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MÖSSBAUER STUDIES ON THE RADIATION DAMAGE PRODUCED BY ELECTRON CAPTURE AND GAMMA RADIOLYSIS IN COBALT (II) AND
IRON (II) SELENATE
J. Ladrière, J. Krack, D. Apers
To cite this version:
J. Ladrière, J. Krack, D. Apers. MÖSSBAUER STUDIES ON THE RADIATION DAM- AGE PRODUCED BY ELECTRON CAPTURE AND GAMMA RADIOLYSIS IN COBALT (II) AND IRON (II) SELENATE. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-434-C2-436.
�10.1051/jphyscol:19792152�. �jpa-00218526�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au n O 3, Tome 40, mars 1979, page C2-434
M ~ S S B A U E R STUDIES ON THE RADIATION DAMAGE PRODUCED B Y ELECTRON CAPTURE AND GAMMA RADIOLYSIS I N COBALT ( 1 1 ) AND IRON ( 1 1 ) SELENATE
S. LadriSre, J.C. Krack and D. Apers
Laboratoire de Chimie Inorganique e t NucZBaire, Universitd de Louvain, Louvain-Za-Iieuve, Be Zgiqw
Rgsum6.- Les effets chimiques produits par capture Glectronique et radiolyse gamma dans divers s616nates de Co(I1) et de Fe(I1) ont Et6 5tudibs par spectroscopie ~zssbauer en Lmission et absorption. On montre qu'en plus des mol6cules d'eau d'hydratation, l'anion SeOc-fournit aussi des radicaux oxydants vis-8-vis de ~ e ~ + .
Abstract.- The chemical effects produced by electron capture and ganrma radiolysis in various Co(I1) and Fe(I1) selenates have been studied using emission and absorption Gssbauer spectros- copy. It is shown that not only the hydration water molecules but also the Sea-anion give rise to oxidizing radicals against ~ e ~ + .
Introduction.-The after effects of the electron cap- ture in 5 7 ~ o have been studied by emission Mzssbauer spectroscopy in a large number of chemical systems.
In 57~o-labelled cobalt compounds with polyatomic ligands, it has been suggested /l/ that the stabi- lization fonns of the iron atom are determined by the redox properties of the free radicals produced by the autoradiolysis of the surrounding ligands of the decayed nucleus. This mechanism is generally well supported by the similarity of the absorption spectra of the iron corresponding compounds after y-ray irradiation. For instance, in the hydrates of co2+ sulfate, the proportion of ferric ions increa- ses with the hydration number /2/ in agreement with the increasing yield of the oxidizing OH radicals originating from the coordinated water molecules /3/. In this work, we have extended this study to several hydrates of co2+ and Fe2+ selenate : CoSeO4.
5H20, CoSe0,,.H20, CoSeOs, FeSe04.5H20
,
FeSe04.H20.Experimental.- CoSe04 .5H20 is obtained by neutrali- zation of a 6N selenic acid solution with 5 7 ~ o : CO(HCO~)~ and precipitated from this solution by addition of alcohol.
CoSe04.H20 and CoSe04 are prepared by dehydration of the pentahydrate by heating this compound under nitrogen at 180'~ and 290°C, respectively. Ferrous selenate is made by action of selenic acid on metal- lic iron and FeSeO4.5H20 is precipitated from the resulting solution by addition of alcohol. Heating of this compound at 105OC, in pure nitrogen, gives rise to the monohydrate.
The chemical purity of these compounds was checked by thermogravimetric analysis. The samples were
irradiated at room temperature and under nitrogen with 6 0 ~ o gamma rays at a dose rate of 1.1 Mrad/hour.
The ~zssbauer spectra were recorded at 298 K using a constant acceleration spectrometer and fitted in Lorentzian lines by means of a least squares inte- rative program.
~esults and discussion.- From the Mzssbauer emis- sion spectra of the various cobalt(I1) selenates (figure l), it is seen that the decayed iron is stabilized mostly as ~ e (inner doublet) and, in ~ + a less extent, as ~ e (outer doublet). This result ~ + is consistent with the characteristic values of quadrupole splittings (A) and isomer shifts ( 6 ) of these two species :
A &(Fe) I ( X )
-
1-
1mm. S m. S
Furthermore, the relative intensities(1) of the Fe3+
doublets indicate that the proportion of ferric ions increases with the hydration number of the co2+ ion.
However,these values are systematically higher than these observed for Co(I1) sulfate, in similar hydra- ted states : CoS04.4H20 : 61 %, Cos04 .H20 : 53 %, COSOI, : 47 % /2/. This suggests that, not only the
--
water molecules, but also the selenate anions, Seo4 give rise to oxidizing radicals against Fe2+, during the Auger cascade.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792152
- VELOCITY ( m m / $ )
-
Fig. 1 : Mzssbauer emission spectra of CoSeO+.SH20, CoSeOt,.HzO and CoSeOc at 298 K (absorber = stain- less steel).
This supposition has been found in good agreement with results obtained by external gamma radiolysis of the corresponding iron(I1) selenates, FeSeO+.5HzO and FeSe04.H20. The ~zssbauer absorption spectrum of unirradiated FeSeOr.5Hz0 (figure 2a) shows four equally intense lines which have been resolved into two quadrupole doublets (A1 = 3.51 m.s- 1
,
A2 = 2.97 mm.s-l) with I?e2+ characteristic isomer shifts (61(Fe) = I .27 mm.s-l, &(Fe) = 1.25 m.s-l).
This compound has two crystallographically inequi- valent ~ e positions as in the isomorphic copper ~ + sulfate, CuSo4.5H20 141. In both sites the cations are surrounded by four water molecules and two oxy- gen atoms from two different selenate ions. The fifth water molecule is hydrogen bonded to two se- lenate ions and to two coordinated water molecules.
The spectrum of FeSeOs.Hz0 shows only one quadru- pole doublet (A = 2 -86 mm-S-') with a Fe2+ characte ristic isomer shift (&(Fe) = 1.23 m.s-') (figure 2d). This compound is isomorphous with FeSOi+.HzO /S/.
Fig. 2 : ~gssbauer absorption spectra at 298 K of FeSeO+ .5H20, : a) unirradiated b) irradiated
(189 Mrads) c) irradiated (902 Mrads) and of FeSeO4 .H20 d) unirradiated e) irradiated (1 76 Mrads) f) irradiated (995 Mrads) .(Source = 5 7 ~ o (Pd)).
The gamma radiolysis of these iron(I1) selenates gives indeed rise to an oxidation of ~ e into ~ + Fe3+ with a yield increasing as a function of the dose and the ~gssbauer parameters of the ferric species are comparable to those observed in the corresponding emission spectra (figure 2). Further- more, the oxidation rates, calculated from yields measurements, are found to be (roughly) ten times higher than the values obtained for the correspon- ding iron(I1) sulfate 131. As a consequence, the iron(I1) selenates are completely oxidized into ferric compounds for relatively lower doses (900 and 1200 Mrads for FeSe0,.5Hz0 and FeSe0,.H20 res- pectively) than in the case of iron(I1) sulfate (:. 5000 Mrads).
It may therefore be concluded that the ~e0;- anion is able to give radicals that can oxidize Fe2+ +U- ring the radiolysis. This conclusion is well suppor- ted by ESR measurements on gamma-irradiated K2Se04,
C2-436 JOURNAL DE PHYSIQUE
i n which S ~ O ; r a d i c a l s have been d e t e c t e d / 6 / . I n R e f e r e n c e s p r e s e n c e of ~ e ' + i o n s t h i s r a d i c a l i s r e a d i l y redu-
c e d , a c c o r d i n g t o t h e r e a c t i o n / I / F r i e d t , J.M. and Danon,J., Radiochim. Acta
1
(1972) 173-190.
~ e + ~S ~ O ; + -t ~ e + ~~e0;- +
.
/ 2 / A d l o f f , J . P . , I n t e r n a t i o n a l Symposium on Chemi- I n f r a r e d s p e c t r a o f t h e r a d i o l y z e d i r o n ( I 1 ) s e l e n a t e s c a l E f f e c t s o f Nuclear T r a n s f o r m a t i o n s , Cambrid-
i n d e e d c o n f i r m t h e p r e s e n c e o f s e l e n i t e a n i o n , Se03
--
ge (1969)./ 3 / Meyers, J . , L a d r i S r e , J . , ChavBe, M., and Apers, a s a r a d i o l y t i c decomposition p r o d u c t . D . , J . P h y s i q u e
37
(1976) C6-905./ 4 / Bauer,N.H. and Rolin,J.L., Acta C r y s t . B E (1972) 1448.
/5/ Oswald,H.R., Helv. Chim. Acta
48
(1965) 64./ 6 / A i k i , K., J.Phys. Soc. Japan
