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TRACK FORMATION AND ENERGY
OF ALPHA PARTICLE
BHABHA ATOMIC RESEARCH CENTRE – INDIA
0 1 2 3 4
unetchable etchable
XCXC
XD
XD
ALPHA INCIDENCES AND TRACK FORMATION
BHABHA ATOMIC RESEARCH CENTRE – INDIA
XC
XD
tBC
tt
tBD
TOTAL TRACK ETCH TIME
BHABHA ATOMIC RESEARCH CENTRE – INDIA
FACTORS GOVERNING FORMATION OF READABLE TRACKS IN SSNTD
• Energy of incident alpha particle
• Angle of incidence
• Developing the tracks (Etching parameters)
• Counting of tracks
BHABHA ATOMIC RESEARCH CENTRE – INDIA
BULK ETCH RATE
Chemical composition of the detector
Etching conditions – Temperature
Concentration
Duration
Preconditioning of the detector
BHABHA ATOMIC RESEARCH CENTRE – INDIA
4 6 8 10 120
1
2
3
4
5
6
Y = -0.07 + 0.31 e-(x/4.09)
Temperature : 700C
Vb (
Mm
h-1
)
MOLARITY OF NaOH
Bulk etch rate with molarity of etchant (Gruhn et al., 1979)
0 /0
kTV V e
BHABHA ATOMIC RESEARCH CENTRE – INDIA
TRACK ETCH VELOCITY
aRbBT eVRV 1
a= 0.16 m-1 ; b = 2.68
(Andriamanantena and Enge)
BHABHA ATOMIC RESEARCH CENTRE – INDIA
Design and parametric validation for LR-115 (type –II) based twin cup dosimeter for
simultaneous measurements of Rn, Tn and progeny concentrations
K.P. EappenHealth, Safety & Environment Group
Bhabha Atomic Research CentreTrombay, Mumbai-400 085, India
Twin cup dosimeter
Rn
Tn
RESPONSE OF LR-115 DETECTOR TO ALPHA PARTICLES IN Rn CUP
BHABHA ATOMIC RESEARCH CENTRE – INDIA
6.2 cm
4.1
cm
SSNTD
222Rn 218Po 214Po Cupwall
RESPONSE OF LR-115 DETECTOR TO ALPHA PARTICLES IN Tn CUP
BHABHA ATOMIC RESEARCH CENTRE – INDIA
6.2 cm
4.1
cm
SSNTD
220Rn 216Po 212Bi 212Po Cupwall
BHABHA ATOMIC RESEARCH CENTRE – INDIA
0.0 0.2 0.4 0.6 0.8 1.00.2
0.4
0.6
0.8
1.0
Theoretical
Experimental
Tr.cm-2/mWL.d : 0.26 + 0.02Eq.Factor (F) : 0.6 - 0.7
Bare detector response with eq.factor (F)
Bar
e ca
rd s
ensi
tivi
ty f
acto
r,
(Tr.
cm2/m
WL
.d)
Equilibrium Factor, F
CALIBRATION FACTORS THEORETICAL & EXPERIMENTAL
(tracks.cm-2 per Bq.d.m-3)
Cup
Radon Thoron
Theore-tical
Experi-mental
Theore-tical
Experi-mental
Mem-brane
0.0234 0.021 - -
Filter 0.0260 0.023 0.0176 0.019
C.F FOR BARE FILM (PER SPECIES): 0.02
BHABHA ATOMIC RESEARCH CENTRE – INDIA
L
C0 C1
SSNTD FILM
FUNCTIONAL DIAGRAM OF THE DOSIMETER CUP
BHABHA ATOMIC RESEARCH CENTRE – INDIA
BHABHA ATOMIC RESEARCH CENTRE – INDIA
02
2
Cdx
cdD
10 CC 0
Lxdx
dc
xx
BeAexC
D
0.56-Transmission ratio /C0
2.187cmDiffusive length (√(D/ξ
0.093cm2 s-1Effective diffusion coefficientDf
4.50cmLength of the dosimeter cupL
0.0564cm Thickness of filter paper
0.0126s-1Decay constant of 220Rn
0.10cm2 s-1Diffusion coefficient of 220Rn in air
D
1.00Bq m-3Thoron concentration at entry point
C0
ValueUnitDetailsTerm
Parameters used for computing transmission ratio
C
BHABHA ATOMIC RESEARCH CENTRE – INDIA
dxxCL
CL
0
)(1
LD
LCC
f tanh
10
BHABHA ATOMIC RESEARCH CENTRE – INDIA
LCothD
L
C
C
e
C is the average concentration of thoron in the cup C is the concentration of thoron inside the cup at entry point
x = (D/); D = 0.1 cm2.s-1 (Diffusion coefficient of thoron in air) and = 0.0126 s-1 (Decay constant of thoron) is the thickness of G.F filter paper; ( 0.0564 cm)L is the radius of the cup; (6.0 cm)De is the effective diffusion coefficient of
thoron (0.093 cm2.s-1) through filter paper
THORON PROFILE OF INSIDE THE CUP
BHABHA ATOMIC RESEARCH CENTRE – INDIA
8 9 10 11 12
0
100
200
300
400
500
600
700
MEASUREMENT OF (Pre-spark 850 V)
Y =
[(a
1-a2
)/{1
+ex
p((
x-x0
)/d
x)}]
+a2
a1=-1
9.65
; a2
=64
4.35
x0=9.
21 ;
dx=
1.18
1
Tra
cks
ob
serv
ed (
Tr.
cm2 )
Track length (m)
BHABHA ATOMIC RESEARCH CENTRE – INDIA
BHABHA ATOMIC RESEARCH CENTRE – INDIA
0 1 2 3 4
0.010
0.015
0.020
0.025
Variation of Calibration Factor as a function of break-down thich ness () for one hour etching.
Ca
libra
tio
n F
ac
tor
(Tr.
/cm
2/d
pe
r B
q/m
3)
Breakdown thickness, (m)
BHABHA ATOMIC RESEARCH CENTRE – INDIA
0 200 400 600 800 1000 1200
0
200
400
600
800
1000
1200
1400
Variation in tracks with prespark voltage
OB
SE
RV
ED
TR
AC
KS
; (t
rack
s cm
-2)
AVERAGE TRACKS; (tracks cm-2)
750 V: Y = 0.87 X 850 V: Y = 1.00 X 1000 V: Y = 1.14 X
Diameters of holes created on LR-115 and Mylar films
BHABHA ATOMIC RESEARCH CENTRE – INDIA
r1>100 m
r2= 12 m
RESULTANT AREA
2m
0 200 400 600 800 1000 1200 1400 16000
2
4
6
8
10
12
14
16
ME
AS
UR
EM
EN
T E
RR
OR
(%
)
TRACKS (Tracks cm-2)
y = m X + C
m = 0.01; C = 1.4E-10
Measurement error with increase in track density
BHABHA ATOMIC RESEARCH CENTRE – INDIA
BHABHA ATOMIC RESEARCH CENTRE – INDIA
21 2
1
2
1 2
where ( )
is the radius of the Al foil hole > 100 m
is the radius of the track hole 6
ST S
a TT T
a r r
r
r
m
CORRECTION FOR SPARK COUNTER
TT – Tracks by microscopeTS – Tracks by spark counter
MODIFICATIONS
Pin hole technique for Rn-Tn separation
Optimization of cup dimensions
BHABHA ATOMIC RESEARCH CENTRE – INDIA
Transmission Fractions of Rn &Tn Through Cellophane Membranes
0.8398.0405
0.1489.3030
0.1790.9225
0.2192.6020
0.2894.3515
0.4296.1610
ThoronRadon
Transmission, Ci/Co (%) Cellophane thickness
(m)
BHABHA ATOMIC RESEARCH CENTRE – INDIA
C
C0
C : Average radon concentration in the compartment volume space
C0: Outside radon concentration
V : Volume of the compartment
A : Area of the hole
J : Radon activity flux at the hole
d : Thickness of the hole
D : Radon diffusion coefficient in air (hole)
: Radon/Thoron decay constant
BHABHA ATOMIC RESEARCH CENTRE – INDIA
BHABHA ATOMIC RESEARCH CENTRE – INDIA
CV JA CV
t
oC C
J Dd
0ADCC ADC
t Vd Vd
;TAD
Vd
T e
0( ) 1 etT
e
C t C e
with initial condition ( 0) 0C t , we can arrive at
0( ) 1 etT
e
C t C e
100% response for 6
e
t
95% response for 3
e
t
63% response for 1
e
t
Response time
Transmission factor at 100% response will be T
e
BHABHA ATOMIC RESEARCH CENTRE – INDIA
Transmission Fractions of Rn & Tn Through Pin Holes of 2 mm Length
18.7699.9310
12.8799.898
7.6799.806
3.5699.554
0.9299.232
ThoronRadon
Transmission (%) Dia. of the hole (mm)
BHABHA ATOMIC RESEARCH CENTRE – INDIA
Response time for Rn & Tn Through Pin Holes of 2 mm Length
31710
3278
4486
41074
44222
ThoronRadon
Response time 95% (min.) Dia. of the hole (mm)
BHABHA ATOMIC RESEARCH CENTRE – INDIA
1 2 3 4 5
5
10
15
20
25
30
Thoron transmission with size of entry hole
Tra
nsm
issio
n (
%)
Pin hole size (radius; mm)
Plate thickness 1 mm 2 mm 3 mm 4 mm 5 mm
BHABHA ATOMIC RESEARCH CENTRE – INDIA
4.6 cm 4.6 cm
RESPONSE OF LR-115 FILM TO RADON IN CUP
Detector
Radon RadiumA RadiumC' Cupwall
BHABHA ATOMIC RESEARCH CENTRE – INDIA
6.0 cm 6.0 cm
RESPONSE OF LR-115 FILM TO THORON IN CUP
Detector
Thoron ThoriumA ThoriumC ThoriumC' Cupwall
BHABHA ATOMIC RESEARCH CENTRE – INDIA
6.0 cm 6.0 cm
RADON RESPONSE IN THORON CUP
Detector
Radon RadiumA RadiumC' Cupwall
BHABHA ATOMIC RESEARCH CENTRE – INDIA
CONTRIBUTION OF TRACKS(tr.cm-2.d-1/Bq.m-3)
0.060.040.02Radon
0.0790.0550.04 x 0.6 =
0.024Thoron
TotalSurfaceVolume
BHABHA ATOMIC RESEARCH CENTRE – INDIA
COMPARISON OF CALIBRATION FACTORS
(Tr.cm-2.d-1/Bq.m-3)
0.0790.019Thoron Cup
0.060.02Radon Cup
Hemi-sphericalCylindricalCup shape
BHABHA ATOMIC RESEARCH CENTRE – INDIA
DESIGN PARAMETERS
75 cm2• Filter area6.0 cm• Radius of the cup
Spherical• ShapeThoron Cup
2 mm• Pin hole length1 mm• Pin hole radius4.6 cm• Radius of the cup
Spherical• ShapeRadon Cup
BHABHA ATOMIC RESEARCH CENTRE – INDIA
DOSIMETER DESIGN
Bare SSNTD
Tn cup
Rn cup
05.09.0816:32 00
BHABHA ATOMIC RESEARCH CENTRE – INDIA
Conclusions…….1. Calibration factors for dosimeter cups depends on:
cup dimensions track development protocols track reading methods
2. Pin holes against filters are better options for separating Rn and Tn in cup dosimeters.
3. Computation of response time enables designing dosimeters with desired exposure period.
4. Optimization of dosimeter dimensions is possible with parametric studies.
BHABHA ATOMIC RESEARCH CENTRE – INDIA
BHABHA ATOMIC RESEARCH CENTRE – INDIA
Eappen K.P, Sahoo B.K, Ramachandran T.V, Mayya Y.S Calibration factor for thoron estimation in cup dosimeter. Accepted for publication in journal Radiation Measurements. Radiation. Meas. 43 S418 - 421(2008).
K.P. EappenFactors Affecting the Registration and Counting of Alpha tracks in Solid State Nuclear Track Detectors. Accepted for publication in Indian journal of Physics (2008)
K.P. Eappen, Y.S. Mayya, R.L. Patnayak, H.S. Kushwaha. Estimation of radon progeny equilibrium factors and their uncertainty bounds using solid state nuclear track detectors. Radiation. Meas. 41 (3), 342 – 348 (2005).
K.P. Eappen, Y. S. MayyaCalibration factors for LR –115 (Type-II) based radon thoron discriminating dosimeter. Radiation Meas., 38, 5 –1 7 (2004).
Y.S Mayya, K.P Eappen, K.S. V. NambiMethodology for Mixed Field Inhalation Dosimetry in Monazite areas using a Twin-cup Dosemeter with Three Track Detectors., RPD, Vol.77, No.3, pp 177-184 (1998)
For further reading……………..