W. Ott

The source of polarized heavy ions (PSI) at the Heidelberg MP tandem

Abstract The new polarized source at the Heidelberg MP tandem is described. The source produces beams of 6 Li , 7 Li and 23 Na ions, which are preaccelerated to 150–200 keV and injected into the MP tandem. The results of the first test runs are presented. A 44 MeV 7 Li beam has been produced and the polarization was detected in a nuclear reaction. A Na beam will be accelerated during one of the next few runs. Improvements of the polarization by laser optical pumping are discussed.

Nuclear spin polarized alkali beams (Li and Na): Production and acceleration

Abstract Recent improvements of the Heidelberg source for polarized heavy ions (PSI) are described. By means of optical pumping in combination with the existing multipole separation magnet the beam figure of merit (polarization 2 × intensity) was doubled. 7 Li and 23 Na atomic beams can now be produced in pure hyperfine magnetic substrates. Fast switching of the polarization is achieved by an adiabatic medium field transition. The hyperfine magnetic substate population is determined by laser-induced fluorescence spectroscopy. In routine operation atomic beams with nuclear polarization p α ≧ 0.85 ( α = z, zz) are obtained. The acceleration of polarized 23 na − ions by a 12 MV tandem accelerator introduces a new problem: the energy at the terminal stripper foil is not sufficient to produce a usable yield of naked ions. For partially stripped ions hyperfine interaction of the remaining electrons with the nuclear spin reduces the polarization. Using in addition the Heidelberg postaccelerator 23 Na 9+ beams of energies between 49 and 184 MeV were obtained with an alignment on target of P zz ≊ 0.45 . 7 Li beams have also been accelerated up to 45 MeV with an alignment of P zz = 0.69.

Elastic and inelastic scattering of polarised 7Li from 120Sn

The differential cross section and analysing powers iT11, TT20, T20, T21 and TT30 have been measured for both the elastic scattering of 44 MeV polarised 7Li from 120Sn and for projectile excitation to the 1/2 state at 478 keV. The data have bee fitted with coupled-channels calculations which include ground-state reorientation of the 7Li and coupling to excited states of 7Li. The sensitivity of the different observables to a number of coupling schemes is discussed. The potentials were derived from a double folding model which explicitly includes the 7Li deformation.

Electron cooling of heavy ions

Abstract The electron cooling device of the Heidelberg cooler storage ring has come into operation and for the first time has cooled ions heavier than protons. These experiments have proven that the cooling force is increasing with the charge of the ion. Cooling in the longitudinal and transverse phase space can increase the phase space density by up to four orders of magnitude. The usefulness of the method to increase the lifetime and the intensity of the stored particles was demonstrated resulting in a number of 3 × 10 10 carbon particles which were successfully cooled and stored.

One year of operation at the Heidelberg TSR

Abstract After one year of operation the heavy ion storage ring TSR at the Heidelberg Max-Planck Institut fur Kernphysik has reached full performance. As designed 1000 turns are accumulated by a combination of multiturn and rf stacking. Due to phase space compression by an electron cooler the momentum spread of the beams is Δp/p = 10−5 −10−4 depending on the heating by intrabeam scattering. The cooled beam lifetime is pushed to the limits set by charge exchange processes as electron capture for bare nuclei and electron stripping for incompletely stripped ion beams. As the vacuum pressure is P ≤ 10−10 Torr at present, beam lifetimes range from τ = 36 h for 21 MeV protons to 20 s for 7 MeV Be+. Intensities of up to 18 mA (3 × 1010 particles) C6+ beam have been stacked by applying phase space cooling during injection. For these high intensities the splitting of the longitudinal Schottky noise signal showed irregular behaviour with respect to the expected Δƒ ∼ I 1 2 scaling law.

Elastic and inelastic scattering of polarized 7Li ions from a 26Mg target

Abstract Differential cross sections and analyzing powers T T 10 , T T 20 , T 20 , T 21 and T T 30 for elastic scattering of 44 MeV polarized 7Li from 26Mg, for projectile excitation to the 1− 2 state at 0.48 MeV, target excitation to the 2+ state at 1.81 MeV and for the double excitation of both these states have been measured. The mechanism of these processes is studied within a coupled channel formalism. A strong influence of the deformation and excitation of the projectile on all measured observables is found. Further the results of the coupled channel calculations underline the importance of the third rank (TT30) analyzing powers in the analysis of polarized 7Li scattering on 26Mg.

The Heidelberg Heavy Ion Test Storage Ring TSR

The Heavy Ion Test Storage Ring TSR [1] is an experimental facility for accelerator, atomic and nuclear physics studies presently under construction at the Heidelberg Max-Planck-Institute. The storage ring is designed for heavy ions of up ∼ 30 MeV/u at a charge to mass ratio of qA = 0.5, corresponding to a magnetic rigidity of Bρ = 1.5 Tm. Phase space compression using electron cooling [2] will be applied in the TSR to produce ion beams of extreme quality and at the same time to reduce the large transverse emittances and momentum spread which build up in the sophisticated injection technique used to reach heavy ion currents in the mA range. The beams equilibrium emittance and momentum distribution after cooling will be limited just by intrabeam scattering and the interaction in an internal target. Furthermore the very broad rigidity acceptance of the TSR will permit operation with simultaneous storage of several neighboring charge states of ions. This report will review the major design features and give the status of the ring project.

Study of the one-neutron transfer reactions induced by polarized 7Li ON 26Mg and 120Sn

Abstract Angular distributions of the cross sections and analyzing powers up to third rank have been measured for the one-neutron transfer reactions 26Mg(7Li,6Li)27Mg, 120Sn(7Li,6Li)121Sn and 120Sn(7Li, 8Li)129Sn initiated by polarized 7Li ions of 44 MeV. Third-rank analyzing power has been measured for the first time in transfer reactions. Coupled-channels calculations in which the ground and first excited states of 7Li are coupled together by collective interactions and one-neutron transfers are calculated in exact finite range explain the experimental data for low-lying states in final nuclei. Extracted spectroscopic factors are in good agreement with those obtained from other one-neutron transfer reactions on the same targets.

Tidal symmetry in scattering of polarised 7Li projectiles

Tidal symmetry is a recently proposed concept which introduces considerable simplifications into the theoretical analysis of heavy-ion scattering and fusion. It also facilitates the understanding of features of nuclear reactions induced by polarised heavy ions. Key pointers to this symmetry are presented and compared with new experimental results and published data for 7Li elastic scattering. The discussion gives an indication of the usefulness of the tidal symmetry concept.

Semiclassical description of analyzing powers in one-nucleon transfer reactions induced by 44MeV polarized 7Li ions on 120Sn

Abstract Analyzing powers of various ranks for the reaction 120 Sn( 7 L , 6Li) at Elab = 44 MeV have been measured as functions of scattering angle and Q-value. The reaction is understood semiclassically as transfer of the neutron from one reaction partner to the other during their relative motion on classical trajectories. An approximate evaluation of transfer amplitudes is presented which takes care of the relative magnitude of amplitudes for various spin quantum numbers and also of the discontinuity of the trajectory angular momentum in the interaction point. Thus simple formulae for analyzing powers are derived. All the characteristic features of the data are reproduced within this model.