1 principles of radiation detection operational radiological safety course u.s. army chemical...

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Principles of Radiation Principles of Radiation DetectionDetection

Operational Radiological Safety CourseOperational Radiological Safety CourseU.S. Army Chemical Biological Radiological & Nuclear SchoolU.S. Army Chemical Biological Radiological & Nuclear School

Edwin R. Bradley Radiological LabEdwin R. Bradley Radiological Lab031RDB01031RDB01

44

Two Main Principles of Two Main Principles of Radiation DetectionRadiation Detection

Electrical collection of ionsElectrical collection of ions– Air IonizationAir Ionization– Gas IonizationGas Ionization

ScintillationScintillation– Light ProductionLight Production

55

Ionization ChamberIonization Chamber

Electrical collection of ionsElectrical collection of ions

No gas amplification (air)No gas amplification (air)

Used to measure dose rateUsed to measure dose rate

Sensitive to environmental changesSensitive to environmental changes

http://www.drct.com/specials/eberline.htm

Battery or High Voltage

Resistor (-) Cathode

+ -

(+) Anode

e-

+

66

Gas Filled Detector (1)Gas Filled Detector (1)

Battery or High Voltage

Resistor (-) Cathode

(+) Anode

+ -

77

Battery or High Voltage

Resistor (-) Cathode

+ -

(+) Anode

e-+

Gas Filled Detector (2)Gas Filled Detector (2)

88

Gas Filled Detector (3)Gas Filled Detector (3)

Battery or High Voltage

Resistor (-) Cathode

+ -

(+) Anodee-

+

99

Gas Filled Detector (4)Gas Filled Detector (4)

Battery or High Voltage

Resistor (-) Cathode

+ -

(+) Anodee-

+

1010

Gas Filled Detector (5)Gas Filled Detector (5)

Battery or High Voltage

Resistor (-) Cathode

+ -

(+) Anode

e-

+

V=IR

1111

Log

of E

lect

rical

Sig

nal

Applied Tube Potential (Voltage)

Recombination

GAS FILLED DETECTORGAS FILLED DETECTORRESPONSERESPONSE

Ionization Region

Proportional Region

Geiger Mueller Region

Breakdown Region

1212

Geiger Mueller CounterGeiger Mueller CounterMost common type of detectorMost common type of detector Gas amplification Gas amplification Multiplication factor 10Multiplication factor 1088-10-101010

Long dead timeLong dead timeEnergy dependenceEnergy dependenceVariety of usesVariety of uses– Count rateCount rate– Dose/Dose rateDose/Dose rate– Surface activitySurface activity

Battery or High Voltage

Resistor(-) Cathode

+ -

(+) Anodee-

+

1313

AN/VDR-2AN/VDR-2

Beta/Gamma ProbeBeta/Gamma Probe

Measures and detects gamma photon energyMeasures and detects gamma photon energy

Detects moderate to high energy BetaDetects moderate to high energy Beta

particle emissionparticle emission

Neon-halogen gas (Gas Ionization)Neon-halogen gas (Gas Ionization)

Display Display µGy and µGyph to Gy and GyphµGy and µGyph to Gy and Gyph

Operates in GM regionOperates in GM region

Gas Filled DetectorGas Filled Detector

1414

AN/PDR 77AN/PDR 77

Beta/Gamma ProbeBeta/Gamma Probe

Measures and detects gamma photon Measures and detects gamma photon energyenergy

Detects moderate to high energy BetaDetects moderate to high energy Beta

particle emissionparticle emission

Neon-halogen gasNeon-halogen gas

Display Display 0 – 999K mR/h0 – 999K mR/h

Operates in GM regionOperates in GM region

Gas Filled DetectorGas Filled Detector

1515

Proportional CountersProportional Counters

Alpha-Beta discriminationAlpha-Beta discrimination

Gas multiplication 10Gas multiplication 1066

Low dead timeLow dead time

Used in labs and neutron detectorsUsed in labs and neutron detectors

Alpha+BetaBeta

Beta

Alpha+Beta

Elec

trica

l Sig

nal

Background

1616

Proportional CountersProportional Counters

1717

Scintillation DetectorScintillation Detector(Light Production)(Light Production)

+

-

Scintillator

Photo Cathode

Focusing cup

Dynodes

HV

Resistor

1818

Scintillation DetectorScintillation Detector(Light Production)(Light Production)

+

-

Scintillator

Photo Cathode

Focusing cup

Dynodes

HV

Resistor

e-

e-

1919

AN/PDR 77AN/PDR 77

Alpha Probe (Zinc Sulfide (ZnS) Scintillator)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 DetectorScintillation 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 the daughter products of Pu239 and U235).

2020

Liquid ScintillationLiquid Scintillation

Low energy beta and alphaLow energy beta and alpha

Solvent mixed with scintillating materialSolvent mixed with scintillating material

Very low backgroundVery low background

Laboratory instrumentLaboratory instrument

+

-

+

-

Photo multiplier tubePhoto multiplier tube

Liquid Scintillation CounterCounting Circuit

LSC Vial

2121

Liquid ScintillationLiquid Scintillation

2222

Multi-Channel AnalysisMulti-Channel Analysis

Channel Number (Energy)

Num

ber

of C

ount

s

Photo Peak

Compton Edge

2323identiFINDER

Multi-Channel AnalysisMulti-Channel Analysis

2424

Thermoluminescent DosimeterThermoluminescent Dosimeter

Stores absorbed energyStores absorbed energy

Crystalline materialCrystalline material

Read by heating and detecting emitted Read by heating and detecting emitted lightlight

Primary occupational dosimeterPrimary occupational dosimeter

2525

Panasonic UD-802AS Dosimeter

Whole Body and Wrist TLD Holders

Harshaw DXT-RAD Ring TLD

Thermoluminescent DosimeterThermoluminescent Dosimeter

2626

Semi Conductor DetectorsSemi Conductor DetectorsHigh energy resolutionHigh energy resolution

Low efficiency for gamma (Diode Detector)Low efficiency for gamma (Diode Detector)

High efficiency for gamma (Ge Detector)High efficiency for gamma (Ge Detector)

Must be liquid nitrogen cooled (PINS)Must be liquid nitrogen cooled (PINS)

http://www.missouri.edu/~glascock/naafig5.gif

2727

High-purity Germanium

Semi Conductor DetectorsSemi Conductor Detectors

2828

SummarySummary

Principles of radiation detectionPrinciples of radiation detection– Electrical collection of ionsElectrical collection of ions

Gas ionizationGas ionization

Air ionizationAir ionization

– Scintillation - Light productionScintillation - Light production

Characteristics of sensitive detectorsCharacteristics of sensitive detectors– Dense detecting mediumDense detecting medium– High efficiencyHigh efficiency– Low backgroundLow background