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NUCLEAR SPECTROSCOPY OF SHORT LIVED ISOTOPES FAR FROM THE STABILITY LINE BY ONLINE LOW TEMPERATURE NUCLEAR ORIENTATION

Objective


First, short lived isotopes were implanted in suitable foils at low temperature. To produce such isotopes, protons or heluim-3 beams with energies up to 800 MeV hit special targets, designed and operated in such a way that a beam of short lived isotopes is produced. The isotopes are separated by a pair of mass analysing magnets and after proper focusing a beam of isotopes is implanted in suitable foils at tempetures as low as 7 mK. Typical foils are magnetized iron in which strong magnetic hyperfine fields exist able to orient the implanted isotopes, or single crystals of zinc in which the implanted ions experience strong electric field gradients.

Thus the obtained nuclear orientation depends on nuclear properties (magnetic dipole and electric quadrupole moments) and on solid state properties (local magnetic fields or local electric field gradients). Nuclear orientation can be used to study nuclear properties like nuclear moments and is very useful for obtaining spectroscopic information by measuring the anisotropic angular distribution ofradiation (notably gamma transitions) of these short lived isotopes, which become oriented after implantation through nuclear hyperfine interaction.

There is an intricate play between nuclar relaxation times and nuclear lifetimes which determines the speed at which nuclei become oriented after implantation in the cooled samples. A technique depending on the time dependence of the anisotropy of radiation from nuclei after pulsed implantation has been developed and exploited. The main nuclei of interest are in the region of platinum to mercury. In this work chains of isotopes with a fixed atomic number (A) occur as a consequence of beta decay, electron capture and gamma ray emission. In some cases alpha emission occurs, lowering A by 4.
The low temperature on-line nuclear orientation techniques allow investigation of the following quantities of short lived exotic nuclei: g-factors and spins of ground states and isomeric states, quadrupole moments of ground states and isometric states, multipolarities of transitions and multipole mixing ratios, parities of excited states, B(M1)- and B(E2)- values of transitions between states, and, combining these, the derivation of decay schemes.
The essential aims are detailed studies of the new regions of nuclear deformation and the transitions regions between spherical and deformed, the search for intruder states, additional investigations concern the phenomenon of shape coexistence and the study of rotational and vibrational properties of exotic nuclei.
In addition to the experiments with the ISOLDE installation at CERN the collaboration plans to perform common experiments in the future with the existing online systems at Leuven and Daresbury and also with the FOLBIS-system in Bonn.

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CSC - Cost-sharing contracts

Coordinator

KATHOLIEKE UNIVERSITEIT LEUVEN
Address
Oude markt 13
3000 Louvain / leuven
Belgium

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Last update: 2 October 1990

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Permalink: https://cordis.europa.eu/project/id/ST2*0393

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