J Vanhaverbeke

Nicole: New on-line orientation facility at ISOLDE/CERN

This paper presents off-line and on-line orientation results obtained with the new on line nuclear orientation device NICOLE in CERN. Magnetic moments of187,185Ptg and186Irm, electric quadrupole moment ratios between Pt isotopes with mass number 185, 187 and 189, the spin of the 2 h isomer of186Ir and a new decay scheme of184Au involving a metastable state are established. The shape variation versus mass number of the Pt isotopes leads to sign change of the spectroscopic quadrupole moment between A=187 and 185.

Shape transition in light Pt isotopes: Magnetic moments and electric quadrupole moment ratios for185,187,189Pt

Nuclear orientation and nuclear magnetic resonance experiments were performed on185, 187, 189Pt isotopes oriented in Fe and single crystal Zn at temperatures down to about 6 mK. The hyperfine splitting frequencies of185Pt and187Pt in iron were determined to be 164.9(2) and 261.1(2) MHz, respectively. With the hyperfine field of −126.1(2.5) T, the g-factors are deduced to be |g(185Pt)|=0.172(3) and |g(187Pt)|=0.272(5).The spectroscopic quadrupole moment of187Pt was found to be negative with magnitude similar to that of189Pt, indicating a predominantly oblate ground state deformation for both isotopes. The spectroscopic quadrupole moment of185Pt was found to be positive, with the ratio Q(185Pt)/Q(189Pt)=−3.6(9), clearly indicating a change to prolate ground state deformation.

Magnetic moments of Po isotopes and the quenching of nuclear magnetism in the 208Pb region

The nuclear magnetic moments of the short-lived isotopes 199mPo, 201mPo, 201Po and 203Po, determined with on-line nuclear orientation, are reported for the first time. Together with other recently measured moments in this region, variations with Z and N can be derived which may offer a clue to an understanding of nuclear magnetism around 208Pb.

Hyperfine interaction aspects of cold implantation of francium in iron

The hyperfine field of Fr in Fe and a highly substitutional occupancy in host Fe after cold implantation (T<1 K) — although Fr is the largest atom in nature —have been deduced from experiment. These aspects are treated in relation to other alkalines and 6sp elements.

First on-line β-decay asymmetry measurements of oriented nuclei

We report the first on-line β-anisotropy measurements with nuclear orientation. Particle detectors operating at 4K are used. The first results were obtained on the mirror nuclei15O,17F and19Ne and on69As. All isotopes were implanted in iron. With the same set-up85KrFe was also measured. Important information on hyperfine fields, site occupancy, spin-lattice relaxation and magnetic moments was obtained.

Anisotropic alpha-emission in the223Ra decay chain

Anisotropic α-emission from nuclei in the decay chain from223Ra to207Tl has been observed using low temperature nuclear orientation in combination with high resolution α-detection at 4.2 K. Information on partial wave amplitudes as well as hyperfine interactions has been extracted.

Magnetic moments close to208Pb from on-line no

The nuclear magnetic moments of the shortlived isotopes199mPo,201mPo,201Po and203Po have been determined with on line nuclear orientation. Together with other recently measured moments in this region, the variations with Z and N may represent a clue to an understanding of the quenching of nuclear magnetism around208Pb.

The interaction of low-energy secondary radioactive beams and magnetic-surfaces

A system was constructed to polarize on-line mass separated radioactive ion beams. They can be either transmitted through very thin foils or be reflected under a grazing incidence angle from a very flat ferromagnetic surface. It will be used to study both nuclear parameters of the ions polarized as well as the magnetic properties of the surfaces.

Alpha-emission of nuclei oriented on-line

The technical realization of particle detection at very low temperatures (4K) has made it possible to study for the first time the anisotropic α-decay of oriented nuclei which have been produced, separated and implanted on line.The measured α-angular distribution reveal surprising new results on nuclear aspects as well as in solid state physics. The nuclear structure information from these data questions the older α-decay theoretical interpretation and urges for more theoretical studies and a reexamination of the earliest work on anisotropic α-decay.

The hyperfine field of krypton in iron

The hyperfine field of krypton nuclei at lattice sites in iron has been determined using nuclear orientation. From the anisotropy of the electrons emitted in the decay of85Kr implanted in iron, a hyperfine field value of +31.2(8) T was deduced for a substitutional fraction of approximately 37%. Also, a relaxation time of the order of 900 see was observed at temperatures between 7 and 11 mK.