1 Principles of Radiation Detection Operational Radiological Safety Course U.S. Army Chemical Biological Radiological & Nuclear School Edwin R. Bradley Radiological Lab 031RDB01

2 Terminal Learning Objective Action: Identify the principles of radiation detection Condition: In a classroom environment, given PowerPoint slides Standards: Identify the 2 principles of radiation detection and the characteristics of sensitive detectors

3 Administrative Data Safety Requirement: None Risk Assessment: Low Environmental Considerations: None Evaluation: Students must score at least 70% (80% for BOLC) on the end-of-course written test.

4 Two Main Principles of Radiation Detection Electrical collection of ions –Air Ionization –Gas Ionization Scintillation –Light Production

5 Ionization Chamber Electrical collection of ions No gas amplification (air) Used to measure dose rate Sensitive to environmental changes Battery or High Voltage Resistor (-) Cathode + - (+) Anode e-e- +

6 Gas Filled Detector (1) Battery or High Voltage Resistor (-) Cathode (+) Anode + -

7 Battery or High Voltage Resistor (-) Cathode + - (+) Anode e-e- + Gas Filled Detector (2)

8 Gas Filled Detector (3) Gas Filled Detector (3) Battery or High Voltage Resistor (-) Cathode + - (+) Anode e-e- +

9 Gas Filled Detector (4) Gas Filled Detector (4) Battery or High Voltage Resistor (-) Cathode + - (+) Anode e-e- +

10 Gas Filled Detector (5) Battery or High Voltage Resistor (-) Cathode + - (+) Anode e-e- + V=IR

11 Log of Electrical Signal Applied Tube Potential (Voltage) Recombination GAS FILLED DETECTOR RESPONSE Ionization Region Proportional Region Geiger Mueller Region Breakdown Region

12 Geiger Mueller Counter Most common type of detector Gas amplification Gas amplification Multiplication factor Long dead time Energy dependence Variety of uses –Count rate –Dose/Dose rate –Surface activity Battery or High Voltage Resistor (-) Cathode + - (+) Anode e-e- +

13 AN/VDR-2 Beta/Gamma Probe Beta/Gamma Probe Measures and detects gamma photon energy Measures and detects gamma photon energy Detects moderate to high energy Beta Detects moderate to high energy Beta particle emission particle emission Neon-halogen gas (Gas Ionization) Neon-halogen gas (Gas Ionization) Display µGy and µGyph to Gy and Gyph Display µGy and µGyph to Gy and Gyph Operates in GM region Operates in GM region Gas Filled Detector

14 AN/PDR 77 Beta/Gamma Probe Beta/Gamma Probe Measures and detects gamma photon energy Measures and detects gamma photon energy Detects moderate to high energy Beta Detects moderate to high energy Beta particle emission particle emission Neon-halogen gas Neon-halogen gas Display 0 – 999K mR/h Display 0 – 999K mR/h Operates in GM region Operates in GM region Gas Filled Detector

15 Proportional Counters Alpha-Beta discrimination Gas multiplication 10 6 Low dead time Used in labs and neutron detectors Alpha+ Beta Beta Alpha+Beta Electrical Signal Background

16 Proportional Counters

17 Scintillation Detector (Light Production) + - Scintillator Photo Cathode Focusing cup Dynodes HV Resistor

18 Scintillation Detector (Light Production) + - Scintillator Photo Cathode Focusing cup Dynodes HV Resistor e-e- e-e-

19 AN/PDR 77 Alpha Probe (Zinc Sulfide (ZnS) Scintillator) Measures and detects alpha particle radiation in disintegrations per minute (dpm). Measures and detects alpha particle radiation in disintegrations per minute (dpm). Scintillation Detector X-ray Probe (Sodium Iodide (NaI) Scintillator) Primary use to detect fission isotopes Measures and detects Pu 239 & U 235 x-ray (17 keV & 60 keV average energies from the daughter products of Pu 239 and U 235 ).

20 Liquid Scintillation Low energy beta and alpha Solvent mixed with scintillating material Very low background Laboratory instrument Photo multiplier tube Liquid Scintillation Counter Counting Circuit LSC Vial

21 Liquid Scintillation

22 Multi-Channel Analysis Channel Number (Energy) Number of Counts Photo Peak Compton Edge

23 identiFINDER Multi-Channel Analysis

24 Thermoluminescent Dosimeter Stores absorbed energy Crystalline material Read by heating and detecting emitted light Primary occupational dosimeter

25 Panasonic UD-802AS Dosimeter Whole Body and Wrist TLD Holders Harshaw DXT-RAD Ring TLD Thermoluminescent Dosimeter

26 Semi Conductor Detectors High energy resolution Low efficiency for gamma (Diode Detector) High efficiency for gamma (Ge Detector) Must be liquid nitrogen cooled (PINS)

27 High-purity Germanium Semi Conductor Detectors

28 Summary Principles of radiation detection –Electrical collection of ions Gas ionization Air ionization –Scintillation - Light production Characteristics of sensitive detectors –Dense detecting medium –High efficiency –Low background