E. van Walle

Nuclear orientation of on-line separated isotopes

Abstract On-line techniques have proven to be successful for the study of nuclei far from stability in performing spectroscopy. Further information on these short-lived nuclei can be obtained by measuring anisotopy coefficients of β- and γ-transitions. These measurements permit the clarifying of decay schemes and the study of nuclear moments. We thus propose the combination of on-line mass-separation with low temperature nuclear orientation. A system for this is being set up at the LISOL facility. The main part consists of a 3 He- 4 He dilution cryostat with high cooling power. It features a side-access port to allow direct implantation on the cold finger. A liquid helium cooled transport line with adjustable baffles makes the connection to the isotope separator. Nuclei with a lifetime down to a few minutes can be continuously implanted into a ferromagnetic host and oriented by the hyperfine field at temperatures lower than 30 mK. The limit of the lifetime is set by the spin-lattice relaxation time. In order to study shorter lived nuclei an “on-line” immediate orienting mechanism is installed: the beam line includes a UHV-chamber, where polarization is achieved by scattering at grazing incidence on a magnetized nickel single crystal. For preserving the obtained orientation during measurement the low temperature implantation is still required. Both mentioned orienting mechanisms completement each other for a nuclear study of short-lived isotopes. Sets of deflection plates and a movable part of the beam line allow a quick transition from one mode to another. Furthermore the cooled collecting foils can be changed in a short time without breaking the cooling cycle it removal of the daughter activities is requested.

On-line nuclear orientation of Au isotopes at KOOL

On-line low temperature nuclear orientation measurements were performed on shortlived185Au,186Au,189mAu,191mHg implanted in an iron matrix. As decay products185IrFe and191mAuFe were studied too. Besides magnetic moment determinations spectroscopic information on spin values of excited levels and mixing ratios of transitions in the daughter nuclei Pt and Au are presented. The results are interpreted in a Nilsson + Coriolis + pairing model.

Nuclear orientation of neutron deficient isotopes in the Z = 50 region

Abstract The first low temperature nuclear orientation measurements on electromagnetically separated short lived nuclei (5.1 min. ⩽ t 1 2 ⩽ 58 min. ) are presented. A systematic magnetic moment study of the series 105–108 In and of 101–102 Ag has been performed. This investigation permitted to deduce ground state characteristics. The spin values of the high spin isomers of the odd-odd indiums have been fixed.

Nuclear orientation techniques applied to on-line separated isotopes

Abstract Recent advances using the on-line nuclear orientation facility KOOL are described. Examples are given from results on nuclear moments, spins and multipolarities in different regions of the nuclear chart. The first on-line nuclear magnetic resonance results are discussed, as well as the first particle anisotropy measurements. Each one of these technical improvements is shown to lead to substantial increase of accuracy and/or surprises in physics. A short review is given of recent experiments aimed at eliminating the lower limit on nuclear lifetimes which exists in pure low-temperature nuclear orientation.

The hyperfine field of Francium in iron and the systematics of alkaline fields

Abstract The hyperfine field of Fr in iron is reported for the first time, obtained from on-line nuclear orientation experiments on Fr isotopes. The completed alkaline systematics are compared with recent self-consistent hyperfine field theories.

First results of alpha-anisotropy measurements at kool

ConclusionFrom the foregoing it is clear that with the technical realization of particle detection at 4K (and in on-line conditions), NO is able to make substantial contributions to α-decay theory and more specifically to the knowledge of nuclear deformation. Moreover, since there is almost no β- and α-feeding to states built upon the state of interest the bandstructure cannot be obtained from decay studies. Therefore the extraction of information on shape and/or spin projection with the method described in this work is very important. Measuring α-anisotropies and more generally particle anisotropies is thus expected to become a very powerful method in on-line applications. From a theoretical viewpoint specific calculations of δ(Q,<2>) for transitional nuclei (triaxiality?) would be very desirable.

The implantation behaviour of indium and silver in iron at low temperature

Abstract 111 In and 103 Ag have been implanted at very low temperatures (30 mK) in iron. Using the nuclear orientation technique it can be shown that the nuclei are ending up almost exclusively in substitutional lattice sites.

The hyperfine field of silver and of indium in cobalt

The hyperfine field of Ag and In in cobalt has been determined using the nuclear orientation technique, as 349(20) and 158(20) kG respectively. For In in cobalt we also determined the sign to be negative. A comparison with different theoretical models is given.

Polarization of on‐line separated isotopes using surface scattering and low temperature implantation

Although on‐line separation has become a widespread technique, no attempt has been reported yet at combination with nuclear polarization. The usefulness of this combination is obvious in clarifying decay schemes as well as in the study of nuclear moments. Therefore a new experimental set‐up has been coupled to the Leuven Isotope Separator On Line at the Cyclone cyclotron. It allows for continuous implantation of a beam of separated ions into a ferromagnetic foil at temperatures below 30 mK: this means that almost any isotope can be oriented to a useful degree without loss of activity. The central part of the set‐up is a high power 3He‐4He dilution refrigerator coupled through helium cooled transport lines and adjustable baffles to the central beam transport line of the isotope separator. To circumvent the limitation to lifetimes below the spin‐lattice relaxation time a secondary ‘‘in beam’’ orientation facility has been installed in the connecting beam line. The orienting mechanism then is based on the ef...

On-line nuclear orientation at KOOL

Since the previous conference we extended our series of on-line γ-anisotropy measurements in the Z=50 and Z=82 region leading a.o. to the identification of the phase transition in the Au isotopes. Besides ‘conventional’ on-line low temperature nuclear orientation, we introduced the first on-line applications of NMR/ON, on-line α-anisotropy measurements and β-decay asymmetry experiments. The intriguing information from these new developments both in the field of nuclear structure and solid state physics is briefly discussed.