Module 7 radiation detection, american fork fire rescue

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Module 7 radiation detection, american fork fire rescue

  1. 1. 1
  2. 2. Objectives  Identify sources of radiation  Describe the basis of radiation  Identify types of radiation  Describe radiation dose and its impact on humans  Identify the common types of radiation detection devices 2
  3. 3. Introduction  Most responder are uncomfortable in dealing with a radiation response  They lack in-depth understanding of radiation and its hazards.  With terrorism on the rise responders need to be comfortable with the detection and monitoring radiation.  Nuclear detonation is very unlikely. 3
  4. 4. Introduction  Radiological dispersion device (RDD) is, using a conventional explosive to distribute radioactive materials.  There is any number of potential sources of radiation that could be used.  Radiation detectors for responders are divided into two major groups.  One measures exposure to radiation.  One measures the current amount of radiation in the area.  To be effective measure radiation you will need at least two detectors. There is not one detector that measures all 5 types of radiation. 4
  5. 5. Sources of Radiation  We are subject to radiation every day  Our bodies have radioactive substances  We eat foods containing radiation every day  We breathe in radiation with out harm everyday  Our exposure to common radiation sources far exceeds those that would be found at a nuclear power plant  Television, Medical test, Elevation  We are subjected to radiation that causes us no harm under normal circumstances 5
  6. 6. How Can Radiation Hurt Us  Basic atom (nucleus)  Electrons, neutrons, and protons  Protons and neutrons reside in nucleus  Electrons are negatively charged and orbit the nucleus  Protons have a positive charge and determine the element or type of atom  Neutrons are same size as protons but neutral 6
  7. 7. How Can Radiation Hurt Us  Each element, with a given number of protons, can assume several forms, or isotopes.   Which are determined by the number of neutrons in the nucleus? The chemical properties of each isotope of an element are the same.  If there are too few or too many neutrons the nucleus becomes unstable. 7
  8. 8. Radioisotopes  Isotopes, whose nuclei are unstable, are radioactive and emit radiation to regain stability.  This emission of radiation, is known as radioactive decay  Usually takes form of Gamma radiation. May also be Alpha, Beta, or Neutron?  Unstable materials may become stable after one or two decays.  Others may take many decay cycles. 8
  9. 9. Radioisotopes  Radioisotope decays by the emission of an alpha or beta particle.  The number of protons in the nucleus changes.  The radioisotope becomes a different element  Examples  Uranium is the base for the development of Radon   Common radioactive gas found in homes Radon decays into lead.  Cobalt-60   Beta and Gamma energy emitted Decays to form Nickel-60 9
  10. 10. Half-Life  Amount of time for half of a radioactive source to decay  Activity of a source of radioactive material is a measure of the number of decays per second that occur within it.  Physical size of radioactive source is not an indicator of radioactive strength or activity. 10
  11. 11. Radiation Dose  As confusing as understanding the makeup of a radioactive material, so is the calculation of the radiation dose.  Three measurements can be used to describe radiation dose. $499  Absorbed dose  Equivalent dose  $595 Effective dose 11
  12. 12. Absorbed Dose  Measurement of energy transferred to a material by radiation  Measured in units called   Gray (Gy) Radiation absorbed dose (rad)  I gray = 100 ra 12
  13. 13. Absorbed Dose  Impact on humans, we need to understand the absorbed energy on the body and potential biological damage of radiation on humans. And convert the absorbed dose to equivalent dose.  Basic unit of equivalent dose is roentgen.  This value provides for the amount of ionization in air caused by X-ray or Gamma radiation.  One roentgen equals 1 REM 13
  14. 14. Absorbed Dose  Radiation monitors measure three scales.  REM (R)  MilliRem (mR)  MicroRem (µR)  The dose of radiation is expressed by a time factor, typically an hour. 14
  15. 15. Radiation Protection  Radiation dose should be kept  “as low as reasonably achievable”  ALARA  Three factors that influence radiation dose.  Time  Distance  Shielding 15
  16. 16. Radiation Protection  Minimize dose,  Stay near the radiation source for as little time as possible.  Stand as far away from the source and place as much shielding between people and the source as possible.  Time is important as in many cases a human can sustain a short exposure to radiation without being harmed.  Example   Limit your exposure to 1 (mR/hr). Your source is 60 (mR/hr) You could be at the source for 1 minute 16
  17. 17. Radiation Protection  Distance from the source also plays a factor.  Inverse square law  Source has a radiation level 20mR/hr at 2 feet  Moving back 4 feet provides an exposure level of 5 mR/hr.  Moving 6 feet would result in an exposure level of 1.25 mR/hr 17
  18. 18. Action Levels  1mR/hr Isolation zones  Public protection levels  5 R Emergency response  All activities  10 R Emergency response  Protecting valuable property  25 R Emergency response  Lifesaving or protection of large populations  ˃ 25R Emergency response  Lifesaving or protection of large population. Only on a voluntary basis for persons who are aware of the risk involved. 18
  19. 19. Radiation Monitors  Current radiation monitors provide two methods of measuring radiation.  REM and counts per minute  REM being the most important to responders. 19
  20. 20. Radiation Monitors  There are a variety of detection devices out there, the important consideration is the probe attached to the unit.  Probe determines the what type of radiation can be detected  Alpha, Beta, Gamma  Most common probe are pancakes, this is useful for Alpha radiation. 20
  21. 21. Radiation Monitors  When the amount of radiation becomes higher we need to switch to the internal probe.  These are designed for the higher level of radiation  When the monitor is turned on it will pick up background radiation.  This is naturally occurring radiation and it should read in micro/rem.  It is important that you go do some field testing in your area to determine normal background.  Then responders know when they are being exposed to radiation at higher levels than background. 21
  22. 22. Types of Radiation Detectors  Three type that are common  Geiger-Mueller tubes  Scintillation crystals  Gamma Spectroscopy 22
  23. 23. Types of Radiation Detectors  GM tubes can detect Alpha, Beta, Gamma  Uses electric current, a reaction takes place when radiation interacts with the walls of the tube.  Electrons are freed from the atom and flows to the anode which is in the center of the tube.  This induces an electrical “pulse” which is used to determine when and how much radiation entered the GM tube.  These detectors are generally coupled with a proportional counter, which counts the electrical impulses.  You have a choice to count in radiation dose or counts per minute 23
  24. 24. Types of Radiation Detectors  Scintillation Crystals  Uses a crystal that emits visible light when hit by radiation.  Most common is sodium iodide  Radiation hits the crystal, a pulse of light is produced which is detected by and amplified.  This produces a electrical signal which is measured to determine the amount of radiation that hit the crystal.  Scintillation detectors are best for Gamma. 24
  25. 25. Types of Radiation Detectors  Gamma Spectroscopy  Radiation Isotope Identifier  Can identify the source of the radiation. 25
  26. 26. Types of Radiation Detectors  Radiation Pagers/ Dosimeter  Detect X-ray and Gamma radiation, but also will detect high levels of beta.  When the pager is turned on it calibrates itself to the background.  They are designed to alert and provide reading of one-ten times above background. 26
  27. 27. Summary  Responders need to become familiar with radiation detection.  Possibility exists for future events.  Many radioactive substances exist and when we deal with unidentified materials we need to check for radiation.  Knowing how to monitor for it is as important as knowing the action levels. 27

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