Dielectronic recombination (DR) of xenonlike W20+ forming W19+ has been studied experimentally at a heavy-ion storage-ring. A merged-beams method has been employed for obtaining absolute rate coefficients for electron-ion recombination in the collision energy range 0-140 eV. The measured rate coefficient is dominated by strong DR resonances even at the lowest experimental energies. At plasma temperatures where the fractional abundance of W20+ is expected to peak in a fusion plasma, the experimentally derived plasma recombination rate coefficient is over a factor of 4 larger than the theoretically-calculated rate coefficient which is currently used in fusion plasma modeling. The largest part of this discrepancy stems most probably from the neglect in the theoretical calculations of DR associated with fine-structure excitations of the W20+([Kr] 4d10 4f8) ion core.Comment: 7 pagers, 4 figures, accepted for publication in Physical Review

The cross section as well as the branching ratios for the dissociative recombination of ground-state CH ϩ ions with electrons have been measured using the heavy-ion storage-ring technique and two-dimensional fragment imaging. Although the absolute value of the cross section at thermal energies is found to be in very good agreement with the theory, several unpredicted narrow resonances are also present in the data. These structures are interpreted as due to an indirect recombination process via core-excited Rydberg states. The branching-ratio measurement shows that at low electron energy the 2 2 ⌸ state, producing carbon fragments C͑ 1 D͒, is the most important dissociative state, although transitions during the dissociation to other dissociative potential curves are also present. Anisotropy in the angular distribution of the dissociating fragments is visible for some of the final states. Dissociative recombination of ions in the metastable excited a 3 ⌸ state is also observed, and the lifetime as well as the excitation energy of this state are deduced from the imaging data.

The term beta-beam has been coined for the production of a pure beam of electron neutrinos or their antiparticles through the decay of radioactive ions circulating in a storage ring. This concept requires radioactive ions to be accelerated to a Lorentz gamma of 150 for 6 He and 60 for 18 Ne. The neutrino source itself consists of a storage ring for this energy range, with long straight sections in line with the experiment(s). Such a decay ring does not exist at CERN today, nor does a high-intensity proton source for the production of the radioactive ions. Nevertheless, the existing CERN accelerator infrastructure could be used as this would still represent an important saving for a betabeam facility. This paper outlines the first study, while some of the more speculative ideas will need further investigations.

A feasibility test of a new method to polarize beams of strongly interacting charged particles circulating in a storage ring is described. The stored particles, here protons, pass through a polarized hydrogen gas target (thickness 6 x 10 13 H/cm 2 ) in the ring some 10 10 times and become partially polarized because one spin state is attenuated faster than the other. The polarization buildup is clearly demonstrated in the present experiment PACS numbers: 29.27.Hj, 29.20.DhThe study of current problems in nuclear and in elementary particle physics often requires the use of spinpolarized projectiles. Polarized protons and polarized neutrons were produced for the first time some 40 years ago in experiments in which an unpolarized target was bombarded with an unpolarized beam [1]. For a number of different reactions, the particles emitted at angles 0^0° were found to be partially polarized. The polarization of the particles was detected as a left-right asymmetry in a second scattering or reaction which served as the polarization analyzer (double scattering).A major difficulty in this method to produce polarized particle beams is the large loss in intensity and the large spread in angle and energy introduced by nuclear scattering from a target. For beams of protons and deuterons, these problems have been overcome by the development of sources of polarized ions, i.e., the preparation of polarized atoms by atomic methods (e.g., Stern-Gerlach separation) and subsequent ionization of the atoms to produce polarized ions [2].Here we report the first feasibility test of a new method to polarize beams of strongly interacting charged particles. The method is of particular interest for the production of polarized antiprotons, for which the construction of polarized ion sources is not feasible, and for which the large loss in intensity resulting from the double-scattering method has so far prevented experiments with beams of polarized antiprotons.The method can be described as spin-selective attenuation of the particles circulating in a storage ring. The idea was first proposed by Csonka [3]: a polarized target-in our case a target of polarized hydrogen gas (t)-is in-serted in a storage ring. The particles stored in the ring pass through the target for a sufficiently long time that a fraction of the particles is lost by nuclear scattering in the target. Since in general the total strong interaction cross section is different for beam and target spins parallel (IT) an d antiparallel (|j), one spin direction of the circulating beam is depleted more than the other, so that the circulating beam becomes increasingly polarized, while the intensity of the beam decreases with time. The method has been referred to as a "spin filter" since the spin-selective attenuation amounts to a filter which is more transparent to one spin state of the beam than the other.For simplicity, we assume that the target has polarization PT in the vertical direction, i.e., normal to the orbit of the ions in the storage ring. The beam can be considered to cons...

In chemistry and biology, chirality, or handedness, refers to molecules that exist in two spatial configurations that are incongruent mirror images of one another. Almost all biologically active molecules are chiral, and the correct determination of their absolute configuration is essential for the understanding and the development of processes involving chiral molecules. Anomalous x-ray diffraction and vibrational optical activity measurements are broadly used to determine absolute configurations of solid or liquid samples. Determining absolute configurations of chiral molecules in the gas phase is still a formidable challenge. Here we demonstrate the determination of the absolute configuration of isotopically labeled (R,R)-2,3-dideuterooxirane by foil-induced Coulomb explosion imaging of individual molecules. Our technique provides unambiguous and direct access to the absolute configuration of small gas-phase species, including ions and molecular fragments.

We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to install the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear groundstate properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR can also be used to remove isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases, technical details of the existing ring facility and of the beam requirements at HIE-ISOLDE, together with the cost, time and manpower estimates for the transfer, installation and commissioning of the TSR at ISOLDE are discussed in the present technical design report.

Recent spectroscopic models of active galactic nuclei (AGN) have indicated that the recommended electronion recombination rate coefficients for iron ions with partially filled M-shells are incorrect in the temperature range where these ions form in photoionized plasmas. We have investigated this experimentally for Fe XIV forming Fe XIII. The recombination rate coefficient was measured employing the electron-ion merged beams method at the Heidelberg heavy-ion storage-ring TSR. The measured energy range of 0 − 260 eV encompassed all dielectronic recombination (DR) 1s 2 2s 2 2p 6 3l 3l ′ 3l ′′ nl ′′′ resonances associated with the 3p 1/2 → 3p 3/2 , 3s → 3p, 3p → 3d and 3s → 3d core excitations within the M-shell of the Fe XIV (1s 2 2s 2 2p 6 3s 2 3p) parent ion. This range also includes the 1s 2 2s 2 2p 6 3l 3l ′ 4l ′′ nl ′′′ resonances associated with 3s → 4l ′′ and 3p → 4l ′′ core excitations. We find that in the temperature range 2-14 eV, where Fe XIV is expected to form in a photoionized plasma, the Fe XIV recombination rate coefficient is orders of magnitude larger than previously calculated values.

In photoionized gases with cosmic abundances, dielectronic recombination (DR) proceeds primarily via nlj → nl ′ j ′ core excitations (∆n = 0 DR). We have measured the resonance strengths and energies for Fe XVIII to Fe XVII and Fe XIX to Fe XVIII ∆n = 0 DR. Using our measurements, we have calculated the Fe XVIII and Fe XIX ∆n = 0 DR rate coefficients. Significant discrepancies exist between our inferred rates and those of published calculations. These calculations overestimate the DR rates by factors of ∼ 2 or underestimate it by factors of ∼ 2 to orders of magnitude, but none are in good agreement with our results. Almost all published DR rates for modeling cosmic plasmas are computed using the same theoretical techniques as the above-mentioned calculations. Hence, our measurements call into question all theoretical ∆n = 0 DR rates used for ionization balance calculations of cosmic plasmas. At temperatures where the Fe XVIII and Fe XIX fractional abundances are predicted to peak in photoionized gases of cosmic abundances, the theoretical rates underestimate the Fe -2 -XVIII DR rate by a factor of ∼ 2 and overestimate the Fe XIX DR rate by a factor of ∼ 1.6. We have carried out new multiconfiguration Dirac-Fock and multiconfiguration Breit-Pauli calculations which agree with our measured resonance strengths and rate coefficients to within typically better than ∼ < 30%. We provide a fit to our inferred rate coefficients for use in plasma modeling. Using our DR measurements, we infer a factor of ∼ 2 error in the Fe XX through Fe XXIV ∆n = 0 DR rates. We investigate the effects of this estimated error for the well-known thermal instability of photoionized gas. We find that errors in these rates cannot remove the instability, but they do dramatically affect the range in parameter space over which it forms.