Velocity Spectrometer for Mössbauer Experiments

An electromechanical feedback system for Mössbauer spectroscopy with a velocity range of 2×10^–5 to 60 cm/sec is described. A reference signal of the desired waveform (triangle, parabola, etc.) to drive the feedback system is produced by the multichannel analyzer and with the help of operational amplifiers. The linearity of the system for a triangular velocity waveform is better than 0.5% during 98% of the half-period

Hyperfine Interactions and Lifetimes of Low-Energy States in W182 and W183

The Mössbauer technique has been used to study the nuclear hyperfine interactions and lifetimes in W182 (2+ state) and W183 (3/2- and 5/2- states) with the following results: g(5/2-)/g(2+)=1.40±0.04; g(3/2-)=-0.07±0.07; Q(5/2-)/Q(2+)=0.94±0.04; T1/2(3/2-)=0.184±0.005 nsec; T1/2(5/2-)≳0.7 nsec. These quantities are discussed in terms of a rotation-particle interaction in W183 due to Coriolis coupling. From the measured quantities and additional information on γ-ray transition intensities, magnetic single-particle matrix elements are derived. It is inferred from these that the two effective g factors, resulting from the Nilsson-model calculation of the single-particle matrix elements for the spin operators sz and s+, are not equal, consistent with the proposal of Bochnacki and Ogaza. The internal magnetic fields at the tungsten nucleus were determined for substitutional solid solutions of tungsten in iron, cobalt, and nickel. With g(2+)=0.24 the results are: Heff(W-Fe)=-715±10 kG; |Heff(W-Co)|=360±10 kG; |Heff(W-Ni)|=90±25 kG. The electric field gradients at the tungsten nucleus were determined for WS2 and WO3. With Q(2+)=-1.81 b the results are: for WS2, eq=-(1.86±0.05)×10^18 V/cm^2; for WO3, eq=(1.54±0.04)×10^18 V/cm^2 and η=0.63±0.02

Spin-23/2- Isomer of Lu177

Investigations of the decay of the three-particle state in Lu177 with spin 23/2- performed with the crystal diffraction technique revealed evidence for three-particle states in Hf177 and rotational bands in Lu177 and in Hf177. Levels with spins to 17/2 were found in the K=7/2+ rotational band in Lu177 while the K=7/2- and K=9/2+ bands in Hf177 were found to be excited up to spin 21/2 levels. From energy and intensity measurements of the cascade, crossover, and interband transitions, the values of a number of parameters pertinent to the collective model were derived. In particular, it was verified for each of the rotational bands that the quantity (gK-gR)/Q0 was a constant within the experimental error

Mössbauer Effect of Te125 in Simple-Cubic and Amorphous Tellurium-Base Alloys

Recoilless resonant absorption of the 35.6-KeV γ ray (3/2+ to ½+ transition) in Te125 has been observed in both simple-cubic and amorphous tellurium-base alloys obtained by rapid cooling from the liquid state. As expected from its cubic symmetry, the simple-cubic (one atom/unit cell) metastable AuTe2 gives a single-peak Mössbauer spectrum with a half-width 0.88±0.05 cm/sec and an isomeric shift of 0.03±0.01 cm/sec. The monoclinic AuTe2, which is the equilibrium form of this compound, unexpectedly shows also a single-peak spectrum with an isomeric shift 0.04±0.01 cm/sec. However, the latter is about 23% broader than the former. On the basis of the atomic arrangement of the monoclinic AuTe2, this line broadening is attributed to a weak quadrupole interaction. These findings are consistent with the fact that both polymorphs exhibit metallic conduction of the same order of magnitude. The Mössbauer spectrum of the metastable amorphous alloy Te70Cu25Au5 exhibits a well-resolved quadrupole splitting of 0.74±0.02 cm/sec, which is about the same as that of crystalline tellurium. The fact that the amorphous alloy has a quadrupole splitting of the same magnitude as that of crystalline tellurium confirms the hypothesis proposed previously that the metastable amorphous tellurium-base alloys consist of randomly oriented spiral chains of tellurium, with the atoms of the minor constituent (s) randomly distributed between the chains. As a consequence of the chain retention in the amorphous alloy, there is predominantly a covalent bonding like that in crystalline tellurium. This conclusion offers a possible explanation of the experimental fact that the amorphous alloy shows a semiconducting behavior similar to that of crystalline tellurium

Experimental evidence for parity impurity in a nuclear gamma transition

In this communication we present a preliminary account of an experimental investigation of parity admixture in nuclear states. Our measurements give evidence of a small parity admixture in a nuclear gamma transition of 482 keV in Ta181

Electronic shielding by closed shells in salts of thulium

Electronic shielding by closed electron shells has been investigated in salts of trivalent thulium, by measuring the temperature dependence of the nuclear quadrupole splitting of the 8.42-keV gamma transition in Tm169. The measurements were performed by using the technique of recoilless nuclear resonance absorption. The nuclear quadrupole interaction was studied for Tm3+ ions in thulium ethyl sulfate, thulium oxide, and thulium trifluoride within a temperature range from 9.6 to 1970°K. The interpretation of the experimental data in terms of the contributions of distorted closed electron shells to the quadrupole interaction yields values for electronic shielding factors. The results lead to amounts of 10% or less for the atomic Sternheimer factor RQ. The experiments also reveal substantial shielding of the 4f electrons from the crystal electric field, expressed by the shielding factor σ2. Values of 250 and 130 are obtained for the ratio (1-γ∞)/(1-σ2) for thulium ethyl sulfate and thulium oxide, respectively, where γ∞ is the lattice Sternheimer factor

Hyperfine Interaction and Isomeric Shift in Pt195

Using the Mössbauer technique the first-excited-state g factor for Pt195 has been determined to be -0.41 ±0.03. The following magnetic fields at the Pt nucleus were found: in an Fe lattice, 1.19±0.04 MG; in a Co lattice, 0.86±0.03 MG; and in a Ni lattice, 0.36±0.04 MG. Isomeric shifts have been detected in a number of compounds and alloys and have been interpreted to imply that the mean square radius for the Pt195 nucleus in the first excited state is smaller than in the ground state

Mössbauer effect in Tm169 and total internal conversion of the 8.42-keV transition

The absolute yield of the Mössbauer absorption of the 8.42-keV transition in Tm169 was determined for a thulium oxide and a thulium metal absorber. The 8.42-keV gamma ray was resolved from the L x rays of erbium by means of a flat lithium fluoride crystal diffraction spectrometer. From the observed Mössbauer absorption effect the total conversion coefficient αtot=325±35 and the magnetic transition rate of B(M1, 3/2→1/2)=5.1×10^-2 (eh/2Mc)^2 was derived

A Moessbauer spectrometer for the mineralogical analysis of the Mars surface: First temperature dependent tests of the detector and drive system

Part of the scientific payload of the Mars-96 mission is a Fe-(57)Mossbauer (MB) spectrometer installed on a small rover to be placed on the surface of Mars. The instrument is under development at the University of Darmstadt. This instrument, with some modifications, is also included in the scientific payload of the proposed MARSNET mission of the European Space Agency (ESA). A similar instrument is currently under development in the US. The reason for developing a Mossbauer spectrometer for space applications is the high abundance of the element iron, especially on the surface of Mars. The elemental composition of Martian soil was determined during the Viking mission in 1976 but not it's mineralogical composition. One believes that it is composed mainly of iron-rich clay minerals, with an iron content of about 14 (plus or minus 2) wt-percent, partly magnetic. Of extremely great interest are the oxidation state of the iron, the magnetic phases and the mineral composition of the Mars surface. To these questions MB spectroscopy can provide important information, which are not available by other methods. We report on first tests of the experimental setup in the temperature range plus 20 C to -70 C, roughly corresponding to the temperature range on the surface of Mars. Also questions concerning the signal/noise ratio (S/N) are discussed