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Calibration of brachytherapy sources using ferrous sulphate-benzoic acid-xylenol orange dosimeter
International Journal of Applied Radiation and Isotopes, 1976, Vol. 27, pp.Ot3 -446. Pergamon Preu. Printed in Northern Ireland
Calibration of Brachytherapy Sources Using Ferrous Sulphate-Benzoic Acid-Xylenol Orange Dosimeter U. M A D H V A N A T H , U. R. K I N I and B. L. G U P T A Division of Radiological Protection, Bhabha Atomic Research Centre, Trombay, Bombay-400 085, India
(Received 25 November 1975; in revisedform 24 February 1976) A solution containing 0.20 mM of ferrous ammonium sulphate, 5.0 mM benzoic acid and 0.20raM xylenol orange in 0.05 N sulphuric acid was used for the calibration of californium-252, caesium-137, radium-226 and cobalt-60 needle sources. A known volume of this solution contained in a pyrex glass tube was irradiated with the source kept in a glass capillary at the centre of the solution. A few hours of irradiation were required for each needle and the absorbanee of the solution was measured at 540 nm against the unirradiated solution. The accuracy of this method was found to be within a few percent and is particularly useful for californium-252 sources as the neutron component of the source contributes significantly to the absorbance produced.
580 nm and p H 10.0 was used for the estimation of xylenol o r a n g e f l ) All dosimetric soluS~At~D radiation sources like caesium-137, tions were p r e p a r e d with triply distilled water. radium-226 and cobalt-60 used in Preparation details were described earlier. ~5) brachytherapy in the form of needles or tubes The simple irradiation tube is shown in Fig. are normally calibrated using a re-entrant type 1, which consists of a Pyrex glass cylindrical ionisation chamber. A dosimeter containing container. The internal diameter of the con0.20 m M ferrous ammonium sulphate, tainer used for californium-252 needles was 5 . 0 m M benzoic acid and 0 . 2 0 m M xylenol 1 4 r a m and that for other sources 19.3 ram. orange in 0.05 N H2SO4 (FBX dosimeter) has The glass apparatus and polyethylene caps been developed by GUPTA.O-s) This dosimeter were cleaned with 10% aqueous nitric acid is very sensitive. ¢5,s) In the present investiga- and washed with water several times. The tion, usefulness of this dosimeter for the cali- apparatus was then rinsed with distilled water bration of sealed radiation sources is d e m o n - and triply distilled water successively. strated. Table 1 gives details of various sources used. The source contained in the glass capillary was positioned at the centre of the 2. EXPERIMENTAL P R O C E D U R E dosimetric solution with the help of the The ferrous a m m o n i u m sulphate, benzoic polyethylene cap (see Fig. l). The outer acid and sulphuric acid used were of analytical diameter of the glass capillary used for grade. Tetra sodium salt of xylenol orange, californium-252 was 2 . 0 r a m and that for reagent grade, obtained from K & K other sources was 4.9 m m . The height of the Laboratories was used in the preparation of solution was 45 m m in all cases. The dosimetdosimetric solutions. The molar absorption ric solutions were protected from light by covcoefficient value of 3.12 × 104 M -1 cm -1 at ering them with black paper. This gives better 443 1. I N T R O D U C T I O N
444
U. Madhvanath, U. R. Kini and B. L. Gupta
L -
Polyethylene cap
-
Glass tube
Dosimetric solution
Source -
-
Pyrex container
Plastic SlOacer
Fro. 1. The apparatus used for irradiation of FBXsolution. reproducibility when very long irradiations are necessary. The dosimetric solutions were irradiated for a few hours for each source. Because of low strengths that were available on hand, overnight irradiations were carried out for californium-252 sources. The absorbance of the irradiated solution was measured against unirradiated solution. These measurements were done in optical cells with one cm path length using a Cary-14 spectrophotometer which could measure absorbance to an accuracy of 0.0005.
3. RESULTS AND DISCUSSION The FBX dosimetric solution was irradiated for about 17 hr with californium-252 needle having neutron output of 1.25 x 106 n/sec.
This irradiation was repeated 4 times. The absorbance of the irradiated solution in one cm cell per hour of irradiation was found to be 0 . 0 0 2 4 7 + 0 . 0 0 0 0 5 . The variation in absorbance per hour of irradiation is within the experimental error. The californium-252 source strengths normally used in brachytherapy are five to ten times higher than the one used in this investigation and hence much shorter duration of irradiation is adequate for one measurement. Further, the neutron to gamma dose ratio in tissue from californium-252 at transverse distance of 0.5 cm from the centre of the source needle of 1.5 cm active length is 2.06. <1°) The response of the FBX dosimeter for fission neutrons is 38.6% of that of y - r a y s f l "6) Therefore, gammas and neutrons from californium-252 contribute almost equally to the response of the FBX dosimeter. Figure 2 gives the plots of absorbance of irradiated FBX system against mCi hours of irradiation for caesium-137, cobalt-60 and radium-226 needles. It is seen that in all the cases the absorbance increases linearly with mCi hours of irradiation. It can also be seen that the slopes for these sources are in proportion to their K factors although the sensitivity for caesium-137 is a little less because of the thick wall and added attenuation of 660 keV photons. As one microgram of californium252 is equivalent to 0.54 mCi, the response of the FBX dosimeter to this source falls close to that of cobalt-60 in Fig. 2. The calibration of therapy sources involves low integral doses given at low dose-rates. This requires a reliable dosimeter which could measure a few tens of rad. The FBX dosimeter is well suited for such low dose measurements. It has an L E T response similar to that
TABLE 1. Strength and dimensions of the sources used Source Californium-252 Caesium-137 Cobalt-60 Radium-226
Strength 0.54/~g 13.6 mCi 8.5 mCi 5.0 mCi
Active length (ram)
External length (ram)
External diameter (mra)
Sheathing (nun)
15.0 13.5 15.0 10.0
18.0 20.0 17.0 13.0
0.95 2.65 1.60 1.65
0.25 (Pt-k) 0.50 (Pt-Ir) 0.30 (Pt-Rh) 0.50 (Pt-Ir)
Calibraion of brachytherapy sources using ferrous sulphate-bezoic acid-xylenl orange dsimeter 0.4 --
E (~
Ra
0.3-
g ~
/
-226J"
J
0.2--
/ F'7 O.I t--
~- j."
15
-.A-'~
30
45
60
75
~o
mCi-hours
needles and tubes for any loss of source due to rupture or leakage while in constant use in a hospital.
Acknowledgements--We are grateful to the International Atomic Energy Agency for loaning us the californium-252 needle used in this work under contract No. 5/IND/1973. We are also grateful to Dr. K. G. VOHRA, Head, Division of Radiological Protection for his keen interest in this work. 1.
FIG. 2 Change in absorbanee of FBX solution on irradiation by cobalt-60 (8.5 mCi), radium226 (5mCi) and caesium-137 (13.6mCi)
2. 3.
sources.
4.
of the ferrous sulphate dosimeter, iS) Besides, the F B X dosimeter is simple to prepare and dose m e a s u r e m e n t is accurate within a few percent. The m e a s u r e m e n t requires only a visible light s p e c t r o p h o t o m e t e r which most of the laboratories m a y have. Of course the g e o m e t r y of the source whose strength has to be measured should be identical to the source against which the calibration has been done. Further, calibration will also depend on the P t - I r sheathing thickness. However, this is not relevant for the periodic check up of the same
445
5. 6. 7. 8. 9. 10.
REFERENCES GLq-rA B. L. Proc. Symp. Radiation Chemistry, BARC, Bombay, February 1970 Rept. BARC489, p. 115 (1970). GDI~A B. L. Microchem. J. 18, 363 (1973). GUPTA B. L. Proc. Syrup. D A E Chemistry, Vol. II, p. 49, I.I.T., Madras (1970). G U P T A B . L . Dosimetry in Agriculture, Industry, Biology and Medicine p. 421. IAEA, Vienna (1973). GUPTA B. L. and GOMATHY K. R. Int. J. appl. Radiat. Isotopes 25, 509 (1974). GLrr'rA B. L., DVORNI~ I. and ZEc U. Phys. Med. Biol. 19, 843 (1974). GUPTA B. L., Kir~I U. R. and BnAT R. M. Int. J. appl. Radiat. Isotopes 27, 31 (1976). GUPTA B. L. Presented at the 28th Indian Radiology Congress Held at Hyderabad (Feb. 7-10, 1975). Gur'rA B. L. Talanta 21, 683 (1974). KRISHNASWAMV V. Phys. Med. Biol. 17, 56 (1972).
E T A L O N N A G E DE SOURCES DE B R A C H Y T H E R A P I E A L'AIDE D'UN D O S I M E T R E A SULFATE F E R R E U X - A C I D E BENZOIQUEXYLENOL ORANGE Une solution contenant 0,20 m M de sulfate d'ammonium ferreux, 5,0 mM d'acide benzoTque et 0,20 mM de X • ylenol orange w en 0,05 N d'acide sulfurique a 6t6 utills&e pour 1 '"etalonnage de californium-252, caesium137, radium-226 et de sources ~ aiguille de cobalt-60. Un volume donn~ de cette solution, contenu dans un tube de verre pyrex a &t6 irradi& par la source qui se trouvait dans un capillaire en verre plac& au centre de la solution. Quelques heures d ' i r r a d i a t i o n ont ~t~ n~c~ssaires pour chaque aiguille et l'extinction de• la solution, en comparaison de la@ solution non. • • • . ~rradiee, a ete mesuree A 540 nm. La precislon de cette m~thode etait dans les limites de quelques pour cent.
446
U. Madhvanath, U. R. Kini and B. L. Gupta
Dans le cas des sources de californium-252 cette m&thode se revele donc comme particuli'erement utile vu que la composante neutronique de la source apporte une contribution significative & l'extinction produite.
KALIBRIERUNG V0N BRACHYTHERAPIE QUELLEN DURCH FERROSULFAT BENZOES~URE - XYLENOL ORANGE DOSIMETER -
Zur Kalibrierung yon Californium-252, Caesium-137, Radlum-226 und Kobalt-60 Nadelquellen, wurde eine L6sung bestehend aus 0,20 mM Ferro-ammonium-sulfat, 5,0 mM_ Benzoes~ure und 0,20-mM_Xylenol orange in 0,05 N Schwefels~ure benutzt. Ein gegebenes Volum~n dieser L6sung wurde in einer Pyrex Glasr6hre bestrahlt, wobei die Quelle sich in einer Glaskapillare im Zentrum der L6sung befand. FGr Jede Nadel waren ein paar Bestrahlungsstunden notwendig, d a n n w u r d e die Extinktion dieser L6sung, verglichen mit der unbestrahlten LSsung, bei 540 nm gemessen. Die Pr~zision dieser Methode war innerhalb einiger Prozente. Bei 0alifcrnium-252 ist dlese Methode speziell angebracht, da die Neutronenkomponente der Quelle bedeutend zur hervorgerufenen Extinktion beitr~gt.
KAZMSPOBKA 5P&XMTEPAHEBTI4qECKMX MCT0qHMKOB C MCHO/IBBOBAHMEM ~EPPOCY/IB~AT-HEH30~HO-KMC/10THOF0 KCM/IEH0/[-0PAH~EBOF0 ~I03MMETPA. ~I/19[ K a a M 0 p O B K M MPOJIBqaTsIX M O T O q H M K O B KaJIM~OpHM~--252, ~esMa'-187, p a A M a - 2 2 6 M K o 6 a a b T a - 6 0 M c n o a , . s o B a a e a p a c T B O p , cozepxamMR 0,~0MM ~eppocyab~aTa aMMOHM~, 5,0MM 6eHSO~HO~ KMCaOTM
0, 20MM Kc~aeHOa EpaHxeBoR
S 0,05 N CepHOfi KMCaETM.
14SBeCTHb*R
o 6 % e M s t o r e p a c T B o p a p 3aKJIDqeHHBI~"B T p y 6 K e M3 cTeKJ1a IIa~peKc, o0ayqaac;[ M C T O q H M K O M , IIoMe~eHHMM B C T e K a a H H O M KanMaJlspe B ~eHTpe paCTBOpa. /~/IH K a x A o R MFO.;IKM nOT p e 6 o B a a O C b HeCKOJIbKO
qacoB oOayqeHM~ s 8 K C T M H K ~ a
paCTBOpa MsMepaaacb
npM 540rim
HO c p a B H e H M m C Heo6JIyqeHHMM E a o T B o p o M . TOqHOOT~. S T O F O M e T o ~ a oKasaJiacl, B npezeaax HeoKoJI~-KMX H p O R e H T O B , MTO O c o 6 e H H O Ho.~eSHO 4112 M O T O q H M R O B KaJIM$OpHM2--252, HOOEOJlbI~y H e ~ T p O H B I ~ K O M n O H e H T MCTOqH~IKa B 3HaqMTe.UbHO~ C T e H e H M C H O O O O C T B y e T 8 KCTMHKL~MM.
l
Calibration of Brachytherapy Sources Using Ferrous Sulphate-Benzoic Acid-Xylenol Orange Dosimeter U. M A D H V A N A T H , U. R. K I N I and B. L. G U P T A Division of Radiological Protection, Bhabha Atomic Research Centre, Trombay, Bombay-400 085, India
(Received 25 November 1975; in revisedform 24 February 1976) A solution containing 0.20 mM of ferrous ammonium sulphate, 5.0 mM benzoic acid and 0.20raM xylenol orange in 0.05 N sulphuric acid was used for the calibration of californium-252, caesium-137, radium-226 and cobalt-60 needle sources. A known volume of this solution contained in a pyrex glass tube was irradiated with the source kept in a glass capillary at the centre of the solution. A few hours of irradiation were required for each needle and the absorbanee of the solution was measured at 540 nm against the unirradiated solution. The accuracy of this method was found to be within a few percent and is particularly useful for californium-252 sources as the neutron component of the source contributes significantly to the absorbance produced.
580 nm and p H 10.0 was used for the estimation of xylenol o r a n g e f l ) All dosimetric soluS~At~D radiation sources like caesium-137, tions were p r e p a r e d with triply distilled water. radium-226 and cobalt-60 used in Preparation details were described earlier. ~5) brachytherapy in the form of needles or tubes The simple irradiation tube is shown in Fig. are normally calibrated using a re-entrant type 1, which consists of a Pyrex glass cylindrical ionisation chamber. A dosimeter containing container. The internal diameter of the con0.20 m M ferrous ammonium sulphate, tainer used for californium-252 needles was 5 . 0 m M benzoic acid and 0 . 2 0 m M xylenol 1 4 r a m and that for other sources 19.3 ram. orange in 0.05 N H2SO4 (FBX dosimeter) has The glass apparatus and polyethylene caps been developed by GUPTA.O-s) This dosimeter were cleaned with 10% aqueous nitric acid is very sensitive. ¢5,s) In the present investiga- and washed with water several times. The tion, usefulness of this dosimeter for the cali- apparatus was then rinsed with distilled water bration of sealed radiation sources is d e m o n - and triply distilled water successively. strated. Table 1 gives details of various sources used. The source contained in the glass capillary was positioned at the centre of the 2. EXPERIMENTAL P R O C E D U R E dosimetric solution with the help of the The ferrous a m m o n i u m sulphate, benzoic polyethylene cap (see Fig. l). The outer acid and sulphuric acid used were of analytical diameter of the glass capillary used for grade. Tetra sodium salt of xylenol orange, californium-252 was 2 . 0 r a m and that for reagent grade, obtained from K & K other sources was 4.9 m m . The height of the Laboratories was used in the preparation of solution was 45 m m in all cases. The dosimetdosimetric solutions. The molar absorption ric solutions were protected from light by covcoefficient value of 3.12 × 104 M -1 cm -1 at ering them with black paper. This gives better 443 1. I N T R O D U C T I O N
444
U. Madhvanath, U. R. Kini and B. L. Gupta
L -
Polyethylene cap
-
Glass tube
Dosimetric solution
Source -
-
Pyrex container
Plastic SlOacer
Fro. 1. The apparatus used for irradiation of FBXsolution. reproducibility when very long irradiations are necessary. The dosimetric solutions were irradiated for a few hours for each source. Because of low strengths that were available on hand, overnight irradiations were carried out for californium-252 sources. The absorbance of the irradiated solution was measured against unirradiated solution. These measurements were done in optical cells with one cm path length using a Cary-14 spectrophotometer which could measure absorbance to an accuracy of 0.0005.
3. RESULTS AND DISCUSSION The FBX dosimetric solution was irradiated for about 17 hr with californium-252 needle having neutron output of 1.25 x 106 n/sec.
This irradiation was repeated 4 times. The absorbance of the irradiated solution in one cm cell per hour of irradiation was found to be 0 . 0 0 2 4 7 + 0 . 0 0 0 0 5 . The variation in absorbance per hour of irradiation is within the experimental error. The californium-252 source strengths normally used in brachytherapy are five to ten times higher than the one used in this investigation and hence much shorter duration of irradiation is adequate for one measurement. Further, the neutron to gamma dose ratio in tissue from californium-252 at transverse distance of 0.5 cm from the centre of the source needle of 1.5 cm active length is 2.06. <1°) The response of the FBX dosimeter for fission neutrons is 38.6% of that of y - r a y s f l "6) Therefore, gammas and neutrons from californium-252 contribute almost equally to the response of the FBX dosimeter. Figure 2 gives the plots of absorbance of irradiated FBX system against mCi hours of irradiation for caesium-137, cobalt-60 and radium-226 needles. It is seen that in all the cases the absorbance increases linearly with mCi hours of irradiation. It can also be seen that the slopes for these sources are in proportion to their K factors although the sensitivity for caesium-137 is a little less because of the thick wall and added attenuation of 660 keV photons. As one microgram of californium252 is equivalent to 0.54 mCi, the response of the FBX dosimeter to this source falls close to that of cobalt-60 in Fig. 2. The calibration of therapy sources involves low integral doses given at low dose-rates. This requires a reliable dosimeter which could measure a few tens of rad. The FBX dosimeter is well suited for such low dose measurements. It has an L E T response similar to that
TABLE 1. Strength and dimensions of the sources used Source Californium-252 Caesium-137 Cobalt-60 Radium-226
Strength 0.54/~g 13.6 mCi 8.5 mCi 5.0 mCi
Active length (ram)
External length (ram)
External diameter (mra)
Sheathing (nun)
15.0 13.5 15.0 10.0
18.0 20.0 17.0 13.0
0.95 2.65 1.60 1.65
0.25 (Pt-k) 0.50 (Pt-Ir) 0.30 (Pt-Rh) 0.50 (Pt-Ir)
Calibraion of brachytherapy sources using ferrous sulphate-bezoic acid-xylenl orange dsimeter 0.4 --
E (~
Ra
0.3-
g ~
/
-226J"
J
0.2--
/ F'7 O.I t--
~- j."
15
-.A-'~
30
45
60
75
~o
mCi-hours
needles and tubes for any loss of source due to rupture or leakage while in constant use in a hospital.
Acknowledgements--We are grateful to the International Atomic Energy Agency for loaning us the californium-252 needle used in this work under contract No. 5/IND/1973. We are also grateful to Dr. K. G. VOHRA, Head, Division of Radiological Protection for his keen interest in this work. 1.
FIG. 2 Change in absorbanee of FBX solution on irradiation by cobalt-60 (8.5 mCi), radium226 (5mCi) and caesium-137 (13.6mCi)
2. 3.
sources.
4.
of the ferrous sulphate dosimeter, iS) Besides, the F B X dosimeter is simple to prepare and dose m e a s u r e m e n t is accurate within a few percent. The m e a s u r e m e n t requires only a visible light s p e c t r o p h o t o m e t e r which most of the laboratories m a y have. Of course the g e o m e t r y of the source whose strength has to be measured should be identical to the source against which the calibration has been done. Further, calibration will also depend on the P t - I r sheathing thickness. However, this is not relevant for the periodic check up of the same
445
5. 6. 7. 8. 9. 10.
REFERENCES GLq-rA B. L. Proc. Symp. Radiation Chemistry, BARC, Bombay, February 1970 Rept. BARC489, p. 115 (1970). GDI~A B. L. Microchem. J. 18, 363 (1973). GUPTA B. L. Proc. Syrup. D A E Chemistry, Vol. II, p. 49, I.I.T., Madras (1970). G U P T A B . L . Dosimetry in Agriculture, Industry, Biology and Medicine p. 421. IAEA, Vienna (1973). GUPTA B. L. and GOMATHY K. R. Int. J. appl. Radiat. Isotopes 25, 509 (1974). GLrr'rA B. L., DVORNI~ I. and ZEc U. Phys. Med. Biol. 19, 843 (1974). GUPTA B. L., Kir~I U. R. and BnAT R. M. Int. J. appl. Radiat. Isotopes 27, 31 (1976). GUPTA B. L. Presented at the 28th Indian Radiology Congress Held at Hyderabad (Feb. 7-10, 1975). Gur'rA B. L. Talanta 21, 683 (1974). KRISHNASWAMV V. Phys. Med. Biol. 17, 56 (1972).
E T A L O N N A G E DE SOURCES DE B R A C H Y T H E R A P I E A L'AIDE D'UN D O S I M E T R E A SULFATE F E R R E U X - A C I D E BENZOIQUEXYLENOL ORANGE Une solution contenant 0,20 m M de sulfate d'ammonium ferreux, 5,0 mM d'acide benzoTque et 0,20 mM de X • ylenol orange w en 0,05 N d'acide sulfurique a 6t6 utills&e pour 1 '"etalonnage de californium-252, caesium137, radium-226 et de sources ~ aiguille de cobalt-60. Un volume donn~ de cette solution, contenu dans un tube de verre pyrex a &t6 irradi& par la source qui se trouvait dans un capillaire en verre plac& au centre de la solution. Quelques heures d ' i r r a d i a t i o n ont ~t~ n~c~ssaires pour chaque aiguille et l'extinction de• la solution, en comparaison de la@ solution non. • • • . ~rradiee, a ete mesuree A 540 nm. La precislon de cette m~thode etait dans les limites de quelques pour cent.
446
U. Madhvanath, U. R. Kini and B. L. Gupta
Dans le cas des sources de californium-252 cette m&thode se revele donc comme particuli'erement utile vu que la composante neutronique de la source apporte une contribution significative & l'extinction produite.
KALIBRIERUNG V0N BRACHYTHERAPIE QUELLEN DURCH FERROSULFAT BENZOES~URE - XYLENOL ORANGE DOSIMETER -
Zur Kalibrierung yon Californium-252, Caesium-137, Radlum-226 und Kobalt-60 Nadelquellen, wurde eine L6sung bestehend aus 0,20 mM Ferro-ammonium-sulfat, 5,0 mM_ Benzoes~ure und 0,20-mM_Xylenol orange in 0,05 N Schwefels~ure benutzt. Ein gegebenes Volum~n dieser L6sung wurde in einer Pyrex Glasr6hre bestrahlt, wobei die Quelle sich in einer Glaskapillare im Zentrum der L6sung befand. FGr Jede Nadel waren ein paar Bestrahlungsstunden notwendig, d a n n w u r d e die Extinktion dieser L6sung, verglichen mit der unbestrahlten LSsung, bei 540 nm gemessen. Die Pr~zision dieser Methode war innerhalb einiger Prozente. Bei 0alifcrnium-252 ist dlese Methode speziell angebracht, da die Neutronenkomponente der Quelle bedeutend zur hervorgerufenen Extinktion beitr~gt.
KAZMSPOBKA 5P&XMTEPAHEBTI4qECKMX MCT0qHMKOB C MCHO/IBBOBAHMEM ~EPPOCY/IB~AT-HEH30~HO-KMC/10THOF0 KCM/IEH0/[-0PAH~EBOF0 ~I03MMETPA. ~I/19[ K a a M 0 p O B K M MPOJIBqaTsIX M O T O q H M K O B KaJIM~OpHM~--252, ~esMa'-187, p a A M a - 2 2 6 M K o 6 a a b T a - 6 0 M c n o a , . s o B a a e a p a c T B O p , cozepxamMR 0,~0MM ~eppocyab~aTa aMMOHM~, 5,0MM 6eHSO~HO~ KMCaOTM
0, 20MM Kc~aeHOa EpaHxeBoR
S 0,05 N CepHOfi KMCaETM.
14SBeCTHb*R
o 6 % e M s t o r e p a c T B o p a p 3aKJIDqeHHBI~"B T p y 6 K e M3 cTeKJ1a IIa~peKc, o0ayqaac;[ M C T O q H M K O M , IIoMe~eHHMM B C T e K a a H H O M KanMaJlspe B ~eHTpe paCTBOpa. /~/IH K a x A o R MFO.;IKM nOT p e 6 o B a a O C b HeCKOJIbKO
qacoB oOayqeHM~ s 8 K C T M H K ~ a
paCTBOpa MsMepaaacb
npM 540rim
HO c p a B H e H M m C Heo6JIyqeHHMM E a o T B o p o M . TOqHOOT~. S T O F O M e T o ~ a oKasaJiacl, B npezeaax HeoKoJI~-KMX H p O R e H T O B , MTO O c o 6 e H H O Ho.~eSHO 4112 M O T O q H M R O B KaJIM$OpHM2--252, HOOEOJlbI~y H e ~ T p O H B I ~ K O M n O H e H T MCTOqH~IKa B 3HaqMTe.UbHO~ C T e H e H M C H O O O O C T B y e T 8 KCTMHKL~MM.
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