Search

In the II-VI compound ZnTe perturbed angular correlation and tracer diffusion experiments with the nuclear probe 100 Pd/ 100 Rh revealed the formation of a defect complex by the observation of a well-defined quadrupole interaction in tellurium-rich crystals. The defect complex is tentatively interpreted as a Pd A-centre with Pd on the chalcogen lattice site. Using the DLTS method no deep levels correlated to implanted palladium could be detected in the range of 0.2 to 0.8 eV above the valence band edge.

Perturbed angular distribution (PAD) measurements were performed on Zn 1− x Mn x S ( x = 0.05, 0.06, 0.10, 0.18, 0.21 and 0.23). In our PAD experiments recoil-implanted 54 Fe ions were used as nuclear probes. By the local magnetic behaviour of the isolated 54 Fe nuclei we obtained information on the probe environment. The crystal having the lowest manganese concentration ( x =0.05) shows only one hyperfine component. The temperature dependence of this component is the same as in that case of pure ZnS. For samples with concentrations x ⪖0.06 two additional hyperfine components are observed. One of them is attributed to β- or γ-MnS clusters, respectively. The other additional component occurs for crystals having Mn-concentrations x ⪖0.10. The behaviour of this component is similar to the one observed with pure α-MnS. From our data we conclude that the additional components observed with Mn concentrations x ⪖0.06 are due to the formation of different types of MnS clusters. Our experimental findings are compared with the data of magnetic susceptibility, photoluminescence and EPR.

The local magnetic behaviours of isolated Fe and Ni impurities in the II-VI semiconductors ZnS and ZnTe have been studied directly after recoil implantation. From the measured magnetic properties, ...

Perturbed angular distribution experiments on19F implanted into fullerites revealed a large fraction of fluorine atoms which are not subject to static quadrupole interactions in contrast to other allotropic forms of carbon.

The neutron-deficient nuclei100,101Cd were identified for the first time in — beam following the reactions58Ni +46,48Ti and58Ni +50Cr at 230 MeV and 245 MeV bombarding energy of the58Ni beams. Theγ-decay of the isotopes100,101,102Cd was studied inpγ, ppγ,nγ, nnγ, andnγγ prompt and delayed coincidence spectra. Isomers were found with spin and half life {ie1-01}=8+, T1/2=52(5) ns in100Cd, {ie1-02}=(19/2+), T1/2=4.6(4) ns in101Cd and {ie1-03}=8+, T1/2=56(4) ns in102Cd. In a PAD experiment theg-factor of the {ie1-04}=8+ isomer in100Cd was measured to be g=1.24(6). Using the reaction36Ar +70Ge at 135 MeV energy of the36Ar beam, theg-factor and the quadrupole moment of the {ie1-05}=8+ isomer in102Cd were measured to be g=1.29(3) and Q=87(10) fm2, respectively. The spectroscopic results are discussed within a shell model approach using a100Sn core, which accounts well for the electromagnetic properties of the proton aligned isomers. The structure of the spherical neutron states, dominated by the close lying vd5/2, g7/2 orbitals, and the gradually developing quadrupole collectivity are reproduced by the shell model calculations.

In general beam development following the described setting and tuning procedures takes about 8 hours including hardware changes which must be done locally by the operator (as e.g. coil changes in the bunchers). It may be possible to cut down this time by still improving the computer assistance, by installing a still more sensitive beam diagnostic system which might allow for automatic beam line tuning and last not least by replacing some of the hardware.

Excited states in97Ag have been identified for the first time following the reactions46Ti(58Ni,α p 2n and64Zn(36Ar,p 2n. The population cross sections were 1.0(5) mb and 0.7(3) mb, respectively. Theγ-decay of the seniorityΝ=3 states below theI π=(17/2−) and (21/2+) isomers was investigated. In a search for short lived isomers half lives oft 1/2=5(2) ns and 2.5(5) ns were found in theN=50 isotones97Ag,I π=(17/2−) and/or (21/2+) and95Rh,I π=(21/2+). A new isomer was identified in97Pd,I π=17/2+ witht 1/2=2.3(5) ns. The implication of the three-proton hole spectrum in100Sn for the empirical residual interaction and shell model predictions is discussed.

The local magnetic behavior of recoil-implanted isolated Sc ions has been studied in II–VI and other semiconducting compounds. In all cases nonmagnetic configurations were observed consistent with an empty d-shell of the Sc ion. Additionally a different influence of nearby defects on the Sc probe ion was observed in the various types of compound semiconductors.

The local magnetic behavior of isolated Fe and Ni ions has been studied in the II–VI semiconductors ZnS, ZnTe, and α-MnS by magnetic hyperfine interactions. The configuration of the electrons in the unfilled shells is directly reflected in the magnetic properties. Small orbital contributions to the hyperfine fields are found to be present at both impurities in most hosts. In ZnS as well as in ZnTe, Fe ions are found to be in the 2+ and in the 1+ state after implantation. Ni in ZnS also populates two different charge states. First interpretations are made on the basis of an intermediate ligand field model.

The local magnetic behavior of isolated Fe and Ni ions has been determined in ZnS and other semiconducting compounds via the hyperfine interaction at the nucleus. It is concluded that in ZnS Fe ions are observed in the 1+ state while Ni is found in two states, the 1+ state, observed as a magnetic component, and, less abundant, the 2+ state in a nonmagnetic configuration. In InP and other semiconducting compounds, Ni is typically found in a nonmagnetic state.

Etude realisee par des mesures de champ hyperfin a l'aide de la methode de distribution angulaire perturbee

A description of the VICKSI facility is given with emphasis on the special properties which make VICKSI particularly suitable for measurements of charge exchange losses during cyclotron acceleration. Measurements of these losses for carbon-, neon- and argon-ions at different vacuum levels are reported. At the normal operating pressure of VICKSI, namely 3 . 10-7 mbar, no losses could be observed for carbon and neon ions, while for argon the transmission to extraction radius was 92%.

Short-lived isomeric states in 108Ag and 110Ag were populated by means of (p, n) and (d, p) reactions. The nuclear g-factors of these states were determined with the pulsed beam DPAD method to be g( 108 Ag ; 215 keV ) = 1.294(6) and g( 110 Ag ; 119 keV ) = 1.277(15) . The results indicate a spin and parity Iπ = 2+ for 108Ag and Iπ = 3+ for 110Ag.

Large negative Knight shift contributions are observed for Sb and Bi in solid Bi. The similar magnitude at both probe atoms rule out p-electron core polarization as a major contribution to the shift. The shift rather seems to scale with the diamagnetic macroscopic susceptibility of bismuth.

The magnetic hyperfine fields at isolated Ni impurities in Pd and Pd-Pt alloys were studied with the perturbed-angular-distribution (PAD) method by measuring the temperature, magnetic field, and concentration dependence of the nuclear-spin Larmor precession of isomeric states in $^{63}\mathrm{Ni}$. The recoil-implanted Ni nuclei, as products of heavy-ion nuclear reactions, are present in extreme dilution (l1 ppm) in the hosts. The positive Larmor frequency shift (Knight shift) observed for Ni impurities in Pd follows a Curie-Weiss-like temperature dependence with a large Curie constant indicating a giant moment behavior. For Ni impurities in the Pd-Pt alloys a considerable positive shift remains even at 30 at. % Pt content. The variation of the shift with Pt concentration and temperature reflects the variation of the Pd-Pt alloy susceptibility. The different contributions to the hyperfine field could be differentiated by comparing the Knight shift for Ni in Pd with its susceptibility contribution obtained from extrapolated susceptibility measurements in dilute Pd-Ni alloys. The negative core-polarization field of the impurity spin moment is compensated for by a transferred hyperfine field correlated with the host polarization in the neighborhood of the impurity. The remaining positive hyperfine field is due to a weak orbital moment of 0.3${\ensuremath{\mu}}_{B}$ at the impurity site. The values obtained for the different contributions are compared with results of the Korringa-Kohn-Rostoker--coherent-potential-approximation calculations for concentrated Pd-Ni alloys extrapolated to the dilute limit.

The magnetic hyperfine field for zinc in nickel has been measured by means of time-differential observation of perturbed angular distribution ofγ-rays following the nuclear reaction64Ni(α,n)67m Zn. Its temperature dependence follows that of the magnetization of nickel within 2%. The value ofH hf(0)=−29.6 (3) kG was extrapolated from the measurements.

The improvements are described resulting from the addition of an 8 MV tandem as a second injector for the VICKSI accelerator combination. For ion beams with masses A < 30 the limitation for high energy beams will be given by the magnetic field of the cyclotron, e.g. 32 MeV/A. The alternate use of the two electrostatic injectors will increase the available beam time. The variety of ions for acceleration with VICKSI will be enlarged considerably by use of sputter sources.

Determination de la dependance avec la temperature, le champ magnetique et la concentration, du champ magnetique hyperfin de Ni dans Pd et PtPd a l'aide de la methode de correlation angulaire perturbee

A large negative term in the Knight shift has been found for a number of open p-shell elements of the 5th and 6th period in the host Bi which disappears at the p-shell closure.

The VICKSI-accelerator combination will be enlarged by installing an 8 MV Pelletron tandem injector. The addition of the new injector will allow acceleration of ions up to 32 MeV/A for masses up to ∼ 30 u and will produce a variety of ions which are not available from the Penning ion source installed in the existing CN injector. The progress of the various subsystems for the new injector is described.

By means of time-differential observation of perturbed angular distributions of $\ensuremath{\gamma}$ radiation following the nuclear reaction $^{66}\mathrm{Zn}(d, p)$,, the electric quadrupole interaction frequency of the isomeric ${\frac{9}{2}}^{+}$ state of $^{67}\mathrm{Zn}$ in zinc metal has been measured as a function of temperature. At room temperature the frequency was determined to be $\frac{{e}^{2}\mathrm{qQ}}{h}=45.5(4)$ MHz. The temperature dependence is compared with previous results for $^{111}\mathrm{Cd}$ in cadmium.

An isomeric level in 107Cd at 845 keV populated by the reactions 107Ag(p, n), 106Cd(d, p) and 104Pd(α, n) has been observed. The half-life of this state is T 1 2 = 77(7) ns , and the spin and parity are I π = 11 2 − . The magnetic moment has been determined by the pulsed beam time-differential perturbed angular distribution method (DPAD) to be μ = −1.012(12) n.m.

Zusammenfassung Das innere Feld von Zn in Eisen wurde mit der DPAD-Methode (Time Differential Perturbed Angular Distribution) gemessen. Dazu wurde 67mZn (T 1 2 = 333 ns ) mit Hilfe des Ruckstosses nach der Reaktion 64Ni(α, n) ins ferromagnetische Gitter implantiert und die Larmor-Prazession des Kernspins (I π = 9 2 + , g =-0.243) im effektiven Magnetfeld beobachtet. Die experimentelle Methode und das Ergebnis, Hhf(T = 0 K) = -191(3) kG, werden diskutiert.

The neutron deficient nucleus96Pd, four proton holes below the doubly magic100Sn, has been studied in the reaction64Zn (36Ar, 2p 2n). Innγ andγγ coincidences levels up to 7 MeV excitation energy were established, and a new neutron core-excited isomer with T1/2=35(4)ns and g=0.83 (5) was identified. A detailed shell model study yields excellent agreement for states within the π(p1/2,g9/2) configuration space but fails to reproduce the isomerism andg-factor for the core-excited state.

The Knight shift and its temperature dependence for a Cd impurity in palladium metal were measured by means of DPAD- and DPAC-methods utilizing the well known 5/2+, 247-keV state in111Cd. The shift at 80 K was found to be KS (CdPd, 80 K)=−0.8(2)%. The observed variation of the KS in the temperature range from 80 K up to 1400 K is 0.5%. For calibration purposes an accurate remeasurement of the magnetic moment of the 5/2+ state in111Cd was necessary and yieldedμ(111Cd, 5/2+, 247 keV)=−0.7697(20) n.m.

Low-lying levels of 72 As have been studied by excitation function, γγ concidenec, and neutron time-of-flight measurements using the reaction 72 Ge (p, n). A new isomeric state at 213.5keV was found. The spin-parity and half-life of this level were determined to be I π = 3 + and T 1 2 = 80(2) ns , respectively. The g-factor has been measured by the pulsed beam time-differential perturbed angular distribution method (DPAD) and found to be g= +0.527(6).

The local susceptibilities and the 3d spin dynamics of isolated nickel ions in various alkali-element hosts have been measured, utilizing the perturbed \ensuremath{\gamma}-ray distribution method after recoil implantation. In the heavy alkali-metal hosts, Cs, Rb, and K, the local susceptibilities of the isolated Ni ions irrespectively show the temperature behavior of a fully localized spin-orbit-coupled 3${\mathrm{d}}^{9}$ configuration. Clear host dependence of the magnetic behavior is seen in the spin-fluctuation rates which increase with decreasing host volume. In Na, the magnetic behavior drastically deviates from that of the purely ionic configuration, and Ni ions in Li as well as in Ca and Ba hosts are nonmagnetic.

A 2π neutron multiplicity filter consisting of 16 detectors filled with NE213 liquid scintillator has been designed and assembled for in-beam γ-ray spectroscopy of neutron deficient nuclei. Results are presented for the efficiency for single and multiple events, detector cross talk by scattering and n-γ discrimination, both, for a 252Cf source and a typical (hi, xn yp zα) reaction.

We report on the measurement of level energies, lifetimes, \ensuremath{\gamma}-ray intensities, and angular distributions in $^{73}\mathrm{Br}$, obtained in the reactions $^{40}\mathrm{Ca}$${(}^{36}$Ar,3p) and $^{40}\mathrm{Ca}$${(}^{40}$Ca,\ensuremath{\alpha}3p). The g factor of the 241 keV isomeric state (\ensuremath{\tau}=50 ns) was determined to be g=1.31(9) from the Larmor precession in an external magnetic field. The fully aligned members of a rotationally aligned ${g}_{9/2}$ band were identified up to spin ${I}^{\ensuremath{\pi}}$${=(33/2}^{+}$; the E2 transition strengths indicate a large prolate deformation decreasing from ${\ensuremath{\beta}}_{2}$=0.37(4) to ${\ensuremath{\beta}}_{2}$=0.33 at rotational frequency \ensuremath{\Elzxh}\ensuremath{\omega}\ensuremath{\approxeq}0.45 MeV. The negative parity yrast bands with signatures \ensuremath{\alpha}=\ifmmode\pm\else\textpm\fi{}1/2 were established up to a probable spin of ${(37/2}^{\mathrm{\ensuremath{-}}}$. The \ensuremath{\alpha}=+1/2 yrast band shows a one quasiparticle to three quasiparticle band transition at the same frequency, probably associated with the alignment of two ${g}_{9/2}$ protons. The structure of $^{73}\mathrm{Br}$, which is very similar to that of $^{75}\mathrm{Br}$, has been interpreted with the Strutinsky-Bogolyubov cranking and deformed configuration mixing models.

The isomeric 605 keV, 9 2 + state in 67 Zn was populated by means of the nuclear reaction 64 Ni(α, n). The half-life was remeasured to be T 1 2 = 333(14) ns and the magnetic moment was determined with the pulsed beam PAD method as μ = − 1.094(9) n.m. These results are compared with half-lives and moments of corresponding 9 2 + neutron states in 67, 69, 71, 73 Ge.

Low-lying states of the doubly odd Br isotopes were populated by means of the nuclear reactions 78, 80, 82Se(p, n)78, 80, 82Br. The g-factors of the first excited 2− states in 78Br and 80Br were measured with the pulsed beam DPAD method and were found to be g( 78 Br ) = − 0.56 ± 0.02 and g( 80 Br ) = − 0.83 ± 0.06 .

The methods of the stroboscopic observation of the nuclear Larmor precession as well as the conventional time-differential spin precession were applied to the 10.2 μsec state of 58Co populated by the nuclear reaction 57Fe(d, n). The ℷ-factor has been determined to be ℷ = +1.046 ± 0.002 . By means of the ℷ-factor and the measured anisotropy of the observed γ-rays the nuclear properties of the low-lying states in 58Co are discussed.

A general description of the VICKSI accelerator facility is given including its experimental facilities. Its operation and its operational limits are explained as well as the improvements of VICKSI by the addition of an 8 MV tandem as alternate injector. The status and timetable for the tandem project is given.

The quadrupole interaction of excited $^{111}\mathrm{Cd}$ nuclei with electric field gradients due to lattice defects in fcc palladium has been studied by the technique of time-differential observation of perturbed angular distribution of $\ensuremath{\gamma}$ rays. The lattice defects were induced by the recoiling ions following the nuclear reaction $^{108}\mathrm{Pd}(\ensuremath{\alpha},n)^{111}\mathrm{Cd}$. A sharp frequency of 87(2) MHz is assigned to trapped interstitials. A broad temperature-dependent frequency distribution arising from various other lattice defects was found. A migration energy of 0.10(2) eV for free interstitials is deduced.

Etude du comportement magnetique local d'impuretes d'elements de transition isolees dans des metaux: localisation des electrons 3d dans des reseaux hotes formes de metaux alcalins, interactions magnetiques des atomes d'impurete sur differents sites du reseau

The Berlin CN-Van-de-Graaff accelerator has been converted into a heavy ion injector. Main parts of this conversion including the high vacuum tube, the differential pumping system, the new geometry of the spinning and the computer control philosophy are described.

The main topics of experimental β-decay and in-beam studies in the 100Sn region are the shell model structure [1–5], the residual interaction [6–9] and spin response phenomena as the quenching of Ml [3,10] and Gamow-Teller strengths [11]. Shell model calculations [3,6–9,12] in a small configuration space are generally in good qualitative agreement with the experiment. There are, however, a few unsolved problems, like e.g. the failure to reproduce the 94Ru and 95Rh B(E2)-values in the middle of the πg9/2 shell [1,6] or the spin gap isomerism in 95Pd [5]. Whether this is due to an inadequate residual interaction and/or configuration space can be studied best as close as possible to 100Sn.

As a part of a systematic search for isomeric states in arsenic isotopes, populated by (p, n) or (d, n) reactions from stable germanium isotopes, a new level at E = 273 keV with a half — life of 27 ns in 74As and the first excited state at E = = 45 keV with T1/2 = 2.6 μs in 76As were investigated and the magnetic moments of both levels were determined.

Hyperfine interactions at isomeric 19 F and 62Cu have been observed in superconducting YBaCu-oxides as well as in the pure Cu-oxides in externally applied magnetic fields. In CuO, the interaction at Cu has also been detected in zero field.

The magnetic hyperfine field for zinc in iron has been measured by the DPAD method following the reaction 64 Ni(α, n) 67 Zn m . Measurements performed with a sandwich target and with 64 Ni( Fe ) alloy targets containing 3% and 6% nickel yielded similar results: H hf (0) = -191 ± 3 kG.

The magnetic field has been determined on F in CuO in the ordered phase. For magnetic fluctuations above the ordering temperature lower limits have been obtained for CuO and La 2−χ Sr χ CuO 4 with x=0.07.

By means of the reaction40Ca (36Ar, 3p), the band structure of73Br connected with the g9/2 single-particle proton orbit has been investigated up to Iπ=33/2+. In contrast to the core spectrum in72Se, which is dominated by the coexistance of different shapes, the nucleus73Br features rotational bands with slowly increasing moments of inertia. Their deformation β2=0.40(2) has been deduced from recoil distanc lifetime measurements.

We have searched for neutrons from a Pd-electrode loaded with deuterium in electrolysis setups similar to those of Fleischmann and Pons [1] and Jones et al. [2]. Within the sensitivity of our neutron detection system corresponding to a neutron source strength of 5 x 10− 2 neutrons/s we did not find any neutrons due to ‘cold nuclear fusion’. We emphasize the necessity of using several independent neutron detectors.