R. Seeböck

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 and electric hyperfine interactions in the system EuSm

Magnetic and electric hyperfine interactions in the system EuSm were investigated with the isomeric 11/2− state in145Eu by applying the time-differential perturbed angular distribution (TDPAD) method. The temperature dependence of paramagnetism was studied between 90 K and 1000 K by measuring the magnetic hyperfine interaction frequency ωL=gNμNħ1 β(T)Bext. The paramagnetic correction factor β strictly follows the Curie-Weiss relation β=1+C/(T-θ), withC=−50(2) K and θ=−29(5) K. This is compatible with a hyperfine field ofBint(0)=−25(1) T, a valence of two for Eu in Sm, and antiferromagnetic order at low temperatures.The temperature dependence of the electric quandrupole coupling constant vQ, investigated between 100 K and 400 K, can be reproduced by a linear temperature variation vQ(T)=vQ(0) (1-AT), with vQ(0)=16.2(4) MHz andA=7.2(8)·10−4 K−1.The paramagnetic relaxation time τrel of the nuclear alignment is proportional to the temperature of the sample, with τrel T−1=3.7(2) ·10−9s K−1.This leads to the Korringa relation τJ T=const=5.1(5)·10−11s K for the relaxation time of the 4f electronic spinJ. Assuming that the relaxation ofJ is mainly caused by exchange interaction between conduction electrons and localized 4f electrons at the Eu site, an exchange integral of |Jeff|=0.10(2) eV can be deduced.

Lattice defects in zinc studied by the perturbed angular correlation method

Abstract After the quenching of polycrystalline zinc, a simple defect is observed between annealing temperatures 150 K ⩽ T A ⩽ 240 K. Arguments are given for a vacancy type defect being mobile in recovery stage III in Zn.

The effect of temperature and concentration on the electric field gradient in binary indium alloys

The concentration and temperature dependence of the quadrupole hyperfine interaction of111Cd in InTl (hcp),InPb (fct),InTl (fct) andInCd (fct and fcc) alloys were studied using the perturbed angular correlation technique. The change in the observed quadrupole interaction frequency with concentration can be described by a linear dependence on the axial ratioc/a in all cases. In the alloys with identical crystal structures the strength of thec/a dependence is independent of the solute, in contrast to the strength of the concentration dependence. In all cases where no phase transition occurs, the change in the electric field gradient with temperature follows the empirical relationVzz(T)=Vzz(0) · (1−B·T3/2), where the coefficientB depends on the lattice structure, on the solute-solvent combination and on the concentration. The phase transitions ofInCd alloys at 293 K could clearly be seen as discontinuities in the temperature curves. A similar series of discontinuities observed around 116 K suggests the existence of a cubic low temperature phase.

Quadrupole Interaction in Noncubic Metals and Alloys

During the last few years the perturbed angular correlation method /1/ has proved to be a powerful experimental tool for investigating the electric field gradient (efg) in metals via the nuclear quadrupole interaction. The basic principles of the method are discussed. Recent experimental results are given for pure metals and highly diluted systems as well as for alloys. Also theoretical aspects of the temperature dependence of the efg in pure non-transition metals are discussed.

Investigation of Lattice Defects in HCP Metals

Because of the microscopic nature of lattice defects, nuclear methods are well suited for their investigation. In these methods an atomic nucleus serves as a probe which monitors its surroundings via the hyperfine interaction on a short range scale of several atomic distances. In the present contribution, the trapping and annealing of lattice defects in the hcp metals Cd and Zn were studied with the perturbed angular correlation (TDPAC) or distribution (TDPAD) methods. For details see ref. /1,2/. The defects were produced (i) by proton irradiation, (ii) by quenching, and (iii) by heavy ions recoiling after a nuclear reaction. As probe ions we used 111Cd (i,ii) and 67Ge, 69Ge, 71Ge, 113Sn, and 116Sn (iii).