New version page

UW-Madison PHYSICS 208 - Lecture 29 Notes

Documents in this Course
Lect 11

Lect 11

19 pages

EM Waves

EM Waves

23 pages

Exam 3

Exam 3

5 pages

Load more
Upgrade to remove ads

This preview shows page 1-2 out of 5 pages.

Save
View Full Document
Premium Document
Do you want full access? Go Premium and unlock all 5 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 5 pages.
Access to all documents
Download any document
Ad free experience

Upgrade to remove ads
Unformatted text preview:

1Thu, Dec. 13 2007 Phy208 Lect291Evaluations• Please fill out evaluation and turn it in.– Written comments are very helpful!• Lecture will start 12:15• Today, evaluate Prof. Rzchowski• If you weren’t here Tuesday,also evaluate Prof. Montaruli today.Thu, Dec. 13 2007 Phy208 Lect292Final Exam• Fri, Dec 21, at 7:45-9:45 am in Ch 2103• 2 equation sheets allowed (HAND WRITTEN!)• About 40% on new material• Rest on topics of exam1, exam2, exam3.Study Tips:1. Download blank exams and take them.2. Download blank quizzes and take them.3. Look through group problems.4. Look through lab question sheets.5. Make up an exam question,explain solution to your study group.Thu, Dec. 13 2007 Phy208 Lect293From last time…• Radioactive decay: alpha, beta, gamma• Radioactive half-lifeToday:• More about beta, gamma, decay• Medical uses of radiation• Nuclear fissionThu, Dec. 13 2007 Phy208 Lect294From last time: Alpha radiationAlpha particle:(2 protons, 2 neutrons)Piece of atom (alpha particle)ejected from heavy nucleusThu, Dec. 13 2007 Phy208 Lect295Decay sequence of 238UNumber of neutronsNumber of protonsα decayBut what are these?Thu, Dec. 13 2007 Phy208 Lect296Beta decayNumber of neutronsNumber of protonsNumber of neutronsdecreases by oneNumber of protonsincreases by oneElectron (beta particle)emittedBut nucleus has only neutrons & protons.2Thu, Dec. 13 2007 Phy208 Lect297Beta decay• Nucleus emits an electron(negative charge)• Must be balancedby a positive chargeappearing in the nucleus.This occurs as a neutronchanging into a protonThu, Dec. 13 2007 Phy208 Lect298Changing particlesNeutron made up ofquarks.One of the down quarkschanged to an up quark.New combination ofquarks is a proton.Thu, Dec. 13 2007 Phy208 Lect299beta decay exampleUsed in radioactive carbon dating.Half-life 5,730 years. ! 614C " 714N + e#8 neutrons6 protons7 neutrons7 protons14 nucleons 14 nucleons6 positivecharges7 positivecharges==+1 electron+1 negative chargeThu, Dec. 13 2007 Phy208 Lect2910Other carbon decays• Lightest isotopes of carbon emit positron– antiparticle of electron, has positive charge!9 neutrons9 protons10 neutrons8 protons+e+This isantimatterThu, Dec. 13 2007 Phy208 Lect2911Thu, Dec. 13 2007 Phy208 Lect2912Antimatter• Every particlehas an antiparticle.• Antimatter (anti-atoms) has been formed.Matter and antimatterannihilatePhotons are created,conserving energy,momentum.3Thu, Dec. 13 2007 Phy208 Lect2913Positron Emission Tomography - PETShort-lived radioactive tracer isotope emits positronPositron annihilates with nearby electron– e+ + e- → 2γ• Two 511 keV gamma rays are produced• They fly in opposite directions (to conserve momentum)Isotope Max. PositronRange (mm)18F 2.611C 3.868Ga 9.082Rb 16.5Gamma Photon #2Thu, Dec. 13 2007 Phy208 Lect2914Emission Detection• If detectors receive gamma rays at the approx. same time, we have adetection• Nuclear physics sensor and electronicsRing of detectorsThu, Dec. 13 2007 Phy208 Lect2915Radioactive tracersWorked on radioactivityas student with Ernest Rutherford.Lodged in nearby boarding home.Suspected his landlady was serving mealslater in the week ‘recycled’ from the Sunday meat pie.His landlady denied this!deHevesy described his first forayinto nuclear medicine:George de Hevesy“The coming Sunday in an unguarded moment Iadded some radioactive deposit [lead-212] to thefreshly prepared pie and on the following Wednesday,with the aid of an electroscope, I demonstrated to thelandlady the presence of the active deposit in the soufflé.”Thu, Dec. 13 2007 Phy208 Lect2916Detect ionizingradiation• ElectroscopeGeiger counterThu, Dec. 13 2007 Phy208 Lect2917Decay of 60Co• This is one of sources used inthe lab.• Decays by electron emission, aspredicted.• But decays to an excited state.• Photons emitted as excitedstate drops to its ground state.Thu, Dec. 13 2007 Phy208 Lect2918Gamma decayAlpha decay (alpha particle emitted), Beta decay (electron or positron emitted), can leave nucleus in excited state– Nucleus has excited states just like hydrogen atom– Emits photon as it drops to lower state.Nucleus also emits photon asit drops to ground stateThis is gamma radiationExtremely high energyphotons.Ni6028Ni60284Thu, Dec. 13 2007 Phy208 Lect2919 Cancer Radiation Therapy• 50-60% of cancer patients treated with radiation• Goal: disable cancerous cells without hurting healthy cells• Typically X and γ-rays (60Co) from 20 KV to 25 MVThu, Dec. 13 2007 Phy208 Lect2920Radiation Levels• rad (radiation absorbed dose)• amount of radiation to deposit 0.01 Jof energy in 1 kg of absorbing material• RBE (relative biological effectiveness =# rads of x-rays that produces samebiological damage as 1 rad of radiationbeing used• rem (roentgen equivalent in man) =dose in rem = dose in rad x RBESafe limit ( US gov )0.50 rem/yrGround 0.30 rem/yrMercury 9 60.6 rem/yr Apollo 14 146.2 rem/yrMIR Station 34.9 rem/yrSpace Station 36.5 rem/yrRadiation type RBEX-rays 1Gamma rays 1Beta particles 1-2Alpha particles 10-20Thu, Dec. 13 2007 Phy208 Lect2921Your exposure in the lab•60Co has an activity of 1 µCurie• Each decay: 1.3MeV photon emitted• Assume half are absorbed by a 10kg section of yourbody for 2 hours.• Energy absorbed =! " 3.7 #104decays / s! 1.3 " 106eV( )123.7 "104decays/ s( )2hr( )3600s /hr( )1.6 "10#19J /eV( )= 2.8 "10#5J ! 2.8 "10#5J /10kg( )1rad / 0.01J / kg( )( )= 3 mrad = 3 mremWhat is yourdose in mrem?A. 0.5 remB. 0.3 remC. 0.1 remD. 0.05 remE. 0.003 remThu, Dec. 13 2007 Phy208 Lect2922Decay summary• Alpha decay– He nucleus (2 protons, 2 neutrons)– Nucleus loses 2 protons, 2 neutrons• Beta- decay– Electron– Neutron changes to proton in nucleus• Beta+ decay– Positron– Proton changes to neutron in nucleus• Gamma decay– Nucleus emits photonas it drops from excited stateThu, Dec. 13 2007 Phy208 Lect2923Decay question20Na decays in to 20Ne, a particle is emitted?What particle is it?Na atomic number = 11Ne atomic number = 10A. AlphaB. Electron betaC. Positron betaD. Gamma20Na has 11 protons, 9 neutrons20Ne has 10 protons, 10 neutronsSo one a proton (+ charge ) changed to aneutron (0 charge) in this decay.A positive particle had to be emitted.Thu, Dec. 13 2007 Phy208 Lect2924Nuclear fission• Nuclear bindingenerges•56Fe is most stable• Move toward lowerenergies by fission orfusion.• Energy releasedrelated to differencein binding energy.5Thu, Dec. 13 2007 Phy208


View Full Document
Download Lecture 29 Notes
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Lecture 29 Notes and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Lecture 29 Notes 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?