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Illinois Institute of Technology

Illinois Institute of Technology. PHYSICS 561 RADIATION BIOPHYSICS Course Introduction: Electromagnetic Radiation; Radioactivity I ANDREW HOWARD 3 June 2014. Radiation Biophysics: Introduction.

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Illinois Institute of Technology

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  1. Illinois Institute of Technology PHYSICS 561 RADIATION BIOPHYSICSCourse Introduction: Electromagnetic Radiation;Radioactivity I ANDREW HOWARD 3 June 2014 Intro; EM Radiation; Radioactivity

  2. Radiation Biophysics: Introduction • What we’re trying to do:provide you with an understanding of what happens when ionizing radiation interacts with biological tissue. • Most of you are in the Health Physics curriculum:there, you’re learning about ionizing radiation • how it is produced • what it is used for • how to deliver it • how to quantify it • how to minimize exposure of people and things to it. Intro; EM Radiation; Radioactivity

  3. Introduction (continued) • You have also learned about the biological effects of radiation in other courses. • In this course the emphasis is on the biological effects, both harmful and beneficial, of radiation. • But to put those biological issues in context: • We’ll discuss radiation physics and radiation chemistry. • We won’t spend a lot of time on those subjects:you’ve dealt with those subjects in other courses. Intro; EM Radiation; Radioactivity

  4. Who is your instructor? • I am primarily in the biology faculty within the Biological and Chemical Sciences Department at IIT. • But my secondary appointment is in the physics department, and my graduate degree is in physics, so I'm reasonably familiar with physics and chemistry as well as biology. Intro; EM Radiation; Radioactivity

  5. Am I qualified to teach this? • I’m a crystallographer: • I use X-ray diffraction to study the 3-D structures of large biomolecules • I am not a health physicist by specialization • My research is often affected by concerns for the radiation safety of my experiments. • I'm a consumer of rad. biophysics knowledge. • I postdoc’d in toxicology in a DOE lab:mechanistic studies stuck with me Intro; EM Radiation; Radioactivity

  6. Why I may be a bit incoherent a few times this summer • http://www.renfair.com/bristol/ Intro; EM Radiation; Radioactivity

  7. How will this course work? • Live meetings: Tuesday and Thursday, 10 am- 12:50pm at IIT from 3 June through 24 July (plus an external final), in Stuart Building Room 213 • Internet: 6-18 hours behind. • Internet students are welcome to visit the live section, which currently has no enrollees • Primarily lectures, but with discussion • Internet students: Communicate with one another and with me via the discussion board and e-mail • It’s the only way I’m going to get to know you. • Be brazen! Be daring! Intro; EM Radiation; Radioactivity

  8. Special schedule, early July • I will be attending a wedding in Oxford UK over Independence Day weekend • Rescheduled classes: • Class on Tuesday 1 July Monday 30 June • Class on Thursday 3 July  Tuesday 1 July • Class on Tuesday 8 July Thursday 10 July • Class on Thursday 8 July  Friday 11 July Intro; EM Radiation; Radioactivity

  9. Homework • We will start every class except this one by going over the homework assignment. • The homework is generally due at 11:59 p.m. on the Friday or Monday, 3-5 days after class, so we won't answer the homework questions in class, but we will discuss how the problems work, and if there are items that require clarification we'll provide them then. • It’s okay to turn assignments in late. Intro; EM Radiation; Radioactivity

  10. Course Plans (continued) • 2 midterms and a final • Midterms 19-20 June, 2-4 July • Final 24-26 July • All exams are closed-book, closed-notes, apart from a help-sheet that I will provide. • You may use a calculator, but not a programmable • All exams will be conducted outside of class sessions: we need all the class time for content • Detailed schedule is on the course Blackboard site Intro; EM Radiation; Radioactivity

  11. Course Sources • Edward L. Alpen, Radiation Biophysics, • 2nd Ed.: San Diego: Academic Press, 1998.520 pp..., cloth. ISBN-10 0120530856. • We’ll work closely from textbook except in our discussion of radiation chemistry (chapter 6) and two lectures at the end of the course on biochemistry, hormesis, and some other supplementary topics • The textbook is not a required purchase;I’ll cover most of what is in the book • Supplemental readings:HTML, books, journal articles Intro; EM Radiation; Radioactivity

  12. Using Blackboard • Portal to online lectures • Posting site for HTML and PowerPoint lecture materials • Exam keys will be emailed to you • Posting site for peer-reviewed literature • Discussion board: Use it! • Your opportunity to mull over the material • Chance to get to know your classmates • Content-related participation does get graded Intro; EM Radiation; Radioactivity

  13. Inconsistencies • It’s possible that you’ll see an inconsistency between the assignments as posted on the Assignments section on Blackboard and the overall Assignments webpage. Which is authoritative? • Answer: the Assignments section on Blackboard • … And while we’re on the subject:Submit your answers to the Blackboard Assignments page too! Intro; EM Radiation; Radioactivity

  14. History of radiation biophysics I • Early characterizers of the properties of X-rays and radioactivity: • Wilhelm Röntgen: X-rays, 1895 • Becquerel: radioactivity • Rutherford: radioactive chain decay • The Curies: radium, polonium Intro; EM Radiation; Radioactivity

  15. History II However: it was his employees, not Edison, who got sick! • Edison’s fluoroscope: 1896Don’t talk to me about X-rays,I am afraid of them. -T.A.E., 1903 Intro; EM Radiation; Radioactivity

  16. Radiation and Medicine: 1895 First medically observable deleterious effect from X-rays was recorded less than six months after Roentgen's discovery of X-rays. So the history of radiation biophysics goes back almost as far as the history of X-rays Intro; EM Radiation; Radioactivity

  17. Quantities, Units, and Definitions • The world of radiation research has gone through a major change in the units that it uses to express quantities. As recently as the 1970's when I was learning radiation quantitation, the traditional units for activity, dose, energy imparted, and equivalent dose were still in common use. In this course we will use the more modern units except in dealing with older research papers. Intro; EM Radiation; Radioactivity

  18. Quantities, Units, Definitions Intro; EM Radiation; Radioactivity

  19. Additional Quantities:Equivalent Dose • Effects of a dose depend on how much energy is deposited per unit mass and on how influential that energy is in the medium: • HT,R = DRWT,R(DR=dose, WT,R= weight factor)for tissue T, radiation type R. • If R is 60Co photons, WR=1 (reference type) • Unit: Sievert (1 J/kg) Intro; EM Radiation; Radioactivity

  20. Honorees • Louis H. Gray (1905-65) • Rolf M. Sievert(1896-1966) Intro; EM Radiation; Radioactivity

  21. RBE (relative biological effectiveness): describes weight factors for specific biological endpoints (e.g. carcinogenesis) as well as specific radiation types. Often used in context of radiation-induced tumors and other long-term problems. Kerma: Kinetic Energy Released to the Medium Let DEK =initial kinetic energy of all charged particles liberated. Then Kerma K = DEK / Dm Dimensions of dose(book says energy—that’s wrong) Units: Gy or rad. RBE and Kerma Intro; EM Radiation; Radioactivity

  22. Fluences and Flux Densities • Let DN = # particles entering a sphere with cross sectional area Da (total area a = 4pr2) • Particles enter during time interval Dt—Then— • Particle fluence = F = DN / Da • Particle flux density = f = DF / Dt Intro; EM Radiation; Radioactivity

  23. Fluence and Flux Visuals • Area through which particles enter = Da • Total Surface area a = 4pr2 • DN particles enter in time Dt • Particle fluence  F = DN/Da • Flux Density = f = DF/Dt DN Da Intro; EM Radiation; Radioactivity

  24. Energy Fluence, Flux Density • Let DEf = sum of energy (exclusive of rest energy) of all particles entering sphere of cross-sectional area Da • Energy fluence: Y = DEf /Da • Energy flux density: y = DY/Dt Intro; EM Radiation; Radioactivity

  25. Linear Energy Transfer (LET) • LET defined as dEL/dl, where dEL is the energy locally imparted to the medium over the length interval dl. • Dimensions: Energy / length; units: J/m • restricted range stopping power: don’t look for energy deposited far from path. Intro; EM Radiation; Radioactivity

  26. What does LET depend on? • Nature of radiation • Alpha particles can be stopped by paper • Betas can be stopped by aluminum • Photons can get through almost anything • Nature of medium (density, chemistry) • Energy of radiation Intro; EM Radiation; Radioactivity

  27. LET’s dependence on energy • Dependence on energy manifests itself often in subtle ways:e.g. more absorption near absorption edges. Intro; EM Radiation; Radioactivity

  28. Charged Particle Equilibrium CPE exists at a point p centered in a volume V if each charged particle carrying a certain energy out of V is replaced by another identical charged particle carrying the same energy into V. If CPE exists, then dose = kerma. Intro; EM Radiation; Radioactivity

  29. Radioactivity Measurements • Let dP be the probability that a specific nucleus will undergo decay during time dt. • Decay constant of a nuclide in a particular energy state is l = dP/dt. • Half-time or half-life: time required for half of starting particles to undergone transitions. T1/2= (ln 2) / l(not ln (2/ l), as the book claims) Intro; EM Radiation; Radioactivity

  30. Activity • Let dN = expectation value (most likely number) of nuclear transitions in time dt. • Then activity A = dN/dt = -lN(note that the minus sign is just keeping track of disappearance rather than appearance) • If you don’t understand that, you will fail the Health Physics Comprehensive Exam! • Dimensions: time-1 • Units: 1 becquerel = 1 disintegration /sec • Old unit: Curie: 3.7•1010 s-1 Intro; EM Radiation; Radioactivity

  31. Electromagnetic Radiation • Much of this course deals with the interaction between electromagnetic radiation (usually ionizing) and matter • So we need to review the properties of electromagnetic radiation • EM radiation encompasses a wide rangeof energy / wavelength / frequency • Ionizing radiation:E = 1KeV - up, l = 0.81 nm -down • Visible light is lower-energy (E~1eV, l~500 nm) Intro; EM Radiation; Radioactivity

  32. The Electromagnetic Spectrum Intro; EM Radiation; Radioactivity

  33. … or in graphical form Intro; EM Radiation; Radioactivity

  34. Laws of Electromagnetism Charles-Augustin de Coulomb • The four major rulesof electrodynamics: • Coulomb’s law(F = kq1q2r-2) • Biot-Savart law(dB = (µ0/4)dlxr/r3) • Faraday’s law(E = -B/t) • Conservation of charge Félix Savart Jean-Baptiste Biot Michael Faraday Intro; EM Radiation; Radioactivity

  35. Maxwell’s contribution • These rules predated Maxwell. He showed they could be made self-consistent by recognizing that a changing electric field induces a magnetic field; thus the integral and differential forms of Maxwell’s equations. James Clerk Maxwell Intro; EM Radiation; Radioactivity

  36. What Maxwell’s laws mean for radiation • The electromagnetic field travels away from its source with velocity = 3 * 108 m /sec. • This turns out to be the velocity of light, so evidently light is an electromagnetic wave! • Relationship between frequency and wavelength:c = nl Intro; EM Radiation; Radioactivity

  37. Planck’s contribution • Planck sought to understand radiation in a cavity by assuming that the atoms in the cavity were electromagnetic oscillators with characteristic frequencies and the oscillators would absorb and emit radiation • He also posited that the oscillators were constrained to have energiesE = (n+½)hnwhere n = frequency, h = a constant Intro; EM Radiation; Radioactivity

  38. Einstein’s photoelectric effect • Energy of photons goes into enabling the electrons to escape from the surface, plus their kinetic energy after they do so:Ephoton =hn = E0 + Kmax • Here E0 is the work function,Kmax is max electron energy Intro; EM Radiation; Radioactivity

  39. Special Relativity • Einstein modified Galilean relativity, under which velocities are additive. • Galileo: automobile velocity with respect to ground = u =v + w • Einstein says: u < c so we need new rules! Intro; EM Radiation; Radioactivity

  40. Special Relativity: Energy • Einstein’s new rules require thattime & distance formulae depend on velocity • Corrections are significant in nuclear reactions, radiation scattering, and accelerators, so we study them here a little • They also give rise to the concept of relativistic energy Hendrick Lorentz Intro; EM Radiation; Radioactivity

  41. Rest energy and mass • If v = 0, E = E0= m0c2; this is rest energyif m0 is the rest mass, i.e. the mass as it is ordinarily defined. • We can summarize the results by defining a relativistic mass m so that we can sayE = mc2 = gm0c2 where m = gm0 • For v = 0.1c, m = 1.05m0;for v = 0.98c, m = 5m0. Intro; EM Radiation; Radioactivity

  42. Atomic Structure • JJ Thomson (1897): heavy nucleus with electrons surrounding it. • Rutherford showed that the nucleus had to be very small relative to the atomic size Intro; EM Radiation; Radioactivity

  43. The Bohr Model • Bohr model: quantized angular momentum so that radiation is emitted in quanta equal to difference between energy levels of the atom. Used classical energy calculations! Intro; EM Radiation; Radioactivity

  44. Bohr model: radius • Quantized angular momentum mvr = nh/2p • But this is associated with coulombic attraction for which the centripetal force must equal the coulombic force:F = mv2/r = kZe2/r2, so r = kZe2/mv2 • Thus v = nh/(2pmr)= 2pkZe2/nh so r = n2h2/(4p2kZe2m) • For n=Z=1,r = h2/(4p2ke2m) = 0.529*10-10 m = Bohr radius Intro; EM Radiation; Radioactivity

  45. Bohr model: Electron Energies • Velocity = v = 2pkZe2/(nh) • Kinetic energy = 1/2mv2 = 2p2k2Z2e4m/(n2h2) • Potential energy = -kZe2/r = -4p2k2Z2e4m/(n2h2) • Total energy = KE + PE = -2p2k2Z2e4m/(n2h2) • Photons emerge from transitions from one value of n to another. • Transition from n = 3 to n = 2 givesphoton energy = -2p2k2Z2e4m / [(1/9 - 1/4) h2]= 1.89 eV Intro; EM Radiation; Radioactivity

  46. DeBroglie Wave Theory • So: we’ve allowed electromagnetic radiation to behave as a wave and a particle. We can express momentum of light asP = E/c = hn/c = h/l • Can we also talk about matter behaving both as a wave and a particle? Yes. • Particles can exhibit interference effects associated with wave behavior. • Wavelength l = h/P = h / (mv) Intro; EM Radiation; Radioactivity

  47. Nonrelativistic approximation:KE = (1/2)mv2 so l = h/(mv) = h(2(KE)m)-1/2 Further, since the angular momentum mvr is quantized (mvr = nh/(2p)), we can say 2pr = nl So we can say that the circumference of the electron’s orbit is an integer multiple of the electron’s wavelength! Standing waves! Wave Behavior in electrons Intro; EM Radiation; Radioactivity

  48. Assignment associated with this lecture: • Alpen, chapter 2, problem 1:Assume an oscillating spring that has a spring constant, k, of 20 Nm-1, a mass of 1 kg, and an amplitude of 1 cm. If Planck’s radiation formula describes the behavior of this system, what is the quantum number, n. What is DE if n changes by 1? Recall from freshman physics that the frequency of a simple oscillator is given by n= (1/2p)(k/m)1/2 Intro; EM Radiation; Radioactivity

  49. Assignment, continued: • Alpen, ch.2, problem 4:A proposed surface for a photoelectric light detector has a work function of 2.0*10-19 J. What is the minimum frequency of radiation that it will detect? What will be the maximum kinetic energy of electrons ejected from the surface when it is irradiated with light at 3550Å (355 nm)? Intro; EM Radiation; Radioactivity

  50. Assignment, continued: • Alpen, chapter 2, problem 5:In the previous problem, what is the de Broglie wavelength of the maximum kinetic energy electron emitted from the surface? What is its momentum? Intro; EM Radiation; Radioactivity

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