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Fast analysis of oxygen in fluoride glasses (ZBLAN) by charged-particle activation [16O(d, n)17F]
Nuclear Instruments North-Holland
and Methods
in Physics
FAST ANALYSIS OF OXYGEN ACTIVATION [ 160(d, n)“F] M.F. BARTHE,
A. GIOVAGNOLI,
Research
B45 (1990) 105-106
IN FLUORIDE
GLASSES
G. BLONDIAUX
105
(ZBLAN)
BY CHARGED-PARTICLE
and J.L. DEBRUN
CNRS-CERI, 3A rue de la F&ollerie, 45071 O&am Cedex 2, France
Y. TREGOAT
and J.Y.
BARRAUD
C.G. E. - Laboratoires de Marcoussis, 91460 Marcoussis, France
Oxygen was analyzed in fluoride glasses of the ZBLAN type (ZrF,-BaF,-LaF,-AIF,-NaF). The method is charged-particle Direct gamma-ray spectrometry is performed on the activation with deuterons at 2.8 MeV; the nuclear reaction is 160(d,n)“F. activated samples, after etching to eliminate surface oxygen. The analysis takes - 15 minutes; the sensitivity is - 25 ppm/we& with the present technolo&y c;i which is sufficient considering that the lowest oxygen content in the glass is - 200 ppm/weight, fabrication.
1. Introduction Fluoride glasses are prepared by mixing various fluorides (ZrF,-BaF,-LaF,-AlF,-NaF). These glasses theoretically have very low losses, of the order of 10m3 dB/Km in the infrared, and were proposed for the making of ultra-low loss optical fibers [l-4]. Extrinsic losses are due to absorption by metallic ions and by hydroxyl groups, and to scattering due to bubbles, crystallites or oxides. It has been shown that the higher the total oxygen content, the higher the losses by scattering [5]. At the present state of the technology for the making of glasses and of fibers, it is at least as important to decrease the total oxygen content as to decrease the level of metallic impurities. This implies a nonnegligible number of oxygen. S. Mitachi et al. [5] have proposed a method on the activation of oxygen by protons, following the ‘*O(p, n)‘*F reaction. This method is time-consuming (the l*F half-life is 110 min), limited in sensitivity because of the low abundance of l8O, and requires energies well above 3 MeV because of the high threshold (E,, = 2.6 MeV). High energies are a problem because bigger accelerators are needed and because more power is dissipated in the samples. The fluoride glasses also have a very poor thermal conductivity and can easily break under beam. In this paper, we propose a method which is fast and only requires the use of a small Van de Graaff. 2. Experimental Method. Radioactivation using the 160(d, n)17F reaction. The radionuclide used, 17F, has a half-life of 66 s and is a pure p’ emitter. 0168-583X/90/$03.50 (North-Holland)
0 Elsevier Science Publishers
B.V.
Irradiations. The 3 MV Van de Graaff of the CERI at Orleans was used. The samples are bombarded with 2.8 MeV deuterons for 3 min, with a current of 200 nA. Etching. About 6-8 ym are removed after irradiation to eliminate surface contamination: oxygen is always present at the surface, absorbed or as a constituent of an eventual hydrated layer. The etching solution is HCl 2N + H,BO,. Calibration. Pure alumina is used as a standard. The average cross-section method was used for the calculations [6], although it is accurate to only - lo%, because this method is fast and because very precise results are not needed. Gamma-ray spectrometty. Due to the high oxygen content 17F can be directly detected in the samples in spite of’ nonnegligible activities from Al [ 27A1(d,P)~‘A~, t 1,2 = 2.3 min, E, = 1779 keV] and from F [1gF(d,p)20F, t 1,2 = 11 s, EY = 1633 keV]. 17F being a pure p’ emitter, the 511 keV peak is used for the analysis; samples and standards have similar geometries and are counted in copper boxes for better positron annihilation. The decay of the 511 keV peak is checked in all cases. Results. The experimental sensitivity is - 25 ppm/ weight. It can be improved if needed, but in this case it is not necessary because the lowest concentration ever found in fluoride glasses is - 200 ppm/weigbt. At this level - the overall precision is - 15% analysis is completed in about 15 min. The overall procedure was checked, as in ref. [5], using glasses doped up to - 3500 ppm/weight by addition of ZrO, or of Al,O,. Concentrations in the glasses were found to range from - 200 up to 500 ppm/weight.
I. NRA
106
M.F. Barthe et al. / Fast analysis of 0 in fluoride glasses
3. Conclusion and discussion The analysis of oxygen in fluoride glasses of the ZBLAN type can be done rapidly and with sufficient accuracy and sensitivity using the I6 O(d, n)17F reaction. As the purity of these glasses improves, other methods may be needed, because the present method will not be sufficiently sensitive. Activation will probably remain a method of interest at lower levels, because it is possible to eliminate surface contaminations. Alpha particles and 3He cannot be used because of the nuclear interference of fluorine at all energies. Protons and deuterons do not offer sufficient sensitivity, unless (for protons) a large dose and a high energy are used, resulting in the probable destruction of the samples. The solution then is triton activation. The 160(t, n)**F reaction is selective (E I 4 MeV) and has a high cross section at low energy. For instance, the intrinsic sensitivity is 0.05 ppm/weight at 3 MeV, for
an irradiation of 10 mm at 100 nA 171. This reaction has already been applied with success to analysis of oxygen in fluoride glasses of the type [8]. The drawbacks of using tritons are that these particles are seldom available, and that the use of “F (t,,, = 110 min) necessitates longer analysis times.
References PI D.A. Pinnow et al., Appl Phys. Lett. 33 (1978) 28.
PI L.G. Van Uitert et al., Appl. Phys. Lett. 33 (1978) 57. 131 C.H.L. Goodman, IEEE J. Solid State Electron. Devices 2 (1978) 129.
[41 P.W. France et al., Br. Telecom. Technol, J. 5 (1987) 28. [51 S. Mitachi et al., Jpn. J. Appl. Phys. 24 (1985) 827. 161 E. Ricci et al., Anal. Chem. 37 (1965) 742. [71 H. Valladon et al., J. Radioanal. Chem. 39 (1977) 385. PI J.L. Debrun et al., unpublished results.
and Methods
in Physics
FAST ANALYSIS OF OXYGEN ACTIVATION [ 160(d, n)“F] M.F. BARTHE,
A. GIOVAGNOLI,
Research
B45 (1990) 105-106
IN FLUORIDE
GLASSES
G. BLONDIAUX
105
(ZBLAN)
BY CHARGED-PARTICLE
and J.L. DEBRUN
CNRS-CERI, 3A rue de la F&ollerie, 45071 O&am Cedex 2, France
Y. TREGOAT
and J.Y.
BARRAUD
C.G. E. - Laboratoires de Marcoussis, 91460 Marcoussis, France
Oxygen was analyzed in fluoride glasses of the ZBLAN type (ZrF,-BaF,-LaF,-AIF,-NaF). The method is charged-particle Direct gamma-ray spectrometry is performed on the activation with deuterons at 2.8 MeV; the nuclear reaction is 160(d,n)“F. activated samples, after etching to eliminate surface oxygen. The analysis takes - 15 minutes; the sensitivity is - 25 ppm/we& with the present technolo&y c;i which is sufficient considering that the lowest oxygen content in the glass is - 200 ppm/weight, fabrication.
1. Introduction Fluoride glasses are prepared by mixing various fluorides (ZrF,-BaF,-LaF,-AlF,-NaF). These glasses theoretically have very low losses, of the order of 10m3 dB/Km in the infrared, and were proposed for the making of ultra-low loss optical fibers [l-4]. Extrinsic losses are due to absorption by metallic ions and by hydroxyl groups, and to scattering due to bubbles, crystallites or oxides. It has been shown that the higher the total oxygen content, the higher the losses by scattering [5]. At the present state of the technology for the making of glasses and of fibers, it is at least as important to decrease the total oxygen content as to decrease the level of metallic impurities. This implies a nonnegligible number of oxygen. S. Mitachi et al. [5] have proposed a method on the activation of oxygen by protons, following the ‘*O(p, n)‘*F reaction. This method is time-consuming (the l*F half-life is 110 min), limited in sensitivity because of the low abundance of l8O, and requires energies well above 3 MeV because of the high threshold (E,, = 2.6 MeV). High energies are a problem because bigger accelerators are needed and because more power is dissipated in the samples. The fluoride glasses also have a very poor thermal conductivity and can easily break under beam. In this paper, we propose a method which is fast and only requires the use of a small Van de Graaff. 2. Experimental Method. Radioactivation using the 160(d, n)17F reaction. The radionuclide used, 17F, has a half-life of 66 s and is a pure p’ emitter. 0168-583X/90/$03.50 (North-Holland)
0 Elsevier Science Publishers
B.V.
Irradiations. The 3 MV Van de Graaff of the CERI at Orleans was used. The samples are bombarded with 2.8 MeV deuterons for 3 min, with a current of 200 nA. Etching. About 6-8 ym are removed after irradiation to eliminate surface contamination: oxygen is always present at the surface, absorbed or as a constituent of an eventual hydrated layer. The etching solution is HCl 2N + H,BO,. Calibration. Pure alumina is used as a standard. The average cross-section method was used for the calculations [6], although it is accurate to only - lo%, because this method is fast and because very precise results are not needed. Gamma-ray spectrometty. Due to the high oxygen content 17F can be directly detected in the samples in spite of’ nonnegligible activities from Al [ 27A1(d,P)~‘A~, t 1,2 = 2.3 min, E, = 1779 keV] and from F [1gF(d,p)20F, t 1,2 = 11 s, EY = 1633 keV]. 17F being a pure p’ emitter, the 511 keV peak is used for the analysis; samples and standards have similar geometries and are counted in copper boxes for better positron annihilation. The decay of the 511 keV peak is checked in all cases. Results. The experimental sensitivity is - 25 ppm/ weight. It can be improved if needed, but in this case it is not necessary because the lowest concentration ever found in fluoride glasses is - 200 ppm/weigbt. At this level - the overall precision is - 15% analysis is completed in about 15 min. The overall procedure was checked, as in ref. [5], using glasses doped up to - 3500 ppm/weight by addition of ZrO, or of Al,O,. Concentrations in the glasses were found to range from - 200 up to 500 ppm/weight.
I. NRA
106
M.F. Barthe et al. / Fast analysis of 0 in fluoride glasses
3. Conclusion and discussion The analysis of oxygen in fluoride glasses of the ZBLAN type can be done rapidly and with sufficient accuracy and sensitivity using the I6 O(d, n)17F reaction. As the purity of these glasses improves, other methods may be needed, because the present method will not be sufficiently sensitive. Activation will probably remain a method of interest at lower levels, because it is possible to eliminate surface contaminations. Alpha particles and 3He cannot be used because of the nuclear interference of fluorine at all energies. Protons and deuterons do not offer sufficient sensitivity, unless (for protons) a large dose and a high energy are used, resulting in the probable destruction of the samples. The solution then is triton activation. The 160(t, n)**F reaction is selective (E I 4 MeV) and has a high cross section at low energy. For instance, the intrinsic sensitivity is 0.05 ppm/weight at 3 MeV, for
an irradiation of 10 mm at 100 nA 171. This reaction has already been applied with success to analysis of oxygen in fluoride glasses of the type [8]. The drawbacks of using tritons are that these particles are seldom available, and that the use of “F (t,,, = 110 min) necessitates longer analysis times.
References PI D.A. Pinnow et al., Appl Phys. Lett. 33 (1978) 28.
PI L.G. Van Uitert et al., Appl. Phys. Lett. 33 (1978) 57. 131 C.H.L. Goodman, IEEE J. Solid State Electron. Devices 2 (1978) 129.
[41 P.W. France et al., Br. Telecom. Technol, J. 5 (1987) 28. [51 S. Mitachi et al., Jpn. J. Appl. Phys. 24 (1985) 827. 161 E. Ricci et al., Anal. Chem. 37 (1965) 742. [71 H. Valladon et al., J. Radioanal. Chem. 39 (1977) 385. PI J.L. Debrun et al., unpublished results.