A Novel Dosimetry System for

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27 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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A Novel Dosimetry System for
Military Use in Response of
Nuclear Emergencies


Mirela Kirr , Craig Yoder, PhD, Christopher
Passmore
, CHP

IRPA 13, 2012





Create a Dosimetry System


Able to measure absorbed dose to tissue (
cGy
)
arising from detonated tactical nuclear weapons



Able to measure dose equivalent for tracking
occupational exposures


Able to withstand severe environmental and
operational conditions


Reliable, light and easy to use


For details on how to use:
http://www.youtube.com/watch?v=VqNEwQ18ISw

or go to
YouTube.com and type in “
RadLight




Dosimetry System Includes


RadWatch
®

Dosimeter


RadLight

®

Reader




2

Purpose of the Study



RadWatch

®

Dosimeter

RadLight

®

Reader

RadWatch

®

Dosimeter


RadWatch

®

Dosimeter


Slide


3 optically stimulated luminescence (OSL)
radiation sensors
-
Al
2
O
3
:C


1 radiofrequency identification (RFID) chip


RFID chips stores all pertinent information
related to the dosimeter and can be
interrogated by the
RadLight

reader


fluorescent nuclear track detector (FNTD) for
low dose neutron measurements (optional)


Base


houses the slide and offers
additional filtration


Cover
-
creates light tight and water
resistant seal for the dosimeter


3



Cover

Base with
Slide

Slide

RadWatch
®

Slide


RadWatch

®

Slide


Sensor 1 (E1)


Filtration
-
cylindrical shaped aluminum cup


Intended for photons detection and when used in



conjunction with E2 provides energy information


Sensor 2 (E2)


Filtration
-
cylindrical shaped aluminum and copper cup


Intended for higher energy photons detection,



also used as reference sensor


Sensor 3 (E3)


Filtration
-
cylindrical shaped aluminum and copper cup


Intended for neutron and photons detection. Neutron
detection is done with the use of
high density
polyethylene

(HDPE).






4

Aluminum
Filter

Copper Filter

OSL

Retaining
Ring

Rear Copper
Filter

RadLight
®

Reader


RadLight

®

Reader


Portable reader that weight 2.2Kg


Operated using 4LR6

(AA) batteries


Analytical Method
-
Pulsed Optically
Stimulated Luminescence (POSL) in
reflection geometry


Stimulating light
-
green LED centered around
530nm


Emitted light
-

blue light centered around
420nm


Light photons counted using Photomultiplier
Tube (PMT)


Reader interrogates RFID chip for dosimeter
calibration data


Reader writes dose information on the RFID
sensor




5



System Characteristics (I)


Energy Response


Photon sources, energy from


29
keV

to 1250
keV
.


Response corrected for element
sensitivity and reader calibration was
normalized to delivered Hp(10)


Element 1 offers good energy
discrimination at lower energies



Linearity


Wide dose range (0.01cGy to 2000cGy)


Dosimeters exposed to Cs
-
137


Linear dose calculation based solely on
element 2 and reader calibration factor


All doses within 5% of delivered dose


Coefficient of Variation (CV) <10% for all
doses except for 0.01cGy where it is15%

6



0.00
1.00
2.00
3.00
4.00
5.00
10
100
1000
Ei/Hp(10)

Photon Energy (keV)

E1/Hp(10)
E2/Hp(10)
E3/Hp(10)
R² = 0.9998

0
500
1000
1500
2000
2500
0
500
1000
1500
2000
Dose Read (cGy)

Delivered Dose (cGy)

System Characteristics (II)


Angular Response


Photons with energy of 73keV,
173keV, 662keV


Angles 0
°
, 40
°
, 60
°
, 90
°

vertical and
horizontal directions


Response at each angle normalized
to delivered dose


Response within 40%


Re
-
readability


Dosimeter read 50 times to establish
depletion equation


Depletion entered in the reader software


=0.998*exp (
-
0.007*read number)


Dosimeter read 20 times, depletion
correction applied


System precision = 1%

7



4.20
4.30
4.40
4.50
4.60
4.70
4.80
0
5
10
15
20
Dose Read (cGy)

Number of Readings

Dose Read
Avg Dose 20
measurements
Intial dose read
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
-90
-60
-40
0
40
60
90
Response Relative to Delivered Hp(10)

Vertical 662 keV
Vertical 73 keV
Vertical 173 keV
Horizontal 662keV
Horizontal 73keV
Horizontal 173keV
RadWatch

®

as Personnel Dosimeter
Performance Results


Dosimeter tested National Voluntary Laboratory Accreditation Program,

ANSI
N13.11
-
2009 Standard


Testing categories:


Photons General

Accident Level


15 dosimeters in the category


Dose range between 0.05Gy to 5Gy


No knowledge of the exposure field


Photons

Protection Level


21 dosimeters in the category


Dose range between 0.5mSv to 5mSv


Energy from 70keV to 1250keV; Angles <=60
°


No knowledge of the exposure field


Performance Evaluation


B
2
+S
2
≤ L
2

, Where B= bias, S = standard deviation, L= performance limit


L=0.24 for accident category, L=0.3 for protection category


8



0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
-0.4
-0.2
0
0.2
0.4
Standard Deviation

Bias

Cat I Limit
Cat II Limit
Hp(10) Cat I
Hp(10) Cat II
Hp(0.07) Cat II


DDE

SDE



B

S

L
2

B

S

L
2

Cat 1A

0.0018

0.05

0.057

N/A

N/A

N/A

Cat 2C

-
0.015

0.058

0.004

0.004

0.063

0.09

Conclusion


RadWatch

®


RadLight

®

System


Capable to be used as a tactical and as a personnel dosimeter


Desirable system for assessing dose in the field and in the
laboratory conditions due to:


Simple dose calculation algorithm


Unique filter design that provides excellent angular response


Re
-
readability, offering the possibility of multiple readings without dose
alteration, when depletion correction is applied


Wide dynamic range that offers the possibility of reading dosimeters
exposed to very high doses without encountering saturation


Unique RFID identification capable of storing pertinent information
related to the dosimeter


Reliability, easy to use, and lightness for the dosimeter and the reader



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