Radiation SafetyRadiation Safetylevel 5level 5

Frits Pleiter

19/04/23 radiation safety - level 5 1

ContentsContents

atomic and nuclear physics (1) interaction with matter (3)

o sources and x-ray equipment (2)o shielding (3)o detection (4)o radiobiology (6)

• objective risk of radiation (6)• subjective risk acceptation (6)

quantities and units (5) regulations (7)

o practical health physics (8 - 10)o waste (11)

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DetectionDetection

ionization detector

scintillation detector

photographic emulsion

electronic equipment

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DetectionDetectionionization detectorionization detector

gas filled detectorionization chamberproportional counterGeiger-Müller counterair, natural gas, noble gas, ...100 - 1500 V

semiconductor detectorgermanium (-radiation)silicon (-radiation, x-ray radiation)500 - 3000 V

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anode wire

cathode wall

counting gas

DetectionDetectionionizationionization

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gas atoompositive ionnegative elektron

ionizing

radiation

cathode wall

cathode wall

anode wire

ionization energy = 34 eV

DetectionDetectiongas amplificationgas amplification

primary electronsare acceleratedcollide with gas atomsand produce secundary ions

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secundary chargepositive ionnegative electron

1 primary charge2

cathode wall

cathode wall

anode wire

ionizing radiation

1

2 2

2

DetectionDetectioninfluence of anode voltageinfluence of anode voltage

I.recombinationII.ionization chamberIII.proportional counterIV.incomplete proportionalityV.Geiger-Müller counterVI.continuous gas discharge

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0

5

10

15

0 500 1000 1500

anode voltage (V)

10lo

g(N

ion)

-particle

I II

III

IV

VVI

-particle

DetectionDetectionproportional counterproportional counter

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proportional counterenergy resolution at 6.4 keV is 17%

DetectionDetectionGeiger-MGeiger-Müller counterüller counter

simple construction and cheap

anode field is shielded by positive ionswhich reduces gas amplificationconstant pulse height > 10 Vdead time > 0.1 ms true count rate > measured count rate

secundary electrons from cathode wall are acceleratedand produce a new signal, etceterato prevent this, a (multiatomic) quench gas is added

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DetectionDetectionexamples of ionization detectorsexamples of ionization detectors

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DetectionDetectionsemiconductor detectorsemiconductor detector

ionization energy 3 eV

proshigh efficiencyexcelent energy resolution

consno gas amplificationmust be cooled to 80 Kexpensive

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DetectionDetectionsemiconductor detectorsemiconductor detector

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Ge-detectorenergy resolution at 661 keV is 0.4%

DetectionDetectionscintillation detectorscintillation detector

inorganic scintillatorNaI, BaF2, ZnS, BGOoften contains a fluorescent additive, e.g. NaI(Tl)

organic scintillatoranthracene, stilbene, plastic, liquidoften contains a fluorescent additivechemical and optical quenching

thermoluminescence detector (TLD)CaF2, LiF, Li2B4O7

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DetectionDetectionphotomultiplier tubephotomultiplier tube

interaction of -photon with scintillator light photonsinteraction of light photon with cathode photo-electronphoto-electron hits 10 - 14 electrodesat each collision 2 - 3 secundary electrons are liberatedin NaI, about 500 eV per photo-electron is required

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ionizing radiation

light

photocathode

dynode

photomultiplier tube

electrons anode

contact pins

scintillation crystal

DetectionDetectionscintillation detectorscintillation detector

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NaI detectorenergy resolution at 5.9 keV is 43.5%

energy resolution at 662 keV is 7%

DetectionDetectionexamples of scintillation detectorsexamples of scintillation detectors

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DetectionDetectionphotographic emulsionphotographic emulsion

film badgeas personal dose registration tool completely replaced by TLD

badge

autoradiogramanalytic tool in chemistry and biochemistrymore and more replaced by semiconductor tools

x-ray picturemedical diagnostic toolmore and more replaced by semiconductor devices

nuclear emulsiondetector for elementary particles in cosmic radiationreplaced by equipment with volumes > 1000 m3

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DetectionDetectiondetector for elementary particlesdetector for elementary particles

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DetectionDetectionproper choice of detectorproper choice of detector

which detector to choose depends largely on what has to be measured (and on the available amount of money)

dose of dose ratecontamination-, -, -radiationidentification of a nuclide

in the last case, energies must be measured (spectroscopy) with the aid of a multichannel analysernowadays hardly more than an interface card in the computer

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DetectionDetectionproper choice of detectorproper choice of detector

dose rate meterreading in sievert per unit of timenot suited for contamination measurements

contamination monitorreading in number of counts per unit of timenot suited for dose rate measurements

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DetectionDetectionproper choice of detectorproper choice of detector

-contaminationZnS with extremely thin windowgas filled detector with extremely thin windowliquid scintillation counter

-contaminationgas filled detector with thin windowSi-detector with thin window(no Ge since it is more sensitive to -ray background)liquid scintillation counter

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DetectionDetectionproper choice of detectorproper choice of detector

-contaminationNaI-detectorgas filled detector with large area and low backgroundGe-detectorSi-detector with thin window (especially for x-ray radiation)liquid scintillation counter (if E < 50 keV)

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DetectionDetectionmultichannel analyzermultichannel analyzer

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DetectionDetectionenergy calibrationenergy calibration

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DetectionDetectionefficiency calibrationefficiency calibration

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