Dariusz Malczewski

222Rn and 220Rn emanations as a function of the absorbed α-doses from select metamict minerals

Abstract Metamict minerals contain uranium and thorium, which contribute to physical degradation or metamictization of their crystal structures over geologic time. The damage occurs primarily through progressive overlapping recoil nuclei collision cascades from ɑ-decay of 238U, 232Th, 235U, and their daughter products. We measured 222Rn and 220Rn emanations from metamict samples of nine oxides (brannerite, davidite, fergusonites, pyrochlores, samarskites, and uraninite), two phosphates (monazites), and eight silicates (cerite, gadolinites, perrierite, rinkite, thorite, turkestanite, and vesuvianite). The total absorbed a-doses ranged from 1.4 × 1015 to 6.1 × 1018 a-decay mg-1 for cerite and uraninite, respectively. The 222Rn emanation coefficients varied from 5 × 10-5% (uraninite) to 2.5% (turkestanite). The 220Rn emanation coefficients varied from 7 × 10-3% (gadolinite Ytterby) to 6.2% (gadolinite Marysin). The lowest 222Rn emanation coefficients occurred among metamict minerals containing the highest concentrations of 238U (i.e., uraninite, samarskites, and brannerite). Overall, the 222Rn and 220Rn emanation coefficients observed in this study fall significantly below previously reported values.

Recrystallization in fully metamict gadolinite from Ytterby (Sweden), annealed in air and studied by 57Fe Mössbauer spectroscopy

Abstract 57Fe Mössbauer annealing studies of fully metamict gadolinite from Ytterby (Sweden) have been carried out in air from 373 to 1473 K. The Mössbauer spectrum of the untreated sample, dated at 1795 Ma and absorbed α-dose 1.07 × 1016 α-decay/mg, is characterized by two broad peaks solely from Fe2+ components in octahedral coordinations. The corresponding quadrupole splitting distribution (QSD) shows two distinct maxima at 1.59 and 2.16 mm/s, which reflect the post-metamictization distributions of Fe2+ positions up to heating at 773 K. Changes in the Mössbauer hyperfine parameters are observed only after heating to 873 K, at which point the first Fe3+ component from the oxidation of Fe2+ appears. The relative contribution of Fe3+/ΣFe reaches a maximum of 0.54 at 1073 K and then decreases with increasing temperature. A new Fe3+ doublet is observed in the samples heated from 1173 to 1473 K. This doublet is characterized by extremely high quadrupole splitting ranging from 2.51 to 2.66 mm/s, implying extreme distortion of the coordination octahedra in partially and fully crystalline gadolinite. The transition from metamict to crystalline structure begins at 1133 K where the Mössbauer spectrum is represented by one Fe2+ doublet and one Fe3+ doublet. Both doublets suggest a uniform transitional octahedral site over the whole structure. With increasing annealing temperature, the line widths of the Fe2+ doublet decrease, and, at high temperatures, an asymmetry of the absorption peaks is observed. The sample becomes completely recrystallized after annealing at 1373 K, and at this point the Mössbauer spectra are nearly exact superpositions of the pure Fe2+ and Fe3+ (present in minor proportion) in synthetic gadolinites.

57Fe Mossbauer study of the oxidation state of iron in stilpnomelane from granite pegmatites in Poland

Abstract The effects of heat treatment on stilpnomelane from granite pegmatites at Zółkiewka (Lower Silesia, Poland) were studied using 57Fe Mössbauer spectroscopy. Samples of naturally altered stilpnomelane and chlorite were also studied. The Mössbauer spectrum of an untreated sample was fitted to two Fe2+ doublets and two Fe3+ doublets. The Fe2+ doublets had similar isomer shifts (1.13 and 1.16 mm/s for the octahedral M1 and M2 sites), different quadrupole splitting values (QS = 2.28 and 2.66 mm/s, respectively), and an M1:M2 area ratio of nearly 1:3. For ferric iron, the first doublet was assigned to the combined M1 + M2 + M4 octahedral positions and had IS = 0.41 and QS = 1.18 mm/s. The second doublet was assigned to the M3 site, with parameters IS = 0.36 and QS = 2.07 mm/s. This is characteristic for stilpnomelane. The oxidation of Fe2+ is fast at low temperatures, with a maximum at 360 °C. Near 1050 °C, the stilpnomelane structure broke down completely, and the spectrum consisted of two sextets and two ferric iron doublets. The predominant phase in this new material is hematite, as represented by the two sextets. The abnormally high fractional Fe2+ content in the altered stilpnomelane (0.70) as compared to the untreated sample (0.45) indicates that the sample was subjected to local hydrothermal processes. Nearly identical divalent iron contents and hyperfine parameters for the Fe2+ and Fe3+ doublets (except Fe3+ in M3) in the altered stilpnomelane and associated chlorite strongly suggest that chlorite is transformed into stilpnomelane.

Preliminary results of 57Fe Mössbauer spectroscopy of metamict samarskite after one-hour high temperature annealing in argon

Abstract The preliminary results of 57Fe Mössbauer spectroscopy and X-ray diffraction (XRD) of fully metamict samarskite dated at ~1500 Ma, which absorbed α-dose of 6.5 × 1017 α-decay mg-1, are reported after one-hour annealing at 673, 873, 1173 and 1373 K in argon atmosphere. Metamict minerals contain radioactive elements that degrade their crystal structures over geological time. All the Mössbauer spectra obtained can be fitted to two quadrupole doublets assigned to Fe2+ and Fe3+ in octahedral positions. The relative contribution of Fe2+ (Fe2+/Fe) reaches a minimum of 0.10 at 1173 K.

Identification of iron-bearing minerals in basalts and pillow lavas of the Kaczawa Mountains using 57Fe Mössbauer spectroscopy

Abstract The Kaczawa Mountains along with the Kaczawa foothill comprise a complicated geological unit that is called the Kaczawa metamorphic (Sudetes, SW Poland). The aim of our work was to identify the iron-bearing minerals in samples of basalts and pillow lavas from the Kaczawa metamorphic using 57Fe Mössbauer spectroscopy. Based on the preliminary results, the Fe3+/Fe2+ ratio in the samples was determined.

In situ measurements of natural radioactivity in selected igneous rocks of the Opava Mountain region

Abstract In situ gamma-ray measurements of four igneous rocks were taken in the Opava Mountains (Eastern Sudetes, Poland). The activity of naturally occurring radionuclides was measured using a portable GX3020 gamma-ray spectrometry workstation. The activity concentrations of 40K varied from 914 ± 17 Bqkg-1 (gneiss, Kamienna Góra) to 2019 ± 37 Bqkg-1 (weathered granite, Sławniowice), while those of 232Th from 7.5 ± 0.6 Bqkg-1 (weathered granite, Sławniowice) to 68 ± 0.9 Bqkg-1 (migmatitic gneiss, Nadziejów). The activities associated with 238U decay series ranged from 10 ± 0.4 Bqkg-1 (weathered granite, Sławniowice) to 62 ± 1.6 Bqkg-1 (gneiss, Kamienna Góra). The results will be used in compiling Radiological Atlas of the Sudetes

High Temperature Study of Metamict Rinkite

Metamict minerals contain radioactive elements that degrade their crystal structure. During the annealing process under ambient pressure in argon atmosphere the sample of metamict rinkite recrystallizes to the primary crystalline form at 700°C. Further heating leads to the formation of a new crystalline phase.

High Temperature Study of Metamict Steenstrupine

Metamict minerals contain radioactive elements that degrade their crystal structure. Unlike other metamict minerals, annealing process under ambient pressure do not lead to direct recrystallization of steenstrupine.

57Fe Mössbauer study of one-hour annealing in argon of radiation damage in metamict gadolinite from Ytterby

Gadolinite, REE2FeBe2Si2O10, belongs to the group of metamict minerals. Metamict minerals incorporate uranium and thorium in their structures. Alpha-decays of uranium and thorium series inside the gadolinite structure cause radiation damage of the crystalline lattice and can produce complete metamictization (amorphization) of the crystal. The original structure of metamict minerals can be restored by heating. This paper presents 57Fe Mössbauer studies of fully metamict gadolinite from Ytterby (Sweden) after a one-hour annealing process in argon atmosphere at high temperatures. Changes in the Mössbauer parameters are sensitive indicators of the thermal recrystallization process and revealed two stages of the structural recovery. The first stage from 873 to 1073 K and the second one from 1133 to 1473 K. These observations are confirmed by X-ray diffraction.