University of Maryland Department of Physics, College Park, MD Physics 199M The Manhattan Project Spring 2012

Transcription

1 University f Maryland Department f Physics, Cllege Park, MD Physics 199M The Manhattan Prject Spring 2012 Instructr: Prf. Thmas Chen (I prefer t be addressed as Tm) Office: 2104 (Physics Building) Phne: chen@physics.umd.edu TA: Chris Verhaaren cver@umd.edu Office Hurs Office hurs are frm 3:00-4:00 Mndays. I am als generally available in my ffice and happy t see students; just drp by--r, better yet, give me a call and then drp by. Curse Descriptin "Hw did the wrld cme t develp nuclear weapns?" This curse seeks t answer this questin. As such it is bth a curse abut histry and abut science. The histry deals with ne f the critical events in the wrldʼs histry--- ne whse ramificatins are f central imprtance tday. Hwever, it is impssible t understand this histry withut understanding the science behind it. The curse will begin with sme essential backgrund: an intrductin t sme f the critical ideas f nuclear physics and a review f sme key histrical develpments beginning at the end f the first wrld war (such as the Great Depressin and the cllapse f Weimar Germany with the rise f the Nazi mvement). Nuclear Physics will be develped in a chrnlgical manner starting with the discvery f radiactivity by Becquerel in 1896, and ging thrugh t the discvery f fissin in Germany in One advantage f this chrnlgical apprach is that students will gain a sense f hw scientific knwledge builds. A key questin in this part f the curse is, "What were the plitical and scial frces which enabled this science t develp?" The curse then turns t the Manhattan Prject, the massive US effrt t develp the atmic bmb (as it was then called). The plitics surrunding the prjectʼs inceptin will be studied extensively. A key questin here is "What were the plitical frces which led the United States t devte massive resurces during war time fr a prject which culd have seemed t be science fictin?" The histry f the Manhattan Prject will be studied in sme detail including the plitical, scientific, military, scial and ecnmic issues. The scientific cmmunityʼs rapid, and secret, develpment f an understanding f fissin is a critical part f this histry. The curse will fcus n sme f the key aspects f this science, including the distinct rles played by slw and fast neutrns, the cncept f critical mass, the qualitative differences between uranium 235 versus uranium 238, the discvery f plutnium and the pssibility f chain-reactins based n either uranium r plutnium. The engineering challenges assciated with the

2 develpment f the bmb are als a central fcus f the curse. These included the need t develp massive facilities t enrich uranium and t breed plutnium. The challenges assciated with the design f the bmbs themselves will als be discussed with an emphasis n why a simple design was pssible fr a uranium weapn but a much mre cmplicated implsin design was needed fr plutnium weapns. In cnsidering the Manhattan Prject, it is useful t cmpare it t the unsuccessful effrt in Germany t develp nuclear weapns and t cnsider what led t the success f ne effrt and the failure f the ther. A final theme in this curse is the set f ethical issues assciated with the Manhattan Prject. A central questin is whether the scientists invlved had a special ethical bligatin t cnsider the ends t which their wrk wuld be used. Mathematical Preparatin This curse has n prerequisites. Hwever, the curse will use mathematics extensively. While the mathematics required des nt g beynd the level f a standard high schl algebra 2 curse class, students will need t be cmfrtable applying mathematics at this level. Students are nt required t have taken a class at the precalculus level; hwever, students might find it helpful t have taken a class at that level. Reading The primary reading fr the curse is The Making f the Atmic Bmb by Richard Rhdes (Simn and Shuster, 1987); ISBN This bk is ften cnsidered a masterpiece and wn numerus awards including the Pulitzer Prize and the Natinal Bk Award. It has been praised by histrians and by frmer Ls Alams weapn scientists. It describes the develpment f the nuclear physics in the first half f the 20th century as well as the develpment f the first nuclear weapns during the Manhattan Prject. There will als be supplementary readings. The curse als has assigns Michael Fraynʼs brilliant play Cpenhagen (Anchr Publisher, 2010 ) ISBN This Tny Award winning play deals with a meeting between Warner Heisenberg and Niels Bhr in Nazi ccupied Denmark in The play raises many f the issue raised by the curse. Students shuld either read the play, r watch a perfrmance f it. There is a DVD f the play (a PBS Hllywd Presents prductin) starring Stephen Rea, Daniel Craig and Francesca Annis; it is available n bth Amazn and Netflix. Pedaggical Apprach The curse will have bth a lectures and discussin sectins. Each f these will address bth the scientific and the histrical aspects f the curse. Lectures: The lectures are intended t be as interactive as pssible given the size f the class and the instructr will encurage students t ask questins. One way t ensure that the lectures are interactive is t explit clicker technlgy. One use f clickers

3 will be via the Mazur peer instructin methd develped at Harvard t aid students in understanding cnceptual issues in science. Students will be asked a carefully crafted questin which fcuses n an imprtant and subtle issue. They will then vte n answers using clickers. Next they will be asked t spend a cuple f minutes discussing the answers with their neighbrs in the lecture rm. The students then vte again with the clickers. There is cnsiderable evidence that the discussin with peers greatly imprve understanding. Clickers will als be used t take plls f student attitudes n ethical questins f relevance t the curse r n brad and cntrversial issues f histry. These pll results will help serve as a basis fr discussin n majr issues in lectures. Finally, clickers will be used fr rapid in-class quizzes. Sectins: Many activities will take place in the discussin sectins. One standard activity, which will ccur mst weeks, will be t wrk thrugh prblems similar t thse n the prblem sets in an infrmal and highly interactive manner. Mst ther activities will be dne in small grups f 4 r 5 students. One f these is aimed at wrking thrugh mre cmplex scientific prblems than a typical student culd handle easily n their wn, but thrugh discussin a grup f students shuld be able t wrk thrugh. At the end f the activity, ne member f the grup can describe the slutin t the full class. Anther small grup activity will be the discussin f questins with histrical r ethical implicatins. These questins will be nes, which are pen in the sense that reasnable peple might cme t different cnclusins, but fr which interesting and insightful analysis is pssible. A typical questin f this srt might be Albert Einstein wrte t Franklin Rsevelt abut the pssibility f `extremely pwerful bmbs f a new typeʼ based n uranium and urged the US gvernment t secure supplies f uranium and speed experimental wrk n uranium. This letter helped launch the Manhattan Prject. In ding this did he betray his pacifist principles? Grups will discuss such questins and try t reach a cnsensus. At the end f the discussin ne member f the grup will reprt t the full class the results f the discussin. All students will be expected t reprt their grupʼs effrts at least nce during the semester. Assignments and Grading Plicies Prblem sets: 10 prblem sets will be assigned during the semester n the scientific aspects f the curse. It is impssible t learn the science withut wrking thrugh examples. The prblem sets will make up apprximately 15% f the curse grade. Nte, nly a representative sample f the prblems will be graded. Slutins fr the prblem sets will be psted n the curse web site. Papers. There will be tw written assignments during the semester. The first f these will be a shrt paper (3-4 pages) analyzing hw the play Cpenhagen deals critical histrical, ethical and scientific issues raised in the curse. The secnd paper will be smewhat lnger (5-8 pages). In it students will fcus n ne f the central figures in the Manhattan Prject and analyze his r her rle in sme key event. Cllectively, these papers will accunt fr apprximately 25% f the final grade with 10% fr the first paper and 15% fr the secnd. Quizzes: There will be quizzes n the reading. Cllectively these will accunt fr 10% f the grade.

4 Class Participatin will be wrth 10% f the grade. This includes bth participatin in the activities in the discussin sectins and with the clicker questins in lecture There will be a midterm exam and a final exam in this curse. Tgether these will accunt fr apprximately 40% f the ttal grade. Grading plicies Grades will NOT in general be given accrding t the scheme in which numerical scres greater than 90 crrespnds t an A, between 80 and 90 a B etc. Rather, the crrespndence between letter grades and numerical scres will depend n many factrs including the difficulty f the assignment. If a student miss a quiz r a prblem set fr a legitimate reasn, he r she will be awarded the average scre btained fr ther quizzes r prblem sets during the semester. Late prblem sets will nt be accepted. Late papers will be accepted. Hwever, scres will be reduced by 10% fr each day late. Papers mre than 10 days late will nt be accepted. Curse Outline A. Backgrund This unit will develp the scientific and histrical backgrund needed t understand the remainder f the curse. Backgrund scientific infrmatin ranging frm the cncept f energy t sme basic ideas abut relativity and quantum mechanics will be intrduced. Key develpments in nuclear physics frm the discvery f radiactivity thrugh the discvery f the nucleus by Rutherfrd and the discvery f the neutrn by Chadwick will be at the cre f this unit. The unit ends with the discvery f nuclear thrugh the discvery f fissin in Histrical backgrund will als be develped. Majr histrical events in the first part f the Twentieth will be reviewed. The circumstances f the late 1930s will be discussed in detail with an emphasis n bth the military and plitical situatin and n the particular issues affecting science and scientists including the large number f Jewish scientists wh fled the Nazis. Reading: Chapters 1-9 in Rhdes Prblem sets: There will be 5 prblem sets n the material in this sectin: 1. Basic prblems cncerning the nature f energy; expnentials 2. Relativistic Mass-Energy relatins; radiactive decay chains 3. Quantum Physics and the statistical nature f nuclear decays; the cncept f half-lives 4. Atmic and nuclear mdels 5. Nuclear energetics and fissin. B. Frm the discvery f fissin t the establishment f Ls Alams This unit cvers the perid frm 1938 thrugh During this perid Wrld War II erupted with the United States entering

5 the war fllwing the Japanese attack n Pearl Harbr n December 7, The unit fcuses largely n the hw the Manhattan Prject emerged and in particular hw the US Gvernment became cmmitted t such a massive and secret undertaking. Scientifically the unit fcuses n fissin. The remarkable scientific advances during the years fllwing 1938 are intrduced with an emphasis n the very different behavir f 235 U and 238 U regarding their respnses t fast and slw neutrns and the implicatins f this fr bth weapns and reactrs. Anther critical scientific issue n which the unit fcuses is the discvery f the transuranic element plutnium with a fissile istpe, 239 Pu. Reading: Chapters in Rhdes; Cpenhagen Paper: A shrt paper (3-4 pages) analyzing hw the play Cpenhagen deals critical histrical, ethical and scientific issues raised in the curse will be due at the end f this sectin. Prblem sets: There will be 3 prblems sets n the material in this sectin 6. Elastic and absrptin crss-sectins 7. Prperties f chain reactins; the nature f expnential grwth 8. The physics f nuclear reactrs C. The develpment f the atmic bmb This unit cvers the perid frm the establishment f Ls Alams in Octber 1942 thrugh the Trinity test in July During this perid many f the scientific challenges were f an engineering nature. There was need fr peratins t separate 235 U and 238 U n an industrial scale fr the uranium bmb prgram. There was als a need t bth breed 239 Pu in reactrs and t chemically separate it frm uranium. Finally the design f the weapns was technically quite challenging particularly fr the case f the plutnium weapns. The science behind these issues will be cvered. On the histrical side, the many issues assciated with running three secret city-sized facilities will be stressed including the prblem f prblem f security and espinage. Reading: Chapters Epilgue in Rhdes Prblem sets: There will be 2 prblem sets n the material in this sectin 9. Enrichment f uranium 10. Mean-free path and critical mass D. Aftermath This unit deals what fllwed the Trinity test. The decisin t use the atmic bmb n Japanese cities is central in this as are sme f the stark mral issues raised by this decisin. The scale f the destructin due t the bmbing f Hirshima and Nagasaki will be central t the unit. Finally the unit deals with attempts f the wrld in the immediate pst war era t cme t grips with living with nuclear weapns will be discussed. Reading: Pages in Rhdes; supplementary readings Paper: A paper f frm 5 t 8 pages fcusing n ne f the central figures in the Manhattan Prject and analyze his r her rle in sme key event will be due at the end f this unit.

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