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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