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A 119Sn Mössbauer emission study of recoil 119Sb atoms after proton reactions in SnTe
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.-Voltimj 39, numder 2 :
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CHEMICAL PHYSICS kITERS
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-.
‘_
lS.&Yrit 1976
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.. :
:
A ’ “Sn
Mi%SBAUER
EMISSION STUDY OF RECOi
’ “Sb
ATOMS
AFTER PRQTDN REACTIONS IN SnTe
Received 4 December 1975
The energetic recoil lr9Sb atoms produced by proton reactions in SnTe were found to come to rest at both the SR and , Te sites of the matrix.
Following earlier investigations on metals and elementary semiconductors [I ,2] , much attention has been paid recently to Mijssbauer studies of criergetic recoil atoms after nuclear reactions in binary [3,4]. Here we report an extension of our ‘19S~ Mijssbauer emission studies [s-8] to recoil ffgSb atoms produced by proton reactions in semihost matrices
cooled directly with water during irradiation. The irradiated samples gave no indication of melting or degradation in appearence, and their Debye-Scherrer patterns showed no change on irradiation. Fig. La &tows a typical emission spectrum of the irradiated ‘20SnTe obtained at 78 K against aBdSrK$ absorber (0.9 mg “gSnjcm2) of the same tempera-
conducting SnTe. Final positions of the ‘l?Sb atoms in the SnTe lattice were determined from the isomer shift of the 23.8 keV Miissbauer emission lines of their daughter, ’ “Sn, the r&oil energy associated with the EC decay of l19Sb to ‘t9Sn being much
smaller than the dispkicement energy in the solid. For an understanding of the stabilization mechanism of energetic recoil atoms in the solid, this system has the foI!owing advantages: the mass of the recoiting
atoms is very close to that of the component atoms of the matrix and the crystal structure of the matrix is simple (NaGtype cubic lattice). Tin metal depleted in ltySn (12’Sn g&39%, 119Sn 0.39%; referred to hereafter as “‘Sn) was used for the preparation of the SnTe samples to minimize the resonant self-absorption of the MGssbauer y-rays in the sources. Powder samples of .x20SnTe were irradiated under a helium atmosphere with 15 MeV prorons accelerated by the IPCR cyclotron. The main nuclear reaction giving rise to t”Sb is estimated to have been the 12oSn (p.2n) ’ 19Sb reaction_ The current density of protons was about 2 j&/cm’ and the integrated current was approximately 100 mC. The backside of the aluminum plate holding the target powder was 294
g6., -4 Relative
0 Velocity
4 fmm/s vs 5a5n03
at 78K)
F&g_1. lfgSn-MGssbauer (a) emission and (b) absorption spectra of proton-irradiated ~20SnTe versus I%&3103 at 78 K.
Volume 39, number 2
CHEhilCAL PHI! SICS LET’fERS
ture. The absqrption spectrum of the irradiated sam.ple me&red with a Ba’19FSn03 source (both at 78 K) is-given in fig- ib. The curves in fig. 1 are the least-squares fit of the experimental points with lorentzians. Within the sensitivity of measurement the absorption spectra of the irradiated *20SnTe samples (fig. 1b) exhibited no trace of daniage of the matrix by the incident protons; they gave only one absorption line with an isomer shift of 3.52 t 0.05 mm/s (relative to BaSn03) corresponding to normal tin atoms in the Sn site of SnTe in accord with their absorption spectra before irradiation. Therefore, the emission spectra of the irradiated “‘SnTe samples are considered to reflect not the bulk radiation effect of protons on the matrix, but the efGct of nuclear processes leading to ‘19Sn. As may be seen in fig. la, the emission spectra of proton-irradiated 120SnTe are composed of two lines with isomer shifts of 2.28 5 0.05 and 3.47 f 0.05 mm/s. The latter line is directly attributed to 119Sn in the normal lattice site of Sn in SnTe, since the isomer shift is essentially the same as that of the absorption line of the sa’me coinpound (see above). We attribute the former emission line to & isomer shift of 2.28 mm/s with respect to the ’ 19Sn atoms in the Te site of SnTe (possibly accompanied with some near-by defects) rather than to interstitials on the basis of the following reasons: Firstly, it is not expected to be due to interstitials, because the line did not disappear even after annealing for 1 lu at 600°C. Secondly. the isomer shift is in the region of l19Sn with tin atoms in the first coordination sphere as in tin metals (absorption lines) and in SnL”Sb and Sn119m Te (emission lines) [9]. As the recoil energy accompanying the EC decay of ’ 19Sb to IL9Sn is much smaller than the threshold energy for displacement of an atom in the solid [7], the final lattice position of recoil ‘lgSb 51 SnTe should have been the same as that of lL9Sn estimated from the emission spectra. Therefore, we conclude that the recoil llgSb atoms have come to rest at both the Sn and Te sites of the irradiated “OSnTe after the proton reactions.
15 April 1976
.It is interesting to note that the l%b atoms were found after recoil in the two distinct lattice positions and that the isomer shift of 119Sn arising from lLgSb in the Sn site exhibited no significant deviation from that of the corresponding absorption line. The observations show that the SnTe lattice is preserved to a large extent in the vicinity of the ‘19Sb atoms and suggest that in the SnT& matrix the ‘lgSb atoms have come to rest at one of the lattice points with a rather unperturbed environment as the result of a replacement collision. This is in accordance with the conclusion of computer simulations that the most important mechanism of energy dissipation for recoil atoms in a matrix with component atoms of similar mass is replacement collisions by knock-on, the primary energetic atoms not becoming interstitiais [IO,1 11. We thank Professors N. Saito, N.N. Greenwood, and H. Sano for their interest and helpful discussions. We are also thankful to Mr. Y. Iimura for DebyeScherrer measurements, and to the staff of the IPCR cyclotron for proton irradiations.
References [1] G.K. Wertheim, in: The electiopic structure of point defects, eds. S. Amelinckx, R. Gcvers and J. Nihoul (North-Holland, Amsterdam, 1971) p. 1. [2] G. Vogl, J. Phys. (Paris) 35 (1974) C6-165. [3] G. Czjzek and W.G Berger, Phys. Rev. Bl (1970) 957. [4] A. Simopoulos and G. Vogl, Phys. Stat. Sol. 59b (1973) 505. [5] F. Ambe, H. Shoji, S- Ambe, hf. Takeda and N. Saito, Chem. Phys. Letters 14 (1972) 522. [6] F. Ambe and S. Amba, Phys. Letters43A (1973) 399. [7] F. Ambe, S. Ambe, H. Shoji and N. S&o, J. Chem. Phys. 60 (1974) 3773. (81 F. Ambe and S. Ambe, BulI. Chem. Sot- Japan 47 (1974) 2875. [9] F. Ambe and S. Ambe, unpublished data. [lo] C. Er$nsoy, G.H. Vineyard and A. Englert, Phys. Rev. 133A (1964) 595. (111 R.O. Jackson, H.P. Leighly Jr. and D.R. Edwards, Thti. Msg. 25 (1972) 1169.
295
.-Voltimj 39, numder 2 :
.
_-
_-
CHEMICAL PHYSICS kITERS
._
-.
‘_
lS.&Yrit 1976
-
.. :
:
A ’ “Sn
Mi%SBAUER
EMISSION STUDY OF RECOi
’ “Sb
ATOMS
AFTER PRQTDN REACTIONS IN SnTe
Received 4 December 1975
The energetic recoil lr9Sb atoms produced by proton reactions in SnTe were found to come to rest at both the SR and , Te sites of the matrix.
Following earlier investigations on metals and elementary semiconductors [I ,2] , much attention has been paid recently to Mijssbauer studies of criergetic recoil atoms after nuclear reactions in binary [3,4]. Here we report an extension of our ‘19S~ Mijssbauer emission studies [s-8] to recoil ffgSb atoms produced by proton reactions in semihost matrices
cooled directly with water during irradiation. The irradiated samples gave no indication of melting or degradation in appearence, and their Debye-Scherrer patterns showed no change on irradiation. Fig. La &tows a typical emission spectrum of the irradiated ‘20SnTe obtained at 78 K against aBdSrK$ absorber (0.9 mg “gSnjcm2) of the same tempera-
conducting SnTe. Final positions of the ‘l?Sb atoms in the SnTe lattice were determined from the isomer shift of the 23.8 keV Miissbauer emission lines of their daughter, ’ “Sn, the r&oil energy associated with the EC decay of l19Sb to ‘t9Sn being much
smaller than the dispkicement energy in the solid. For an understanding of the stabilization mechanism of energetic recoil atoms in the solid, this system has the foI!owing advantages: the mass of the recoiting
atoms is very close to that of the component atoms of the matrix and the crystal structure of the matrix is simple (NaGtype cubic lattice). Tin metal depleted in ltySn (12’Sn g&39%, 119Sn 0.39%; referred to hereafter as “‘Sn) was used for the preparation of the SnTe samples to minimize the resonant self-absorption of the MGssbauer y-rays in the sources. Powder samples of .x20SnTe were irradiated under a helium atmosphere with 15 MeV prorons accelerated by the IPCR cyclotron. The main nuclear reaction giving rise to t”Sb is estimated to have been the 12oSn (p.2n) ’ 19Sb reaction_ The current density of protons was about 2 j&/cm’ and the integrated current was approximately 100 mC. The backside of the aluminum plate holding the target powder was 294
g6., -4 Relative
0 Velocity
4 fmm/s vs 5a5n03
at 78K)
F&g_1. lfgSn-MGssbauer (a) emission and (b) absorption spectra of proton-irradiated ~20SnTe versus I%&3103 at 78 K.
Volume 39, number 2
CHEhilCAL PHI! SICS LET’fERS
ture. The absqrption spectrum of the irradiated sam.ple me&red with a Ba’19FSn03 source (both at 78 K) is-given in fig- ib. The curves in fig. 1 are the least-squares fit of the experimental points with lorentzians. Within the sensitivity of measurement the absorption spectra of the irradiated *20SnTe samples (fig. 1b) exhibited no trace of daniage of the matrix by the incident protons; they gave only one absorption line with an isomer shift of 3.52 t 0.05 mm/s (relative to BaSn03) corresponding to normal tin atoms in the Sn site of SnTe in accord with their absorption spectra before irradiation. Therefore, the emission spectra of the irradiated “‘SnTe samples are considered to reflect not the bulk radiation effect of protons on the matrix, but the efGct of nuclear processes leading to ‘19Sn. As may be seen in fig. la, the emission spectra of proton-irradiated 120SnTe are composed of two lines with isomer shifts of 2.28 5 0.05 and 3.47 f 0.05 mm/s. The latter line is directly attributed to 119Sn in the normal lattice site of Sn in SnTe, since the isomer shift is essentially the same as that of the absorption line of the sa’me coinpound (see above). We attribute the former emission line to & isomer shift of 2.28 mm/s with respect to the ’ 19Sn atoms in the Te site of SnTe (possibly accompanied with some near-by defects) rather than to interstitials on the basis of the following reasons: Firstly, it is not expected to be due to interstitials, because the line did not disappear even after annealing for 1 lu at 600°C. Secondly. the isomer shift is in the region of l19Sn with tin atoms in the first coordination sphere as in tin metals (absorption lines) and in SnL”Sb and Sn119m Te (emission lines) [9]. As the recoil energy accompanying the EC decay of ’ 19Sb to IL9Sn is much smaller than the threshold energy for displacement of an atom in the solid [7], the final lattice position of recoil ‘lgSb 51 SnTe should have been the same as that of lL9Sn estimated from the emission spectra. Therefore, we conclude that the recoil llgSb atoms have come to rest at both the Sn and Te sites of the irradiated “OSnTe after the proton reactions.
15 April 1976
.It is interesting to note that the l%b atoms were found after recoil in the two distinct lattice positions and that the isomer shift of 119Sn arising from lLgSb in the Sn site exhibited no significant deviation from that of the corresponding absorption line. The observations show that the SnTe lattice is preserved to a large extent in the vicinity of the ‘19Sb atoms and suggest that in the SnT& matrix the ‘lgSb atoms have come to rest at one of the lattice points with a rather unperturbed environment as the result of a replacement collision. This is in accordance with the conclusion of computer simulations that the most important mechanism of energy dissipation for recoil atoms in a matrix with component atoms of similar mass is replacement collisions by knock-on, the primary energetic atoms not becoming interstitiais [IO,1 11. We thank Professors N. Saito, N.N. Greenwood, and H. Sano for their interest and helpful discussions. We are also thankful to Mr. Y. Iimura for DebyeScherrer measurements, and to the staff of the IPCR cyclotron for proton irradiations.
References [1] G.K. Wertheim, in: The electiopic structure of point defects, eds. S. Amelinckx, R. Gcvers and J. Nihoul (North-Holland, Amsterdam, 1971) p. 1. [2] G. Vogl, J. Phys. (Paris) 35 (1974) C6-165. [3] G. Czjzek and W.G Berger, Phys. Rev. Bl (1970) 957. [4] A. Simopoulos and G. Vogl, Phys. Stat. Sol. 59b (1973) 505. [5] F. Ambe, H. Shoji, S- Ambe, hf. Takeda and N. Saito, Chem. Phys. Letters 14 (1972) 522. [6] F. Ambe and S. Amba, Phys. Letters43A (1973) 399. [7] F. Ambe, S. Ambe, H. Shoji and N. S&o, J. Chem. Phys. 60 (1974) 3773. (81 F. Ambe and S. Ambe, BulI. Chem. Sot- Japan 47 (1974) 2875. [9] F. Ambe and S. Ambe, unpublished data. [lo] C. Er$nsoy, G.H. Vineyard and A. Englert, Phys. Rev. 133A (1964) 595. (111 R.O. Jackson, H.P. Leighly Jr. and D.R. Edwards, Thti. Msg. 25 (1972) 1169.
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