Sources of ionizing radiation Atomic structure and radioactivity Radiation interaction with matter Radiation units and dose Biological effects

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1 INTRODUCTION TO RADIATION PROTECTION Sources of ionizing radiation Atomic structure and radioactivity Radiation interaction with matter Radiation units and dose Biological effects 3/14/2018 1

2 Wilhelm C. Roentgen ( ) In 1895, while working with electricallyenergized, sealedglass Crookes tubes, he discovered that photographic plates kept near the tubes become darkened. 2

3 X-Ray Photography Roentgen assumes previously unknown X-RAYS are escaping the tube. Roentgen makes photo images with x-rays and shows they easily penetrate soft tissue. 3

4 Henri Becquerel ( ) In 1896, discovered other invisible rays coming from natural Uranium would also darken photo plates. 4

5 Roentgen and Becquerel had discovered IONIZING RADIATION Ionizing Radiations (causing alteration of photo media) are generated by high energy natural or manmade processes occurring within the atom. 3/14/2018 5

6 Ionizing Radiation Possess enough energy to remove electrons from atoms, creating ion pairs. These ion pairs then go on to create highly reactive chemicals that can damage DNA and other important cellular molecules. 3/14/2018 6

7 We live in a sea of ionizing radiation Terrestrial Cosmic Human generated Accelerators Reactors Medical procedures Industrial (radiography, airports, interrogation) 3/14/2018 7

8 Radiation Use Availability and use of radioactive materials exploded after World War II. 3/14/2018 8

9 Radiation in the Workplace Research Medicine Radiation Therapy Laboratory Use Irradiations Nuclear Medicine 3/14/2018 9

10 Radiation in the Workplace Measurement and Quality Control Measure Thickness Static Control Industrial Radiography Measure Density 3/14/

11 Radiation in the Workplace Baggage X-ray 3/14/

12 Radiation in the Environment Biomedical/Industrial wastes or byproducts Lost sources 3/14/

13 Radiation in the Environment Active Production or Processing Sites Closed/Abandoned Production or Processing Sites 3/14/

14 Radiation in the Environment Nuclear Accidents 3/14/

15 Detecting Incoming Radioactive Materials Seaports Borders Airports 3/14/

16 Where does it come from? Can be naturally occurring or man-made Produce radiation at all times, but decays away over time. If unsealed and loose, it can be easily spread around (contamination). 3/14/

17 ISOTOPE ½ Life APPLICATIONS Uranium billions of years Natural uranium is comprised of several different isotopes. When enriched in the isotope of U-235, it s used to power nuclear reactor or nuclear weapons. Carbon y Found in nature from cosmic interactions, used to carbon date items and as radiolabel for detection of tumors. Cesium y Blood irradiators, tumor treatment through external exposure. Also used for industrial radiography. Hydrogen y Labeling biological tracers. Iridium d Implants or "seeds" for treatment of cancer. Also used for industrial radiography. Molybdenum h Parent for Tc-99m generator. Technicium-99m 6 h Brain, heart, liver (gastroenterology), lungs, bones, thyroid, and kidney imaging, regional cerebral blood flow, etc.. 3/14/

18 Where does it come from? Machine Produced X-ray Machines, cyclotrons, accelerators, etc. Most produce x-rays but particles also possible. Only produce radiation when energized. High energy machines can activate materials to create radioactive materials. 3/14/

19 Atomic Structure and Radioactivity Nuclear notation Terminology Decay modes X-rays Half life 3/14/

20 Nuclear notation Not actual size Not to scale Li-7 3/14/

21 Terminology Radioactivity process Radiation - energy Activity quantity Contamination material Half life - time 3/14/

22 Radioactivity The process by which an energetically unstable nucleus spontaneously transforms to a more stable energy state and in the process emits radiation.

23 Radiation means matter or energy moving outward from a point of origin. Radiation from a point source decreases as a function of the square of the distance (1/R 2) 3/14/

24 Five basic types of radiation From the nucleus From the electron shells 3/14/

25 Electromagnetic Radiation No Mass No Charge Very Penetrating 3/14/

26 X-ray/Gamma Same except for origin Photon Can be stopped by layers of lead or concrete Hazardous to tissues and organs Common photon emitters: Tc-99m, I-125 Characteristic x-rays and gamma are essentially monoenergetic Bremsstrahlung x-rays can be a spectrum

27 Characteristic X-rays Characteristic X-rays are emitted when outer-shell electrons fill a vacancy in the inner shell of an atom, releasing X-rays in a pattern that is "characteristic" to each element. 3/14/

28 Bremstrahlung x-rays 3/14/

29 Alpha α Made up of 2 neutrons and 2 protons (nucleus of the Helium atom) Travel short distances, stopped by paper and dead layer of skin Mainly an internal hazard in the body Common Alpha emitters: Uranium, Thorium, Radon and radon daughters Characteristically mono energetic

30 Beta β Energetic electron Can be stopped by 1 cm of plastic Hazard to skin and eyes and when taken internally Common Beta emitters: Phosphorus, Tritium, Carbon, Sulfur Spectrum of energies are emitted (β max ) Most beta emitters are also gamma emitters

31 Neutron Has no charge Range in air is very far. Easily can go several hundred feet. High penetrating power due to lack of charge Can be a hazard to whole body Common neutron emitter: Cf-252

32 Radioactive Decay After Time Pure Sample Full Activity Decayed Sample Lower Activity 3/14/

33 Half life The radioactive half-life for a given radioisotope is the time for half the radioactive nuclei in any sample to undergo radioactive decay.

34 Simple Half-Life Calculation Activity decreases over time by a rate defined as the half-life Where n is the number of half lives: A = A o /2 n Thus after one half-life the nuclide will be half of its original activity, after two half-lives, one quarter, and etc. After 7 half lives less than 1% of the original activity remains 3/14/

35 Activity Activity describes how much radioactive material is present at any given time Curie (Ci): 37 Billion transformations per second Usually expressed as milli (10-3) or micro (10-6) Bequerel (Bq): 1 transformation per second Usually expressed in Mega (10 6 ) or Giga (10 9 ) 3/14/

36 Interaction of ionizing radiation with matter Alpha and Beta energy is lost by transfer of energy to electrons via electrostatic interaction Photons all or part of its energy is transferred to an orbital electron via collision Neutron energy and material dependent (Z#) <0.5 MeV - elastic scattering with nucleus >0.5 MeV - inelastic scattering with nucleus Thermal absorption in the nucleus 3/14/

37 Interaction of ionizing radiation with matter 3/14/

38 Penetration ability of some radiations 3/14/

39 Radiation Absorbed Dose (rad) Rad- A measure of energy deposition per unit mass irradiated 1 Rad = 100 ergs per gram of material SI Unit is Gray 1Gy = 1 joule per kilogram (J kg 1) 1 Gy = 100 rad

40 Dose equivalent (rem) rem: absorbed dose (D) modified by a radiation weighting factor (wr ) or quality factor (Q) which accounts for the different biological effects of different types of radiation rem = rad x Q In the SI system of units, it is replaced by the special name sievert (Sv) where Sv = Gy x wr 1 Sv = 100 rem

41 Quality Factor (10CFR20) Type of radiation Quality Factor X-, gamma, or beta radiation 1 Alpha particles, multiple-charged particles, fission fragments and heavy particles of unknown charge 20 Neutrons of unknown energy 10 High-energy protons 10 3/14/

42 Average dose equivalent = 620 mrem/yr

43 3/14/

44 Typical medical doses Chest X-ray = 2 mrem Mammogram = 13 mrem Abdomen CT = 1000 mrem (1 rem) Heart stress test = 585 mrem

45 Terrestrial Radiation Levels 3/14/

46 Cosmic Radiation Levels 3/14/

47 Health physics nerd fun What is the radiation dose equivalent for flying across the United States? Seattle WA - Washington DC: 37, 000 ft; 4.1hours msv (which is how many millirem?) Reference: DOT/FAA/AM-03/16 Office of Aerospace Medicine Washington, DC What Aircrews Should Know About Their Occupational Exposure to Ionizing Radiation 3/14/

48 Radiation Hazards Usually much greater at entrance than exit. May come from inhalation, ingestion, injection, absorption, or injury Could be partial or whole body. External vs. Internal Often concentrates in particular organs. 3/14/

49 Biological Effects Acute effects Chronic effects Linear non-threshold model Basis for regulatory limits 3/14/

50 Biological Effects Many groups and individuals exposed to ionizing radiation at high levels resulted in adverse effects Somatic effects Prompt - skin burns and cataracts Delayed - cancer Genetic effects Teratogenetic effects

51 Biological Effects Biological effects are caused by chemical changes in the cell brought about by the conversion of kinetic energy to chemical energy Direct effects caused by initial ionization Indirect effects free radicals and ions (mostly from water) interact with cell material

52 Fate of Early Radiologists 3/14/

53 Radiologist Fingers 3/14/

54 Early Radiation Injury 1898 Photograph shows severe chest burn on a United States soldier in the Spanish-American War, caused by repeated exposure to X rays. 3/14/

55 Internal Dose Caused by radioactive material inside the body Routes of entry: Inhalation Ingestion Absorbtion Injection Organs can concentrate based on chemical affinity (e.g. thyroid, bone, kidneys) 3/14/

56 Radiation Health Effects High-level radiation effects are acute effects which are manifested shortly after (hours, days, weeks) a large exposure (1 Sv or 100 rem+). Low-level radiation effects are described as latent effects, appearing many years after a non-lethal acute dose, or chronic effects after many years of small doses (like radiation workers). 3/14/

57 High Level Radiation Effects Acute Radiation Syndrome Bone Marrow Injury (over 1 Sv or 100 rem) may cause death if injury is severe. GI Tract Injury (over 6 Sv or 600 rem) causes death in days or weeks. Central Nervous System Injury (over 50 Sv or 5000 rem) causes death in hours or days. Radiation Burns (over 2 Sv or 200 rem) local or whole body Cataracts (over 1.5 Sv or 150 rem) 3/14/

58 Dose (Rads*) Effects First sign of physical effects (drop in white blood cell count) Threshold for vomiting (within a few hours of exposure) ~ 50% die within 60 days (with minimal supportive care) ~50 % die within 60 days (with supportive medical care) 1,000 ~ 100% die within 30 days

59 500+ rad X-Ray Burns 5,000+ rad

60 Cancer Radiation can damage cells through two methods; Production of free radicals and Direct damage to the DNA Risk factor for radiation dose: 4% increase in risk of dying of cancer for every 100 rem of dose. Normal cancer risk is 20%.

61 Low Level Radiation Health Effects Cancer 0.1 Sv (10 rem) given to 100 people in U.S. population would be expected to cause about 1 extra cancer over a lifetime. About 42 of these people would be expected to get cancer from natural causes. BIER VII Report 3/14/

62 Dose Response Relationship 0.03 Risk of death fromcancer Risk Is not Predictable below 20 rem Effect is Detrimental risk level is uncertain Predictable Effects Committed Lifetime Dose (rem)

63 Low Level Radiation Health Effects Genetic mutations has not been observed in humans, but has been observed in experimental animal populations Teratogenesis - abnormalities induced in an exposed fetus depends on dose and period of pregnancy. The risk of abnormality is considered negligible at 5 rad or less when compared to the other risks of pregnancy. (NCRP Report 54) 3/14/

64 Relative hazard summary 1 rem received in a short period or over a long period is safe we don t expect observable health effects. 10 rem received in a short period or over a long period is safe we don t expect immediate observable health effects, although your chances of getting cancer might be very slightly increased. 100 rem received in a short time can cause observable health effects from which your body will likely recover, and 100 rem received in a short time or over many years will increase your chances of getting cancer. 1,000 rem in a short or long period of time will cause immediately observable health effects and is likely to cause death

65 Health physics nerd fun How much energy is absorbed in the body for an LD 100/30 day whole body acute dose of gamma radiation? LD 100/30 day dose is 1000 rads; person = 87kg (160lb) 1000 rads x (100 ergs/gm/rad) x (87kg) = 8.7e+6 ergs 8.3 BTU to raise 1 gallon (3.76 kg) of water 1 F = 8.8e+10erg (1 BTU = 1.06e+10 erg) (87kg/3.76kg) x 8.8e+10 erg = 2e+12erg to raise the body 1 F 8.7e+6erg/2e+12 erg per 1 F= 4.3e-6 F 3/14/

66 Health physics nerd fun Compute your radiation dose exercise 3/14/

67 Information sources Health Physics Society National Council on Radiation Protection - Nuclear Regulatory Commission American Nuclear Society Radiation Answers - 3/14/