H. Haas

The new CERN-ISOLDE on-line mass-separator facility at the PS-Booster

The ISOLDE on-line isotope separators have been operated since 1967 at the CERN-SC. This 600 MeV proton synchro-cyclotron had to be shut down in December 1990 after 33 years of service and it was decided to move ISOLDE to a new experimental area. The new on-line mass-separator facility is now under construction at the CERN PS-Booster. This accelerator provides an average current of about 2-mu-A of 1 GeV protons in very short high intensity pulses at low repetition rate. The beam can hit either one of the two target stations, the general purpose separator (GPS), a reconstructed ISOLDE-2 type machine (which can deliver beams simultaneously into three beam lines), and the high resolution separator (HRS), which is essentially the slightly modified ISOLDE-3 separator. The central GPS beam line and the HRS feed a common beam transport system to which most of the experiments will be connected. The new facility will be taken into operation in spring 1992.

Unusually large substitutional fraction for Fr implanted in Fe observed by emission channelling

Abstract An emission channelling study has been performed on α-emitting Fr implants in Fe. The implantation dose was kept below 10 11 atoms cm 2 to assure single cascade conditions. Low dose was possible as the experiment was done on line, and data was recorded with a position sensitive detector. The study revealed 45% of francium in substitutional sites at room temperature and 57% in substitutional sites at 120 K. No evidence for vacancy trapping was found, suggesting a small trapping radius for Fr in Fe.

Ion-optical correction elements for on-line mass separators

Abstract To adjust on-line mass separators, variable magnetic or electrostatic multipoles are most desirable. Such elements were built and subsequently included in the ISOLDE-3 on-line mass separator at CERN. In first tests a mass resolving power m †m > 10 000 (FWHM) was achieved, which allowed the isobaric separation of 37Ca from 37K using a tungsten-surface ionization source.

Nuclear structure study of the neutron deficient cadmium isotopes100, 101, 102Cd

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.

Mixtures of molten metals and graphite as targets for on-line mass separators

Targets consisting of fine-grained powders of graphite and metals which do not form thermostable carbides have been investigated. The targets were heated to temperatures well above the melting point of the respective metals. A target of Pt powder mixed with graphite powder is found to be suitable for production of neutron deficient Au isotopes, when irradiated with 910 MeV 3He projectiles. The yields of neutron deficient Cd isotopes from a target of Sn powder mixed with graphite powder are also reported.

Quadrupole moments of Cd and Zn nuclei: When solid-state, molecular, atomic, and nuclear theory meet

The nuclear quadrupole moment of the 5/2+ isomeric state of 111Cd, of particular importance to the interpretation of Perturbed Angular Correlation experiments in condensed matter, was determined by combining existing PAC data with high-level ab initio (CCSD(T)) calculations for Cd-dimethyl and hybrid density functional theory for metallic Cd. A revised value of is found, much reduced from earlier estimates. Using the new result together with the values for other Cd isotopes from atomic data, also recently revised, the trend of Q for the 11/2− states in Cd is in perfect agreement with new nuclear covariant density functional theory calculations. Similar theoretical work for metallic Zn and the ZnS molecule, combined with atomic calculations, also results in an equivalent reduction for the reference value of the 67Zn 5/2− ground-state quadrupole moment to .

Hyperfine interactions and Rutherford backscattering studies of Cd and Hg in CdTe single crystals and thin films

Abstract First results obtained with the e−-γ PAC technique recently installed at CERN/ISOLDE and Rutherford backscattering measurements for as grown and 111mCd and 197mHg implanted CdTe single crystals and thin films are presented. Both probes, Cd and Hg, have a completely different behavior. While most of the Hg atoms have a cubic surrounding in the CdTe lattice, after ion implantation only a small fraction of the Cd atoms occupy regular lattice sites without defects even after high temperature implantation or furnace annealing.

Study of theβ+/EC decay of the neutron deficient nuclei76,78Sr and79Y

The β+/EC decay of the neutron deficient nuclei76,78Sr and79Y was studied employing mass separated molecular beams of SrF+ and YF2+ from the ISOLDE mass separator. The halflives of76,78Sr and79Y were measured as t1/2=8.9(3)s, 159(8)s and 14.4(15)s, respectively, and decay schemes were established for76Sr and79Y. In the78Sr decay 10 new γ-ray transitions were identified.

The 68mCu/68Cu isotope as a new probe for hyperfine studies: The nuclear moments

Time Differential Perturbed Angular Correlation of γ-rays (TDPAC) experiments were performed for the first time in the decay of 68m Cu produced at the ISOLDE facility at CERN. Due to the short half-life of the source isotope, the measurements were carried out online. The intermediate state offers the unique opportunity to study the electromagnetic fields acting at a copper probe in condensed matter via hyperfine interactions. The present work allowed determination of the nuclear moments for this state. The electric quadrupole moment was obtained from an experiment performed in Cu2O and the magnetic dipole moment from measurements in cobalt and nickel foils. The results are discussed in the framework of shell model calculations and the additivity rule for nuclear moments with respect to the robustness of the N = 40 sub-shell.

ON-LINE PERTURBED ANGULAR CORRELATION STUDIES WITH THE SHORT LIVED 127CS PROBE

Abstract On-line Perturbed Angular Correlation (PAC) experiments were performed on the 66.0 keV excited state of 127 Cs, using the γ (114.7 keV)–e − L (66.0 keV) cascade from the decay of the short-lived 127 Ba ( T 1/2 =13 min) isotope produced at the ISOLDE facility at CERN. The PAC experiments were performed with an optimized γ–e − spectrometer coupled to the ISOLDE beam line, which allowed simultaneous implantation and measurement. The optimization of the experiment is described and the first results on metallic foils and single crystals of Al, Be, Ga, Zn, and Ni are presented and discussed. The derived nuclear moments of the 66.0 keV excited state of 127 Cs are | μ |=2.9(2) μ N and | Q |=0.58(12) b . Applications of this new PAC isotope are outlined.