1. 4/2003 Rev 2 II.3.1 – slide 1 of 30 Part IIQuantities and Measurements Module 3Principles of Radiation Detection and Measurement Session 1Ionization Chambers Session II.3.1 IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources

2. 4/2003 Rev 2 II.3.1 – slide 2 of 30 Overview  In this session we will discuss the principle of measuring radiation using ionization chambers.

3. 4/2003 Rev 2 II.3.1 – slide 3 of 30  As humans, we are virtually incapable of detecting the presence of radiation  Individuals who have been exposed to high levels of radiation have reported feeling “a burning sensation” in their eyes, nausea, dizziness and other symptoms, however, these symptoms have all resulted from exposure to lethal or near lethal doses  Exposure to radiation doses within the occupational limits produce no apparent indications of exposure  As a result, we must employ devices to detect and measure radiation Human Perception

4. 4/2003 Rev 2 II.3.1 – slide 4 of 30  Types of Interactions:  Excitation  Ionization  Media in which the interactions occur:  Solid  Liquid  Gas Interaction with Matter

5. 4/2003 Rev 2 II.3.1 – slide 5 of 30 Ion chambers are the simplest of all gas filled detectors An electric field is used to collect all the ionizations (positive and negative charged particles) produced by the incident radiation in the gas volume Ion Chamber

6. 4/2003 Rev 2 II.3.1 – slide 6 of 30 W value (eV/ion pair) Gas Fast Electrons Alphas CH 4 30.229.0 O2O2O2O232.232.2 He32.531.7 Air35.035.2 N2N2N2N235.836.0 H2H2H2H238.037.0 “W” Factor In most gases, the energy needed to ionize the least tightly bound electrons is 10-20 eV however, the “average” energy is higher since some energy is lost in “non-ionizing” encounters (typically 30-35 eV/ion pair)

7. 4/2003 Rev 2 II.3.1 – slide 7 of 30 The current (flow of free electrons) is directly related to the radiation intensity If recombination of free electrons and positively charged atoms is eliminated, then the current flow is a direct measure of the amount of radiation incident on the chamber Free Electrons

8. 4/2003 Rev 2 II.3.1 – slide 8 of 30 Recombination Region Regions of a Gas Filled Chamber

9. 4/2003 Rev 2 II.3.1 – slide 9 of 30 RecombinationIonizationProportional Limited Proportional Geiger Mueller Continuous Discharge Operating Regions of a Gas Filled Detector

10. 4/2003 Rev 2 II.3.1 – slide 10 of 30 Free Air Chamber

11. 4/2003 Rev 2 II.3.1 – slide 11 of 30 Electronic Equilibrium This is what we see; a thin walled chamber full of air Based on the densities of the materials, this is what the photon radiation sees; a massive block of material surrounding a small volume of air

12. 4/2003 Rev 2 II.3.1 – slide 12 of 30 Photon Energy (MeV) Density Thickness (g/cm 2 ) 0.020.0008 0.050.0042 0.10.014 0.20.044 0.50.17 10.43 20.96 52.5 104.9 Electronic Equilibrium

13. 4/2003 Rev 2 II.3.1 – slide 13 of 30 Free Air Chamber

14. 4/2003 Rev 2 II.3.1 – slide 14 of 30 Dose rate meters measure the operational quantity of ambient dose equivalent rate For most applications, this measurement gives a good approximation of the effective dose rate to our bodies Ion Chamber Measurements

15. 4/2003 Rev 2 II.3.1 – slide 15 of 30 Condenser R Chamber

16. 4/2003 Rev 2 II.3.1 – slide 16 of 30 Condenser R Chamber

17. 4/2003 Rev 2 II.3.1 – slide 17 of 30 Ion Chamber

18. 4/2003 Rev 2 II.3.1 – slide 18 of 30 Ion Chamber

19. 4/2003 Rev 2 II.3.1 – slide 19 of 30 Ion Chamber

20. 4/2003 Rev 2 II.3.1 – slide 20 of 30 Ion Chamber

21. 4/2003 Rev 2 II.3.1 – slide 21 of 30 Ion Chamber

22. 4/2003 Rev 2 II.3.1 – slide 22 of 30 Pressurized Ion Chamber Model 450P pressurized Model 450 non-pressurized Model PIC-6 pressurized

23. 4/2003 Rev 2 II.3.1 – slide 23 of 30 Extrapolation Chamber Bohm Model 2535

24. 4/2003 Rev 2 II.3.1 – slide 24 of 30 Extrapolation Chamber

25. 4/2003 Rev 2 II.3.1 – slide 25 of 30 Five linear ranges: 0-5 mR/h to 0-50 R/h Energy range 12 keV to 7 MeV Weight only 1.4 kg A compact, rugged, lightweight ion chamber dosemeter for beta, gamma and X-ray detection and measurements of superficial or deep doses in pulsed or static fields. Sample Ionization Chambers Bicron RSO 50E True electronic range switching is included, avoiding reed switches and their susceptibility to magnetic fields. The 1000 mg/cm 2 shutter makes deep dose versus shallow dose measurements routinely possible.

26. 4/2003 Rev 2 II.3.1 – slide 26 of 30 DETECTOR Five linear ranges: 0-5, 0-50, 0-500 mR/hr; 0-5, 0-50 R/h Air filled ionization chamber vented to atmosphere Detector Volume 13.4 in 3 1,000 mg/cm 2 walls Chamber window 7 mg/cm 2 Beta shield 1,000 mg/cm 2  30% from 8 keV to 6 MeV  15% from 33 keV to 6 MeV EXTERNAL CONTROLS Rotary switch for Off, Battery check, Zero, 5, 50, 500 mR/h; 5-50 R/h Zero knob PHYSICAL Size: 20.1 x 10.7 x 19.6 cm Weight: 1.6 kg Sample Ionization Chambers Eberline Model RO2

27. 4/2003 Rev 2 II.3.1 – slide 27 of 30 Sample Ionization Chambers Eberline Model RO2

28. 4/2003 Rev 2 II.3.1 – slide 28 of 30 Sample Ionization Chambers Eberline Model RO2

29. 4/2003 Rev 2 II.3.1 – slide 29 of 30 The 440RF/D is a highly sensitive, low energy, RF shielded survey meter suited for fast, accurate measurements of background and other low radiation levels. It is the basis of measurement for radiation exposure in the color television industry. This instrument is also used to measure radiation from radar and transmission towers where RF may be present. Internal software-controlled pressure transducer and temperature sensor automatically apply standard air density correction factors from 70 to 106 kPa to the unsealed ion chamber Sample Ionization Chambers Victoreen Model 440RF/D Range (  Sv/hr) Response(sec)0-107 0-307 1-1005 0-3005 0-10005

30. 4/2003 Rev 2 II.3.1 – slide 30 of 30 Where to Get More Information  Cember, H., Introduction to Health Physics, 3 rd Edition, McGraw-Hill, New York (2000)  Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8 th Edition, 1999 update), Wiley, New York (1999)  International Atomic Energy Agency, The Safe Use of Radiation Sources, Training Course Series No. 6, IAEA, Vienna (1995)