W. Klinger

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.

Investigation of delayed fission in 236U

Abstract The fission isomer of 236 U was produced by the reaction 235 U(d, p) 236 U using pulsed beam techniques. The half-life of the fission isomer was determined to be T 1 2 = 116 ± 7 ns . An isomeric to prompt fission ratio σ i / σ f = (1.24 ± 0.06) × 10 −5 was obtained. The measurements were performed with parallel-plate avalanche detectors which proved to be a high efficiency low background system.

Lifetime and g-factor of the 181 keV level in 78Br

Abstract Low-lying states of 78 Br were populated by means of the nuclear reaction 78 Se(p, n) 78 Br. The observed γ-transitions were fitted into a level scheme. The half-life of the isomeric state at 181 keV was remeasured. Our result T 1 2 = 80 ± 2 μ s differs from the measurements of other groups. The g -factor of this state was determined to be g = +1.02 ± 0.02 with the pulsedbeam DDCA method.

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.

The magnetic moment of the first excited state in 66Ga

Abstract The g-factor of the first excited state in 66Ga (Eγ = 43.8 keV; Jπ = 1+) was measured by the DPAD method. The experimental value is g = −0.504±0.009. A comparison with shell-model calculations for different configurations is carried out. A re-measurement of the half-life yields T 1 2 = 24.6±2.0 ns .

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.

The magnetic moment of the 92+ state in 85Rb, mesonic contributions in the z = 37 region and blocking of core polarization in the 1f52 proton shell

Abstract The g -factor of the 9 2 + state in 85 Rb ( E = 513 keV ; T 1 2 = 1015 ns ) was measured by the TDPAD and the SOPAD methods. The experimental value corrected for diamagnetism and the Knight shift is g = +1.369±0.010. The analysis of this g -factor together with the g -factors of the ground states in 85, 87 Rb shows that the effects usually attributed to mesonic exchange currents depend rather strongly on the corrections for core polarization. A comparison of g -factors of 9 + 2 states in As, Br and Rb isotopes shows a linear increase of the magnetic moments with increasing number of nucleons in the 1 f 5 2 proton shell as predicted by the M1 core polarization theory.

The g-factor of the isomeric 92+ state of 81Br

Abstract The g-factor of the isomeric 9 2 + state of 81Br at 541 keV ( T 1 2 = 32 μs ) was measured by the stroboscopic method. The experimental value g = 1.261 ± 0.010 is compared with shell model calculations.

The analyzing power of the reaction 3He(d, p)4He for vector-polarized deuterons between 2 and 13 MeV

Abstract The analyzing power Ay(θ, E) of the reaction 3He(d, p)4He was measured with vector-polarized deuterons for 23 energies from 2.23 MeV to 13.0 MeV and at lab. angles between 20° and 160°. Angular distributions of the unpolarized differential cross section σ0 were also obtained. The angular distributions of σ0 and of the product σ0Ay, were fitted with Legendre polynomials. The energy dependence of the Legendre coefficients of the expansion σ0Ay, seems to indicate that more than one energy level of the 5Li compound nucleus is responsible for the broad anomaly in the cross section of the 3He(d, p)4He reaction, observed at an excitation energy of ∼ 20 MeV in 5Li. From 5 MeV to 13 MeV the reaction 3He(d, p)4He is an excellent analyzer for deuteron vector polarization if tensor polarization effects are taken into account. A comparison of the analyzing power Ay to polarization parameters of the reaction 3He(d, p)4He measured by other authors, indicates that forces such as tensor forces should be included in a theoretical treatment of the reaction.

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.