Magnetic Properties of Neutron-Irradiated RPV Steel by Mössbauer Spectroscopy

The neutron irradiated reactor pressure vessel (RPV) steels at various doses of 010¹⁸ n/cm² have been studied with Mössbauer, X-ray diffraction, and VSM. The Mössbauer data show that the value of a magnetic hyperfine field of Fe atom that exists at the martensite is 330 kOe at site 1, and 305 kOe, at site 2. At room temperature, the total absorption area of Mössbauer spectra with respect to irradiation of neutron is constant for the dose of 010¹⁶ n/cm², while over the dose of 10¹⁷ cm² the absorption area decreases rapidly. But the doublet area for the dose of 010¹⁶ n/cm² is constant, while over the dose of 10¹⁷ cm² it increases with an increase in the fluence level of neutron. The value of IS and QS at site 1,2 varied slightly with an increase in the fluence level of neutron. However, at a doublet site existing Fe³⁺ state, over the dose of 10¹⁷ cm², the values of IS and QS increase with an increase in the fluence level of neutron. Note that over the dose of 10¹⁷ n/cm² the neutron irradiated sample loses crystal structure slowly. The coercivity and remanence of the neutron irradiated samples do not change significantly. But the maximum induction decreases by 5% at 10¹⁸ n/cm², us compared with that of the as-received sample.     

Ion beam induced phase transformation in Fe–Mn bilayers: a Mössbauer study

Ion‐beam mixing of Fe–Mn bilayers induced by 100 keV krypton ions in the dose range (0.1-15)×10¹⁵ ions/cm²has been studied by means of conversion electron Mössbauer spectroscopy and X‐ray diffraction. The results indicate that a dose of about 1 ×10¹⁵ Kr⁺/cm² is sufficient to induce an appreciable mixing between the two atomic species. The α-Fe(Mn)solid solution presents a maximum at this dose, while at higher doses also the ? and γFe–Mn phases are formed in an appreciable amount. Heating of irradiated samples evidences the metastable character of ? phase and favours the growth of the terminal structures γ-Fe(Mn) and α-Mn(Fe) of the Fe–Mn equilibrium phase diagram.     

237Np and 57Fe Mössbauer study of NpFeGa5

⁵⁷Fe and ²³⁷Np Mössbauer ōmeasurements have been performed for NpFeGa₅, which is one of the so-called neptunium 1-1-5 compounds. The ⁵⁷Fe Mössbauer spectra below T _N = 118 K show the magnetically ordered state. The magnitude of the hyperfine magnetic field at the ⁵⁷Fe nucleus is determined to be 1.98 ± 0.05 T at 10 K. From the ²³⁷Np Mössbauer spectrum at 10 K, the hyperfine magnetic field at the ²³⁷Np nucleus is 203 T and the hyperfine coupling constant is determined to be 237 T/μ_B using the Np atomic magnetic moment of 0.86 μ_B determined by the neutron diffraction study.     

Magnetic structure of ion-implanted bubble garnets

The surface magnetic structure of bubble garnet films implanted with 80 keV Ne⁺ ions has been investigated by conversion-electron Mössbauer spectroscopy in conjunction with backscattered X-ray Mössbauer spectroscopy. For lower doses (～1–3 × 10¹⁴Ne⁺cm^-2) a ferrimagnetic component with in-plane magnetization coexists with a smaller paramagnetic phase in the implanted layer; for a dose of 5 × 10¹⁴Ne⁺cm^-2 only a paramagnetic phase is observed.     

Study of the effect of SHI irradiation on nanocrystalline vacancy doped (La,Sr)(Mn,Fe)O system and its comparison with hydrostatic pressure using Mössbauer spectroscopy

The swift heavy ion irradiated La_0.9Mn_0.8Fe_0.2O₃ (La-deficient) system with 200 Mev Ag^16?+? ion beam at fluence 5 × 10¹² ions/cm² was studied with X-ray diffraction (XRD) and Mössbauer spectroscopic measurements. Comparison of Mössbauer parameters with those of unirradiated sample showed an increase in line width on irradiation which may be due to reduction in particle size as well as due to creation of defects. An increase in quadrupole splitting with no appreciable change in isomer shift showed ion-induced structural disorder in the material after irradiation. An attempt is made to compare the effect of fluence with the hydrostatic pressure on the sample.     

Neutron diffraction and Mössbauer study on FeGa x Cr2−x S4

Ga doped sulphur spinel FeGa _x Cr_2?x S₄ (x = 0.1 and 0.3) have been studied with X-ray, neutron diffraction, and Mössbauer spectroscopy. Rietveld refinement of X-ray, neutron diffraction, and Mössbauer spectroscopy lead to the conclusion that the samples are in inverse spinel type, where most Ga ions are present at octahedral site (B). The neutron diffractions on FeGa _x Cr_2?x S₄ (x = 0.1) above 10 K show long range interaction behaviors and reveal a ferrimagnetic ordering, with the magnetic moment of Fe²⁺(?3.45 μ_B) aligned antiparallel to Cr³⁺ (+2.89 μ_B) at 10 K. Fe ions migrate from the tetrahedral (A) site to the octahedral (B) site with an increase in Ga substitutions. The electric quadrupole splittings of the A and B sites in Mössbauer spectra give direct evidence that Ga ions stimulate an asymmetric charge distribution of Fe ions in the A site.     

Mössbauer study of phase separation in Ni80 57Fe1P19 amorphous alloys

Mössbauer spectroscopy, X-ray diffractometry, scanning calorimetry and electrochemical measurements were used to study the crystallization process of Ni₈₀ ⁵⁷Fe₁P₁₉ amorphous alloys kept in melt at different temperatures before quenching. Samples were heated up to 430°C and 720°C at a rate of 20°C/min, in order to reach characteristically different stages of crystallization. Even at the same crystallization, stage the room temperature Mössbauer spectra and the X-ray differactograms were different depending on the temperature (1050°C or 1400°C) at which the samples were kept before quenching the melt. The Mössbauer spectra showed a paramagnetic component and two sextets (H=267 kOe and H=245 kOe) at 430°C while at 720°C there was only one sextet (H=267 kOe) besides the paramagnetic component. The changes in the Mössbauer spectra of different samples due to crystallization are consistent with the explanation that phase separation occurs in Ni₈₀ ⁵⁷Fe₁P₁₉ rapidly quenched from the melting temperature of 1050°C.     

New mineralogical phases identified by Mössbauer measurements in Morasko meteorite

The 0.9FeTiO₃–0.1Fe₂O₃ solid solution was prepared by solid state reaction with FeTiO₃ and α-Fe₂O₃ powders, and studied by x-ray diffraction, Mössbauer spectroscopy, and vibrating sample magnetometer (VSM). The crystalline structure was found to be single phase rhombohedral structure with lattice constant a?=?5.089 Å and c?=?14.051 Å. Mössbauer spectra of 0.9FeTiO₃–0.1Fe₂O₃ solid solution were taken at various temperatures ranging from 4.5 to 300 K. The anomalous absorption curves at low temperature are observed. Mössbauer spectra at 4.5 K was fitted to four six-line hyperfine pattern with magnetic hyperfine fields H _hf?=?504, 424, 115, and 58 kOe, respectively. At 40 K the spectrum shows the mixture of ferromagnetic six-line pattern and paramagnetic two-line and above 50 K it show asymmetry two-line patterns. The fitted curves at room temperature are obtained by superimposing two doublets corresponding to Fe^2?+ and Fe^3?+. The isomer shift δ and quadrupole splitting ΔE _Q of sample are 0.92 and 0.69 mm/s for Fe^2?+ and 0.14 and ??0.29 mm/s for Fe^3?+, respectively. Corresponding relative absorption subspectral areas are 89.2% for Fe^2?+ and 10.8% for Fe^3?+. Magnetization measurements indicate ferromagnetic behaviour with 92 Oe coercivity value at 50 K but at 300 K it show no hysteresis loop.     

The magnetic hyperfine interaction of iron atoms isolated in a xenon matrix in the presence of an external magnetic field

The Mössbauer effect has been used to measure the magnetic hyperfine interaction of isolated ⁵⁷Fe atoms in solid xenon with an applied external magnetic field. A field dependent Mössbauer absorption spectrum is observed. The ground state of these iron atoms is a triplet, which is split in the external field. The Mössbauer spectrum was analyzed taking into consideration relaxation effects. For an applied external field of 28 kOe an internal magnetic field at the ⁵⁷Fe nucleus of 700± 15 kOe was observed (external field included).     

A cems study of119Sn ion-implanted into Ni

Conversion electron Mössbauer spectroscopy (CEMS) was applied to study the behaviour of¹¹⁹Sn atoms implanted into Ni at the accelerating energy of 100–400KeV and doses of 5×10¹⁵–5×10¹⁶ ions/cm² at room temperature. All CEMS spectra were measured at room temperature and successfully analyzed by two components. The energy and dose dependence of CEMS spectra were well explained by the depth distribution of¹¹⁹Sn atoms.     

Mössbauer studies on ultraporous Fe-Oxide/SiO2 aerogel

Magnetic aerogels with very low volume density of ～0.2 g/cm³ were prepared by sol-gel method and supercritical drying. The resulting materials were monolithic and displayed high surface area. By X-ray diffraction and Mössbauer spectroscopy the crystalline phase formed inside the mesopores of the SiO₂ matrix was identified as a spinel iron oxide. Comparison of the magnetic measurements with Mössbauer spectra at various temperatures contributed to the elucidation of the magnetic state of this nanocomposite system with restricted magnetic interactions, in particular its transition to a superparamagnetic state.     

Mechanosynthesis of nanocrystalline MgFe2O4—neutron diffraction and Mössbauer spectroscopy

The evolution of nanocrystalline n-MgFe₂O₄ by high-energy milling a mixture of MgO and α-Fe₂O₃ for periods of between 0 h and 12 h has been investigated by neutron diffraction in addition to previous Mössbauer, XRD and HRTEM measurements. Complete transformation of the milled products to n-MgFe₂O₄ only occurs on milling to ～8 h even though the average particle size decreases to <?～10 nm after milling for 2 h. The applied field Mössbauer spectra of n-MgFe2O4 can be well described by two subspectra representing core and shell regions with different cation distributions and spin canting angles. The neutron pattern of nanocrystalline MgFe₂O₄ is described well by two components comprising nanoparticles of core and shell dimensions ～7(1) nm and ～0.7(1) nm, respectively, in support of the Mössbauer core-shell model.     

155Gd Mössbauer investigation of the magnetic order and spin-reorientation in Gd3Ag4Sn4

In a recent study of the magnetic order in Gd₃Ag₄Sn₄ by neutron powder diffraction and ¹¹⁹Sn Mössbauer Spectroscopy we showed that both the Gd(2d) and Gd(4e) sublattices order antiferromagnetically at 28.8(2) K. We also demonstrated that the ‘magnetic event’ around 8 K is in fact a ‘plane to axis’ spin-reorientation of the Gd magnetic structure. Here, we extend our study with ¹⁵⁵Gd Mössbauer Spectroscopy. The initial magnetic ordering at 30(2) K is clear for both sites and substantial changes in the hyperfine fields are observed at 8 K when the magnetic structure reorients.     

Mössbauer study of amorphous alloys irradiated with energetic heavy ions

The Mössbauer spectroscopy was applied to study radiation damage in metal-metalloid amorphous alloys irradiated with⁴⁰Ar/E=225 MeV/ or¹³²Xe/E=120 MeV/ ions at room temperature. The observed dose dependent changes in the intensity of the Mössbauer lines and of the hyperfine field distributions can be associated with structural changes in short-range order of the irradiated amorphous alloys.     

Formation of Fe i –B pairs in silicon at high temperatures

We report on the detection of Fe _i –B pairs in heavily B doped silicon using ⁵⁷Fe emission Mössbauer spectroscopy following implantation of radioactive ⁵⁷Mn⁺ parent ions (T _1/2?=?1.5 min) at elevated temperatures >?850 K. The Fe _i –B pairs are formed upon the dissociation of Fe _i –V pairs during the lifetime of the Mössbauer state (T _1/2?=?100 ns). The resulting free interstitial Fe_i diffuses over sufficiently large distances during the lifetime of the Mössbauer state to encounter a substitutional B impurity atom, forming Fe _i –B pairs, which are stable up to ～1,050 K on that time scale.     

Study of plastic deformation and proton irradiation influence on phase transitions in C18N9T stainless steel

Transmission and post-nuclear-reaction emission Mössbauer spectroscopy was used for investigation of radiation effects and plastic deformation influence on C18N9T steel. The rolled foil was annealed in 10^?6 Torr vacuum at 870 K during 2 hours and was irradiated by 30 MeV protons at current density of 0.8μ A up to doses of 5×10¹⁷ cm^?2 on the isochronous cyclotron at the liquid nitrogen cooling of the target. The Mössbauer spectra obtained before and after the sample irradiation in transmission geometry are identical. The emission spectrum is analogous to the spectrum of the plastically deformed sample. It is concluded that during irradiation in the steel the processes take place which are similar to those at plastic deformation and connected with redistribution of the alloy component atoms.     

Magnetic Study of Nanocrystalline Ferrites and the Effect of Swift Heavy Ion Irradiation

100 MeV Si⁺⁷ irradiation induced modifications in the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ nanoparticles have been studied by using X-ray diffraction, Mössbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mössbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mössbauer spectra after ion irradiation. Mössbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles.     

Lattice site location and electronic structure of Te in GaAs

High purity <100> wafers of GaAs were implanted with radioactive^129mTe and stable¹²⁸Te at 110 keV to total doses of 2×10¹⁴ and 2×10¹⁵ Te/cm² respectively and studied with RBS/ channeling and Mössbauer spectroscopy on the 27.8 keV level of¹²⁹I. After implantation and/or annealing at temperatures between 200–300°C the Mössbauer spectra are dominated by a single line. Channeling reveals an appreciable residual damage in the host lattice, but also points to a substitutional position of the Te atoms. After annealing above ≌500°C, where nearly complete lattice damage recovery is obtained, the Te atoms become defect-associated. The results clearly point to the formation of Te_As?V_Ga complexes.     

Investigations of redistribution of iron in a zirconium alloy due to neutron irradiation

Data were obtained with the help of ⁵⁷Fe Mössbauer spectroscopy about the redistribution of iron atoms between intermetallic precipitates and between precipitates and the solid solution phase in E635-type alloy (Zr-1.2 wt% Sn-0.34 wt% Fe-1.0 wt %Nb-0.03–0.05 wt% O) due to neutron irradiation.     

57Fe hyperfine interactions in M1 and M2 sites of olivine from Omolon meteorite: study using Mössbauer spectroscopy

Study of olivine (Fe, Mg)₂SiO₄ from Omolon meteorite was performed using Mössbauer spectroscopy with a high velocity resolution at 295 and 90 K. Components related to ⁵⁷Fe in crystallographically non-equivalent M1 and M2 sites in olivine were determined and its Mössbauer hyperfine parameters were evaluated at both temperatures. A Fe^2?+?–Mg^2?+? distribution coefficient and a temperature of cation equilibrium distribution for olivine from Omolon were evaluated on the basis of Mössbauer parameters.