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Radioactive119In+ ions (T1/2=2.1 min) obtained from the ISOLDE facility at CERN have been implanted into silicon single crystals at room temperature. Mössbauer emission spectra from the 24 keV ?-radiation of the daughter119Sn have been measured by fast resonance-counting technique. Five independent lines, characterized by their hyperfine parameters and Debye temperatures, have been found in the spectra. From the bonding configurations, deduced for the Sn impurity atoms, these are concluded to be located in four different defects in the silicon lattice. Simple models are proposed for the defects.

The implantation behaviour of stable119Sn+ ions and radioactive119In+,119mSn+,119Sb+ and119mTe+ ions in SiC has been investigated by, respectively, conversion-electron Mössbauer spectroscopy on the 24 keV transition of119Sn, and by Mössbauer emission spectroscopy on the 24 keVγ radiation emitted by the119Sn daughter after the decays of the radioactive isotopes. The Mössbauer spectra could be decomposed in most cases into two groups of lines, one originating from119Sn atoms on substitutional Si sites, the other from various Sn-vacancy complexes distinguished by their Mössbauer parameters. Annealing experiments reveal a strong dependence of the structure of the defects and the formation and annealing kinetics on the chemical nature of the impurities. Defects formed in 297 K implantations with119mSn and119Sb anneal above 500 ‡C, resulting in a preferential location of the impurities on substitutional Si sites, whereas119mTe atoms are efficient defect-trapping centres and no stable, substitutional fraction is observed on either lattice site. Possible structures for the Sn-vacancy complexes are discussed and comparison is made to similar defect complexes in group IV and in III–V semiconductors.

The internal oxidation of the ion-implanted radioactive precursors119Cd and119Sb to the Mössbauer isotope119Sn in silver has been investigated. The oxidation is monitored by the intensity of a line in the Mössbauer spectra, which is characteristic of SnO2 (δ=(0–0.23)mm/s relative to CaSnO3, ΔEQ ≈ 0.5 mm/s, ϑ ≈ 220 K). This line is attributed to an internal oxidation of the implanted impurities by interstitially diffusing oxygen pairs. The formation and annealing kinetics of the impurity-oxygen complexes are interpreted in terms of the diffusion coefficients of oxygen and the sp-impurities in silver, respectively, and the reactivity between them. Comparison is made to Mössbauer experiments on SnAg alloys and to PAC measurements on111cd in silver.

The valence-electron configuration of substitutional Sn-donor and acceptor impurities in III–V compound semiconductors has been studied by Mössbauer spectroscopy on the 24-keV γ radiation of 119Sn. The Sn dopants have been implanted site-selectivity on the two inequivalent lattice sites. The isomer shift of the Mössbauer γ radiation has been determined. The Sn electronic configuration is found to depend on the dehybridization of the covalent bonds with increasing bond length and on the fractional ionicity fiof the host bonds. For materials with fi≲ 0,3 no influence of ionicity is indicated and the Sn-donor and acceptor states have the same basic valence-electron configuration (Sn°) as in a homopolar semiconductor of equivalent bond length. For materials with higher ionicities, positive and negative charges are accumulated on the Sn atoms for donor and acceptor states, respectively.

The kinetic V/K isotope effect upon peroxidation of (1R)-[1-2H1]ethanol by liver catalase was studied by using a radiochemical assay with both 3H ad 14C as tracers. The value of 1.9 found is in agreement with the value of 2.52 for peroxidation of (1R)-[1-3H1]ethanol according to the ‘Swain equation’ [Swain, Stivers, Ruver & Schaad (1958) J. Am. Chem. Soc. 80, 5885-5893]. There was no isotope effect on V, the catalase haem up to 500 min-1. Even at rates 20-fold higher the isotope effect on V may not be different from 1. A detailed description of the synthesis of the 2H- and 3H-substituted ethanol compounds and the analysis of these has been deposited as Supplementary Publication SUP 50110 (5 pages) at the British Library Lending Division, Boston Spa, Wetherby, W. Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978) 169,5.

1. Simultaneous determination of the rate of appearance of 3H in water from [(1R)-1-3H1] ethanol and the rate of acetaldehyde formation in the presence of rat or ox liver catalase under conditions of steady-state generation of H2O2 allowed calculation of the 3H isotope effect. The mean value of 2.52 obtained for rat liver catalase at 37 degrees C and pH 6.3-7.7 was independent of both ethanol concentration and the rate of H2O2 generation over a wide range. At 25 degrees C a slightly lower mean value of 2.40 was obtained with the ox liver catalase. 2. Neither the product, acetaldehyde, nor 4-methylpyrazole influenced the two rates measured in the assay. 3. Relating the value obtained for the 3H isotope effect to a known value for the 2H isotope effect strongly supports the view that both values are close to the true isotope effect with the respective substituted compounds on the rate constant in the catalytic step involving scission of the C-H bond. 4. The constancy of the isotope effect under various conditions makes it possible to use it for interpretations in vivo. 5. It was established that beta-D-galactose dehydrogenase exhibits B-specificity towards the nicotinamide ring in NAD.