Line width of single-crystal Mössbauer absorption

The Mössbauer line broadening method for the determination of Lamb–Mössbauer factors f_LM cannot be applied directly in the determination of the probability of the resonant absorption f_LM for single-crystalline absorbers with quadrupole splitted Mössbauer spectra. The line width Γ_exp for single crystals with quadrupole splitted Mössbauer spectra has been computed for various absorber thicknesses. The polarization effects are important and have been taken into account. The linear dependence has been adapted for Lamb–Mössbauer factor measurements by introducing a polarization-dependent coefficient. This method has been tested on measurements of guanidinium nitroprusside (GNP) (CN₃H₆)₂[Fe(CN)₅NO] single crystals.     

Depth distribution of martensite in xenon-implanted stainless steels

The amount of stress-induced martensite and its distribution in depth in xenon-implanted austenitic stainless-steel poly- and single crystals have been measured by Rutherford backscattering and channeling analysis, depth-selective conversion-electron Mössbauer spectroscopy, cross-sectional transmission electron microscopy and X-ray diffraction analysis. In low-nickel 17/7, 304 and 316 commercial stainless steels and in 17:13 single crystals the martensitic transformation starts at the surface and develops towards greater depth with increasing xenon fluence. The implanted layer is nearly completely transformed, and the interface between martensite and austenite is rather sharp and well defined. In high-nickel 310 commercial stainless steel and 19:15 and 19:20 single crystals, on the other hand, only insignificant amounts of martensite are observed.     

Sn Mössbauer spectroscopy investigation of heavily P-doped silicon

Utilizing radioactive ^119mSn probe atoms in isoconcentration P-doped silicon, by ¹¹⁹Sn Mössbauer emission spectroscopy the formation of probe atom-vacancy complexes is observed as a function of rapid thermal annealing temperature and doping level. The results are discussed within the framework of a previously proposed model.     

Iron-implanted sintered alumina studied by RBS, CEMS AND SEM techniques

Sintered plates of alumina have been implanted at room temperature with 1.2 × 10^{17 57}Fe⁺/cm² at 110 keV. Rutherford backscattering spectrometry and conversion electron Mössbauer spectrometry have been used to characterize respectively the depth distribution and charge states of iron. A theoretical approach of the as-implanted iron profile has been carried out by using a modified TRIM code which takes into account the fluence, the sputtering effects and the modification of the surface composition during ion bombardment. The iron profile and charge-state evolutions after isochronal air annealings from 200° C to 1600° C have been investigated. Correlations with the surface topography evolution investigated by SEM are proposed.     

Study of the trapping of Co---Fe impurities at the internal wall of nanosized Si voids

The trapping of transition metal impurities to cavities in c-Si recently attracted much interest, stemming from the possibility to use the process for proximity gettering. Mössbauer spectroscopy is employed on ion-implanted ⁵⁷Co/⁵⁷Fe to elucidate the nature of the site of the impurity atom at the internal surface of the voids. We observe a trapping effect upon thermal treatment, hampering normal silicide formation. Also a pre-existing silicide phase can be partially dissolved in favour of cavity trapping. The binding energy for cavity trapping is found to be lower than for silicide formation.     

Mössbauer investigations of palygorskite from Xuyi, China

The original palygorskite clay mineral has been collected from Longwangshan, Xuyi, Jiangsu Province, China. XRF analysis was performed to study its chemical compositions. Thermogravimetric analysis and differential thermogravimetric analysis (TGA/DTA) were used to study the weight loss due to dehydration and dehydroxylation. Then eight samples were prepared by heating at various temperatures. X-ray diffraction (XRD) patterns and Mössbauer spectra were measured to study the crystal evolvement and the occupation of iron cations. It revealed that the iron ions occupied the M1 and M2 with the ratio closed to 3:1. Hematite has been observed when heated at 650 °C, which indicated that iron cations mainly occupy M1 sites. An unknown silicate was identified when heated at 750 °C and dominated at 850 °C.     

Magnetic ordering in superconducting YBa2(Cu1−xFex)3Oy oxide

Magnetic susceptibility measurement and the zero-field muon-spin-relaxation experiment have been made for the YBa₂(Cu_1−xFe_x)₃O_y system. The susceptibility has been measured in the field strong enough for the magnetic flux to penetrate the superconductor and the resultant temperature dependence has demonstrated the field cooled effect and a cusp at low temperatures below T_c. The cusp has been observed when the high field has been applied. The dynamical depolarization rate of the muon obtained by the muon-spin-relaxation experiment has shown the maximum at the same temperature as the cusp. The results suggest that the spin glass freezing of localized magnetic moment takes place at the temperature of the cusp, which is consistent with the previous Mössbauer effect experiments. The magnetic phase diagram for the system has been obtained.     

Non-equilibrium intragrain concentration redistribution of the alloying elements in austenitic steels under irradiation

Radiation-induced and thermally activated decomposition of austenitic 16Cr15Ni3Mo1Ti, 32Ni, 34Ni steels at high temperature (500–650°C) were examined. High doses (up to 10–200 dpa ) in 16Cr15Ni3Mo1Ti stainless steel with 1.5 MeV Kr ions and 450 keV Fe ions at 550–650°C lead to the appearance of relatively large regions (up to 200–400 nm) of concentration-oscillations with ‘mosaic’ dark–white diffraction contrast in TEM images. The radiation-induced redistribution of alloying elements takes place thanks to inverse Kirkendall effect and, in particular, removal of Cr to cell volume from boundaries of coarse cellular structure. The competing formation of ultrafine subgrains and grains 10–50 nm in size structure in Ti-free steel (16Cr15Ni3Mo) impedes the development of large ingrain segregations. The Mössbauer investigations showed that the 32Ni and 34Ni steels with purposefully produced concentration-oscillations were fully homogenised in that high-temperature region. This fact indicated the absence of the thermal decomposition dome in the Fe–Ni equilibrium diagram.     

Study of radiation-induced degradation of RPV steels and model alloys by positron annihilation and Mössbauer spectroscopy

The influence of different microstructural processes on the degradation due to radiation embrittlement has studied by positron annihilation and Mössbauer spectroscopy. The materials studied consisted of WWER-440 base (15Kh2MFA) and weld (10KhMFT) RPV steels which were neutron-irradiated at fluence levels of 0.78 × 10²⁴ m⁻², 1.47 × 10²⁴ m⁻² and 2.54 × 10²⁴ m⁻²; WWER-1000 base (15Kh2NMFAA) and weld (12Kh2N2MAA) irradiated at a fluence level 1.12 × 10²⁴ m⁻²; three different model alloys implanted with protons at two dose levels (up to 0.026 dpa), finally the base metal of WWER-1000 (15Kh2NMFAA) was thermally treated with the intention to simulate the P-segregation process. It has been shown possible to correlate the values of parameters obtained by such techniques and data of mechanical testing (ductile-to-brittle transition temperature and upper shelf energy).     

On the validity of 57Fe hyperfine field distribution calculations from Mössbauer spectra of magnetic amorphous alloys

The approximations which are made in ⁵⁷Fe hyperfine field distribution calculations from magnetic amorphous alloys are discussed. A diagram which gives an immediate indication of the validity of a given hyperfine field distribution obtained using first order perturbation theory is proposed. The assumption about the distribution of the polar angles of the hyperfine field direction with respect to the EFG principal axes in transition metal-metalloid amorphous alloys is discussed. The asymmetries of the Mössbauer spectra of the latter alloys are also considered.     

Cold moving mice: A microfoil internal conversion electron detector for low and intermediate energy Mössbauer transitions

A microfoil internal conversion electron (MICE) detector is described which permits direct Doppler shifting of resonance radiation up to velocities of ± 20 cm/s, and gives large improvements in signal-to-background ratios for many Mössbauer isotopes, when compared with transmission geometry. The detector described has efficiency of nearly unity, and it allows for cooling the reciprocating microfoil module to 100 K, which improves signal-to-background substantially over room temperature operation. We give an analysis of the signal-to-background that can be expected for this MICE detector, and for a corresponding transmission experiment. In a table of neutron produced isotopes we find more than 10 cases which are favorable to the MICE approach as compared with the more conventional transmission geometry. The signal-to-background enhancement predicted for several Mössbauer isotopes is substantial for the MICE geometry compared to transmission geometry. Direct measurements of the Mössbauer conversion electron spectrum for the 46.5 and 99.1 keV transitions of ¹⁸³W and the 100.1 keV transition in ¹⁸²W are reported and compared with our analysis. In the case of ¹⁸³W (46.5 keV) we observe over 500% signal-to-background, and this experimental result agrees well with our analysis of the expected size of the effect. Satisfactory agreement is also found for the 99.1 keV ¹⁸³W and 100.1 keV ¹⁸²W spectra. Based on the analysis given it is possible to determine nuclear resonance cross sections and thereby infer internal conversion coefficients for the resonance transitions. Thus, we are able to determine the internal conversion coefficient for the 46.5 keV transition in ¹⁸³W to be α = 13 ± 3.     

Improving the validity of Mössbauer hyperfine parameter distributions: The maximum entropy formalism and its applications

The maximum entropy principle from information theory is applied to the problem of determining hyperfine distributions from Mössbauer spectra. This method is compared to the usual matrix method and it is shown that the smoothing parameter of the latter can be avoided. The method is applied to several simulated spectra calculated from model distributions, and to an experimental spectrum showing a spin density wave (or Overhauser) distribution. It is shown that the maximum entropy method can lead to a more model-independent determination of the distribution. It is especially useful in cases where the hyperfine distribution contains a sharp maximum.     

A method for improving the depth selectivity of conversion-electron Mössbauer spectroscopy

The possibility of improving the depth selectivity of conversion-electron Mössbauer spectroscopy by mathematical processing of the initial experimental results is demonstrated. The method constructs Mössbauer spectra for electrons from a thin layer of matter localized at an arbitrarily chosen depth of a specimen by a linear combination of the initial Mössbauer spectra. It is shown that the method allows to a higher depth resolution to be obtained than by conventional instrumentational method.     

A method for improving the surface selectivity of resonance electron Mössbauer spectroscopy with a proportional counter

The surface selectivity of resonance electron Mössbauer spectroscopy with a proportional counter can be improved by detecting sum signals of K-conversion and K-Auger electrons. The probing depth is estimated from the range of K-Auger electrons to be approximately 120 nm in the case of ⁵⁷Fe Mössbauer measurements. Furthermore, depth-selective Mössbauer spectroscopy (DSMS) for two layers becomes possible by observing the above mentioned spectrum and the conventional resonance electron Mössbauer spectrum, the probing depths of which are 120 nm and 300 nm, respectively. In order to record several Mössbauer spectra simultaneously, as in the case of the DSMS, we used a microcomputer equipped with interface circuits.     

Comparison of the oxyhemoglobin deoxygenation and radiolysis by γ-rays and electrons: Study by Mössbauer spectroscopy

Mössbauer spectroscopy was applied for analysis of the iron containing species resulting from oxyhemoglobin irradiation by γ-rays and electrons with different energies and doses. The results obtained showed the different effects of various types of radiation. The oxyhemoglobin deoxygenation was common for all studied cases while protein destruction was realized in different ways. A comparison of oxyhemoglobin deoxygenation and destruction on the basis of Mössbauer study was made and possible pathways of oxyhemoglobin radiolysis were proposed.     

A high quality source for iodine Mössbauer spectroscopy

Iodine Mössbauer-effect sources in the form of Mg₃TeO₆ and Ca₃TeO₆ were developed. Due to the unusual solid state properties of these crystals and the high coordination symmetry of Te in their matrices, it is possible to obtain single and narrow emission lines with a recoilless fraction at room temperature of 0.55, ten times larger than that of the conventional Zn and Sn telluride sources. The compounds can be prepared and repeatedly irradiated without any perceivable radiation damage and with negligible residual activity from the other constituent elements. This allows for the first time the use of ¹²⁹I Mössbauer spectroscopy at room temperature and significantly improves the performance of ¹²⁷I at low temperatures. It is suggested to adopt the Mg₃TeO₆ as a standard iodine Mössbauer source.     

The micro structural study of 15Kh2MFA and 15Kh2NMFA reactor pressure vessel steels using positron-annihilation spectroscopy, mössbauer spectroscopy and transmission electron microscopy

The micro structure of the non-irradiated low-alloyed steels (15Kh2MFA and 15Kh2NMFA) was studied using different spectroscopic methods as the positron annihilation lifetime and Doppler broadening techniques, the Mössbauer spectroscopy, and the Integral low-energy electron Mössbauer spectroscopy as well as the Transmission electron microscopy. Differences in the microstructural parameters of these types of RPV steels are well detectable using all methods. It was confirmed that the heat-affected zone of these steels is the most sensitive place for thermal embrittlement in the reactor. Positron-annihilation lifetime measurements on the successive annealed specimens (XTA, YTA), which simulated the heat-affected zone, showed the rapid increase in the vacancy-type defects formation in the temperature region 525–600°C. Therefore these specimens were studied using Transmission electron microscopy in more detail.     

Channel electron multiplier detector for conversion electron Mössbauer spectroscopy at temperatures between 4 and 300 K

A technique is presented for measuring conversion electron Mössbauer spectra at temperatures between 4 K and 300 K, using a cryogenic channel electron multiplier detector in combination with a continuous-flow helium cryostat. The described setup is characterized by a very high signal-to-noise ratio. In particular, for ¹¹⁹Sn, a resonant effect of up to 2000% was measured, likely the largest ever observed in Mössbauer spectroscopy. Other advantages are top-loading capability, easy sample access, high cooling rate, capability of simultaneous Mössbauer transmission measurements, and adaptability to on-line experiments. Some observations of the performance of channel electron multipliers at low temperatures are also described. The setup presented in this work can be used both for CEMS measurements as a function of temperature and as a highly efficient resonant detector for measurements with weak Mössbauer sources or for detecting weak resonant signals.     

Analysis of a Mössbauer spectrum with the help of derivatives with respect to Doppler velocity

A new method for analyzing a Mössbauer spectrum is proposed, which is faster and more stable than the conventional method for the analysis.