TheKπ=0− bands in even uranium nuclei were studied in the compound reactions231Pa(p, 2n)230U,230, 232Th(α,2n)232, 234U and236U(d, pn)236U. In-beamγ-rays were measured in coincidence with conversion-electrons, which were detected with an iron-free orange spectrometer. The negative-parity levels are observed up to intermediate spins (I<13−). In addition, the 1− and 3− levels in230U were confirmed by a decay study with an isotope separated230Pa source. For the heavier isotopes (A≥232) the properties of theKπ=0− bands (energies andγ-branchings) are consistent with a vibrational character of these bands. For230U theKπ=0− band lies at rather low energy (E(1−)=367 keV), and the level spacings within this band are very similar to those of the isotones228Th and226Ra, which might indicate the onset of a stable octupole deformation.

Low lying levels in203Hg and205Hg were studied with the (d, p) deuteron break-up reaction atEd=14 and 18 MeV. Gamma-rays and conversion-electrons were measured in coincidence with protons. In addition delayed spectra were recorded with us and ms beam pulsing. Thei13/2 neutron hole state was identified in205Hg and confirmed in203Hg. The known level structure of205Hg below 2 MeV is confirmed and extended. For203Hg we observe theγ-decay of several levels below 1.5 MeV, which were previously known from transfer reactions.

High-spin states in 224,226,228Th were investigated using conversion-electron and γ-ray spectroscopic methods following 226Ra(α, xn) reactions. The Kπ = 0+ and 0− rotational bands are observed, which in 224,226Th merge into a single band characteristic for reflection asymmetric shape. The systematics of the level energies and El transition rates of 220–230Th are discussed in terms of a stable octupole deformation.

The rotational bands built on the excited 112− levels in 191Au and 193Au were investigated in (α,4n) reactions with in-beam γ-ray and conversion electron spectroscopy. Half-lives of the rotation-aligned levels in these bands were determined from e−e− time spectra, which were measured with a new double-orange spectrometer. In addition, some information on the magnetic moments of the rotation-aligned levels was obtained from integral perturbed angular distribution measurements. Finally, the previously unknown low-energy 312− → 272− transition in 191Au was identified from conversion electron measurements. From these data it is concluded that the rotation-aligned Hg cores have predominantly νvi1322 structure, contrary to the earlier suggestion of a πh1122 core structure.

Gamma-ray and conversion electron spectra were measured in the reaction of 25 MeV deuterons on174Yb,196,198Pt,202,204Hg, and232Th. The (d,pxn) deuteron break-up reactions were studied by the measurement ofpγ- andγγ-coincidences. Levels with spins up to approximately 10ħ are observed in the (d,pn) reactions, with a strong preference of the population of yrast states. In the Pt and Hg nuclei the ground bands are seen up to the 6+ states and in196,198pt the semi-decoupled 5−, 7−, and 9− yrast levels are populated most strongly. In202,204Hg we observe fairly strongly new levels with tentative assignments of 5− and 7−. In addition a number of previously unknown levels are identified in the Pt and Hg nuclei, for which no spin-parity assignments could be obtained. A discussion of the level structure in terms of the interacting boson model (196,198Pt) and the shell model (202,204Hg) is given.

The complex of external ion source facilities at the Bonn Isochronous Cyclotron is described. A universal ion source of the Penning type was developed for the production of intense beams of multiply charged ions. Details of this ion source and performance figures are presented. An atomic beam polarized ion source is used for the production of polarized protons and deuterons. A modified atomic-beam...

Control systems have been developed for the stabilization of the external cyclotron beam with respect to the horizontal and vertical alignment, the beam energy and the beam intensity. The operating characteristics of the feedback circuits are presented and the joint operation is discussed. The incorporation of the control systems into a microcomputer controlled energy variation program makes it possible to obtain a reliable and convenient system for the automatic measurement of excitation functions with an isochronous cyclotron.

An automatic 3 MeV variation of a 30 MeV α-beam was performed in 300 steps at the Bonn Isochronous Cyclotron. A microcomputer in connection with a control unit adjusted the cyclotron and the monochromator system parameters. This combination allowed a direct and precise measurement of broad excitation functions. Using fast magnetic field stabilization an energy-shift was accomplished to an accuracy of better than 1 part in 105 within 20 s. The stability of the beam position on the target was about 0.05 mm.

A very high energy stability of an isochronous cyclotron beam can be achieved with a feedback control of the Dee-voltage where the feedback signal is taken from the analyzing slit of a monochromator system. The principle of regulating is described with the aid of the energy-phase distribution of the beam pulses. The residual instabilities of the rf-amplitude and/or the rf-frequency are well compensated. A fast response can be achieved. The practical realization of a feedback controlled energy stabilization at the Bonn Isochronous Cyclotron yields a short- and long-term stability of better than 1 × 10−4. The developed feedback control can be applied to other isochronous cyclotrons, too, especially to the large separated-sector machines.

The present state of the polarized proton and deuteron source at the Bonn cyclotron is described. At the end of the source, which is of the atomic beam type, typical ion beam intensities are 2 μA for protons and 3 μA for deutrons. The overall transmission from the source to the first stopper after extraction from thecyclotron is 3%. Target currents with an energy resolution E/ΔE = 500 are 20 nA for deuterons and 10 nA for protons. For the proton beam a polarization P = −0.71 was measured. For the deuteron beam a pure vector polarization Pz = −0.47 or various mixtures of vector and tensor polarization are obtained.

The lay-out and the ion-optical structure of the beam handling system at the Bonn Isochronous Cyclotron is described. The following beam preparation modes are possible with two double monochromator systems: (1) double dispersive with an extremely high momentum resolution of 30 000; (2) double dispersive with an adjustable dispersion matching with a magnetic spectrograph; (3) nondispersive, nearly isochronous, variable momentum resolution up to 8000, adjustable time of flight resolution below 0.5 ns; (4) achromatic with a transmission of 100%. The practical experiences in operating the system and achieving the design performances are discussed. The results of rigorous test measurements are given.

The g-factor of the 10− isomeric state in 208Bi has been measured by the method of inbeam NMR-PAD. From the experimental value ¦g¦= 0.2666(27) the magnetic moment of the i132 neutron hole state is deduced. The result is compared with experimental values of neighbouring nuclei and theoretical predictions.