Some problems to be solved for automatic analysis of a CR-39 nuclear track detector in space radiation

Transcription

1 The 10th Workshop Sep NIRS, JAPAN Some problems to be solved for automatic analysis of a CR-39 nuclear track detector in space radiation A.Nagamatsu JAXA/ KEK Grad. Univ. Advanced Studies H.Tawara KEK / JAXA T.Nakamura, N.Fujimoto, K.Murakami, M.masukawa JAXA H.Kumagai AES

2 Plan of Presentation 1. Introduction ~ PADLES system ~ Dosimeters (CR-39 / TLD) Dosimetric quantities : LET(keV/μm), D(Gy) ), H(SV) Exclusive hardware and software for PADLES 2. Some problems to be solved for the analysis of CR-39 used for space radiation dosimetry Etching depth dependence of LET distributions above several kev/μm and its effect on dosimetric results Thresholding of bitmap images to get etch-pit mouths as binary objects and its effect on calibration curves of CR-39 Bubble-like like etch pits increasing with the exposure time in space and its effect on dosimetric results 3. A future plan for PADLES experiments inside ISS JEM

3 1. Introduction ~Dosimeters (CR-39 / TLD) ~ PADLES ( Passive Dosimeter for Life-science Experiments in Space) TLD-MSO MSO-S (thermoluminescent dosimeters) Mg 2 SiO 4 :Tb Tb powder enclosed a pyrex glass with Ar gas ( Kasei Optonics industry ) CR-39 (plastic nuclear track detectors ) CR-39 25mm TLD 25mm t=4mm Acrylic resin HARZLAS TD-1 1 are doped with 0.1%wt NAUGARD D 445 ( Fukuvi Chemical industry ) CR-39 CR-39 TLD-MSO

4 1. Introduction ~ Dosimetric quantities ~ Total absorbed dose : D TOTAL (Gy-water) D = = ( D = H = TOTAL D D = D 10keV / mm-water TLD TLD TOTAL -kd + CR-39 + (1 -k ) D 10keV/ mm- water D ) + D CR-39 + H > 10keV / mm-water CR-39 Total dose equivalent : H TOTAL (Sv) > 10keV / mm- water ( DTLD-kD CR-39) + HCR -39 r c to a F lity a u Q ICRP60 QF-LET relation CR TLD LET (kev/mm) κ : mean TL efficiency for high-let particles from TLD (TLD TLD-MSO 1)

5 1. Introduction ~ Exclusive hardware and software for PADLES ~ We will realize a data offering time less than 2 weeks per experiment. Chemical etching, Washing, drying : 5days TL reader measurement : 1min 30 min /1cm / 2 Manual measurement : month Auto PADLES : several minutes Data input, file output : 1min Manual calcuration : several days Auto PADLES :within 30 sec

6 2. The present problems on CR-39 analysis Etching depth dependence of LET distributions above several kev/mm m and its effect on dosimetric results Thresholding of bitmap images to get etch-pit mouths as binary objects and its effect on calibration curves of CR-39 Bubble-like like etch pits increasing with the exposure time in space and its effect on dosimetric results

7 Comparison of RRMD-III and CR-39 (STS-84 and STS-91) r) ) -1 te a -w m/ V (ke -1 s -1 sr -2 m (c x lu F iḟ D RRMD-III (GCR+Trapped proton) RRMD-III (GCR) CR-39 (corrected) LET (kev/ mm-water) STS-91 Motivation The particle fluxes obtained from RRMD-III were two or three times higher than those obtained from the CR-39 plates. Bulk Etch = 33~40μm Selected only conical etch pits for LET measurements Were short-range particles lost in CR-39 measurements in this study? (H. Tawara et.al )

8 Etch Pit analysis for LET measurements 1. Manual measurement (before STS-95 in JAXA) Operators selected only the sharp pointed pointed conical etch pits by observing the bottom of the etch pits with adjusting a focus. As the results, short-range range particles (roughly R < Bulk etch) were rejected in LET measurements. 2. Automatic measurement (the present method in JAXA) Thresholding 8-bit bitmap image binary image Rejection Shallow pits Ellipse fitting Measurements of the major and minor axes The ellipse fitting program developed by NIRS, SEIKO precision inc. i

9 Etching depth dependence of LET distributions STS-95 : 29/10/1998 7/11/1998( days, Orbital Inclination: 28.45,, Orbital Altitude: 574 km) Joint research between ERIL resarch. and JAXA using STS-95 sample 1. Detected particle fluxes increased with decreasing bulk etch amounts. 2. ERI results (B=46mm, m, semi- automatic) well agreed with JAXA results (B=23mm, m, manual). The high altitude caused a high intensity of protons,and consequently, increased targetfragments (short-range and high LET particles) in measurements of LET distributions. 3. B=8 mm m measurements was effective for detecting short- range and high-let target fragments (>( about 100 kev/mm). m). Now JAXA adopts the double detector method (a combination of the 8um and 23um bulk etch) to PADLES.

10 Measurable range of space radiation by PADLES 10 4 ) n ro ic /m V e (k r te a w in T E L Bulk proton He Li Be B CR-39 TLD-MSO Fe O N C B Be Li He C N O Fe H Range in CR-39 (um) Range in CR-39 (mm) vs. LET-water (kev/mm) by SRIM 2003

11 Comparison of results from B=8mm m and B=23 mm m inside ISS ISS Russian segment :launched at 31/8/2001 (71days), 51.6, ~400 km 1.E +03 ) ] m u / x V lu e Fk l( ia / tr ns e/ r2 f em if c D / y a d [ / 1.E E E E E E E days L ET(L RP+SRP) L R P SRP For 71-day flight, the LET distribution from B=8 mm agreed well with those from B=23 mm. JAXA assumes samples Low earth orbit such as ISS flight are adopted only 8um etching method in future. 1.E E+00 1.E E+02 1.E+03 1.E+04 LET (kev/ um)

12 Thresholding of bitmap images Motivation : 1. Loading periods High track density causes overlapping of etch pits. 2. Shallow pits Many bubble-like etch pits appeared in ISS-SM sample (446 days) sample. 3. Track dip angle Tail of etch pits affects the ellipse fitting. 4. Etching depth Surface becomes rough by heavy etching. and so on. Optimum threshold levels depends on: STS days (46um) ISS SM 446 days (23um) Threshold 150 Threshold 170 Therefore, We investigated different calibration curves for threshold levels.

13 B=23 mm m calibration curves Fe mono,threshold 150~170 The major axis:3.3 % S :11.1 % LET: 11.2% 0 ) (S g-0.5 lo C mono, Threshold 150~170 The major axis:11.1 % S :21.9 % LET: 16.8% um um um um um log(rel-12)

14 B=8 mm m calibration curves Fe mono,threshold 150~170 The major axis:3.6 % S :15.7 % LET: 6.1 % 0 ) -0.5 g (S 170 8um lo 165 8um um C mono, Threshold 150~170 The 150 8um -1.5 major axis:11.4 % S :22.7 % 155 8um LET: 16.7 % log(rel -12)

15 Bubble-like like etch pits in a long-term flight Motivation So far, we have participated two long-term flight experiments. ISS Russian segment flight experiment 31/8/ /11/2002 ( days) Space radiation damage test of HDTV CCD device for HTDV images The MATROSHKA project Now loading! 29/01/2004??/09/2005 (1.8 year) 26/02/ /08/2005 (539 days) Simulation as exact as possible an astro -naut while he leaves the protective area of the spaceship to carry out work in space

16 Bubble-like like etch pits increasing with exposure time in ISS-SM SM ISS Russian segment : 31/8/ /11/2002, 51.6, ~400 km 8μm m etching ( SRP) days 23μm m etching (LRP) days 446days 71days 257days 446days

17 Bubble-like like etch pits increasing with exposure time in ISS-SM SM 1. The density of bubble-like like etch pits increased with increasing a loading time from 71 days to 446 days in ISS SM. 2. The bubble-like like etch pits contributed to a lower LET region, mostly less than 10 kev/mm. m. 3. The bubble-like like etch pits must be short-range range particles (R<23mm.) m.) ) ) -1 m /m V (ke -1 sr -1 day -2 m (c x lu F iḟ D days: LRP without bubbles with bubbles LET-water (kev/mm) SRP(B=8um) SRP What are source radiation for such bubble-like like etch pits, proton?

18 Bubble-like like etch pits increasing with exposure time in ISS-SM SM 10 4 Both etch pits (blue and red) are recognized as the same LET particle, if the same calibration curve. However, the LET of rounded etch pit (blue one) must be underestimated. So, we could not conclude at the present study that the bubble- like etch pits are attributed to low-energy (SRIM SRIM-2003 protons. J.F.Ziegler) ) n ro ic /m V e (k r te a w in T E L Range in CR-39 (um) Range in CR-39 (mm) vs. LET-water (kev/mm) by SRIM 2003 Fe O N C B Be Li He H

19 A future plan for PADLES experiments inside ISS JEM Cell Biology Experiment Facility (CBEF ) PADLE package for ISS ( under manufacturing) Biological sample Culture chamber Japanese experiment module kibo The Minus Eightys Degree Celsius Laboratory Freezer for the ISS (MELFI ) Biological experiment unit ISS biological research experiments A personal dosimetry for Japanese astronauts inside ISS and during EVA Monitoring radiation environments inside JEM

20 Conclusions 1.Etching depth dependence of LET distributions Considering Short Range Particles (SRP) such as target fragmentations, we introduced the double detector method (combination of B=8mm and B=23mm) through the joint research with ERIL Research (Dr. E. Benton). In the low earth orbit around 400 km such as ISS, LET distributions would be measured by using only the 8um-etch sample. 2.Thresholding of bitmap images to get etch-pit mouths as binary objects and its effect on calibration curves of CR-39 Optimum threshold levels depends on loading periods, depth of etch pits,track dip angle, etching depth, and so on. We need calibration curves corresponding to different threshold levels to obtain the consistent dosimetric results. 3.Bubble Bubble-like like etch pits increasing with the exposure time in space and its effect on dosimetric results The density of bubble-like like etch pits increased with increasing a loading time from 71 days to 446 days in ISS SM. These etch pits contributed to a LET region less than 10 kev/mm. m. The bubble-like like etch pits must be short-range range particles (R<23mm.) m.) The bubble-like like etch pits are probably attributed to low-energy protons.

21 Acknowledgements From JAXA, Special Thanks to... Dr. E. ERIL RESEARCH, INC. A joint resarch between ERIL RESERCH and JAXA - ANALYSIS OF NASDA CR-39 PLASTIC NUCLEAR TRACK DETECTORS EXPOSED ON THE STS-95 SPACE SHUTTLE MISSION ( Jan. 2003) Dr. N. Yasuda et. NIRS and SEIKO precision inc. A high-speed and semi-automatic analysis system for track detectors with an ellipse fitting algorithm inside AUTO PADLES Dr. Y.Uchibori and ICCHIBAN Working Group JAXA participates all passive runs of ICCHIBAN project from Thanks you for your attention!!

22