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Principles of Radiation
DetectionOperational Radiological Safety Course
U.S. Army Chemical Biological Radiological & Nuclear School
Edwin R. Bradley Radiological Lab031RDB01
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Two Main Principles of
Radiation Detection
Electrical collection of ions
Air Ionization Gas Ionization
Scintillation
Light Production
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Ionization Chamber
Electrical collection of ions
No gas amplification (air)
Used to measure dose rateSensitive to environmental changes
http://www.drct.com/specials/eberline.htm
Battery or
High
Voltage
Resistor(-)
Cathode
+ -
(+)
Anode
e-
+
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Gas Filled Detector (1)
Battery or
High Voltage
Resistor(-) Cathode
(+) Anode
+ -
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Battery or
High Voltage
Resistor(-) Cathode
+ -
(+) Anode
e-+
Gas Filled Detector (2)
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Gas Filled Detector (3)
Battery or
High Voltage
Resistor(-) Cathode
+ -
(+) Anodee-
+
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Gas Filled Detector (4)
Battery or
High Voltage
Resistor(-) Cathode
+ -
(+) Anodee-
+
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Gas Filled Detector (5)
Battery or
High Voltage
Resistor(-) Cathode
+ -
(+) Anode
e-
+
V=IR
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Lo
g
ofElectric
alSignal
Applied Tube Potential (Voltage)
Recombination
GAS FILLED DETECTORRESPONSE
Ionization Region
Proportional Region
Geiger Mueller
Region
Breakdown Region
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Geiger Mueller Counter
Most common type of detectorGas amplification
Multiplication factor 108-1010
Long dead timeEnergy dependence
Variety of uses
Count rate
Dose/Dose rate
Surface activityBattery or High
Voltage
Resistor
(-) Cathode
+ -
(+) Anodee-
+
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AN/VDR-2
Beta/Gamma Probe
Measures and detects gamma photon energy
Detects moderate to high energy Beta
particle emissionNeon-halogen gas (Gas Ionization)
Display Gy and Gyph to Gy and Gyph
Operates in GM region
Gas Filled Detector
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AN/PDR 77Beta/Gamma Probe
Measures and detects gamma photon
energyDetects moderate to high energy Beta
particle emission
Neon-halogen gas
Display 0 999K mR/h
Operates in GM region
Gas Filled Detector
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Proportional Counters
Alpha-Beta discrimination
Gas multiplication 106
Low dead time
Used in labs and neutron detectors
Alpha+BetaBeta
Beta
Alpha+Beta
Background
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Proportional Counters
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Scintillation Detector(Light Production)
+
-
Scintillator
Photo Cathode
Focusing
cup
Dynodes
HV
Resistor
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Scintillation Detector(Light Production)
+
-
Scintillator
Photo Cathode
Focusing
cup
Dynodes
HV
Resistor
e-
e-
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AN/PDR 77
Alpha Probe (Zinc Sulfide (ZnS) Scintillator)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 Pu239 & U235
x-ray (17 keV & 60 keV average energies from thedaughter products of Pu239 and U235).
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Liquid Scintillation
Low energy beta and alpha
Solvent mixed with scintillating material
Very low background
Laboratory instrument
+
-
+
-
Photo multiplier tubePhoto multiplier tube
Liquid Scintillation Counter
Counting
Circuit
LSC
Vial
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Liquid Scintillation
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Multi-Channel Analysis
Channel Number (Energy)
Num
berofCounts
Photo Peak
ComptonEdge
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Multi-Channel Analysis
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Thermoluminescent Dosimeter
Stores absorbed energy
Crystalline material
Read by heating and detecting emittedlight
Primary occupational dosimeter
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Panasonic UD-802AS Dosimeter
Whole Body and Wrist TLD Holders
Harshaw DXT-RAD Ring TLD
Thermoluminescent Dosimeter
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Semi Conductor Detectors
High energy resolutionLow efficiency for gamma (Diode Detector)
High efficiency for gamma (Ge Detector)
Must be liquid nitrogen cooled (PINS)
http://www.missouri.edu/~glascock/naafig5.gif
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High-purity Germanium
Semi Conductor Detectors
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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