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Measurement of gamma dose by means of a cellulose nitrate solid state nuclear track detector
N U C L E A R I N S T R U M E N T S AND METHODS 152 (1978)
591-593 ; ©
N O R T H - H O L L A N D PUBLISHING CO.
MEASUREMENT OF GAMMA DOSE BY MEANS OF A CELLULOSE NITRATE SOLID STATE NUCLEAR TRACK DETECTOR* M. VARNAGY Institute of Experimental Physics, Kossuth University, H - 4001 Debrecen 1, P.O. Box 105, Hungary Received 9 December 1977 CA 80-15 cellulose nitrate sheet has been found to be suitable for measurement of gamma doses in the interval of 1-3 MRad with a resolution of 0.2 MRad applying either etching rate or optical absorbance measurements. The investigations are important in surgical instrument sterilisation.
In a previous paper 1) it was shown that the TCellit detector is suitable for measurements of Xray and electron doses above 1 MRad. Now investigations are in progress 2) to apply various types of solid state nuclear track detectors to gamma dose and dose distribution measurements. This detector type has a number of advantages against other dosimeters: it is inexpensive, does not disturb the dose-field, can be stored as a document, etc. The dependence of the bulk etch rate3), the OlStical abPaper presented at the 2nd Meeting on Nuclear physics in industry, Kecskem6t, Hungary (14-16 August, 1977).
sorbance 4) and the concentration of stable free radicals 5) of polymers upon gamma dose was employed to evaluate the detector plates exposed to gamma rays. For polymers of various types it was found that the information fixed by different gamma doses remained during five years2). The best resolution was obtained for cellulose nitrate. In this paper the results for CA 80-15 cellulose nitrate ~ obtained by bulk-etch-rate and optical absorbance methods will be presented. The results related to .free radicals are discussed in another paper6). Note that relatively stable and simple free radicals were formed only in polycarbonates (figs. 1-3). "r Manufactured by Kodak Pathe, France.
h
J
¢--
e
J
b
e
~86.9gaussj Fig. 1. First derivate e.p.r, spectrum at room temperature of gamma-irradiated samples: (a) T-Cellit, (b) Triafol TX, (c) Triafol TN (cellulose acetates); (d) Melinex O (polyester), (e) Makrofol E, (f) Makrofol KG, (g) Lexan (polycarbonates), (h) CAB, (i) Triafol BN (cellulose acetate butyrates), (j) CN (cellulose nitrate).
Fig. 2. First derivate e.p.r, spectrum at 77 K of gamma-irradiated samples: (a) T-Ce.'.lit, (b) Triafol TX, (c) Triafol TN, (d) Makrofol E, (e) Makrofol KG, (f) Lexan, (g) CAB, (h) Triafol BN, (i) CN.
592
M. VARNAOY
EPR s p e c t r o m e t e r : JES - ME -3X, JEOL, 1.5
(3350 + 50) G 5 G Amplification: 71x Field:
Modulation:
1.0
Sweep:
I
Time
2.5
min
constant:
0.3''
~ .6 i
il
2.5 MRad 9.5 MRad 34.5 MRad
Makrofol E Lexan
Makrofol KG
mm
%0
[e 9.5 MRad ]+ 34.5 MRad
< i
mm
0.5
iOO
''~._ w
O
i
i00
~0"-------"--'-0
--o--~
~
i
,
i
200
300
400
500
t x
0
i
9900 time t(h)
Fig. 3. Amplitude of first derivate e.p.r, spectrum normalized to 9.5 MRad exposed Makrofol E sample vs time from the end of the gamma irradiation (see fig. 1).
Five "stacks" each containing ten CA 80-15 circular sheets (with 22 mm diameter and 1 0 0 a m thickness) were exposed in air to 0.5-1 MRad/h gamma-ray doses of 1.08, 1.80, 2.20, 2.95, 3.80 MRad (___3%) emerging from a 6°Co gammasource. For comparison one "stack" remained unexposed. The "stacks" were irradiated in Debrecen at the MEDICOR Corporation's sterilization room*. The temperature of air was under 50°C and the dose-field was relieved from the ozon. Following the exposure the sheets were stored at room temperature during six months away from light to avoid the UV-accumulation, which would give an effect similar to a gamma-dose, as well as to reach chemical equilibrium6). Then five plates of each "stack" were etched in 25°/6 NaOH solution at (60_0.1)°C with an interruption of 15 min. After washing (15 min in running water + 15 min in distilled water) and drying (10 min, room temper* Established by Atomic Energy of Canada Ltd.
o.s
CN i00 ~m
/Of390nm
O 1> t2 > II
0
25 ~ N a O H / ~ 60°C d'/1
/
,q t) ll
>
~
1.3
~ O/ /j "~ " v = exp(kD) d" f," k = (0.0669 Z ./>.~" O .OO18 )MRad -I J.
; ,'
1.2
1.1 II I
o
Vo = (O.8218 O.OO42)mg/cm2h
s /s l
l
i
l
1
2
3
4
absorbed
dose
1.O
D (MRad)
Fig. 4. The variation of relative extinction (AE) and etchingrate (Vo/Vo) as a function of absorbed gamma dose. The 95% confidence belt is indicated by dotted-dashed lines.
M E A S U R E M E N T OF GAMMA DOSE
ature) the mass decrease was measured. The Vo/V0 ratio was calculated as described in ref. 1 (VD is the average of bulk etch rates of the plates exposed to D MRad dose, V0 is the same quantity of unexposed sheets). The results are shown in fig. 4. A function of the form Vo/V0 = exp kD (1) was fitted to the measured points as proposed in ref. 8; here D is the absorbed dose and k is a constant. For the curve of fig. 4 k = (0.0669 _ 0.0018) MRad- i. Applying formula (1) the calculated values of VD/Vo deviated from the measured ones by an amount of less than 1%, and for a new measured value (in fig. 4 marked symbol ©) was derived as 2.60MRad with a 95°/6 confidence interval of (2.46;2.83). The chlorbenzene dosimeter gave a value of (2.65_ 0.13) MRad. For the relative extinction measurement (AE=ED-Eo) a UNICAM SP. 800 spectrophotometer was used. The average of dE for five plates can be seen in fig. 4 at the wavelength that gives the best resolution. The error bars include the reproducibility of the spectrophotometer and the standard deviation of the relative extinctions for five plates. The curve was drawn without the-
593
oretical considerations. A change in colour was noticeable even by the eye for the plates exposed to 0, 1.08, 1.80, 2.95 and 3.80MRad doses. Note that there was no measurable change either in the Vo/V0 or in the AE values when repeating the measurements after 6 months. Therefore it seems that this detector type can be applied for documentation purposes. The author would like to express his appreciation to Drs. 1~. Dfivid, E. Molnfir and A. Rockenbauer for their help in measurements and for valuable discussions, and to Profs. J. Csikai and I. Angeli for helpful discussions. References t) M. Vgtrnagy, J. Csikai and S. Szegedi, Nucl. Instr. and Meth. 119 (1974) 261. 2) M. Vfirnagy, E. Moln~ir and I~. Dfivid, Proc. 2nd Meeting on Nuclear physics in industry, Kecskem6t, Hungary (1977). 3) A. L. Frank and E. V. Benton, Rad. Eft. 2 (1970) 269. 4) M. Nicolae, Rev. Rom. Phys. 18 (1973) 887. 5) D. S. Hamidov et al., Vysokomolecularnie Soedinenia, A14 (1972) 834. 6) M. Vfirnagy, to be published. 7) M. Vfirnagy, E. Gyarmati and T. Sztaricskai, Nucl. Instr. and Meth. 133 (1976) 371. 8) p. B. Price and R. L. Fleischer, Ann. Rev. Nucl. Sci. 21 (1971) 295.
591-593 ; ©
N O R T H - H O L L A N D PUBLISHING CO.
MEASUREMENT OF GAMMA DOSE BY MEANS OF A CELLULOSE NITRATE SOLID STATE NUCLEAR TRACK DETECTOR* M. VARNAGY Institute of Experimental Physics, Kossuth University, H - 4001 Debrecen 1, P.O. Box 105, Hungary Received 9 December 1977 CA 80-15 cellulose nitrate sheet has been found to be suitable for measurement of gamma doses in the interval of 1-3 MRad with a resolution of 0.2 MRad applying either etching rate or optical absorbance measurements. The investigations are important in surgical instrument sterilisation.
In a previous paper 1) it was shown that the TCellit detector is suitable for measurements of Xray and electron doses above 1 MRad. Now investigations are in progress 2) to apply various types of solid state nuclear track detectors to gamma dose and dose distribution measurements. This detector type has a number of advantages against other dosimeters: it is inexpensive, does not disturb the dose-field, can be stored as a document, etc. The dependence of the bulk etch rate3), the OlStical abPaper presented at the 2nd Meeting on Nuclear physics in industry, Kecskem6t, Hungary (14-16 August, 1977).
sorbance 4) and the concentration of stable free radicals 5) of polymers upon gamma dose was employed to evaluate the detector plates exposed to gamma rays. For polymers of various types it was found that the information fixed by different gamma doses remained during five years2). The best resolution was obtained for cellulose nitrate. In this paper the results for CA 80-15 cellulose nitrate ~ obtained by bulk-etch-rate and optical absorbance methods will be presented. The results related to .free radicals are discussed in another paper6). Note that relatively stable and simple free radicals were formed only in polycarbonates (figs. 1-3). "r Manufactured by Kodak Pathe, France.
h
J
¢--
e
J
b
e
~86.9gaussj Fig. 1. First derivate e.p.r, spectrum at room temperature of gamma-irradiated samples: (a) T-Cellit, (b) Triafol TX, (c) Triafol TN (cellulose acetates); (d) Melinex O (polyester), (e) Makrofol E, (f) Makrofol KG, (g) Lexan (polycarbonates), (h) CAB, (i) Triafol BN (cellulose acetate butyrates), (j) CN (cellulose nitrate).
Fig. 2. First derivate e.p.r, spectrum at 77 K of gamma-irradiated samples: (a) T-Ce.'.lit, (b) Triafol TX, (c) Triafol TN, (d) Makrofol E, (e) Makrofol KG, (f) Lexan, (g) CAB, (h) Triafol BN, (i) CN.
592
M. VARNAOY
EPR s p e c t r o m e t e r : JES - ME -3X, JEOL, 1.5
(3350 + 50) G 5 G Amplification: 71x Field:
Modulation:
1.0
Sweep:
I
Time
2.5
min
constant:
0.3''
~ .6 i
il
2.5 MRad 9.5 MRad 34.5 MRad
Makrofol E Lexan
Makrofol KG
mm
%0
[e 9.5 MRad ]+ 34.5 MRad
< i
mm
0.5
iOO
''~._ w
O
i
i00
~0"-------"--'-0
--o--~
~
i
,
i
200
300
400
500
t x
0
i
9900 time t(h)
Fig. 3. Amplitude of first derivate e.p.r, spectrum normalized to 9.5 MRad exposed Makrofol E sample vs time from the end of the gamma irradiation (see fig. 1).
Five "stacks" each containing ten CA 80-15 circular sheets (with 22 mm diameter and 1 0 0 a m thickness) were exposed in air to 0.5-1 MRad/h gamma-ray doses of 1.08, 1.80, 2.20, 2.95, 3.80 MRad (___3%) emerging from a 6°Co gammasource. For comparison one "stack" remained unexposed. The "stacks" were irradiated in Debrecen at the MEDICOR Corporation's sterilization room*. The temperature of air was under 50°C and the dose-field was relieved from the ozon. Following the exposure the sheets were stored at room temperature during six months away from light to avoid the UV-accumulation, which would give an effect similar to a gamma-dose, as well as to reach chemical equilibrium6). Then five plates of each "stack" were etched in 25°/6 NaOH solution at (60_0.1)°C with an interruption of 15 min. After washing (15 min in running water + 15 min in distilled water) and drying (10 min, room temper* Established by Atomic Energy of Canada Ltd.
o.s
CN i00 ~m
/Of390nm
O 1> t2 > II
0
25 ~ N a O H / ~ 60°C d'/1
/
,q t) ll
>
~
1.3
~ O/ /j "~ " v = exp(kD) d" f," k = (0.0669 Z ./>.~" O .OO18 )MRad -I J.
; ,'
1.2
1.1 II I
o
Vo = (O.8218 O.OO42)mg/cm2h
s /s l
l
i
l
1
2
3
4
absorbed
dose
1.O
D (MRad)
Fig. 4. The variation of relative extinction (AE) and etchingrate (Vo/Vo) as a function of absorbed gamma dose. The 95% confidence belt is indicated by dotted-dashed lines.
M E A S U R E M E N T OF GAMMA DOSE
ature) the mass decrease was measured. The Vo/V0 ratio was calculated as described in ref. 1 (VD is the average of bulk etch rates of the plates exposed to D MRad dose, V0 is the same quantity of unexposed sheets). The results are shown in fig. 4. A function of the form Vo/V0 = exp kD (1) was fitted to the measured points as proposed in ref. 8; here D is the absorbed dose and k is a constant. For the curve of fig. 4 k = (0.0669 _ 0.0018) MRad- i. Applying formula (1) the calculated values of VD/Vo deviated from the measured ones by an amount of less than 1%, and for a new measured value (in fig. 4 marked symbol ©) was derived as 2.60MRad with a 95°/6 confidence interval of (2.46;2.83). The chlorbenzene dosimeter gave a value of (2.65_ 0.13) MRad. For the relative extinction measurement (AE=ED-Eo) a UNICAM SP. 800 spectrophotometer was used. The average of dE for five plates can be seen in fig. 4 at the wavelength that gives the best resolution. The error bars include the reproducibility of the spectrophotometer and the standard deviation of the relative extinctions for five plates. The curve was drawn without the-
593
oretical considerations. A change in colour was noticeable even by the eye for the plates exposed to 0, 1.08, 1.80, 2.95 and 3.80MRad doses. Note that there was no measurable change either in the Vo/V0 or in the AE values when repeating the measurements after 6 months. Therefore it seems that this detector type can be applied for documentation purposes. The author would like to express his appreciation to Drs. 1~. Dfivid, E. Molnfir and A. Rockenbauer for their help in measurements and for valuable discussions, and to Profs. J. Csikai and I. Angeli for helpful discussions. References t) M. Vgtrnagy, J. Csikai and S. Szegedi, Nucl. Instr. and Meth. 119 (1974) 261. 2) M. Vfirnagy, E. Moln~ir and I~. Dfivid, Proc. 2nd Meeting on Nuclear physics in industry, Kecskem6t, Hungary (1977). 3) A. L. Frank and E. V. Benton, Rad. Eft. 2 (1970) 269. 4) M. Nicolae, Rev. Rom. Phys. 18 (1973) 887. 5) D. S. Hamidov et al., Vysokomolecularnie Soedinenia, A14 (1972) 834. 6) M. Vfirnagy, to be published. 7) M. Vfirnagy, E. Gyarmati and T. Sztaricskai, Nucl. Instr. and Meth. 133 (1976) 371. 8) p. B. Price and R. L. Fleischer, Ann. Rev. Nucl. Sci. 21 (1971) 295.