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Dosimetry methods to estimate external exposure to natural radiation; their calibration
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Dosimetry for External ExposureMeasuring methods used
Component Type Equipment
low LET (e-, γ, HE protons)
active IC, GM counters, plastic scintillators,
APD’s passive TLD, OSLD, RPL
high LET (neutrons,HECP)
active Moderator based (spectrometry,
modifications) passive Track etch detectors, Bubble detectors
all active Tissue equivalent proportional counters
Si-energy deposition spectrometers
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Passive detectors
• Bubble detectors
• Track etched detectors
• Thermoluminescent detectors
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Bubble detectors BTI
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Relative response of bubble detectors to neutrons
0
0,5
1
1,5
0,01 0,1 1 10 100En, MeV
Rel
ativ
e re
spon
se
BD 100RPND
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Pretahnout obrazek No.2 z lonske prezentace ECE detektor, detaily ECE a CE stop
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Track detectors response to neutrons
Energy dependence of PADC
0,1
1
10
0,1 1 10 100En, MeV
Resp
onse
, rela
tively
to
252
Cf
ST-etching2F-etching
neutrons, response per H*(10), mSv
1,E+01
1,E+02
1,E+03
0,01 0,1 1 10 100 1000En, MeVtra
cks
ST
2F
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TLDs – CaSO4 :Dy of INRNE
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Energy response of CaSO4 :Dy to photons
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Relative response of TLDs to neutrons
TLD -relative kerma to tissue
0,01
0,1
1
10
100
0,01 0,1 1 10 100En, MeV
Kerm
a re
lativ
e to
tiss
ue
7LiFCaSO4Al2O36LiFLi2B4O7Al-P glass
RR of TLD's to monoenergetic neutrons
1,E-03
1,E-02
1,E-01
1,E+00
0 5 10 15 20En, MeV
Relat
ive re
spon
se
LiF7LiFCaSO4Al2O3:Na
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Relative thermoluminescent yields - p,alpha
0,01
0,1
1
10
1 10 100 1000LET in water, keV/µm
Rela
tive
TL y
ield
LiF-PTL710Al-P glassAl2O3:NaAl2O3:CCaSO4:Dy
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Active detectors• MDU-Liulin spectrodosimeter
• Tissue equivalent proportional counters
• Moderator- type “rem”-counters
• Scintillator based environmental monitors
• GM-based environmental monitors
• Ionization chambers (ISS 112)
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MOBIL DOSIMETRY UNITS (MDU)
SPECIFICATIONS OF MDUSPECIFICATIONS OF MDU-- Dose range: 0.093 Dose range: 0.093 –– 1.56 mGy;1.56 mGy;-- Flux range: Flux range: -- 0.01 0.01 -- 1250 part/cm2s;1250 part/cm2s;-- Energy loss range: Energy loss range: -- 0.0407 0.0407 –– 20.83 MeV;20.83 MeV;-- Pulse height range: 19.5 mV Pulse height range: 19.5 mV –– 5.0 V; 5.0 V; -- LET (Si) range: 0.27LET (Si) range: 0.27-- 69.4 keV/m;69.4 keV/m;-- Temperature range: 0oC Temperature range: 0oC -- +40oC;+40oC;-- Power consumption: typically 52 mW;Power consumption: typically 52 mW;
--Size 100x100x50 mm;Size 100x100x50 mm;--Total mass (including 2x 0.1 Total mass (including 2x 0.1 kg SAFT LSH20 3.6 V Likg SAFT LSH20 3.6 V Li--ion ion batteries): 0.33 kg. batteries): 0.33 kg. -- Operation time 110 daysOperation time 110 days
External view of MDUExternal view of MDU Internal view of MDUInternal view of MDU
Detector + preamp.
Electronics
D-size Li-ion Batteries
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Relative event distributions MC calculation-experiment comparison
1,0E-07
1,0E-06
1,0E-05
1,0E-04
1,0E-03
1,0E-02
1,0E-01
1,0E+00
0 500 1000 1500 2000Edep, keV
rela
tive
coun
ts p
er h
our
Cs-137 experimentCo-60 experimentCs-137 calculationCo-60 calculation
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Relative response of MDU's to neutrons
0,0001
0,001
0,01
0,1
1
0,1 1 10 100Average EN ,MeV
D(S
i)/H
*(10
1,0
1,2
1,4
1,6
1,8
Rat
io M
DU
01/M
DU
0
Is otopic s ource sCERN fie ldsPTB ne utronsM DU01/M DU02
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RESULTS – Measurements on aircraft
General remarks:• Event and D(Si) distributions very similar
to those in CERN concrete reference field• Since April 2000 measurements performed
during more than 1000 individual flights• To interpret D(Si) in terms of radiation
protection quantities, CERF/concrete and other measurements used; threshold energy deposited 1 MeV; obtained apparent H*(10); some examples are given in Figures
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Onboard aircraft long term monitoring CSA flights 30/05-25/07/01
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TEPC in the flight case
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Examples of TEPC measured spectra
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,01 0,1 1 10 100 1000y in keV/µm
y * d
(y)
Fluka
Hawk#004
Hawk#010
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0,01 0,1 1 10 100 1000
y in keV/µm
y * d
(y)
Fluka
Hawk#004
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,01 0,1 1 10 100 1000
y in keV/µm
y * d
(y)
FLUKA (Photons)FLUKA (neutrons)Measurement (total)FLUKA (total)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.01 0.1 1 10 100 1000
y in keV/µm
y * d
(y)
FLUKA (Neutrons)FLUKA (Photons)FLUKA (total)ARCS-TEPC (total)
60Co N 0.5 MeV
N AmBe CERF
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Plastic scintillator NB 3201
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GM counter RP 114
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IBERIA measuring flight set
RSS 112
Rem-counters
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Moderation type of neutron detectors
• Principle: While the neutron effects are more important at higher energies, the cross sections of their interactions at low;typical example: thermal neutron detector at
the centre of a moderator, preferentially spherical geometry
• Fluence measurements : ~ 5 inches• H - measurements (rem-meters):
10 (12) inches or comparablealways – overestimation intermediateunderestimation over 10 MeV
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Integral ambient dose equivalent measured with the different systems for the round trip
CDG-FAI-NRT
Method Non-neutron component
(µSv)
Neutron component
(µSv)
Total (µSv)
TEPC 49 69 118 Silicon detector 58 84 142 GM counter 78 - - EPD 65 - - TLDs + etched track 51 77 124 Bubble detector - 67 - Average 54 ± 5* 76 ± 9* 129 ± 10*
* One standard deviation
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Relative sensitivity of different detectorsDetector - Equipment Component Threshold, µSv
NRPB passive survey box total 60 Single individual - TLD non-neutron 100 - 1000
Single individual - track etched neutron 200 - 2000 Single - bubble ( 1 bubble per 1 µSv) neutron 150 Electronic dosimeter ( Hmin ~ 1 µSv) non-neutron 8
Ionization chamber-, scintillator-, Geiger Muller tube-based non-neutron 0.4 Tissue Equivalent Proportional Counter total 1 - 4 Tissue Equivalent Proportional Counter non-neutron 0.4
Si-diode energy deposition spectrometer LIULIN total 4 Si-diode energy deposition spectrometer LIULIN non-neutron 0.4
“Rem-meters“, LINUS included neutron 1
Threshold: ± 15 % at 2s (95%)
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CALIBRATIONQuantity to be determined:
Ambient dose equivalent H*(10)
Low LET component (γ, e-1, mesons):Gamma radiation (60Co, 137Cs), in terms of Kair;
H*(10)/ Kair = 1.20 (Cs); 1.16 (Co)
High LET component (neutrons):Radioisotope neutron sources (AmBe; 252Cf); andHigh energy radiation reference fields – CERF;JINR Dubna;
In both cases directly in H*(10) determined independently (MC calculation, TEPC)
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CERF – top concrete irradiation area; mostly passive detectors
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Remarks to calibration – problems to treat!
• Low LET component detectors:Sensitivity to neutrons (particularly high energy!);Low response to muons;
• Neutron component detectors:Low response to high energy neutrons (UNSCEAR93 – 26 µSv; UNSCEAR2000 – 48 µSv per year);Not-negligible response to high energy charged particles;