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TRACK FORMATION AND ENERGY OF ALPHA PARTICLE BHABHA ATOMIC RESEARCH CENTRE – INDIA.

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Presentation on theme: "TRACK FORMATION AND ENERGY OF ALPHA PARTICLE BHABHA ATOMIC RESEARCH CENTRE – INDIA."— Presentation transcript:

1 TRACK FORMATION AND ENERGY OF ALPHA PARTICLE BHABHA ATOMIC RESEARCH CENTRE – INDIA

2  unetchable etchable XCXC XCXC XDXD XDXD ALPHA INCIDENCES AND TRACK FORMATION BHABHA ATOMIC RESEARCH CENTRE – INDIA

3 XCXC XDXD t BC t t BD TOTAL TRACK ETCH TIME BHABHA ATOMIC RESEARCH CENTRE – INDIA

4 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

5 BULK ETCH RATE  Chemical composition of the detector  Etching conditions – Temperature Concentration Duration  Preconditioning of the detector BHABHA ATOMIC RESEARCH CENTRE – INDIA

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7 TRACK ETCH VELOCITY a= 0.16  m -1 ; b = 2.68 (Andriamanantena and Enge) BHABHA ATOMIC RESEARCH CENTRE – INDIA

8 Design and parametric validation for LR-115 (type –II) based twin cup dosimeter for simultaneous measurements of Rn, Tn and progeny concentrations K.P. Eappen Health, Safety & Environment Group Bhabha Atomic Research Centre Trombay, Mumbai , India

9 Twin cup dosimeter

10 RnRn TnTn

11 RESPONSE OF LR-115 DETECTOR TO ALPHA PARTICLES IN Rn CUP BHABHA ATOMIC RESEARCH CENTRE – INDIA 6.2 cm 4.1 cm SSNTD 222 Rn 218 Po 214 Po Cupwall

12 RESPONSE OF LR-115 DETECTOR TO ALPHA PARTICLES IN Tn CUP BHABHA ATOMIC RESEARCH CENTRE – INDIA 6.2 cm 4.1 cm SSNTD 220 Rn 216 Po 212 Bi 212 Po Cupwall

13 BHABHA ATOMIC RESEARCH CENTRE – INDIA

14 CALIBRATION FACTORS THEORETICAL & EXPERIMENTAL (tracks.cm -2 per Bq.d.m -3 ) Cup RadonThoron Theore -tical Experi- mental Theore- tical Experi- mental Mem- brane Filter C.F FOR BARE FILM (PER SPECIES): 0.02 BHABHA ATOMIC RESEARCH CENTRE – INDIA

15  L C0C0 C1C1 SSNTD FILM FUNCTIONAL DIAGRAM OF THE DOSIMETER CUP BHABHA ATOMIC RESEARCH CENTRE – INDIA

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17 0.56-Transmission ratio/C cm Diffusive length (√(D/  ξ 0.093cm 2 s -1 Effective diffusion coefficientDfDf 4.50cmLength of the dosimeter cupL cmThickness of filter paper  s -1 Decay constant of 220 Rn 0.10cm 2 s -1 Diffusion coefficient of 220 Rn in air D 1.00Bq m -3 Thoron concentration at entry point C0C0 ValueUnitDetailsTerm Parameters used for computing transmission ratio BHABHA ATOMIC RESEARCH CENTRE – INDIA

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19 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 cm 2.s -1 (Diffusion coefficient of thoron in air) and = s -1 (Decay constant of thoron)  is the thickness of G.F filter paper; ( cm) L is the radius of the cup; (6.0 cm) D e is the effective diffusion coefficient of thoron (0.093 cm 2.s -1 ) through filter paper THORON PROFILE OF INSIDE THE CUP BHABHA ATOMIC RESEARCH CENTRE – INDIA

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23 Diameters of holes created on LR-115 and Mylar films BHABHA ATOMIC RESEARCH CENTRE – INDIA r 1 >100  m r 2 = 12  m RESULTANT AREA 2 m

24 Measurement error with increase in track density BHABHA ATOMIC RESEARCH CENTRE – INDIA

25 CORRECTION FOR SPARK COUNTER T T – Tracks by microscope T S – Tracks by spark counter

26 MODIFICATIONS  Pin hole technique for Rn-Tn separation  Optimization of cup dimensions BHABHA ATOMIC RESEARCH CENTRE – INDIA

27 Transmission Fractions of Rn &Tn Through Cellophane Membranes ThoronRadon Transmission, Ci/Co (%)Cellophane thickness (  m) BHABHA ATOMIC RESEARCH CENTRE – INDIA

28 C C0C0 C : Average radon concentration in the compartment volume space C 0 : 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

29 with initial condition, we can arrive at

30 100% response for 95% response for 63% response for Response time Transmission factor at 100% response will be BHABHA ATOMIC RESEARCH CENTRE – INDIA

31 Transmission Fractions of Rn & Tn Through Pin Holes of 2 mm Length ThoronRadon Transmission (%) Dia. of the hole (mm) BHABHA ATOMIC RESEARCH CENTRE – INDIA

32 Response time for Rn & Tn Through Pin Holes of 2 mm Length ThoronRadon Response time 95% (min.) Dia. of the hole (mm) BHABHA ATOMIC RESEARCH CENTRE – INDIA

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37 CONTRIBUTION OF TRACKS (tr.cm -2.d -1 /Bq.m -3 ) Radon x 0.6 = Thoron TotalSurfaceVolume BHABHA ATOMIC RESEARCH CENTRE – INDIA

38 COMPARISON OF CALIBRATION FACTORS ( Tr.cm -2.d -1 /Bq.m -3 ) Thoron Cup Radon Cup Hemi- spherical CylindricalCup shape BHABHA ATOMIC RESEARCH CENTRE – INDIA

39 DESIGN PARAMETERS 75 cm 2 Filter area 6.0 cm Radius of the cup Spherical Shape Thoron Cup 2 mm Pin hole length 1 mm Pin hole radius 4.6 cm Radius of the cup Spherical Shape Radon Cup BHABHA ATOMIC RESEARCH CENTRE – INDIA

40 DOSIMETER DESIGN Bare SSNTD Tn cup Rn cup :32 00 BHABHA ATOMIC RESEARCH CENTRE – INDIA

41 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

42 ………….THANK YOU

43 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 S (2008). K.P. Eappen Factors 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. Mayya Calibration 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. Nambi Methodology for Mixed Field Inhalation Dosimetry in Monazite areas using a Twin-cup Dosemeter with Three Track Detectors., RPD, Vol.77, No.3, pp (1998) For further reading……………..


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