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The behaviour of radioiodine in TeO2
J. Incrg. Nucl. Chem.. 1965, Vol.27. pp. 29 to 32. ]PergamonPrem Ltd. Printedin Northern Ireland
THE BEHAVIOUR OF RADIOIODINE IN TeO, J. STEVOWd, LJ. JA~IMOVId and S. R. VmJKOVI~ Institute "Boris Kidrich" and Faculty of Science, Beograd, Yugoslavia
(Received 26 March 1964: in revised form 6 June 1964) Abstract--The radioiodine 1-131 was produced by neutron irradiation of TeOn. The distribution of
valency forms was studied,mainly as two groups: reduced forms containingIn + I- and oxidimd forms containingIOs- '+ I04-. Thcir separationwas done by using ion-entcbanptechnique. Tlns effect of the length of irradiation on the distribution of those forms was found. The percentage of reduced forms increases with the increase of integral nentron flux. The same type of the change is found when TeOn was heated after the irradiatiom. That phenomenon is radically diffei~t from the corresponding results for solid iodates. Possible interaction with the target material was s u i t e d , being primarily chemical in its nature, and depending on the isotopic relations of the componmts.
RADIOISOTOPES of iodine can be formed by neutron irradiation of tellurium and subsequent beta decay. When compounds containing oxygen, such as I-I6TeO0 and TeO 2, are used, the radioiodine is usually found in higher oxidation states (mainly iodate ions). ¢I-~) Similar behaviour is shown by the radioiodine formed in most solid iodates by l~I(n, gamma)lnI reaction: 4) The conditions of dissolution of the target may modify this distribution.(2) One can expect that the presence of the oxygen greatly influences processes in the hot spot. Post-irradiation annealing of solid iodates results in most cases in an increase ~n retention. (4) Similar behaviour might be expected of iodine in Te-O targets. The distribution of valency forms of I-131 after post-irradiation annealing of TeO I is described below. EXPERIMENTAL TeOn (BDH) was recrystallized twice from 0.5 N NaOH, by precipitation with acetic acid, w a s l ~ with water and dried at 120°C. Samples were enciosed in quartz ampoules containing air, and irradiated in the reactor R A in Vincba. The integral neutron flux was varied from 3 x 10~0nitro* to 7"7 x 10t° n/cm n, in order to see its influence on the distribution of iodine valency fonm. The temperature of the irradiation was 130°C 4- 10°C. Irradiations ~ r e done in moot eaam'in parallel in the reactor core and in graphite channels to find possible contributions from fast neutron damage. The accompanying 7 doses were: 9.7 x~10 v Rad/hr in the central channels and'l.2 x 10v Radfhr in the graphite. After irradiation the ampoules were heated in an oil bath. Temperature fluctuations were not greater than 4-0"5°C. Coofing was done in ice. The target TeO, was dissolved in 0.05N N a O H containing carrier ions and the radioiodine was separated on an Amberlite IRA-400 column in nitrate form. c'~ Two fractions were isolated: a uJ R. CON'S'rANT,Proc. 2nd UNlnt. Conf.pUAE, Gendve, 28, 168 ('1958). "~ M. BERTEr, "Transformation chimiques associ6es a rirradiation neutronique de racide tellurique." Thi~-s p r ~ c n t ~ s a la Facult6 des Sciences de i'Universit6 de Paris. CEA 2286 (1963). isJ N. G. ZAICEVAand Lo VEN-D2uN, Radiohimija 2, 614 (1960). ~ R. E. CL]zAgY,W. H. HAmLL and R. R. WILUA~.tS,2.. Amen. Chem. Soc. 74, 4675 (1952). c6~ M. L. GOOD, M. B. Ptr~Dv and T. HOE~NO, 2". Inorg. Nucl. Chem. 6, 73 (1958). 29
30
J. ST~vow~, IA. JA61MOW6 and S. R. VELJKOVI(~
reduced form co~ttaining I and L and an oxidized form containing IO,- and IO=- ~Counting was done on a scintillation spec!rometer (Nal crystal Harshaw 7S8) with a stand/ard error" of 1 ,°~o. RESULTS
AND
DISCUSSION
The results indicate that at the lower integral fluxes--up to 10.7 n/cm~--the reduced forms comprise 15,~ 2~/o, and the oxidized forms are 84 ~ 2,°/o of the total radioiodine. This distribution/is seriously affected by further increase in the integral neutron flux or by heating. Figure 1 demonstrates the effect of the integral neutron flux on the distribution. 80
70--
/
,~f" f
Soturotion
6O
o
50
i
+
40
H 30
20
I0
I 0
x105
I
I l IOS(ft)3 n/era z
2
FIO.l.--Dependenceoftheyieldofreducediodineon integralneutronflux: (ft)l"/a. The samples irradiated in the center of the reactor do not show more of the reduced forms than those irradiated in the graphite. In some cases an increase of up to 5 per cent was observed. The neutron flux in the graphite channels being somewhat lower than in the central ones, the 7, doses amounted to very similar values in parallel experiments at the same integr?l neutron flux. The 7 doses were of the order of 109 Radl for fluxes hig he r than 101 8 n/cm.= It appears that the effects of 7 radiation are
important ill determining the fate of the radioiodine in TeO=. It is also interesting to note that the cubic root dependence in Fig. 1 is similar to the dependence of radiation damage on the dose in metals and other systems, re) Figure 2 represents the annealing of radioiodine in TeO2. It is given in the form of isochronal curves for 3 hr heating. This is the time at which the plateau in the isothermal curves is reached. Differential presentation of the results from Fig. 2 indicates a maximum near 250°C, where the change is greatest. An estimation of ~*~T. H. BLewrrt, R. R. COLTMA~,R. E. JAMISONand J. K. P,.eDMAN,I. Nucl. Materials 2, 277 (1960).
The behaviour of radioiodine in TeOi
31
the activation energy near that temperature was done using the relation: 2.303A (log r)/A(1/T)
E/R
=
v is the reaction velocity obtained from the corresponding isothermal curves. E was found to be 4 kcal/mole. Such values are found in some diffusion processes and may reflect' a similar phenomenon here. In general, it appears that some diffusion dependent interaction of radioiodine with radiation defects increases reduction.
,oo
3xlOZen/cm z 80 m
70 - t=3hr 60
ateach
T*
--
-II~
50 --
0
3 , 6 x I01 e n / c m 2 40
--0
30
--o
7,7xldSn/¢m 2
20 - -
o
I
50
I
Ioo
[
t3o
I
200 T "C
I
23o
I
300
I
35o
FIG. Z--Dependence of IO.- ÷ IO.- yield on the post-irradiation
heating of target TeOI. In order to eliminate the effect of the radiolysis of TeO I or iodate ions, their radiation and thermal stability was checked. No measurable changes were found at the fluxes in the work and at temperatures up to 300°C. The effect of heat is in the same direction as that of the neutron flux accompanying y doses. This may suggest that the reduction is dependent on classical kinetic factors such as the temperature and concentration of reacting speci~. The behaviour of radioiodine in TeOs is very different from the behaviour of 1-128 in alkali iodates. (e A similar phenomenon was found for arsenic and phosphorus when nonisotopic targets were used.(T,s,°) The reduction by radiation defects was suggested as a possible explanation. C°) (7~ G~ B. BAROand A. H. W. ATEN, Jr., Chemical Effects of Nuclear Transformations IAEA, Vienna 11, 233 (1961). ~8) j. S. B ~ W O R T H and J. G. CAMI'BBLL,TranS. Faraday Soc. 59, 1411 (1963). (9) A. ADAMSand J. G. CAMPeELL, Trans. Faraday Soc. 59, 2001 (1963).
32
J. S'r~vow~, LJ. JAc~I~W~and S. R. VeL~ovx~
Our work confirms the importance of the induced radiation damage in targets. It is, however, dit~cult to explain the different action of defects in isotopic targets, where an increase in retention is caused l~y 7 irradiation in most cases. Reactions in isotopic matrices give a variety of chemical products with a preponderance of the parent type. Reactions in nonisotopic targets may be simpler and analogous to some catalyzed decomposition on solids.
THE BEHAVIOUR OF RADIOIODINE IN TeO, J. STEVOWd, LJ. JA~IMOVId and S. R. VmJKOVI~ Institute "Boris Kidrich" and Faculty of Science, Beograd, Yugoslavia
(Received 26 March 1964: in revised form 6 June 1964) Abstract--The radioiodine 1-131 was produced by neutron irradiation of TeOn. The distribution of
valency forms was studied,mainly as two groups: reduced forms containingIn + I- and oxidimd forms containingIOs- '+ I04-. Thcir separationwas done by using ion-entcbanptechnique. Tlns effect of the length of irradiation on the distribution of those forms was found. The percentage of reduced forms increases with the increase of integral nentron flux. The same type of the change is found when TeOn was heated after the irradiatiom. That phenomenon is radically diffei~t from the corresponding results for solid iodates. Possible interaction with the target material was s u i t e d , being primarily chemical in its nature, and depending on the isotopic relations of the componmts.
RADIOISOTOPES of iodine can be formed by neutron irradiation of tellurium and subsequent beta decay. When compounds containing oxygen, such as I-I6TeO0 and TeO 2, are used, the radioiodine is usually found in higher oxidation states (mainly iodate ions). ¢I-~) Similar behaviour is shown by the radioiodine formed in most solid iodates by l~I(n, gamma)lnI reaction: 4) The conditions of dissolution of the target may modify this distribution.(2) One can expect that the presence of the oxygen greatly influences processes in the hot spot. Post-irradiation annealing of solid iodates results in most cases in an increase ~n retention. (4) Similar behaviour might be expected of iodine in Te-O targets. The distribution of valency forms of I-131 after post-irradiation annealing of TeO I is described below. EXPERIMENTAL TeOn (BDH) was recrystallized twice from 0.5 N NaOH, by precipitation with acetic acid, w a s l ~ with water and dried at 120°C. Samples were enciosed in quartz ampoules containing air, and irradiated in the reactor R A in Vincba. The integral neutron flux was varied from 3 x 10~0nitro* to 7"7 x 10t° n/cm n, in order to see its influence on the distribution of iodine valency fonm. The temperature of the irradiation was 130°C 4- 10°C. Irradiations ~ r e done in moot eaam'in parallel in the reactor core and in graphite channels to find possible contributions from fast neutron damage. The accompanying 7 doses were: 9.7 x~10 v Rad/hr in the central channels and'l.2 x 10v Radfhr in the graphite. After irradiation the ampoules were heated in an oil bath. Temperature fluctuations were not greater than 4-0"5°C. Coofing was done in ice. The target TeO, was dissolved in 0.05N N a O H containing carrier ions and the radioiodine was separated on an Amberlite IRA-400 column in nitrate form. c'~ Two fractions were isolated: a uJ R. CON'S'rANT,Proc. 2nd UNlnt. Conf.pUAE, Gendve, 28, 168 ('1958). "~ M. BERTEr, "Transformation chimiques associ6es a rirradiation neutronique de racide tellurique." Thi~-s p r ~ c n t ~ s a la Facult6 des Sciences de i'Universit6 de Paris. CEA 2286 (1963). isJ N. G. ZAICEVAand Lo VEN-D2uN, Radiohimija 2, 614 (1960). ~ R. E. CL]zAgY,W. H. HAmLL and R. R. WILUA~.tS,2.. Amen. Chem. Soc. 74, 4675 (1952). c6~ M. L. GOOD, M. B. Ptr~Dv and T. HOE~NO, 2". Inorg. Nucl. Chem. 6, 73 (1958). 29
30
J. ST~vow~, IA. JA61MOW6 and S. R. VELJKOVI(~
reduced form co~ttaining I and L and an oxidized form containing IO,- and IO=- ~Counting was done on a scintillation spec!rometer (Nal crystal Harshaw 7S8) with a stand/ard error" of 1 ,°~o. RESULTS
AND
DISCUSSION
The results indicate that at the lower integral fluxes--up to 10.7 n/cm~--the reduced forms comprise 15,~ 2~/o, and the oxidized forms are 84 ~ 2,°/o of the total radioiodine. This distribution/is seriously affected by further increase in the integral neutron flux or by heating. Figure 1 demonstrates the effect of the integral neutron flux on the distribution. 80
70--
/
,~f" f
Soturotion
6O
o
50
i
+
40
H 30
20
I0
I 0
x105
I
I l IOS(ft)3 n/era z
2
FIO.l.--Dependenceoftheyieldofreducediodineon integralneutronflux: (ft)l"/a. The samples irradiated in the center of the reactor do not show more of the reduced forms than those irradiated in the graphite. In some cases an increase of up to 5 per cent was observed. The neutron flux in the graphite channels being somewhat lower than in the central ones, the 7, doses amounted to very similar values in parallel experiments at the same integr?l neutron flux. The 7 doses were of the order of 109 Radl for fluxes hig he r than 101 8 n/cm.= It appears that the effects of 7 radiation are
important ill determining the fate of the radioiodine in TeO=. It is also interesting to note that the cubic root dependence in Fig. 1 is similar to the dependence of radiation damage on the dose in metals and other systems, re) Figure 2 represents the annealing of radioiodine in TeO2. It is given in the form of isochronal curves for 3 hr heating. This is the time at which the plateau in the isothermal curves is reached. Differential presentation of the results from Fig. 2 indicates a maximum near 250°C, where the change is greatest. An estimation of ~*~T. H. BLewrrt, R. R. COLTMA~,R. E. JAMISONand J. K. P,.eDMAN,I. Nucl. Materials 2, 277 (1960).
The behaviour of radioiodine in TeOi
31
the activation energy near that temperature was done using the relation: 2.303A (log r)/A(1/T)
E/R
=
v is the reaction velocity obtained from the corresponding isothermal curves. E was found to be 4 kcal/mole. Such values are found in some diffusion processes and may reflect' a similar phenomenon here. In general, it appears that some diffusion dependent interaction of radioiodine with radiation defects increases reduction.
,oo
3xlOZen/cm z 80 m
70 - t=3hr 60
ateach
T*
--
-II~
50 --
0
3 , 6 x I01 e n / c m 2 40
--0
30
--o
7,7xldSn/¢m 2
20 - -
o
I
50
I
Ioo
[
t3o
I
200 T "C
I
23o
I
300
I
35o
FIG. Z--Dependence of IO.- ÷ IO.- yield on the post-irradiation
heating of target TeOI. In order to eliminate the effect of the radiolysis of TeO I or iodate ions, their radiation and thermal stability was checked. No measurable changes were found at the fluxes in the work and at temperatures up to 300°C. The effect of heat is in the same direction as that of the neutron flux accompanying y doses. This may suggest that the reduction is dependent on classical kinetic factors such as the temperature and concentration of reacting speci~. The behaviour of radioiodine in TeOs is very different from the behaviour of 1-128 in alkali iodates. (e A similar phenomenon was found for arsenic and phosphorus when nonisotopic targets were used.(T,s,°) The reduction by radiation defects was suggested as a possible explanation. C°) (7~ G~ B. BAROand A. H. W. ATEN, Jr., Chemical Effects of Nuclear Transformations IAEA, Vienna 11, 233 (1961). ~8) j. S. B ~ W O R T H and J. G. CAMI'BBLL,TranS. Faraday Soc. 59, 1411 (1963). (9) A. ADAMSand J. G. CAMPeELL, Trans. Faraday Soc. 59, 2001 (1963).
32
J. S'r~vow~, LJ. JAc~I~W~and S. R. VeL~ovx~
Our work confirms the importance of the induced radiation damage in targets. It is, however, dit~cult to explain the different action of defects in isotopic targets, where an increase in retention is caused l~y 7 irradiation in most cases. Reactions in isotopic matrices give a variety of chemical products with a preponderance of the parent type. Reactions in nonisotopic targets may be simpler and analogous to some catalyzed decomposition on solids.