(1) Museo Storico della Fisica e Centro Studi e Ricerche...

101oCongressoNazionaleSocietàItalianadiFisica

Roma,24September2015

F.Cocce@(1),G.Curzio(3),M.Furini(2),C.Gessi(2),V.GiusH(3),A.Margo@(2),R.Nania(2),G.C.Righini(1)(1)MuseoStoricodellaFisicaeCentroStudieRicerche"EnricoFermi";(2)INFN-SezionediBologna;(3)UniversitàdiPisa-DiparHmentodiingegneriameccanica,nucleareedellaproduzione;

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TheFermiacondisplayintheBradburyScienceMuseuminLosAlamos.

FabrizioCocce@

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ExactreplicaoftheFermiacbuiltattheOfficineINFNofBologna.

FabrizioCocce@

•  TheFERMIAC(MonteCarlotrolley,Fermi’strolley)wasinventedbyEnricoFermiandconstructedbyPercyKingatLosAlamosin1947.

•  ItisananalogcomputerusedtodeterminethechangeinneutronspopulaHonwithHmeinanucleardevice(viatheMonteCarloMethod).

•  ConceivedwhileENIACwasunavailable,usedfortwoyearsbytheBengtCarlson'sTdivisiongroup.

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AirCooledNeutronicReactorApplicaHonMay29,1945,SerialNo.596465U.S.PatentNo.2836554–PatentedMay27,1958byEnricoFermiandLeoSzilard

FabrizioCocce@

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FrontView

Reactortype:Uranium-Graphite,cooledbyAir.

GraphiteCUBE,side:~6mWithmanySymmetricalCells!!

FabrizioCocce@

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•  Thepencilisusedtodrawtheneutrontrajectory;•  TheluciteplagormservesasaneutrondirecHonselector;

•  PosteriorDrum:measuretheelapsedHmebasedonthevelocity(F~2MeVorS~0.0253eV)oftheparHcularneutroninquesHon;

•  AnteriorDrum:measurethedistancetraveledbytheneutronbetweencollisionsbasedonneutronvelocityandtheproperHesofthematerialbeingtraversed.


1.  Determinethesiteofthefirstcollisioneachofthesourceneutrons(100wereiniHallyused)

2.  Establishthenatureofthecollisionofeachneutron(ElasHc,InelasHcscajering,Fission(ifthematerialallows))

3.  Followthefateofeachneutron.


1.  TipofthepointerAisplacedinthelocaHonofoneofthesourceneutrons.2.  CalibratedwheelC(50eq.spacedcalib.)issetto0.WheelCmeasureselapsed

Hme(funcHonofvelocity:ForS).WheelCissetondrumD(2speeds).3.  CalibratedwheelE(20eq.spacedcalib.)measurethedistancetraveledbythe

neutron(funcHonofvelocityandmaterial).DrumF(10steps)representsthetypeofneutron(ForS)andthetypeofmaterialunderthepointer.

4.  Drawrandomdigit.TheFermiacisrotatedaboutpointerA.5.  Drawrandomnumber.Distancetothenextcollisionisset.Distanceisreadon

WheelE.Ifthepointercrosstoadifferentmaterial,shimofthewheelEondrumF.

6.  Whenthepointerarrivesatthecollisiondistance:randomnumber.Determinethenatureofthecollision:–  ElasHc:setwheelEto0,andrepeatprevioussteps–  InelasHc:wheelCandwheelEmayhavetobereposiHonedtotakecareofchangeinvelocity–  Fission:neutronhistoryterminated.Follownewneutrons


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