Electron paramagnetic resonance of Sc3+-stabilized CO 3 3− molecule-ion in natural calcite

Electron paramagnetic resonance (EPR) spectra of CO ₃ ^3– molecule-ions stabilized by Sc³⁺ in natural calcite were identified and studied at X-band frequencies and room temperature. The principal values of the g-tensor (g _xx= 1.9997, g _yy = 2.0030, g _zz = 1.9972) and the direction cosines of the g and A tensors for CO ₃ ^3– -Sc³⁺ center were found to be close to that for the well-known CO ₃ ^3– -Y³⁺ center. A quantitative comparison of different impurity contents in calcite samples and analysis of the intensities of forbidden transitions were used to identify Sc³⁺. An estimation of the unpaired electron spin density on the nuclei of paramagnetic centers confirms that both centers, CO ₃ ^3– -Sc³⁺ and CO ₃ ^3– -Y³⁺, have the same nature.     

Determination of the principal reflectances of an absorbing uniaxial mineral,ilmenite, from measurements on random sections

We show the steps followed for obtaining the principal reflectances of an absorbing uniaxial mineral, ilmenite, by use of the inference method derived from statistical reflectance parameters of the sample. The values obtained in air, at 580 nm, with this method are: R =19.6±0.3 and R =17.8±0.3.     

An optical transform and Monte Carlo study of the diffuse X-ray scattering in mullite,Al2(Al2+2xSi2−2x)O10−x

Diffuse X-ray scattering distributions have been recorded for reciprocal layers normal to c ^* of a synthetic mullite with composition Al₂(Al_2+2xSi_2–2x) O_10–xx, where represents an oxygen vacancy and x is close to 0.4. The effect on the diffuse scattering pattern of different schemes for ordering of the oxygen vacancies and the accompanying cation shifts within a single ab-layer of mullite has been investigated using optical diffraction analogue experiments in conjunction with Monte Carlo simulation.A simple scheme in which the only driving force for the ordering is that the O_c oxygens are precluded from being bonded to four T/T^* cations, results in a 2D diffuse intensity distribution which displays many of the features that are observed in the x-ray scattering patterns. An alternative scheme in which bonding to four T/T^* cations was favoured, resulted in a domain structure consisting of islands of the -alumina structure within a matrix of sillimanite. This gave diffraction patterns bearing no resemblance to the observed x-ray patterns and can, we believe, be discounted completely.     

Primary and secondary bifurcation in baroclinic instability

In modelling atmospheric flows the baroclinic instability of the flow in a differentially heated rotating annulus plays a central role. This paper deals with an experimental study using LDV and flow visualization techniques. Usually the temperature difference,T, was kept fixed while the angular velocity,, was varied. On crossing the stability boundary, the primary bifurcation, the basic flow gives way to a baroclinic wave flow. For a given annulus geometry the wave number,m, of the first wave pattern was found to be uniquely defined byT. The measured critical values of, _crit, agree reasonably well with those obtained by other authors. On increasing above _crit the wave number changed, this process showing hysteresis. The situation might indicate secondary bifurcation phenomena. Flow visualization using aluminium particles shows surface flow details.This paper is dedicated to Prof. Dr. K. Gersten on the occasion of his 60th birthday     

Hydration thermodynamics of the SWy-1 montmorillonite saturated with alkali and alkaline-earth cations: A predictive model

The aim of the present work was to study the thermodynamic equilibria between water and a homo-ionic montmorillonite SWy-1 saturated by different cations. The choice of this smectite is justified by the large set of experimental data available from the literature for eight different interlayer cations: Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺. In particular, studies by [Cases et al., 1992], [Cases et al., 1997] and [Bérend et al., 1995] are providing heat of adsorption data, pairs of desorption-adsorption isotherms, and information about the partition of adsorption-desorption water molecules between external surfaces and internal spaces. By calculating the effective amount of hydration water as the difference between the so-called gravimetric water and the surface covering water, a thermodynamic model was then developed, based on the concept of Ransom and Helgeson (1994) considering an asymmetric subregular binary solid solution between a fully hydrated and a anhydrous smectite. A set of six thermodynamic parameters ( and four Margules parameters) was extracted by a least square method from measurements of enthalpies of adsorption and paired adsorption-desorption isotherms for each interlayer cation. These six initial parameters were then used to determine a complete set of standard thermodynamic hydration parameters (, heat capacity, molar volume, and number of interlayer H₂O) and quantify, for each cation, the number of moles of hydration water molecules as a function of relative humidity and temperature. The validation of the standard state thermodynamic properties of hydration for each end member was carried out using three approaches: (1) a comparison with experimental isotherms obtained on hetero-ionic and homo-ionic SWy-1 smectite at different temperatures; (2) a comparison with the experimental integral enthalpy and entropy of hydration of the SWy-1 smectite; and (3) a comparison with experimental isotherms acquired on various smectites (Upton, MX80, Arizona) with different layer charges.Eventually, the present work demonstrates that, from a limited number of measurements, it is possible to provide the hydration thermodynamic parameters for hydrated smectites with different compositions and under different conditions of temperature and relative humidity, using the newly developed predictive model.     

Titania precipitation in sapphire containing iron and titanium

Titania, TiO₂, precipitation in natural blue sapphire (Fe, Ti: -Al₂O₃) has been investigated using high resolution and analytical transmission electron microscopy. The structure and habit of the TiO₂ precipitate depends on both the Ti⁴⁺ concentration and the temperature at which the precipitate formed. Tetragonal TiO₂ (Rutile) grows at 1350° C but at 1150° C an orthorhombic non-equilibrium TiO₂ polymorph precipitates. Both TiO₂ polymorphs nucleate in the (0001)s plane as lens shaped discs twinned along their diameter. The crystallographic alignment of each type of TiO₂ precipitate with respect to the -Al₂O₃ host matrix provides a high degree of structural coherency with minimal lattice mismatch. Electron diffraction analysis established the following precipitate/host orientation relationships: tetragonal TiO₂: {011}r {11 07B;100}r(0001)s and 01 r10 0s twinned along the (011)r planeand orthorhombic TiO₂: {021}{11 0}s, {100}(0001)s and 0 2 10 0s twinned along the (021) plane.     

Electrical conductivity,thermopower and <Superscript>57</Superscript>Fe Mössbauer spectroscopy of aegirine (NaFeSi<Subscript>2</Subscript>O<Subscript>6</Subscript>)

DC and AC electrical conductivities were measured on samples of two different crystals of the mineral aegirine (NaFeSi₂O₆) parallel () and perpendicular () to the [001] direction of the clinopyroxene structure between 200 and 600 K. Impedance spectroscopy was applied (20 Hz–1 MHz) and the bulk DC conductivity _DC was determined by extrapolating AC data to zero frequency. In both directions, the log _DC – 1/T curves bend slightly. In the high- and low-temperature limits, differential activation energies were derived for measurements [001] of E_A 0.45 and 0.35 eV, respectively, and the numbers [001] are very similar. The value of _DC [001] with _DC(300 K) 2.0 × 10^{–6 –1}cm^–1 is by a factor of 2–10 above that measured [001], depending on temperature, which means anisotropic charge transport. Below 350 K, the AC conductivity () (/2=frequency) is enhanced relative to _DC for both directions with an increasing difference for rising frequencies on lowering the temperature. An approximate power law for () is noted at higher frequencies and low temperatures with () ^s, which is frequently observed on amorphous and disordered semiconductors. Scaling of () data is possible with reference to _DC, which results in a quasi-universal curve for different temperatures. An attempt was made to discuss DC and AC results in the light of theoretical models of hopping charge transport and of a possible Fe²⁺ Fe³⁺ electron hopping mechanism. The thermopower (Seebeck effect) in the temperature range 360 K < T <770 K is negative in both directions. There is a linear – 1/T relationship above 400 K with activation energy E 0.030 eV [001] and 0.070 eV [001]. ⁵⁷Fe Mössbauer spectroscopy was applied to detect Fe²⁺ in addition to the dominating concentration of Fe³⁺.     

Thorium sorption in the marine environment: Equilibrium partitioning at the hematite/water interface,sorption/desorption kinetics and particle tracing

Thorium(IV) sorption onto hematite (-Fe₂O₃) was examined as a function of pH and ionic strength. Sorption behaved Langmuirian over an eleven order of magnitude range in adsorption densities, : 10^–12 to 10^–1 moles Th sorbed per mole hematite sites, indicating that the overall free energy of Th adsorption is independent of adsorption density. Modeling of Th sorption was conducted with the Triple Layer Model of Davis and Leckie; reactions considered included solution-phase hydroxy and carbonato complexes of thorium, and carbonate/hematite surface complexes. The entire Th sorption isotherm can be modeled with a single surface complex formation reaction

Co2+ in trigonal fields of oxygen based structures: Electronic absorption spectra of buetschliite-type K2Co(SeO3)2, K2Co2(SeO3)3 and zemannite-type K2Co2(SeO3)3 · 2H2O

Polarized single crystal absorption spectra, in the spectral range 40 000–5 000 cm^-1, were obtained on Co²⁺ in trigonally distorted octahedral oxygen fields of buetschliite-type K₂Co(SeO₃)₂ (I), K₂Co₂(SeO₃)₃ (II) and zemannite-type K₂Co₂(SeO₃)₃ · 2H₂O (III). Site symmetries of Co²⁺ are m (D_3d) in I, 3m (C_3v) in II, and 3 (C₃) in III. The spectra can be interpreted on the basis of an electric dipole mechanism, wherein transitions of Co²⁺ in the centrosymmetric site in I gain intensity from dynamic removal of the inversion centre by vibronic coupling. In accordance with the elongation of the CoO₆ octahedra along the trigonal axis, the split component E_(g) of the ground state ⁴T_1g in octahedral fields is the ground state in all three compounds. Trigonal field parameters Dq_(trig), D, D and the Racah parameters B have been fitted to the energies of spin allowed transitions (293 K) as follows: I: 744, 94, -16, and 838 cm^-1, resp.; II: 647, 227, 42, and 798 cm^-1, resp.; III: 667, 181, 21, and 809 cm^-1, respectively. Racah parameters C were estimated from the energy of some observed spin-forbidden transitions to be 3770 (I), 3280 (II), and 3465 cm^-1 (III). Values of Dq and of the Racah parameters B and C indicate slight differences of Co²⁺-O bonding in I as compared to II and III, with somewhat higher covalency in compounds II and III which contain face-sharing CoO₆ octahedra with short Co-Co contacts. Also, in II and III the observed D values do not agree with theoretical D values, predicted from the magnitude of the mean octahedral distortions.     

Diamagnetic anisotropies of oxide minerals

The diamagnetic anisotropy of oxide minerals is analyzed in terms of a new model, in which the anisotropy is assigned to the individual chemical bond in the [MO₆] octahedral unit of the crystal. The diamagnetic principal axis of the individual M-O bond is assumed to be parallel to the direction of the bond. The calculated anisotropy based on this model shows a good correlation with the measured diamagnetic anisotropy, , for various minerals such as talc, sericite, kaolinite of the sheetsilicate group, forsterite of the orthosilicate group, and corundum of the hematite group. The values of many diamagnetic minerals are still unknown since the measurement is difficult to perform by means of conventional methods. The magnetic grain orientation recently observed in the mineral suspensions is effective for estimating the value, when the single crystal of the mineral cannot be obtained. The observation of fieldinduced crystal oscillation in the high magnetic fields can be applied for measuring the minerals with small values of less than 5 × 10^–10 emu/cc. The chemical bond model on the diamagnetic anisotropy can be confirmed, when the compiling of data on various mineral is made by means of the above two methods.     

Orschallite,Ca3(SO3)2 · SO4 · 12H2O,a new calcium-sulfite-sulfate-hydrate mineral

Summary The new mineral orschallite, Ca₃(SO₃)₂SO₄ · 12H₂O, was found at the Hannebacher Ley near Hannebach, Eifel, Germany. Crystal structure analysis of the mineral, chemical analysis and water determination on synthetic material gave the composition Ca₃(SO₃)₂SO₄ · 12H₂O. The mineral crystallizes in space group with a = 11.350(1), c = 28.321(2) Å, V = 3159.7 ų, Z = 6, D_c = 1.87 Mg/m³, D_m = 1.90(3) Mg/m³. It is uniaxial positive with the optical constants = 1.4941, = 1.4960(4). The strongest lines in the powder pattern are (d-value (Å), I, hkl) 5.73, 100, 1 0 4/8.11, 80, 0 1 2/2.69, 80, 3 0 6/3.63, 60, 1 1 6/3.28, 40, 3 0 0. Refinement of the crystal structure led to a weighted residual of R_w = 0.043 for 600 observed reflections with I > 2(I) and 52 variable parameters.

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Orschallit, Ca₃(SO₃)₂SO₄ · 12H₂O, ein neues Kalzium-Sulfat-Sulfat-Hydrat-Mineral

Zusammenfassung Das neue Mineral Orschallit, Ca₃(SO₃)₂SO₄ · 12H₂O, wurde in der Hannebacher Ley bei Hannebach, Eifel, Deutschland gefunden. Eine Analyse der Kristallstruktur an einem Einkristall des natürlichen Materials, chemische Analyse und Wasserbestimmung an synthetischem Material ergaben die Zusammensetzung Ca₃(SO₃)₂SO₄ · 12H₂O. Das Mineral kristallisiert in der Raumgruppe mit a = 11.350(1), c = 28.321(2) Å, V = 3159.7 ų, Z = 6, D_c = 1.87 Mg/m³, D_m = 1.90(3) Mg/m³. Es ist optisch einachsig mit den optischen Konstanten = 1.4941, = 1.4960(4). Die stärksten Linien des Pulver-diagramms liegen bei (d-Wert (Å), I, hkl) 5.73, 100, 1 0 4/8.11, 80, 0 1 2/2.69, 80, 3 0 6/3.63, 60; 1 1 6/3.28, 40, 3 0 0. Die Verfeinerung der Kristallstruktur ergab einen gewichteten Residualwert R_w = 0.043 für 600 beobachtete Reflexe mit I > 2(I) und 52 variable Parameter.

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With 5 Figures     

Kutnohorite from the Chvaletice pyrite and manganese deposit,east Bohemia

Summary Kutnohorite-quartz veins penetrate through a weakly metamorphosed Late Proterozoic sedimentary rhodochrosite carbonate in pyrite shales. Kutnohorite is pleochroic ranging from colourless () to pinkish grey (), =1.735, =1,543,d=3.066g·cm^–3;a ₀=4.852(1),c ₀=16.219(7) Å. A quantitative chemical analysis leads to the formula (Ca_0.95Mn_0.05)_1.00(Mn_0.64Mg_0.23Fe_0.13)_1.00(CO₃)_2.04. An electron microprobe scanning reveals considerable microscale inhomogeneity in cleavage rhombohedrons taken from a coarsely grained aggregate. It is mostly of the character of periodic fluctuations of the main element contents around an average value. There is a strong prevalence of an Fe+Ca–Mn+Mg antagonism, the extremes of compositonal differences lying in distances of 0.0X mm. The fluctuation maxima amount to about 9% for FeO, 6% for MnO, 3% for CaO, and 1.5% for MgO. In one of the samples even a two phase character with the above antagonism between the two phases was detected by X-rays. The inhomogeneities are due, partly at least, to the Fe-metasomatic processes that followed the formation of the kutnohorite by Alpine-paragenesis hydrothermal metamorphism.

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Kutnohorit aus der Pyrit-und Manganlagerstätte von Chvaletice (Ostböhmen)

Zusammenfassung Kutnohorit-Quarzgänge durchdringen ein schwach metamorphes jungproterozoisches sedimentäres Rhodochrositkarbonat in pyritischen Schiefern. Der Pleochroismus von Kutnohorit liegt zwischen farblos () und rosagrau (), =1,735, =1,543;d=3,066 g·cm^–3;a ₀=4,852(1),c ₀=16,219(7) Å. Die quantitative chemische Analyse des Minerals ergibt Formel (Ca_0,95Mn_0,05)_1,00(Mn_0,64Mg_0,23Fe_0,13)_1,00(CO₃)_2,04. Elektronenmikrosondenuntersuchungen zeigen eine starke mikroskopische Inhomogenität in den Spaltrhomboedern von einem grobkörnigen Kutnohoritaggregat. Sie ist meistens durch periodische Schwankungen der Hauptelementgehalte um einen Mittelwert hervorgerufen. Antagonistische Beziehungen von Fe+Ca und Mn+Mg überwiegen, die extremen Werte von Elementgehalten liegen in Abständen von 0,0X mm. Die höchsten Schwankungen erreichen etwa 9% für FeO, 6% für MnO, 3% für CaO und 1,5% für MgO. In einer Probe konnten röntgenographisch sogar zwei Kutnohoritphasen mit dem erwähnten Antagonismus zwischen den Phasen bewiesen werden. Die Inhomogenitäten wurden wahrscheinlich meistens durch Fe-metasomatische Vorgänge nach der Kristallisation des Kutnohorits während der hydrothermalmetamorphen Prozesse der Alpinen Paragenese hervorgerufen.

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With 4 Figures     

Machatschkiit,ein neues Arsenatmineral aus der Grube Anton im Heubachtal bei Schiltach (Schwarzwald,Bundesrepublik Deutschland)

Zusammenfassung Machatschkiit ist ein neues wasserhaltiges Calciumarsenat, das in der Grube Anton bei Schiltach im mittleren Schwarzwald (BRD) 1960 gefunden wurde. Es kommt zusammen mit Gips, Pharmakolith, Pikropharmakolith und Sainfeldit als Sekundärbildung krustenförmig auf Granit vor.Als charakteristische Form tritt das Rhomboeder auf. Keine Spaltbarkeit, Bruch muschelig, Härte 2–3,G=2,5 bis 2,6 g·cm^–3,D _x =2,50 g·cm^–3, farblos, durchsichtig bis durchscheinend. Optische Daten:n =1,585±0,002,n =1,593±0,002, einachsig oder schwach zweiachsig, negativ.Gitterkonstanten:a ₀=15,10,c ₀=22,59 Å,a ₀c ₀=11,4960,Z=12;a _rh =11,52 Å, =81°52,Z=4. Mögliche Raumgruppen:R32,R3m, . Stärkste Linien des Pulverdiagramms: 8,59 (10) (110), 5,34 (8) (210), 3,59 (8) . Eine chemische Analyse ergab nach Umrechnung folgende Zusammensetzung: CaO 29,5%, As₂O₅ 40,8%, SO₃ 0,5%, H₂O 29,2%, Summe 100,0%. Dies kommt der Formel Ca₃(AsO₄)₂ · 9 H₂O sehr nahe. In verdünnter HCl und HNO₃ ist der Machatschkiit leicht löslich.

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Machatschkiite, a new arsenate mineral from the Anton Mine in the Heubach valley near Schiltach (Black Forest, Federal Republic of Germany)

Summary Machatschkiite is a new hydrous calcium arsenate which was found 1960 in the Anton Mine near Schiltach in the central Black Forest. It is a secondary mineral which occurs in crusts on granite in association with gypsum, pharmacolite, picropharmacolite and sainfeldite.The characteristic form is the rhombohedron . No cleavage, fracture conchoidal, hardness 2–3,G=2.5–2.6 g·cm^–3,D _x =2.50 g·cm^–3, colourless, transparent to translucent. Optical data:n =1.585±0.002,n =1.593±0.002, uniaxial or weakly biaxial, negative.Unit-cell dimensions:a ₀=15.10,c ₀=22.59 Å,a ₀c ₀=11.4960,Z=12;a _rh =11.52 Å, =81°52,Z=4. Possible space groups:R32,R3m, . Strongest lines of the powder pattern: 8.59 (10) (110), 5.34 (8) (210), 3.59 (8) . A chemical analysis gave the following composition after recalculation: CaO 29.5%, As₂O₅ 40.8%, SO₃ 0.5%, H₂O 29.2%, total 100.0%. This agrees well with the formula Ca₃(AsO₄)₂ · 9 H₂O. Machatschkiite is easily soluble in diluted HCl and HNO₃.

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Mit 3 Abbildungen     

A statistical comparison of various source formulations for explosions and earthquakes

Stochastic models are derived for two source formulations for explosions. Using this kind of model, a comparison is made between source time functions due to Blake, Haskell, Mueller and Murphy, and Von Seggern and Blandford, for explosions, and between -square (Aki, Brune)and -cube (Aki, Haskell)models for earthquakes. When seeking a stochastic model for records of Rayleigh waves from atmospheric explosions, the k-model corresponding to Haskell's time function was found to be an appropriate choice.     

Molecular force constants in dynamical model of α-quartz

Ab initio force constants of structural fragments of -quart, Si-O-Si bridge and SiO₄ tetrahedron, are calculated by the gradient (force) method for molecules accessible to spectroscopic investigation, disiloxane and tetramethoxysilane respectively. The comparison of theoretical frequencies with experimental ones enables the empirical scaling of quantum chemical force constants. A generalized approach to the inverse vibrational problem in spectroscopy of solids is outlined. It consists of a joint treatment of vibrational spectra and properties of a crystal related to its homogeneous deformation, namely compressibility and elastic constants. The importance of analyzing the microscopic structure of compressibility for testing the force field model is emphasized. The scaled molecular force constants complemented by the force constants of nonbonded O...O interactions at shortest distances after slight empirical correction are found to be sufficient to reproduce all mechanical properties of -quartz accessible to experimental determination. A discussion of results in terms of structure and bonding including the analysis of various versions of a force field model is presented. The calculated shapes of normal coordinates and uniform strains are validated by satisfactory reproduction of IR intensities and piezoelectric constants.     

Pressure-volume-temperature behavior of fayalite based on static compression measurements at 400° C

Twenty-one energy-dispersive X-ray diffraction spectra for fayalite at 400° C constitute the basis for an elevated-temperature static compression isotherm for this important silicate mineral. A Murnaghan regression of the resulting molar volumes yields 103.8 GPa and 7.1 for the 400° C, room-pressure values of the isothermal bulk modulus (K ₀) and its first pressure derivative (K₀), respectively. When compared to the room-temperature static compression isotherm of Yagi et al. (1975), our 400° C value for K ₀ yields 5.4 ×10^–2 GPa/deg for (K/T)₀₀. When combined with literature volume data, our measurements indicate that the fayalite isochores are strongly concave toward the pressure axis [( ² T/P ² ) _v <>This is publication number 1125 of the School of Earth Sciences, Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA     

Pb-isotope evidence for the timing of episodic mineralization in the Llanrwst and Llanfair-Talhaiarn orefields, North Wales

Galenas from the Llanrwst and Llanfair-Talhaiarn orefields in North Wales have a restricted range of Pb-isotope values. M₁ and M₂ mineralizations at Llanrwst are isotopically separate in ²⁰⁶Pb/²⁰⁴Pb versus ²⁰⁷Pb/²⁰⁴Pb space, while the isotopic composition of the M₃ mineralization exceeds the combined M₁ and M₂ range. The lead source for the Llanrwst orefield is believed to be the underlying Ordovician volcanic arc material. Data from the related Llanfair-Talhaiarn orefield suggest lead was derived from the host Silurian sediments in addition to the Ordovician basement. The time separation of the M₁ and M₂ veins at Llanrwst has been calculated using and data from Dixon et al. (1990) at 11 Ma and 15 Ma respectively.     

31P solid-state nuclear magnetic resonance spectroscopy of aluminum phosphate minerals

This study examines the links between ³¹P solidstate NMR studies of aluminum phosphate minerals and their crystallographic structures. We found that ³¹P isotropic chemical shift values, _iso, carry little information about mineral structures. There seems to be no relation between the chemical shift anisotropy, =₃₃–₁₁ (₃₃>₂₂> ₁₁), and indicies of phosphate-tetrahedra distortion. ³¹P¹H heteronuclear magnetic dipole interactions, on the other hand, carry important information about hydrous phosphate mineral structures, information that should prove to be quite valuable in studies of phosphate adsorbed on mineral surfaces. This interaction can be measured through a variety of qualitative and quantitative experiments. It appears that spin diffusion is so rapid that subtle differences in hydrogen-bonding environments cannot be resolved.     

Capillary Pressure Curves from Centrifuge Data: A Semi-Iterative Approach

The problem of determining capillary pressure functions from centrifuge data leads to an integral equation of the form _a ^x K(x,t)f(t)dt=g(x),x[a,b],(1)where the kernel K is known exactly and given by the underlying mathematical model. g is only known with a limited degree of accuracy in a finite and discrete set of points x ₁,...,x _M . However, the sought function f(t) is continuous. By the nature of the right-hand side, g(x), equation (1) is a discrete inverse problem which is ill-posed in the sense of Hadamard [9]. By a parameterization of the sought function, equation (1) reduces to a system of linear equations of the form Ac=b+ ,where b is the observation vector and A arises from discretization of the forward problem. is the error vector associated with b, and c contains the model parameters. The matrix A is usually ill-conditioned. The ill-conditioning is closely connected to the parameterization of the problem [23].In this paper a semi-iterative regularization method for solving the Volterra integral equation in the ₂-norm, namely, Brakhage's -method [2], is investigated. The iterative method is tested on synthetically generated, and on experimental data.