Mössbauer isomer shifts and quadrupole splittings in osmium compounds

From Mössbauer spectra of the 36.2keV and 69.5keV gamma rays of¹⁸⁹Os, isomer shifts and electric quadrupole interactions for a number of chemical compounds of osmium in the oxidation states +8, +6, +4, +3, and +2 were obtained. The results show that the dependence of the isomer shifts on the oxidation state of Os follows the general pattern established for other transition elements like Ru and Ir. A comparison of the isomer shift data with electron densities at the Os nuclei resulting from relativistic self-consistentfield calculations for free Os ions yieldsΔ 〈r²〉 [36 keV]=?2.0 · 10^?3 fm² andΔ 〈r²〉 [69 keV]=?0.13 · 10^?3 fm³ for the changes of the mean-square nuclear charge radius of¹⁸⁹Os. These values are in qualitative agreement with an interpretation of the low-energy level scheme of¹⁸⁹Os in terms of two rotational bands.     

Isomer shifts and chemical bonding in ruthenium complexes

Isomer shifts of the recoilless 90 keV γ-rays of⁹⁹Ru were observed in a number of octahedrally coordinated complexes of ruthenium and reveal the influence of different ligands on the electron density at the ruthenium nuclei. For a given oxidation state the observed shifts are correlated with the spectrochemical series; the backbonding properties of ligands like CN^?1 and NO⁺ cause a considerable increase of the electron density. This behaviour is largely similar to that found for compounds of iron and some 5d elements.     

Änderung des quadratischen Kernladungsradius bei Rotationsanregung

Isomer shifts ofγ rays from rotational bands of deformed nuclei have been determined in Mössbauer effect measurements. The following changes of the mean square nuclear charge radii have been deduced:Δ〈r ²〉(¹⁵⁶Gd, 89keV)=(+2.6±0.8)·l0^?3fm²,Δ〈r ²〉(¹⁷⁰Yb, 84keV)=(+1.2±0.3)·10^?3fm²,Δ〈r ²〉(¹⁷¹Yb, 67keV)=(+1.1±0.2)·10^?3fm². The results are compared with theoretical calculations and additional experimental data, to study the effect of the Coriolis and centrifugal forces in rotational excitation on the motion of the nucleons.     

Magnetic moment and change of the mean square charge radius of the 83.4 keV rotational state in153Eu

From Mössbauer effect measurements the magnetic momentμ=(+1.80±0.08) nm of the 83.4 keV rotational state of¹⁵³Eu and the ratio of the changes of the mean square charge radiiΔ〈r ²〉 (¹⁵³Eu, 83 keV)/Δ〈r ²〉 (¹⁵³Eu, 103 keV)=+0.025±0.008 were determined. The results are interpreted on the basis of mixing of rotational bands by the Coriolis force.     

Möβbauereffekt am61Ni

With the Möβbauer technique the hyperfine splittings of the 67.4 keV transition of⁶¹Ni in compounds and alloys have been studied. A magnetic momentΜ _61,4=+ (0,477 ±0.031)Μ _n of the first excited state has been determined. From isomer shifts an order of magnitude estimate of the change in radius ofδ〈r ²〉/〈r ²〉=?6· 10^?4 can be inferred. The electric quadrupole interaction of the first excited level has been observed in Ni-J-boracite. In addition the hyperfine fields at the nickel sites were determined in the alloy series Ni _x Fe_1-x (0≦x≦1). In one case an effect of polarization in a high external field is measured. The fields in some rare earth (RE) intermetallic compounds of the form RENi₂ were deduced from linewidth to be less than 15 kOe.     

Investigation of the decay rate for71Ge in chemical compounds and calibration of the Mössbauer isomer shift of the 67 keV γ-transition of73Ge

Changes of the radioactive decay rate of⁷¹Ge (T _1/2=11.43 days) have been studied experimentally for⁷¹Ge in some compounds of bivalent and quadrivalent germanium. Relative changes Δλ/λ of the electron capture probability have been measured, and the chemical changes Δρ(0) of the electron density at the germanium nuclei have been determined from these measurements. Values for the Mössbauer isomer shift calibration constants for the 67 keV γ-transition of⁷³Ge have been estimated:C=δ/Δρ(0)=(0.061±0.020) mm·s^?1/a.u., Δ〈r ²〉=(21±7)·10^?3 fm², ΔR/R=(6.9±2.3)·10^?4.     

The decay of105Tc to levels in105Ru

Theβ ^?-decay of 7.6-min¹⁰⁵Tc has been investigated byβ- andγ-ray singles and coincidence measurements. The activities have been produced by thermal-neutron-induced fission of²³⁵U or²³⁹Pu and subsequent chemical separation of the technetium fraction from the fission product mixture. AQ _β-value of 3.2±0.2 MeV has been determined. In a delayed coincidence experiment the lifetime of the first excited state in¹⁰⁵Ru at 20.55 keV has been measured to be 340±15 nsec. A level scheme of¹⁰⁵Ru is proposed and compared with the results of recent nuclear reaction studies like¹⁰⁴Ru(d, p) and¹⁰⁴Ru(n, γ). From beta branching ratios to levels in¹⁰⁵Ru, ground state spin and parity of 5/2⁺ can be suggested for¹⁰⁵Tc in accordance with the trend observed in neutron rich technetium isotopes.     

Isotope shift in the Ca I resonance line and changes in mean-square nuclear charge radii of the stable Ca isotopes

The isotope shift of all stable Ca isotopes was studied in the Ca I resonance line. Enriched isotopes were used in an atomic beam, passing through the center of a spherical Fabry-Perot interferometer. The measured isotope shifts were separated into mass shift and field shift by comparing the optical isotope shift with δ〈r ²〉 values derived from recent muonic x-ray measurements. The results are discussed together with known data on the isotope shift in the Ca I intercombination line and data from Hartree-Fock calculations. The following mean values are obtained for the change in nuclear charge distribution δ〈r ²〉 [fm²]∶ [40, 42] 0.23(3); [40, 43] 0.13(3); [40, 44] 0.28(4); [40, 46] 0.14(7); [40, 48] 0.00(2).     

New determination of the 127I and 129I Mössbauer isomer shift calibration constants

New experimental data on the chemical changes δλ/λ of the probabilities λ of electron capture by ¹²³I and ¹²⁵I nuclei are treated taking into account the dependence of the exchange and overlap effect on the state of the electronic shell of the atom. The change δ?(0) in the electronic charge density at the iodine nucleus is evaluated and used for determination of the changes δ〈r²〉 in the mean square charge radius of the ¹²⁷I and ¹²⁹I nuclei on transition from the ground state to the first excited state. The δ〈r²〉 values determined, ?(10.0 ± 1.0) × 10^?3 fm² for ¹²⁷I and (13.0 ± 1.3) × 10^?3 fm² for ¹²⁹I, are in excellent agreement with the “best” values, recommended by Ruby and Shenoy.     

Mössbauer effect study of hyperfine interactions in145Nd

The magnetic hyperfine splitting of the 72.5 keV γ rays of¹⁴⁵Nd was investigated in intermetallic compounds of Nd and in the paramagnetic salts Nd _x Y _1-x Cl₃·6H₂O (withx=0.02 andx=0.05) at 4.2 K. With the magnetic hyperfine tensorA of Nd_0.01Y_0.99Cl₃·6H₂O known from EPR spectroscopy, the analysis of the unresolved magnetic hyperfine spectra yieldsI _e =5/2 for the spin of the 72.5 keV state, in contradiction to a previous result. The multipolarity of the 72.5 keV γ transition was found to be essentiallyM1 with δ²=0.010±0.014, and the magnetic moment of the 72.5 keV state was determined as μ(5/2)=?0.319±0.004 nm. For various divalent and trivalent Nd compounds as well as for metallic Nd the isomer shift IS of the 72.5 keV γ line was measured. A value for the change of the mean square nuclear charge radius during the 72.5 keV γ transition of Δ〈r ²〉=+(1.9±0.9)·10^?3fm² was deduced using electron density differences from free-ion Hartree-Fock calculations.     

Mössbaueruntersuchungen an195Pt und201Hg

Using the Mössbauer technique the magnetic hyperfine splitting of the 130 keV transition in¹⁹⁵Pt has been observed in a Pt-Fe alloy. The derived magnetic moment is μ₁₃₀=(0.81 _?0.25 ^+0.13 μ _k . Isomershift measurements with the 130 keV and the 99 keV transitions in alloys yielded Δ〈r ²〉₁₃₀/Δ〈r ²〉₉₉=1.5±0.2 for the ratio of the changes in the mean square charge radius of the two excited states. From isomershifts of the 99 keV transition in compounds an estimate of Δ〈r ²〉₉₉/〈r ²〉=?(1.6 _?0.9 ^+4.4 ) · 10^?4 is made for the change in radius of the first excited state. The linewidth of the Mössbauer spectrum of the 32.2 keV transition in²⁰¹Hg gives a lower limit of 0.1 ns for the half-life of the second excited state. The results are compared with values for other nuclides in this mass region.     

Electron capture ratios in206Bi

The level scheme of⁹⁷Tc has been investigated by observing theγ-rays following the decay of 2.9-d⁹⁷Ru.γ-singles andγγ-coincidence measurements were carried out with Ge(Li)-detectors. The time difference of coincident γ-rays was measured as a third parameter. From the coincidence events, the intensities ofγγ-cascades were extracted. The⁹⁷Ru decay gives rise to 18γ-lines which could be fitted into a level scheme of⁹⁷Tc consisting of 9 levels. Spin and parity assignments of the levels were made from log(ft) values andγ-ray branching ratios. Discrepancies concerning the energy of the first 3/2^? state and the existence of a 946 keV level are discussed.     

Prompt γ-ray emission in the reactions of 120 MeV 20Ne with 27A1

The emission of prompt γ-radiation in the de-excitation of the products of the reactions of 120 MeV ²⁰Ne with ²⁷Al has been studied. Three NaI detectors placed at angles of 35°, 90° and 145° to the direction of the ²⁰Ne beam were used to detect γ-rays in coincidence with reaction products having 6 ≦ Z ≦ 20, detected in a counter telescope. Data were obtained with the counter telescope in the same plane, as well as in a plane perpendicular to the plane defined by the beam and the NaI detectors. The average multiplicities 〈M_γ〉, average energies 〈E_γ〉, primary γ-ray energy spectra and the variation of 〈M_γ〉 and 〈E_γ〉 with angle of observation and kinetic energy of the detected products are presented and discussed in terms of the dominant reaction mechanisms.     

Mößbauereffekt in157Gd und155Gd

Using the Mössbauer technique electric hyperfine interactions of the first excited non-rotational states at 64 keV in¹⁵⁷Gd and at 86.5 keV in¹⁵⁵Gd have been determined in GdF₃ and GdCl₃· 6H₂O. For the ratio of quadrupolmoments the ratiosQ ₆₄ ¹⁵⁷ /Q _g ¹⁵⁷ =1.74±0.04,Q _86.5 ¹⁵⁵ /Q _g ¹⁵⁷ =?0.07 ± 0.21 andQ _g ¹⁵⁵ /Q _g ¹⁵⁷ =0.78 ± 0.06 were found. In addition isomer shifts were observed from which a ratio δ〈r²〉 ₆₄ ¹⁵⁷ /δ〈r²〉 _86.5 ¹⁵⁵ =?2.6±0.15 can be inferred.     

Isotope shift in Ni I and changes in mean-square nuclear charge radii of the stable Ni isotopes

The isotope shift in the Ni I spectrum was studied in 17 lines for all stable isotopes by means of a photoelectric recording Fabry-Perot spectrometer with digital data processing. The measured isotope shifts were separated into mass shift and field shift by comparing the optical isotope shift with model-independent δ〈r ²〉 values derived from a combined elastic electron scattering and muonic x-ray data analysis. The ratios of the observed field shifts in different types of transitions could be explained quantitatively by Hartree-Fock calculations. The relative changes in mean-square nuclear charge radii were found to be: [58, 60] 1.293(15); [60, 62]1; [62, 64] 0.641(16); [60, 61] 0.382(9). The absolute value δ〈r ²〉^60,62=0.170(35) fm² was derived using fine structure as well as hyperfine structure data for the determination of the change in the electron charge density at the nucleus in 4s-4p transitions.     

Mössbauer scattering of the 166 keV gamma rays of139La

The Mössbauer scattering of the 166 keV γ-rays of¹³⁹La was observed with a source of¹³⁹Ce in CeO₂ and scatterers of La₂O₃, La(OH)₃, LaF₃, K₃LaF₆, LaB₆, and LaC₂. The isomer shifts obtained for these compounds are compared with isomer shift data for the analogous Pr compounds. From this comparison it is inferred that the change of the mean square nuclear charge radius for the 166 keV transition is positive and of the order of 10^?2 fm².     

Der Zerfall des125m Xe,des127m Xe und des127g Xe

The decay of^125m Xe produced by the reaction¹²²Te(α, n)^125m Xe using a target enriched in¹²²Te (95.4%) and the decay of^127m Xe produced by the reaction¹²⁷J(d, 2n)^127m Xe have been investigated: ^125m Xe decays with a half-life ofT _1/2=(56±3) sec by ayy- cascade withE _γ1=(140.4 ±0.5) keV andE _γ2=(110.5 ±0.5) keV. The experimental conversion coefficients yield multipolarities ofE3 for the 140.4 keV isomeric transition and predominantlyM1 for the 110.5 keV-transition. ^127m Xe decays with a half-life ofT _1/2=(71±2) sec. The decay also proceeds by aγγ-cascade with an isomeric E3 transition ofE _γ1=(172.5±0.3) keV and a predominantlyM1 transition ofE _γ2=(124.6±0.3) keV. In the decay of^127g Xe an additional branching of the electron capture to a level at (618.1±0.3) keV was observed. The relative probability forK-captureP _K618/P_K375=0.40 ±0.07 yields a total transition energyQ _EC=(664 ±4)keV. A spin of 1/2⁺ was assigned to the ground state.     

Relation of contact densities with Mössbauer isomer shifts for 35.46 keV M1 transition of125Te

The internal conversion electron and Mössbauer isomer shifts associated with the 35.46 keV M1 transition of¹²⁵Te were observed for different metal samples into which radioactive¹²⁵I as probe atoms were introduced by means of ion-implantation. From the correlation between the Mössbauer isomer shifts and intensity ratios of O shell to N_I shell conversion electrons, a relation between 5s-electron contact densityp _5s(0) in a.u. and isomer shift δ in mm/s was deduced to bep _5s(0)=106+30.3 δ±4.3[(δ?0.30)²+0.069]^1/2, where δ was measured relative to ZnTe in mm/s. The change of the nuclear charge radius in the 35.46 keV M1 transition of¹²⁵Te was found to be ΔR/R=(0.85±0.12)×10^?4 (corresponding to Δ<r ²>=(3.7±0.5)×10^?3 fm²) when a theoretical 4s-electron contact density of 928 a.u. was used.     

On the observability of enhancement effects in isochromat spectroscopic investigations of Pd and Rh

We have investigated theγ-rays from the decay of 46-min⁵¹Mn produced by the⁵⁰Cr (d, n) reaction. Twelveγ-rays were observed. Theseγ-rays have been incorporated into a level scheme of⁵¹Cr with levels at 0, 749.1, 1164.4, 1353.3, 1557.4, 1899.4, 2001.4, 2312.5 and 2829.7 keV. Branching ratios, logft values, and j^π assignments are discussed for these levels. The lifetime of the 749.1 keV level was measured to be T_1/2=7.6 ± 0.3 ns by utilizing the⁵¹V(p, n γ ⁵¹Cr reaction produced by a 3.8 MeV pulsed proton beam. The 749 keV,E2 transition is hindered by a factor of 34 compared to the Weisskopf estimate.