Trident II (submarine-based missile; up to 8 warheads each; in the past had 2700 warheads on 14 submarines). US W-88 warhead: 470 kT. 1.75 m long, 0.55 m max diameter, ∼ 360 kg mass. Delivery systems Delivering nuclear weapons Centrifuge enrichment Iran’s centrifuges Both the USA and the USSR have had a triad of delivery systems: Proliferation • Orbits Airplane delivery (originally “dumb” air-dropped bombs; now “smart” or guided bombs using laser targeting, or GPS). Slow, but can be recalled. • Modern variant: bombers carrying Air-Launched Cruise Missiles (ALCMs) with ∼ 30 m circular error probable (CEP) or targeting accuracy. • Land-based InterContinental Ballistic Missiles (ICBMs): ∼ 30 minute flight time, circular error probable (CEP) or targeting accuracy of 80–100 meters. One missile can carry multiple warheads. • Submarine-based or Sea-Launched Ballistic Missiles (SLBMs): ∼ 20 minute flight time, circular error probable (CEP) of 90–120 m. Deep, quiet “boomer” or ballistic missile submarines with nuclear power plants are very difficult to detect. Delivery systems B-52 with AGM-86B Centrifuge enrichment Iran’s centrifuges Proliferation Orbits B-52 carrying AGM-86B cruise missiles (one B-52 can carry 20). The AGM-86B is 20 feet long, weighs 3200 pounds, and has a range of over 1500 miles. We have about 85 B-52s in service. Delivery systems Minuteman III ICBM Centrifuge enrichment Iran’s centrifuges Proliferation Orbits Present sites (450 single-warhead missiles on active duty) Minuteman III silo Delivery systems Ohio class submarines Centrifuge enrichment Iran’s centrifuges Proliferation Orbits Ohio-class submarine: artist rendering of missile launch. One sub can carry up to 24 Trident II missiles; or 154 Tomohawk sea-launched cruise missiles, including those with W80 (150 kt) warheads. We have 14 Ohio-class subs in service. Delivery systems Trident II missile Centrifuge enrichment Iran’s centrifuges Proliferation Orbits Trident II missile launched from a submarine. With a load of four W88 (475 kt) or eight W76 (100 kt) warheads, the missile has a range of around 7000 miles. Delivery systems Nuclear war strategies Centrifuge enrichment • Ballistic missile warheads arrive at ∼ 15; 000 mph and are Iran’s centrifuges maneuverable; missile defense is not easy! Proliferation • Orbits Mutual Assured Destruction (MAD): if you hit me, I’m sure to hit you. • Destroying a city (mutually assured destruction, or MAD): a few 1,000 kt TNT equivalent (i.e., megaton yield) at 1–2 mile accuracy is sufficient to kill a large fraction of the population in even the largest cities. China reached this capability ca. 1975 even as a poor, agrarian society. • Does MAD hold any meaning with enemies who practice suicide bombings? • MAD requires knowing the return address::: • First strike: I try to knock out all of your missiles, so you can’t hit me. • No need to target cities. • “Winnable” or limited nuclear war? “Use ‘em or lose ‘em”–but you can’t be sure of knocking out 100%. • Was actively discussed by the “nuclear priesthood” during Reagan’s presidency (USA)/Brezhnev’s premiership (USSR). Delivery systems Gas centrifuges Centrifuge enrichment Iran’s centrifuges The modern approach to uranium enrichment: put UF6 in centrifuges at 6 Proliferation 50–70 krpm to get gravitational force of about 10 g. Use 10–20 stages 235 238 Orbits to get good enhancement of U relative to U. Delivery systems Gernot Zippe Centrifuge enrichment • Austrian physicist working for Iran’s centrifuges Proliferation Luftwaffe during WW II. Orbits • Captured by USSR at end of WW II, and ended up leading their centrifuge program. • Released by USSR in 1956. Found western centrifuge programs to be way behind. • University of Virginia, late 1950s: recreated USSR design. Left US after Gernot Zippe demand that he become a citizen to (1917–2008), from continue this work. www.uranuss.at • Returned to Europe, and was a founder of the UK/Dutch/German centrifuge enrichment company URENCO. Delivery systems Centrifuges in Iran Centrifuge enrichment Iran’s centrifuges Proliferation Orbits • Centrifuge technology likely spread from France to Pakistan, and from there to Iran. • Countries that sign the nuclear Non-Proliferation Treaty (NPT; 1968) gain the right to develop peaceful uses of nuclear power, with monitoring from the International Atomic Energy Agency (IAEA). • Iran is part of NPT and says it is only developing uranium enrichment for nuclear power. Reactors only require enrichment from 0.7% to 2.5–3.5%. IAEA found Iran to be in non-compliance with nuclear materials reporting obligations in 2005. • The pictures that follow: from the New York Times on April 29, 2008; and March 14, 2009.

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