Initial studies of the gamma resonance of the <Superscript>109<Emphasis Type="Italic">m</Emphasis></Superscript>Ag isomer with a gravitational gamma spectrometer

The problem of observing the Mössbauer resonance absorption of gamma rays from long-lived isomers is briefly outlined, first and foremost for ^109m Ag taken as an example. Experiments indicative of a small broadening of the Mössbauer gamma line of this isomer in metallic silver are described. This circumstance made it possible to develop and manufacture a gravitational gamma spectrometer and to perform the first experiments with it, which confirm once again the previous data on a small width of the gamma line in question. The broadening factor obtained from these data proved to be 6.3 _?1.9 ^+5.2 .     

The Gamma Resonance Problem of Long-Lived Nuclear Isomers

A review is given of the studies relating to the problem of γ-resonant (Mössbauer) excitation of long-lived nuclear isomers. The theoretical estimates of possible γ-line broadening are presented. Earlier experiments are described with ^107mAg and ^109mAg isomers using polycrystalline samples of pure Ag and Ag-Pd alloys. The results of these experiments did not contradict the theoretical predictions. The series of papers using Ag single-crystal γ-sources is reviewed. Their results were interpreted as indications of a rather small ^109mAg γ-line broadening, which cannot be explained by modern theory. The results of the last experiments by ITEP group with ^109mAg are also presented. These data may be coordinated with results of other research, if one takes into account the Zeeman splitting of the γ-spectra by Earth's magnetic field.     

Small broadening of the Mössbauer gamma line of the isomer <Superscript>109<Emphasis Type="Italic">m</Emphasis></Superscript>Ag as yet another indication of the protracted character of the emission of photons from nuclei and their absorption

Nine experiments performed to date by three research groups in order to observe the Mössbauer effect in the case of gamma rays emitted by the long-lived isomer ^109m Ag yielded results suggesting an anomalously small broadening of the Mössbauer gamma line of this isomer. In turn, this indicates that the emission of photons from nuclei and their resonance absorption cannot proceed within a time interval much shorter than the characteristic time of the change in the energy of hyperfine dipole—dipole interaction, because the photon energy would otherwise be determined by the sum of the instantaneous value of the energy of this interaction and the nuclear-transition energy, in which case the broadening of the Mössbauer gamma line would reach five to six orders of magnitude, as opposed to one to two orders of magnitude broadening observed experimentally.     

First experiments on the observation of gamma resonance of a long-lived <Superscript>109<Emphasis Type="Italic">m</Emphasis></Superscript>Ag isomer using a gravitational gamma spectrometer

The first measurements of the resonant Mössbauer self-absorption of the long-lived ^109m Ag isomer gamma rays as a function of the declination angle of the gamma beams from the horizontal direction are presented for a gamma source that represents a single-crystal silver plate doped with a parent ¹⁰⁹Cd nuclide. The resonant absorption is manifested as a minimum of the counting rate ratio of the ^109m Ag and ²⁴¹Am (control gamma source) gamma-line intensities at a zero-declination angle for one of two detectors and an angle of about 1° for another detector. The magnitude of the effect is in agreement with the results of our previous experiments performed on another setup. It follows, from the data obtained, that the angular width of the gamma-resonance profile is less than two degrees, which corresponds to a broadening factor of the Mössbauer gamma line of less than five. The value of this factor calculated from the measured relative magnitude of the ^109m Ag gamma-ray resonant absorption is 6.3 _?1.9 ^+5.2 .     

Observation of the gamma resonance of a long-lived <Superscript>109<Emphasis Type="Italic">m</Emphasis></Superscript>Ag isomer using a gravitational gamma-ray spectrometer

Experiments confirming the previous data on the small real width of the γ resonance of ^109m Ag have been performed with a gravitational gamma-ray spectrometer. The achieved resolution is eight orders of magnitude higher than that of Mössbauer spectrometers using gamma rays from a ⁵⁷Fe nuclide. The theoretically predicted broadening of the Mössbauer gamma line of ^109m Ag by five orders of magnitude (due to the dipole-dipole interaction between the magnetic moments of neighboring nuclei) has not been observed.     

Inhomogeneous and homogeneous broadening effects onnuclear resonance experiments

Inhomogeneous broadening of resonance lines causes a reduction of absorption in nuclear resonance experiments. This is particularly devastating to the observation of the Mössbauer effect in isomers like ¹⁰⁷Ag with a half-life of 44s.It has been suggested in the literature that homogeneous broadening can provide overlap of resonance lines and thus theMössbauer effect can be recovered. The analysis presented in this paper shows that this is not the case for Mössbauer experiments, unless the radiative width Γ_Γ also increases. Although overlap occurs when the lines are homogeneously broadened to a total width Γ_{_}H which exceeds the natural width Γ, and the inhomogeneous width Δ, the Mössbauer absorption remains low because it is proportional to the factor of Γ_γ/Γ _H.     

Status of the search for the Mössbauer effect in109Ag

Our search for the Mössbauer Effect in¹⁰⁹Ag using the self-absorption method is summarized. Measurements have been made using two different¹⁰⁹Cd-doped single-crystal silver samples. In our method the silver K_α and K_δ x rays, as well as, the 88-keV γ rays are considered. The results are analyzed using the ratio of the number of x-ray to γ-ray counts. A positive effect is observed.     

Internal oxidation of sp-Impurities in silver studied by119Sn Mössbauer spectroscopy

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, ? ≈ 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 Mössbauer effect in109Ag revisited

The 40-sec, 88-keV, first-excited state of¹⁰⁹Ag provides a difficult case for the observation of the Mössbauer effect. The major difficulty is associated with the long lifetime which corresponds to a natural linewidth of only 10^?17 eV. Our results indicate a 0.2% Mössbauer effect.     

Transient Mössbauer spectroscopy with57Fe

Transient Mössbauer experiments with⁵⁷Fe are described. A time resolution of 0.7 ns is achieved with a BaF₂ scintillator. Polar polyvinylidene fluoride film is shown to be well suited for producing fast mechanical modulation. Pulses of recoilless gamma radiation, of width ≈30 ns and heigth 3.5 times the Mössbauer absorption, are generated with stepwise source motion. The efficiency of transient methods in extracting Mössbauer data is demonstrated with sinusoidal motion.     

Mössbauer antineutrinos: Recoilless resonant emission and absorption of electron antineutrinos

Basic questions concerning phononless resonant capture of monoenergetic electron antineutrinos (Mössbauer antineutrinos) emitted in bound-state β-decay in the ³H-³He system are discussed. It is shown that lattice expansion and contraction after the transformation of the nucleus will drastically reduce the probability of phononless transitions and that various solid-state effects will cause large line broadening. As a possible alternative, the rare-earth system ¹⁶³Ho-¹⁶³Dy is favoured. Mössbauer-antineutrino experiments could be used to gain new and deep insights into several basic problems in neutrino physics.     

Experimental observation of vibrations produced by pulsed laser beam in MgO:57Fe

We report the first observation of a laser-produced vibration with the aid of Mössbauer techniques. Thin platelets of MgO single crystals were doped by diffusion of ⁵⁷Fe atoms. The illumination of the MgO:⁵⁷Fe sample with a pulsed Nd:YAG laser produced a significant broadening of the Mössbauer spectrum. In order to find out what caused these changes, we performed a series of time-domain experiments, in which the Mössbauer spectra were collected only during a 2.5 μs gate interval. This gate interval was swept from 5 μs to 190 μs over the time interval between the two laser pulses. After laser irradiation, the position of the Mössbauer line was found to be changing in time as a decaying oscillations of well-defined frequency, which can be due to the vibration of the sample induced by the laser pulse.     

67Zn Mössbauer spectroscopy

Investigations on⁶⁷Zn Mössbauer spectroscopy are reviewed In the theoretical part, mainly phenomena to be observed due to the long nuclear lifetime of the Mössbauer state are discussed. Such phenomena include e. g. transient effects due to the phase modulation, the exceptionally large relative contribution of the second order Doppler shift and the narrowest line width observable today. Finally, a historical review of the⁶⁷Zn Mössbauer measurements is presented. Results of the experimental investigations of various research groups are given in chronological order.     

An ESCA study of Sn organometallic compounds: Solid state broadening effects

X-ray photoelectron spectra have been recorded for a number of solid and gaseous organotin compounds. Solid-state charging effects (such as differential charge broadening) can be large, though we have almost eliminated them by subliming very thin films onto platinum metal. In this way, we have obtained solid-state Sn 3d line widths that are within 10% of the analogous gas-phase values. The quality and reproducibility of the solid-state spectra likewise approach those of gases.The general correlation between ESCA Sn 3d line widths and Mössbauer quadrupole splittings indicates that the broadening of the Sn 3d lines is due to crystal-field splitting from the C₂⁰ term (the quadrupole term) in the crystal-field expansion. There is a general correlation between ESCA binding energies and Mössbauer isomer shifts for the solids.     

Experimental test of the theory of effect of natural strong narrowing of Mössbauer lines and a more general effect of collapse of the hyperfine structure because of fluctuations of the Fermi contact field. Role of virtual transitions in these effects

To test the theory of the effect of natural strong narrowing (NSN) of Mössbauer lines on long-lived isomers and a more general effect of collapse of the hyperfine structure (CHFS) because of fluctuations of the Fermi contact field (S.V. Karyagin, JETP Lett. 98, 174 (2013)) with the use of the data obtained by the team led by Davydov (Yu.D. Bayukov et al., JETP Lett. 90, 499 (2009)), the yield of 88.034-keV gamma-ray photons from a silver plate with the ^109m Ag isomer has been analyzed in two variants: (i) the hyperfine structure is resolved and the yield depends on the angle ψ between the wave vector of the photon and the external field H _ex, and (ii) the yield is independent of ψ because of CHFS. It has been shown that variant (ii) better reproduces the experimental data: experimental average count numbers at ψ = 0 and ～π/2 differ from each other only in systematic error the same at 4.2 and 295 K and, moreover, the count numbers with the exclusion of resonance should be independent of ψ; this condition is strongly violated in variant (i) and is well satisfied in variant (ii). The threshold condition of the CHFS for the Fermi field has been obtained with allowance for virtual transitions. The collapse of the hyperfine structure is possible at any lifetimes of nuclear levels at any transitions not only in the gamma range but also in other radiation ranges. It results in the complete depolarization of nuclei and radiation. To estimate the Fermi field from experiments, the field |H _ex| ～ 10⁴ G is necessary.     

Generation of long-lived isomeric states via bremsstrahlung irradiation

A method to generate long-lived isomeric states effectively for Mössbauer applications is reported. We demonstrate that this method is better and easier to provide highly sensitive Mössbauer effect of long-lived isomers (>1 ms) such as ¹⁰³Rh. Excitation of (γ,γ) process by synchrotron radiation is painful due mainly to their limited linewidth. Instead, (γ,γ’) process of bremsstrahlung excitation is applied to create these long-lived isomers. Isomers of ⁴⁵Sc, ¹⁰⁷Ag, ¹⁰⁹Ag, and ¹⁰³Rh have been generated from this method. Among them, ¹⁰³Rh is the only one that we have obtained the gravitational effect at room temperature.     

Space-time analysis of the Mössbauer radiation scattering

Microscopic theory of the Mössbauer effect is formulated. Nuclei interactions with local magnetic fields and lattice vibrations are taken into account. The analysis is based on the precisely solvable quantum mechanical model of Mössbauer scattering. The process of Mössbauer photon emission and its subsequent scattering on one and two nuclei are analyzed in detail. It is shown that some phenomenological concepts proposed for explanation of fine experiments with 109 Ag nuclei do not obtain microscopic justification.     

Features of the radioactive decay of Mössbauer isotopes in the presence of an intrinsic gamma-radiation field

A limit for the concentration of radioactive nuclei (3 × 10¹⁴ 1/cm³) of the Mössbauer emitters ^119m Sn and ^125m Te below which the earlier demonstrated effect of the collective nuclear decay vanishes is experimentally found in the framework of a study aimed at the control of the decay of nuclear levels. A general theoretical concept of the phenomenon is presented. Based on this concept, the parameters of the nonexponential decay are numerically estimated. The notion of the width of the Mössbauer γ photon is introduced.     

Diffusion of Fe in iron tellurides by Mössbauer spectroscopy

The diffusional line broadening of the Mössbauer spectra of iron in β-, δ^′- and ε-phases of iron telluride was studied in the temperature range from 573 to 1023 K. The jump frequencies in the β- and δ^′-phases calculated from Mössbauer line broadening were 1.6×10⁸ and 4.7×10⁶ s^?1 at the temperature of 90% of each peritectic point, respectively. The jump frequency in the ε-phase was too small to measure even at 873 K near the peritectic point being less than 2×10⁶ s^?1. These data indicate that the jump frequency is likely to be dependent on the distance between the iron atom and the nearest neighboring sites.     

Celtic gold coins in the light of Mössbauer spectroscopy, electron microprobe analysis and X-ray diffraction

Celtic gold coins found in Southern Germany were studied by Mössbauer spectroscopy, electron microprobe analysis and X-ray diffraction with special attention to coins rich in silver and copper. In such coins the electron microprobe analyses reveal a gold enrichment in a surface layer of more than 100 μm thickness. ¹⁹⁷Au conversion electron Mössbauer spectroscopy also shows that the surface of the coins consists of two phases, one of which is strongly enriched in gold compared to the bulk composition. In comparison with laboratory experiments the observed phenomena suggest that coin production in Celtic times may have involved deliberate heating and etching steps to enrich the surface layer in gold by depleting it of silver and copper.