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The magnitudes and signs of twenty eight E2 and three M1 matrix elements involving 17 low-lying excited states in 104Ru have been measured by Coulomb excitation using 208Pb, 136Xe and 58Ni ions. The completeness of the set of E2 matrix elements is sufficient to extract, directly from the data, the expectation values of the intrinsic-frame E2 moments that provide considerable insight into the underlying collectivity. The measured E2 properties strongly correlate with macroscopic quadrupole collective degrees of freedom. Detailed comparison of the experimental results and theoretical microscopic calculations within the general quadrupole collective Bohr Hamiltonian are presented. Very good agreement of calculations and experiment is achieved without any parameters fitted to the 104Ru experimental data. Results of phenomenological γ-unstable and γ-rigid models are also given.

The Radioactive beam EXperiment (REX) at CERN-ISOLDE has been commissioned and the first experiments successfully completed during 2002 and 2003. The concept used for post-acceleration has proven to be flexible and the experimental program has therefore been extended during the past year. This paper relays some experiences drawn from using the machine in the current program and also conveys some plans for the future.

MINIBALL a highly efficient, position sensitive γ -spectrometer is under construction for upcoming radioactive-beam experiments. In contrast to high spin arrays the total full energy peak efficiency and not the resolving power is optimized with a factor of two larger efficiency for γ -ray energies up to 10 MeV and for low to medium γ -ray multiplicity events. Cluster detectors, incorporating three or four Ge crystals, will be employed to provide high flexibility and to accomodate the various demands of the experiments.

REX-ISOLDE [1] is an experiment at ISOLDE/CERN with a twofold aim: (i) to demonstrate a novel efficient scheme for the acceleration of radioactive ions from the online mass separator ISOLDE to energies around the Coulomb barrier. (ii) to perform first nuclear physics experiments by studying the structure of the neutron-rich (N = 20, N = 28) nuclei by Coulomb excitation and neutron transfer reactions. An overview on the different components of the radioactive beam accelerator is given with special emphasis on the separation possibilities and ion number capabilities of the system.

Three promising scintillation materials, namely GSO(Ce), YAP(Ce), and CsI (pure), were investigated under 50MeV 12 C and 100MeV 32 S heavy-ion irradiation. The radiation resistance, light output and time structure of the scintillation were measured. The measurements were complemented by studies of the transmittance and thermoluminescence of the irradiated crystals. GSO(Ce) and CsI(pure) show an excellent radiation resistance together with a high light output. Maintaining a time resolution in the nanosecond regime, their applicability for heavy-ion detection with accumulated doses up to 5 × 10 13 ions/cm 2 was demonstrated. This enables their continuous operation in counting applications with high average ion rates occurring, e.g., at heavy-ion storage rings. A CsI(pure) scintillation detector realized on the basis of these measurements for electron-ion recombination experiments at the Heidelberg heavy-ion storage ring TSR is described.

Collisions between the circulating ions in an ion storage ring and electrons of an electron cooler can be used for the experimental determination of long atomic lifetimes. Our interest is in the 2s2p 3 P 1 0 level in Be-like ions and the 3s3p 3 5 S 2 0 level in Si-like ions. A time variation of the signal due to ionization of the circulating ions in the residual gas is tentatively used to extract the lifetime of the long-lived excited level in Be-like N 3+ and O 4+ .

Absolute rates and cross sections for dielectronic recombination and ionization of Na-like Fe15+ (1s22s22p63s) ions were measured at electron impact energies between 0 and 1030 eV using the Heidelberg heavy ion storage ring TSR with the cooling device as an electron target. In the region where excitation-autoionization and related resonant processes are relevant, variations of the ionization cross sections below 0.5% were observed with an energy resolution of 4 to 5 eV FWHM. The theoretical calculations are in good overall agreement with the measured cross sections but do not reproduce all the details of the rich resonance structures revealed by our experiment. In the lower energy range we made use of the magnetically expanded electron beam with a transverse temperature corresponding to only kT⊥ = (15 ± 3) meV. This resulted in an excellent energy resolution in the measurements of dielectronic recombination associated with 3s → 3p, 3d, 4l core excitations. Here, theory and experiment are in very good agreement.

Laser induced two-step recombination is used to populate Rydberg states in highly charged ions and to measure the fine structure of inter-Rydberg transitions. The experimental procedure employs photoionization in order to reduce the background due to one-photon recombination. In the spectrum for Rydberg levels of heliumlike C4+, transitions between low-l states are resolved. The signal due to the unresolved high-l states is possibly enhanced due to the mixing between the l levels in the radiation field at high laser intensities.

The decay of e+e− at rest into four photons has been measured in a 20-day experiment at the Heidelberg-Darmstadt Crystal Ball. From a total of 4.9 × 1010 annihilations observed, 406 4gg events with an estimated background contamination of less than 5% have been isolated. Energy and angular distributions are found to agree excellently with simulations based on QED. Using a parallel measurement of 3γ-annihilation for a reduction of systematic uncertainties, the branching ratio Γ4γ/Γ2γ is obtained to be (1.50±0.07(stat.) ±0.09(syst.)) × 10−6, in agreement with lowest-order QED.

PET cameras had their breakthrough as an imaging instrument for clinical application studies due to the large variety of radioactively labeled tracer molecules [1]. These tracers carry an e emitting isotope to e.g. a tumor. Annihilation of the positron into two back-to-back 511 keV photons allows to restrict the source origin in 2 dimensions onto a line of response (LOR). Superimposing the LORs of different decay events locates the source distribution of the emitter in 3D. Modern PET systems reach a spatial resolution of 3-10 mm. A disadvantage of this technique is the diffusion of the positron before its decay with a typical range of ca. 1 mm (depending on its energy). This motion and Compton scattering of the 511 keV photons within the patient limit the performance of PET. We present a nuclear medical imaging technique, able to reach submillimeter spatial resolution in 3 dimensions with a reduced activity application compared to conventional PET. This ’gamma-PET’ technique draws on specific e sources simultaneously emitting an additional photon with the β decay. Exploiting the triple coincidence between the positron annihilation and the third photon, it is possible to separate the reconstructed ’true’ events from background [2,3]. Therefore the spatial uncertainty introduced by the motion of the e or by Compton scattering within the patient can be strongly reduced in the direction normal to the annihilation. Especially Sc is of interest, which β decays into Ca, emitting an 1157 keV photon. With its halflife of 3.9 h, Sc has to be produced from a Ti generator (t1/2 = 60.4 a) [4]. Presently this cannot be performed in clinically relevant quantities, however, this may change with the soon expected availability of highly brilliant gamma beams [2]. Sc has already been applied in patient studies [5]. We combined the Compton camera technique, i.e. the measurement of photon energies and positions of Compton scattering interactions, with a PET camera defining the LOR. Due to the Compton kinematics and subsequent photon absorption, a Compton camera can reconstruct the origin of a primary photon on the surface of a ’Compton cone’ [6]. Superimposing such cones from different events reduces

The level scheme of 137 Nd has been investigated by methods of in-beam γ-ray and conversion electron spectroscopy as well as by observing the γ-transitions following the β-decay of 137 Pm . We measured γ-ray and conversion electron singles spectra, γγ coincidences and angular distributions of prompt γ-rays and conversion electrons. The experimental data result in a detailed level scheme of 137 Nd and allow the assignment of spin and parity to the β-decaying level in 137 Pm , i.e. I π = 11 2 − . Members of a disturbed rotational band based on the 11 2 − isomeric state of 137 Nd and populated by prompt γ-transitions (high spin levels) as well as by the β-transitions of 137 Pm (low spin levels) are identified. The negative parity levels are discussed in a particle-plus-rotator model with Coriolis coupling. Though the analysis results in evidence for a weak prolate deformation of 137m Nd , a quantitative description of the observed level scheme is not achieved. There are features which suggest that a γ-deformation of the core has to be taken into account.

The broad range of applications of the Darmstadt-Heidelberg crystal ball is illustrated. First results are discussed which have been obtained in investigations of the nuclear structure of rapidly rotating nuclei, in studies of nuclear reaction mechanisms, and in experiments with radioactive sources.

Angular and multiplicity distributions for the γ-decay of 164 Er compound nuclei have been measured with the Darmstadt-Heidelberg Crystal Ball. Combining this information with the fusion cross section of (500 ± 50)mb, a compound nuclear spin distribution has been derived which almost exhausts the unitarity limit for lower partial waves. Near the limiting angular momentum of (52 ± 2)ℏ the distribution of partial wave cross sections exhibits a steeper fall-off than predicted by barrier fluctuation and coupled channel calculations.

The cross sections for inelastic scattering, nucleon transfer and transfer-induced fission have been measured for 184 W + 238 U as a function of bombarding energy near the interaction barrier. The inelastic scattering cross section for 183 W + 238 U has also been measured at one energy. The two- nucleon and one-nucleon transfer cross sections, for neutron stripping at least, are similar in magnitude which suggests a substantial enhancement for the two-nucleon transfers. The probabilities for fission following the transfer reactions show in some cases strong dependence on bombarding energy, which demonstrates that simultaneous Coulomb excitation plays an important part in transfer reactions between very heavy ions.

γ-ray energies and multiplicities and neutron multiplicities from Cf spontaneous fission were measured with Nal detectors in 4π at the Heidelberg-Darmstadt Crystal Ball together with the mass and kinetic energy of the fission fragments. The correlation of neutron multiplicity with fragment mass and kinetic energy is presented and discussed in the context of nascent fragment deformation. The γ-multiplicity unfolded for individual fragments is found to be rather independent of mass. A high-energy component in the γ-spectra is found in the vicinity of symmetric fission. The results are discussed in the framework of current fission models.

A position sensitive parallel plate detector has been developed and tested with a 252 Cf source as well as with in-beam experiments. The detector has a time resolution τ = 250 ps, an energy-loss resolution δ ΔE / ΔE ∼ 15% and a position sensitivity Δx ν > 30 kHz) and high integral doses of fission fragments ( N > 5 × 10 9 ) without showing any radiation damage.

Coulomb excitation of states in 178, 180 Hf has been observed to 16 + and 12 + , respectively, with Kr and Xe ions. A strong up bend in the moment of inertia above the 12 + level is seen in 178 Hf and is well reproduced by cranked shell model calculations. For the first time in Coulomb excitation, population of the lowest K π = 8 - isomer in 178 Hf was observed.

The high energy component above 10 MeV in the γ decay following the 128 Te + 34 S compound nucleus reaction is studied by exploiting the new experimental possibilities provided by the NaI crystal ball spectrometer.

The level scheme of 135 Pr has been investigated by means of off-beam γ-ray and conversion electron measurements as well as by methods of in-beam γ-spectroscopy. We measured γ-ray and conversion electron singles spectra, off-beam and in-beam γγ coincidences and γ-angular distributions. From the experimental data a detailed scheme of 22 excited levels for 135 Pr has been constructed. In addition to members of the decoupled band based on the 11 2 − state six further negative parity states were identified. These states are strongly populated in the β-decay of a 9 2 isomer in the parent nucleus 135 Nd. A comparison of all the negative parity states with predictions of the alignment coupling model showed a nearly quantitative agreement, if softness of the core is taken into account. In this case, a prolate deformation with a deformation parameter β ≈ 0.13 was obtained for the 11 2 − isomer in 135 Pr.

Our present understanding of the spectroscopic properties of fission isomers is discussed. Recent progress has been achieved by applying newly developed and improved experimental techniques such as the charge plunger method and the recoil shadow technique to measure quadrupole moments, moments of inertia, and spins of fission isomeric states. The data establish the evidence for shape isomerism in the actinide region and a second minimum in the fission potential.

Differential cross sections are measured for the elastic and inelastic scattering of 104 MeV α-particles from 20Ne, 22Ne, 24Mg, 26Mg and 28Si. The experimental results are analyzed in terms of coupled channels on the basis of the rotational model and prove to be quite sensitive to both the magnitude and sign of the quadrupole and hexadecapole deformation. The extracted β4 deformation parameters show a systematic trend through the region A = 20–28. Prolate shapes of 20Ne, 22Ne and 24Mg, and the oblate shape of 28Si are confirmed. The (α, α') scattering results are compared to results of other experimental and theoretical investigations.