R. Böhm

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.

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 2+ state in22Ne

\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.

Correlated radiation damage in cadmium

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.

Hyperfine interactions of highly diluted Eu in Sm

Theg-factor of the 1,275 keV 2+ state in22Ne has been measured by means of the time-differential recoil-into-vacuum (plunger) technique. An analysis including excited heliumlike electronic configuration was performed. A fit, which includes all these electronic states, provides a value of ¦g¦=0.36±0.03.