Introduction to Radiation Biophysics

Transcription

1 Introduction to Radiation Biophysics Radiation Protection & Biology Rhodes Statkewicz 7 th ed Chapt. 1 & 2 Bushong 10 th ed pg 2-12 Chapts 2 & 3

2 Radiation Biophysics the study of the effects of radiation on cells, tissues, biomolecules, and living organisms

3 Benefit Versus Risk Worth the risk to have the exam Mammography Fractured bone Repairs Educating the public

4 ALARA As Low as Reasonably achievable = Optimization for Radiation Protection (ORP) Image Gently Campaign 2008 campaign to reduce radiation dose for pediatric exams Image Wisely Campaign ASRT- minimize adult dose

5 Background Equivalent Radiation Time ( BERT) Compares risk between two or more activities Radiography frequently uses life span shortening BERT EXAMPLES Your textbook table 1-1 page 10 Other Similar Comparisons Smoking one cigarette = 10 minutes of life lost Home accidents = 95 days of life lost Overweight by 20% = 2.7 years life lost 1 REM(.01 Gy) of occupational exposure = 1 day Medical x-rays US average= 6 days Dowd, 2 nd ed, Practicle Rad protection

6 Importance of Radiation Biophysics Diagnostic Efficacy The degree to which the diagnostic study accurately reveals the presence or absence of disease in the patient. Diagnostic Efficacy Imaging Procedure Justified by physician Minimal Radiation Exposure Optimal Image Produced Presence or Absence of Disease Revealed

7 Efficacy, Ethics & Competency Radiographer has repeated images on chest due to necklace Radiographer has six repeated images on a shoulder exam Radiographer takes 3 images on a larger patient abdomen Radiographer does right foot instead of left Patient has chest x-ray followed by CT of the chest Radiographer brings best friend in after hours to image toe

8 Thinking it Over Any radiation exposure that does not benefit a person in terms of diagnostic information obtained for clinical management of medical needs or that does not enhance the quality of radiologic examinations is called: a. Artificial radiation b. Enhanced natural background radiation c. Human-made radiation d. Unnecessary radiation

9 Terminology

10 Historical Development - Atomic & Nuclear Physics Light and Electricity

11 Historical Development- 2 Effects of Radiation on Early Experimenters Erythema Epilation Anemia 1904 Clarence Dally 1st American Fatality from x-rays ( )

12 Francis Hauksbee ( ) 18 th center English Scientist Worked on electricity and electrostatic repulsion Built Electrical Generators Generator built by Francis Hauksbee

13 Plucker, Geissler, and Hittrof Julius Plucker ( ) Studied Cathode Rays that led to the discovery of the electron Heinrich Geissler ( ) Discharge tube technology Fore Runner of Crookes tube Johann Hittorf ( ) Worked with vacuum tubes Measured current in a vacuum Electrical current through gases Heinrich Geissler Johann Wilhelm Hittorf Julius Plücker Geissler Tube

14 Eugen Goldstein ( ) Early investigator of discharge tubes Named the light emitted as cathode rays. Cathode rays were later identified as electrons Crookes Tube

15 William Crookes ( ) Chemistry & Physics Discovered Thallium Investigated the properties of cathode rays ( Electron Streams) Worked with radioactivity and separating uranium Invented the Crookes Tube Electrical discharge tube Partial vacuum Various shapes Sir William Crookes

16 Gustav Ludwig Hertz ( ) Developed isotope separation technique Designed & built a mass spectrometer to determine the isotopic composition of uranium Worked on uranium enrichment

17 Wilhelm Conrad Röntgen ( ) Used Crookes tube to study cathode rays Discovery of X-rays 1901 received 1 st Nobel prize in Physics

18 Antoine Henri Becquerel ( ) Worked with the Curies Phosphorescent materials such as uranium salts 1903 Nobel Prize in Physics for discovery of Radioactivity shared with Curies Later radiation measurement named for him

19 Pierre & Marie Curie Pierre worked with brother & discovered piezoelectricity US basis Radioactivity in uranium ore Worked with Henri Becquerel Discovered elements of polonium and radium 1903 Nobel prize in Physics Radiation measurement named after them

20 Joseph John Thompson ( ) Identified that cathode rays were a previous unidentified negative charged particle. the electron. Discovered isotopes in non-radioactive elements 1906 Nobel prize in Physics for discovery of electron

21 Robert Andrews Millikan ( ) Measurement of the electron charge and its mass Photoelectric effect

22 Ernest Rutherford ( ) Concept of the nuclear atom and radioactivity Named the particles of alpha, beta, proton & neuton 1908 Nobel prize in Chemistry Radioactive Half-life

23 Hermann Joseph Muller Radiation genetics studying fruit flies Radiation induced genetic alterations In 1946 Muller was awarded the Nobel Prize in Physiology Worked to control nuclear weapons

24 James Chadwick ( ) Defined Beta Particle energy ranges Proved the existence of the neutron that was suggested & named by Rutherford 1935 Nobel prize in Physics

25 James Watson (1928- ) Worked with RNA & DNA Double Helix design of DNA Human Genome Project Nobel prize in medicine for work

26 Module 1 Rhodes

27 Atom Miniature solar system Fundamental particles Proton Neutron Electron Utilize Atomic Mass Units AMU to describe mass of particles Electrically neutral

28 Electrons Particles Carry one unit of negative electrical charge Revolve around nucleus in fixed orbits energy shells Mass is 9.1 x kg Mass is so small AMU = O

29 Protons Reside in nucleus Mass is x kg 1 AMU 1 unit of positive electrical charge

30 Neutron Reside in nucleus Mass is x kg 1 AMU O units of charge

31 Characteristics of Fundamental Particles Particle Location Mass AMU # Charge Electron Shell x kg Proton Nucleus x kg Neutron Nucleus x kg 0 Negative 1 Positive 1 Neutral 31

32 Quarks Smaller particles that compose protons & neutrons Particles are usually paired Up/Down Charm/Strange Top/Bottom The Particle Adventure

33 Leptons - neutrinos Point like particles without internal structure 6 named leptons exist today Electrons are leptons Three of the leptons are neutinos Solitary particles that do not interact with other particles Produced in particle decay Identified due to mass of the neutino needed to balance conservation of momentum formulas in decaying atoms

34 Size of an Atom If a basket ball = a uranium nucleus Electron orbits would be 7.2 miles away Atom mostly empty space

35 Orbital shells K- Q Different Binding energies for shells & atoms Principle Quantum Number Formula 2n 2 Octet Rule - Outer shell electrons never more than 8 electrons

36 Binding Energy Larger Atoms Higher binding energies for respective shells 36

37 Variations Arrangement Atomic Number Atomic Mass Number Neutron Number Isotope Same Different Different Isobar Different Same Different Isotone Different Different Same Isomer Same Same Same 37

38 Ionization 38

39 Methods of Ionization Exposure of matter to x or gamma rays Exposure of Matter to a stream of Electrons Spontaneous Decay of Radionuclides Exposure of Certain Elements to light Chemical Ionization Thermionic emission Ions traveling through plasma 39

40 Radioactivity The emission of particles and energy in order to become stable Transforms into another atom Atoms that can do this are called Radionuclides

41 Radioisotopes Undergo disintegration to bring neutrons & protons into stable arrangement Barium Radioisotopes Bushong page 37 Artificially produced or naturally occurring Ex: Uranium that decays to Radon Emit Alpha & Beta particles & gamma rays

42 Carbon 14

43 Beta Emission Beta ejected from nucleus Nucleus loses mass and one unit of negative charge Neutron undergoes conversion to proton Iodine is now Xenon

44 Alpha Emission Alpha particle = 2 protons & 2 neutrons = 4 AMU Violent reaction very unstable atom

45 Half Life (Semi-Log Graph) The time required for a quantity of radioactivity to be reduced to one half its original value 3.3 half lives = 1 tenth life Radioactive Decay Law provides T ½ Graph shows amount of radioactivity after time in days

46 Half Live (Linear Graph) Semi log easier to read for some elements Original value always assigned 100%

47 Half Life Calculations 10 mci quantity of technetium Tc (t ½ = 6 hrs) is available at 8 am. At 2:00 pm on that day, how much radioactivity is left? 100% 8 am 50% 2 pm 6 hours

48 Half Life Calculations 10 mci quantity of technetium Tc (t ½ = 6 hrs) is available at 8 am. At what time will it have decayed to 25% of its original value 100% 8 am 50% 2 pm 25% 8 pm 6 hours 6 hours 12 hours

49 Half Life Calculations 10 mci quantity of technetium Tc (t ½ = 6 hrs) is available at 8 am. How long will it take to decay to less than 10% of its original value 100% 8 am 50% 25% 2 pm 8 pm 12.5% 2 am 6.25% 8 am 6 hours 6 hours 6 hours 6 hours Approximately 24 hours

50 Types of Ionizing Radiation Particulate Alpha Beta Other Neutrons smaller ones Electromagnetic Gamma X-rays

51 Particulate Alpha Helium Nucleus 2 protons & 2 neutrons 2 + charges 4 amu 4 7 MeV ( Mega 10 6 ) Ionizes 40,000 atoms for every cm of travel Beta High speed electron O AMU 1 unit of negative charge From nucleus Beta neg or Beta positive ( Positrons)

52 Electromagnetic Radiation X-rays & Gamma Called Photons Travel at the speed of Light 3 x 10 8 m/s Looses intensity with distance but never reaches zero Chart in Bushong Page 42

53 Particles in Magnetic Field Experiment to show particle charges Beta particles with negative charge move to positive pole of magnet Alpha particles with positive charge move to neg end of magnet Gamma, neutron, neutral magnet no effect on these l

54 Sources of Ionizing Radiation Natural 3 millisieverts/year Man-made 3.2 millisieverts/year

55 Natural Sources Cosmic Rays Sun & Stars Terrestrial Radiation Uranium, thorium, radium deposits in earth Internally deposited radionuclides Potassium 40 Radon Largest dose from this area >55%

56 Terrestrial Exposure in North America

57 Man-made Sources Diagnostic X-rays largest source Doses are averaged over entire population Nuclear power Research Industrial Consumer items

58 Radiation Exposure in US

59 CALCULATE YOUR EXPOSURE tml YOUR Risk from Radiographs -

60 Web Search Class Ideas Natural Sources Man-Made Sources

61 NCRP Report #160 Lists five major areas of radiation exposure in U.S. Ubiquitous background, including Radon Medical procedures Consumer products Industrial and security activities Occupational exposure Carlton/Adler Text chapt.8