Due to the virtual photon exchange between atomic nuclei and the field of zero-point electromagnetic oscillations, some nuclei of a given sample are in a virtual excited state with the lifetime ∼ħ/ E , where E is the energy of nuclear level. For 57 Fe nuclei, whose first excited state has an energy of 14.4 keV, this time is equal to ∼4.6×10 −20 s. If a thin 57 Fe Mössbauer gamma-ray absorber is surrounded by a thick screen of the same atoms, the number of virtual excited nuclei in the absorber decreases and, at first glance, it should more strongly absorb Mössbauer gamma rays emitted by an external source and passing through the absorber. In this work, the ratio of the intensities of 14.4-keV gamma rays emitted by the 57 Fe nuclide and passing through the thin resonant absorber is measured in the absence and presence of the resonant screen around the absorber. Comparison shows that these ratios measured for the gamma source at rest and in the oscillating state differ by 0.00123±0.00075. This value should be treated as the upper limit for the desired effect under these experimental conditions.

The aims of the present experiments were direct observation and investigation of the controlled gamma-decay of radioactive nuclei by delayed gamma-gamma coincidence method. In the experiments with gamma-source Co-57 (Fe-57*) and with gamma-absorber made of stable Fe-57 isotope we have discovered the change (increase) of radiative lifetime of excited nucleus (in relation to resonant Mossbauer gamma-channel of decay) by 10-40% and total lifetime (including noncontrolled non-Mossbauer gamma-radiation and noncontrolled electron conversion channels of excited nucleus decay) by 1%.

The local spin configurations of Fe atoms in the magnetically ordered alloys Rh 1− x Fe x ( x =0.1, 0.2, and 0.3) have been investigated by Mössbauer spectroscopy. The Mössbauer absorption spectra are measured in the range from 5 K to temperatures of the transition to the paramagnetic state. The measurements in magnetic fields with a strength up to 5 T are carried out at a temperature of 4.2 K. Analysis of the magnetic-hyperfinefield distribution functions demonstrates that Fe atoms form discrete sets of collinear spin configurations corresponding to different net moments of the nearest coordination sphere. The spin structure of the alloys is governed by a random distribution of Fe atoms over the lattice sites and the competition between the Fe-Rh ferromagnetic exchange interaction and the antiferromagnetic interaction of the neighboring Fe atoms. No spin frustration and spin “melting” effects characteristic of spin glasses are revealed in the Rh-Fe alloys.

The problem of acceleration and long-distance transportation of high-radioactive beams and short-lifetime radioactive nucleus beams is interesting for future beam and nuclear technologies. The method of short-lifetime radioactive nuclei and high-radioactive beams spontaneous decay braking and suppression at long distance transportation and acceleration is the most optimal solution of this problem. The paper discusses the successful experiments on controlling the probability of spontaneous gamma-decay and life-time of radioactive and excited nuclei of several isotopes.

The thermal evolution of the competition between the ferro-and antiferromagnetic exchange interactions in (Fe0.65Ni0.35)1−xMnx alloys, which display different magnetic properties, depending on composition and temperature, is investigated. The distribution functions of the magnetic hyperfine fields P(Bhf) for 57Fe are determined by Mössbauer spectroscopy in the temperature range 5–300 K for the alloys with x=0, 0.024, 0.082, 0.136, 0.195, and 0.252. The temperature dependence of the integrated intensity I s (T) is analyzed for the low-and high-field portions of P(Bhf). The features found in the behavior of I s (T) are interpreted as results of variation of the ratio between the competing exchange interactions of different signs as a result of the thermal destruction of antiferromagnetic Fe-Fe exchange bonds. It is shown that the changes in the spin structure in the low-temperature range are due to the thermal destruction of Fe-Fe exchange bonds. One of the consequences of this destruction is “reentrance” (an increase in the hyperfine field with increasing temperature for some of the Fe atoms). The relationship between the thermal destruction of Fe-Fe exchange bonds and the magnetic transitions of the Fe-Ni-Mn system to the spin-glass state is considered.

The influence of temperature on the distribution function P(Bhf) of the magnetic hyperfine fields for 57Fe in (Fe0.65Ni0.35)1−xMnx alloys (x=0, 0.024, 0.034) are investigated by Mössbauer spectroscopy. The Mössbauer absorption spectra are measured in the temperature interval 5–300 K; in the interval 5–80 K the measurements are performed in a magnetic field of 0.2 T. Anomalies are found in the temperature curves of the intensity of the principal maximum of the functions P(Bhf)[Bhf=30–38 T] and the total (integrated) intensities of the low-field components [Bhf=(4–13) T]. The detected anomalies in the behavior of the total intensities are interpreted as resulting from a change in the balance of competing exchange interactions due to the thermal annihilation of antiferromagnetic Fe-Fe exchange interaction. The emergence of strong satellite lines in the interval Bhf=20–29 T in Mn-doped alloys is attributed to reorientation of the spins of Fe atoms under the influence of strong antiferromagnetic Mn-Fe exchange interaction.

This paper discusses the control process of the radioactive Mössbauer nuclei spontaneous decay probability. The possibility of using this effect in order to produce an optimized gamma-laser is considered. For the first time, the experiment has shown radioactive lifetime doubling for 57Fe nuclei and a general lifetime increase (including conversion and non-Mössbauer decay channels) by 2%.

The magnetic hyperfine fields B(hf) for impurity Sn-119 atoms substituted for Zn in intermetallic compounds RZn (R=Sm, Gd, Tb, Dy and Ho) are measured with the Mossbauer spectroscopy technique. These fields and B(hf) for Sn-119 atoms in rare earth metals from Gd to Ho [5-8] can be represented by the linear B=aS(z)+bL(z) dependence as a function of the spin S(z) and orbital moment L(z) projections. For Sn-119 atoms in rare earth metals and intermetallides of RZn and RAl2 the ratio b/a almost-equal-to -0,1 is found. The ratios B(hf)(R) : B(hf)(RAl2) : B(hf)(RZn) of the B(hf) values for Sn-119 atoms in rare. earth metals from Gd to Ho and intermetallides of RAl2 [3] and RZn are independent of the concrete rare earth element within the accuracy of about 10%. This means that within about the same accuracy the radial dependences of the partial contributions of Gd, Tb. Dy, Ho and, apparently, Sm ions into B(hf) for Sn-119 atoms coincide.

Changes were found in the magnetic structures of NdGa, HoGa, and ErGa at 18-22, 10-22, and 8-16 K respectively. Such changes were sought and examined in RGa intermetallics (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) by investigating the hyperfine interactions for 119 Sn impurity atoms replacing gallium atoms. The Mossbauer absorption spectra measured between 5 K and the Curie temperatures include one magnetic sextet. The magnetic structure changes were established from the observed temperature dependences of the quadrupole shifts of hyperfine structure components

A series of synthetic acicular and natural goethite samples was examined by Mössbauer spectroscopy in the temperature range 5 to 290 K. From the temperature dependence of magnetic moment fluctuations the anisotropy constant has been estimated and the results have been compared with results of the magnetic measurements.

The neutron irradiation influence on Mössbauer spectra of goethite is studied. The results are compared with the data obtained on small particle goethite samples and it is concluded, that the magnetic behaviour of goethite is especially influenced by the particle size.

The EPR, optical and Mossbauer spectra of iron impurity in glasses of composition (mol%) 58ZrF4-6LaF3-32BaF2-4AlF3 (ZL) are investigated. The glasses were doped with FeF3 at concentrations from 0.02 to 0.5 wt%. EPR observations were made at X-band and Q-band frequencies at different temperatures. Optical absorption spectra were measured in the range from 180 to 2500 nm. Mossbauer spectra with a 57Co γ-ray source were obtained at 293, 77 and 4.2 K. It follows from optical and Mossbauer spectra that iron is present in ZL glasses predominantly as Fe2+ ions in octahedral coordination. The presence of Fe3+ ions is supported by EPR spectra. There are presumably two kinds of Fe3+ ions in ZL glasses: one is characterized by D ⩾ hv and the other by D ≪ gβH (where D is the fine-structure constant). However, a single broad distribution of D values for Fe3+ ions in ZL-glasses cannot be excluded.

Semiconducting barium vanadate glasses doped with Fe2O3 ranging from 0.1 to 10 wt% were studied. Electrical DC and AC conductivity measurements, Mössbauer and EPR investigations in the Q-band were made. In addition to this, X-ray diffractograms were obtained with the heat-treated samples. The concentration dependence of DC-conductivity, σ−, exhibits a minimum at 5 wt% Fe2O3; the energy activation, ΔE, increases with increasing Fe2O3 content up to 6–7 wt% and remains unchanged at higher concentrations of Fe2O3; the pre-exponential term, σ0, increases weakly in the range from 0 to 5 wt% Fe2O3 and then increases very rapidly. Inspection of the temperature dependence of the DC-conductivity shows that the effect of Fe2O3 additives on it is considerable at low temperature for small concentrations of Fe2O3 (⩽ 3 wt%) and remains almost unchanged at higher contents of Fe2O3. Above 300 K the plots of log σ− versus 1000/T are linear for all the Fe2O3-doped glasses.

The magnetic hyperfine interaction for 119Sn impurity atoms in the GdMnSi host has been studied by Mossbauer spectroscopy. The hyperfine field for Sn atoms at 5 K is Bhf = (−27.6 ± 0.3) T. The temperature dependences of Bhf and magnetization are practically identical. As follows from the comparison of the results to data for GdCoSi host and an analysis of the satellite structure of the spectrum in Gd0.95Y0.05MnSi host, the contribution to the transferred hyperfine field from 3d moments in GdMnSi vanishes. Both experimental results and obtained empirical function of the radial dependence of the gadolinium contribution to Bhf emphasize the short-range nature of the hyperfine interaction for Sn impurity atoms in Gd-based magnetic alloys. [Russian Text Ignored].