Transport of intense beams of highly charged ions

The new generation of ion sources delivers beams with intensities of several mA. This requires a careful design of the analysing system and the low-energy beam transport (LEBT) from the source to the subsequent systems. At INFN-LNS, high intensity proton sources (TRIPS [L. Celona, G. Ciavola, S. Gammino et al., Rev. Sci. Instrum. 75(5) 1423 (2004)], PM-TRIPS [G. Ciavola, L. Celona, S. Gammino et al., Rev. Sci. Instrum. 75(5) 1453 (2004)]) as well as ECR ion sources for the production of highly charged high-intensity heavy ion beams are developed (SERSE [S. Gammino, G. Ciavola, L. Celona et al., Rev. Sci. Instrum. 72(11) 4090 (2001), and references therein], GyroSERSE [S. Gammino et al., Rev. Sci. Instrum. 75(5) 1637 (2004)], MS-ECRIS [G. Ciavola et al., (2005), 11th Int. Conf. on Ion Sources, Caen, (in press)]).

In this paper, we present ion-optical design studies of various LEBT systems for ion-sources devoted to the production of intense beams. Calculations were performed using the computer codes GIOS [H. Wollnik, J. Brezina and M. Berz, NIM A 258 (1987)], GICO [M. Berz, H.C. Hoffmann, and H. Wollnik, NIM A 258 (1987)], and TRANSPORT [K.L. Brown, F. Rothacker and D.C. Carey, SLAC-R-95-462, Fermilab-Pub-95/069, UC-414 (1995)]. Simulations take into account the expected phase space growth of the beam emittance due to space-charge effects and image aberrations introduced by the magnetic elements.     

Shock compression of condensed matter using intense beams of energetic heavy ions

In this paper is presented, with the help of sophisticated two-dimensional hydrodynamic simulations, a suitable design with optimized parameters for a heavy-ion beam-matter interaction experiment that will be carried out at the Gesellschaft fur Schwerionenforschung (GSI) Darmstadt by the end of the year 2001 when the upgrade of the existing accelerator facility will be completed. Our simulations show that this upgraded heavy-ion beam is capable of generating strong shocks in solid targets that compress the target material to supersolid densities and generate multi-mbar pressures. This will open up, at the GSI, the possibility of investigation of the equation-of-state properties of matter under such extreme conditions. Numerical simulations can predict the experimental results with reasonable accuracy, which is helpful in designing the diagnostic tools for the experiment.     

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.     

Physics with beams of radioactive nuclei

A survey of the latest results from experiments devoted to studying the structure of nuclei and nuclear-reaction mechanisms by means of accelerated radioactive beams is given. Results obtained in Dubna with the aid of the DRIBs accelerator complex and at other radioactive-beam factories are presented.     

Nuclear astrophysics with fast radioactive beams

I summarize some of the open questions and recent developments in nuclear astrophysics concerning the role of unstable nuclei in cosmic phenomena. This includes a brief discussion of the rapid neutron capture and rapid proton capture processes, as well as some recent experimental results using radioactive beams from fragmentation at the National Superconducting Cyclotron Laboratory.     

Production of secondary radioactive beams from 44 MeV/u Ar projectiles

Secondary beams have been produced through interaction of a 1760 MeV Ar beam with a 99 mg/cm² Be target. An achromatic spectrometer is used to select the magnetic rigidity corresponding to a given beam, and to transport this beam over a distance of about 18m. The beam purity is studied using a solid state ΔE-E telescope. Beams of³⁸S and³⁹Cl are produced with a purity of about 80%, and production rates of 1.5·10^?6 I₀ and 5·10^?5 I_o respectively. Here I₀ denotes the primary beam intensity. Beams of³⁸Ar,³⁹Ar and⁴¹K are produced with about the same abundances as³⁹Cl but with lower purities. It is shown that, by setting properly the experimental parameters, the beam production can be improved by a factor 2 to 5. This could lead to intensities of about 2·10⁶ pps for³⁸S, and of 10⁷ to 10⁸ pps for the four other beams. The possibility of purifying these beams by placing a degrader between the two dipoles of the spectrometer is shown experimentally.     

Surface physics with radioactive ion beams

Nuclear methods using radiation detection are very well suited for surface and interface investigations, since they generally require only a small number of radioactive probe nuclei. Virtually isolated probe atoms can be investigated. The use of an isotope separator to solve the central problem in the application of radioactive atoms for the study of surfaces, the clean deposition of the probe nuclei, is described. First physics experiments include studies of desorption isochrones and characterization of adatom sites on flat and vicinal surfaces by PAC. A particularly complete picture could be obtained for Cd and In on the Pd(111) surface, where five different sites successively populated in the surface diffusion process were observed. Other nuclear methods suitable for a future extension of the surface investigations, such as Mössbauer spectroscopy, decay recoil angular distribution and emission channeling, are briefly discussed.     

Diffusion studies with radioactive ions

An overview of the modified radiotracer based diffusion studies carried out at IGISOL is provided. The experimental procedures are briefly described followed by examples involving IGISOL as the key facility. In this respect the studies related to silicon-germanium (Si_1???xGe_x) alloys and on the related diffusion systematics are summarized. Another group of examples is related to mobility determination of lead isotopes in glass for verifying retrospective radon measurements. Finally an outlook to future possibilities related to employing radiotracers in solid state research is provided.     

Experimental nuclear astrophysics with radioactive ion beams

Reactions involving unstable nuclei play an important role in many astrophysical sites. Radioactive ion beams provide a unique tool to investigate the structure of such unstable nuclei as well as the cross sections for many reactions of astrophysical relevance. This paper provides a brief survey of some recent results in experimental nuclear astrophysics with Radioactive Ion Beams, particularly for processes which take place during explosive hydrogen burning in novae and X-ray bursts. Some prospects for future studies at next generation facilities are also briefly discussed.     

Projectile Coulomb excitation with fast radioactive beams

We report a search for γ rays emanating from Coulomb excitation of fast (30–46 MeV/u) radioactive projectiles⁸He,^11,12,14Be interacting with a lead target. These are clearly identified by their Doppler shift. The 320 keV 1/2^? → 1/2⁺ γ transition from¹¹Be was observed with a cross-section of 191±26 mb which is noticeably less than expected from the known lifetime and in the perturbation limit of pure Coulomb excitation. In the other nuclei rather stringent upper limits of 0.01 to 0.2 Weisskopf units, are placed on the hypothetical transition to 1^? states.     

Giant-resonance studies with radioactive beams: Perspectives

First-generation radioactive ion-beam facilities have already been in operation for some time. Advanced facilities that will deliver high-intensity radioactive nuclear beams ranging in energy from below the Coulomb barrier to up to several hundred MeV per nucleon (MeV/u) are either starting operation, or under construction or in the planning stage. In this paper the perspectives of using radioactive nuclear beams to study giant resonances in nuclei far from the valley of stability are explored. In particular, emphasis will be made on information on certain nuclear properties that can be gained from such studies. Received: 1 May 2001 / Accepted: 4 December 2001     

Isomeric ratios in reactions with radioactive beams

The isomeric ratios and excitation functions have been calculated for the ^112,110Cd(⁶⁽⁸⁾He,p)^117mg In and ¹¹⁴Cd(α, p)^117mg In reactions. The data obtained are compared with the refined experimental values in the reactions with α particles.     

Nuclear reactions of astrophysical interest with radioactive beams

The ARENAS³ facility, coupling the two cyclotrons of Louvain-la-Neuve, is intensively been used over the past years for cross-section measurements of nuclear reactions of astrophysical interest. We will describe the characteristics of the available beams and the experiments going on using these beams. The ¹⁹Ne(p,γ)²⁰Na reaction, of considerable importance for the reaction flow between the CNO and the NeNa mass region in high-temperature hydrogen burning conditions, will be discussed in particular. The proposed low-energy resonance at 0.447 MeV has been measured in inverse kinematics using novel activation techniques. An upper limit (90% C.L.) of 18 meV is obtained for the strength of this first particle-unbound state of ²⁰Na together with preliminary values for the strength of the higher excited states.     

Reactions with fast radioactive beams of neutron-rich nuclei

The neutron dripline has presently been reached only for the lightest nuclei up to the element oxygen. In this region of light neutron-rich nuclei, scattering experiments are feasible even for dripline nuclei by utilizing high-energy secondary beams produced by fragmentation. In the present article, reactions of high-energy radioactive beams will be exemplified using recent experimental results mainly derived from measurements of breakup reactions performed at the LAND and FRS facilities at GSI and at the S800 spectrometer at the NSCL. Nuclear and electromagnetically induced reactions allow probing different aspects of nuclear structure at the limits of stability related to the neutron-proton asymmetry and the weak binding close to the dripline. Properties of the valence-neutron wave functions are studied in the one-neutron knockout reaction, revealing the changes of shell structure when going from the beta-stability line to more asymmetric loosely bound neutron-rich systems. The vanishing of the N = 8 shell gap for neutron-rich systems like ¹¹Li and ¹²Be, or the new closed N = 14, 16 shells for the oxygen isotopes are examples. The continuum of weakly bound nuclei and halo states can be studied by inelastic scattering. The dipole response, for instance, is found to change dramatically when going away from the valley of stability. A redistribution of the dipole strength towards lower excitation energies is observed for neutron-rich nuclei, which partly might be due to a new collective excitation mode related to the neutron-proton asymmetry. Halo nuclei, in particular, show strong dipole transitions to the continuum at the threshold, being directly related to the ground-state properties of the projectile. Finally, an outlook on future experimental prospects is given.     

Propagation of non-diffracting intense ultraviolet beams

Ultraviolet pulses of 200 ps duration are focused in vacuum, and launched into the atmosphere through an aerodynamic window. Instead of diffracting, above a threshold of 100 mJ, the beam propagates in a self-induced waveguide in air. The peak electric field and beam profile are consistent with the eigenfunction of a modified nonlinear Schrödinger equation. The evolution of the beam waist with distance is calculated by a combination of the nonlinear Schrödinger equation and an equation for the nonlinear losses.     

Generating intense beams of low-energy molecules

A method for obtaining intense pulsed beams of molecules possessing low kinetic energies is proposed. The method is based on the formation of a cold pressure shock (shock wave) in an intense pulsed molecular beam interacting with a solid surface, which serves as a source of the secondary beam of low-energy molecules. The proposed method was successfully used to obtain intense beams of H₂, He, CH₄, and Kr molecules with kinetic energies not exceeding 10 meV, and H₂/Kr and He/Kr beams with kinetic energies of H₂ and He molecules below 1 meV.     

Experimental study of intense screw beams with trapped electrons

The velocity spread and average oscillatory energy of intense screw beams of gyrotrons are experimentally studied in the presence of electrons reflected from a magnetic mirror and captured in an adiabatic trap. The results of the experiments indicate a significant influence of trapped electrons on the parameters of beams, especially in systems forming quasilaminar beams. Modifications of magnetron-injector guns are considered in which a certain reduction of the influence of reflected electrons is reached.Institute of Applied Physics, Russian Academy of Science, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 8, pp. 860–869, August, 1995.     

Fission experiments with secondary beams

Nuclear fission from excitation energies around 11 MeV was studied at GSI, Darmstadt for 76 neutron-deficient actinides and pre-actinides by use of relativistic secondary beams. The characteristics of multimodal fission of nuclei around ²²⁶Th are systematically investigated and related to the influence of shell effects on the potential-energy and on the level density between saddle point and scission. A systematic view on the large number of elemental yields measured gave rise to a new interpretation of the enhanced production of even elements in nuclear fission and allowed for a new understanding of pair breaking in fission.