W. Sandner

Temperature dependence of the electric field gradient in noncubic metals

The quadrupole hyperfine interaction of111Cd in Cd, In, Sn, and of67Zn,69Ge in Zn was measured with high accuracy using TDPAC and TDPAD methods; in addition the systems117In in Cd and In, and113Sn in Cd were investigated. The temperature dependence of the electric field gradienteq(T) can be reproduced by the simple relationeq(T)/eq(0)=1—B⋅T3/2 over a range of temperatures from a few K up to the melting point. A comparison with other experiments was carried out to test the universality of this empirical relation. In particular, high precision NQR experiments on Ga, In and Sb strongly support this relation. It is discussed whether lattice vibrations can explain the observed temperature variation or whether the experimental data indicate the need for a new description. Some new ideas suggesting a basically different model are given.

Magnetic moments of the 11/2− states in145, 147, 149Eu and paramagnetism in the system EuSm

The g-factors of the 11/2− states in145, 147, 149Eu were measured by the TDPAD method in metallic Sm-targets. The temperature dependence of the paramagnetism in the system145EuSm follows strictly a Curie-Weiß law Beff=B0[1+¯C/(T-θ)] with C=−50(2)K and θ=−29(5)K. Extrapolation to T→∞ yields g(145Eu)=+1.356(8), g(147Eu)=+1.28(1) and g(149Eu)=+1.27(5). In addition, the quadrupole coupling constantνQ=12.5(5) MHz, and a lower limit for the paramagnetic relaxation time τ = 1 us was determined at room temperature for the 11/2− state of145Eu in Sm.Extensive studies of the anomaly of magnetic moments in the vicinity of the closed neutron shells N=50 and N=126 have unambiguously revealed an anomaly of the proton gl factor of δgl≈0.1 [1]. In the present letter we report on a similar investigation for the closed neutron shell N=82. For this purpose the g-factors of the first excited 11/2− states in the rare earth isotopes145, 147, 149Eu were measured. Due to paramagnetic effects, a measurement of nuclear g-factors in the rare earth region requires the investigation of the paramagnetic behaviour of the probe atoms in the chosen target material.The g-factors in145,147,149Eu were measured by the method of the time differential perturbed angular distribution (TDPAD) of the deexcitationγ-rays. The 11/2− states in145Eu(EX=716 keV, T1/2=0.49 gms) and in149Eu(EX=497 keV, T1/2=2.43 μs) were populated and aligned by the nuclear reaction144,148sm(d,n)145,149Eu with the pulsed deuteron beam (Ed=11 MeV) of the Erlangen tandem accelerator. Enriched metallic Sm targets of 89%144Sm and 95%148Sm were used. The 11/2− state in147Eu(EX=625 keV, T1/2=0.77 μs) was excited by the reaction147Sm(p,n)147Eu with a pulsed proton beam (Ep=10 MeV) using a 93% enriched147Sm target.A detailed description of the experimental set-up and the evaluation procedure for the present TDPAD measurements is given in ref. [2]. The deexcitation γ-rays of the isomeric Eu states were detected by two NaJ(T1) detectors encompassing an angle of Δθ=90°, and placed in a plane perpendicular to the external applied magnetic field direction. The magnetic field was calibrated by measuring the very precisely known g-factor of the isomeric 5/2+ state of19F in a BaF2 target. The Sm targets were mounted either in an oven for the high-temperature measurements or into a copper cooling-rod for temperatures down to liquid nitrogen.

Magnetic moments of the isomeric 112− states in 145,147,149Eu☆

The nuclear g-factors of the isomeric 112− states in 145,147,149eu were measured by the TDPAD method. The results, corrected for paramagnetism, are g(145Eu) = + 1.356(8), g(147Eu) = + 1.28(1) and g(149Eu) = + 1.27(5). A semiempirical analysis of the g-factor of the isomeric state in 145Eu together with the g-factors of the ground states in 139La and 141Pr yields an orbital g-factor of the proton gl = 1.11(3). The decrease of the g-factor values of the isomeric states in the heavier Eu isotopes indicates an increasing degree of collectivity with increasing neutron number.

Lattice defects in cadmium studied by the angular correlation method

AbstractThe perturbed angular correlation of the 173 keV—247 keVγ-γ-cascade in111Cd was measured for proton-irradiated and quenched cadmium as a function of the annealing temperature. Three distinct defect configurations were identified by the quadrupole interaction frequencies:D1 with

The magnetic moment of the first excited state in138La

\left| {v_Q } \right| = \left| {\frac{{eQV_{zz} }}{h}} \right| = 103\left( 3 \right)

Correlated radiation damage in silver

MHz visible for annealing temperaturesTA between 110 K and 130 K,D2 with |vQ| between 4 and 22 MHz observed for 110 K ≦TA≦150 K, andD3 with no electric field gradient. The fractionD3 is seen from 77 K to room temperature. The defect configurationsD1 andD2 are of vacancy type. It is argued thatD1 originates from simple defect structures (probably mono- or divacancies) whileD2 is attributed to small vacancy agglomerates. Because of its larger stability,D3 is ascribed to defect loops. The experiment shows clearly that a vacancy-like defect is mobile in recovery stage III in Cd.

Temperature dependent perturbation of γ-ray angular distribution by radiation damage in lead

Abstract Radiation induced lattice defects significantly influence the nuclear quadrupole interaction of 69 Ge and 67 Zn in Zn. The experimental data can be explained by a model based on the diffusion of point defects.

The influence of radiation damage on the quadrupole interaction of69Ge in Zn

Theg-factor of the first excited state in the odd-odd nucleus138La (Ex=73 keV,Iπ,T1/2=116 ns) was measured by the time-differential perturbed angular distribution (TDPAD) method. The result, corrected for Knight shift and diamagnetic shielding, isg=+0.962±0.016. This value can be fairly well reproduced using the additivity relation for magnetic moments, empirical values for the odd-proton and odd-neutrong-factors, and an experimentally deduced wave function for the 3+ state.