Dependence of the evaporation residue production on the excitation energy of the compound nucleus in the reaction40Ar+164Dy

With the velocity filter SHIP at the heavy ion accelerator UNILAC the energy dependence of the evaporation residues production in the reaction⁴⁰Ar+¹⁶⁴Dy was investigated. The results show a much smaller shift of the (²⁰⁴Po, xn) excitation functions with respect to theoretical predictions than has been reported by other authors.     

High dose implantation of Eu into α-Fe

Abstract

At the UNILAC injector at GSI ¹⁵¹Eu was implanted into an α-Fe foil [8]. According to our simulation code of the energy loss of the implanted ions an energy of 1.5 MeV was chosen to minimize the sputter yield during implantation and to produce the highest possible Eu concentration near the surface of the sample. After the irradiation with a dose of 3.6 · 10¹⁷ Eu/cm² the implantation profile should reach its maximum of 8 at. % Eu at the surface of the sample and its width should be 1700 Å.     

Recombination of Au25+ with free electrons at low energies

The origin of the widely observed enhancement of rates for electron-ion recombination at very low energies is still unknown. We investigated the recombination of Au²⁵⁺ with free electrons in a merged-beams experiment at the UNILAC accelerator of the GSI in Darmstadt. At E _rel= 0 eV we found an enormous enhancement factor of 365 compared to the theory of radiative recombination. An increase of the electron density by a factor of 10 had not much influence on the measured rate coefficient. This revised version was published online in July 2006 with corrections to the Cover Date.     

Alpha decay studies of very neutron deficient isotopes of Hf,Ta, W,and Re

Very neutron deficient isotopes in the Hf-Re region were produced by bombarding targets of^{107, 109}Ag,^{nat, 108, 110}Pd, and¹⁰³Rh with⁵⁸Ni accelerated by the linear accelerator UNILAC at GSI. After separation from the projectile beam by the velocity filter SHIP, the fusion products were implanted with their full recoil energy into a silicon surface barrier detector. The subsequent alpha decay of the implanted ions was measured with the same detector. In some of the experiments the evaporation residues were implanted into a position sensitive silicon surface barrier detector. With a newly developed position and time correlation technique parent daughter relationships, half lives, andα branching ratios of a large number of isotopes could be determined. In the investigated reactions the eleven new isotopes^161–164Re,¹⁶⁰W,^157–161Ta, and¹⁵⁶Hf could be identified. The measuredQ _α values, half lives, and a branching ratios are discussed. Two new high energyα. transitions of (7,408±10) keV and (7,804±15) keV were also found with half lives of 2.7 ms and 0.52 ms, respectively.A tentative mass and atomic number assignment givesA=153–156 andZ=70–72. The energies of the excited isomeric states are between 2 MeV and 3 MeV. From the systematics of alpha ground state transitions in even nuclei a hindrance of 10⁵ can be deduced for both transitions, possibly indicating orbital angular momenta on the order of 10? for the alpha emitting states. The isomers are proposed to belong to shell model isomers beyond¹⁴⁶Gd.     

Heavy ion range measurements in some glasses using back track etching technique

The samples of soda, quartz and barium phosphate (BP-1) glasses were irradiated by different heavy ions from UNILAC, GSI, Darmstadt. The range of these heavy ions in these glasses were measured by using back track etch technique. The experimental values of heavy ion ranges were compared with the theoretical values computed from Mukherjee and Nayak (1979), TRIM-95 and SRIM-97 computer codes based on the formulations of Ziegler et al. (1985).     

Commissioning and early experiments of the PHELIX facility

At the Helmholtz center GSI, PHELIX (Petawatt High Energy Laser for heavy Ion eXperiments) has been commissioned for operation in stand-alone mode and, in combination with ions accelerated up to an energy of 13 MeV/u by the heavy ion accelerator UNILAC. The combination of PHELIX with the heavy-ion beams available at GSI enables a large variety of unique experiments. Novel research opportunities are spanning from the study of ion–matter interaction, through challenging new experiments in atomic physics, nuclear physics, and astrophysics, into the field of relativistic plasma physics.     

Yrast excitations in129Te

Using an 11.4MeV/u¹³⁶Xe beam of the UNILAC accelerator of GSI and a^natW target, A=184 isobars were produced and separated by using an on-line mass separator. A new isomeric state was found in¹⁸⁴Hf. This state decays with a half-life of 48(10) s and emits three -rays of 73, 482, and 555 keV as well as lower-lying cascade transitions. The hindrance of the 73 keV-E1 transition with K=8 is compared with those of other even-even hafnium isotopes. The half-life of¹⁸⁴Lu was estimated to be between 15 and 25s.     

Large electron polarization of H-like20Ne-ions traversing gd foils at very high velocities

It is shown that transient magnetic fields in Gd-host for²⁰Ne ions at a mean velocity of 12.5v₀(v₀=c/137), considerably beyond the Bohr velocity of 1s electrons of Ne ions (v_1s=10v₀), are dominated by the Fermi contact field of these electrons. The first excited 2⁺-state of²Ne was used as probe. The derived value for the mean degree of polarization p_1s=0.32(13), is surprisingly large, though still consistent with values obtained at lower velocities. Present calculations of spin exchange cross sections severely underestimate the observed polarization at this high velocity.The authors are grateful to the operating staff of the UNILAC for providing excellent beam conditions. They also thank Dr. P. Maier-Komor for preparing the delicate targets. Support by the BMFT is acknowledged.     

Recombination of electrons with highly charged heavy ions at very low energies

Recombination of highly charged ions with free electrons is studied in merged-beams experiments at the UNILAC accelerator in Darmstadt and at the heavy-ion storage ring TSR in Heidelberg. Unexpected high recombination rates are observed for a number of ions at very low energiesE _cm in the electron-ion center-of-mass frame. In particular, theoretical estimates for radiative recombination are dramatically exceeded by the experimental recombination rates of U²⁸⁺ ions nearE _cm=0 eV. The observations point to a general phenomenon in electron ion recombination depending onE _cm, on the ion charge state, and possibly also on electron density, electron beam temperature, and strength of external magnetic fields.     

Recombination measurements at low energies with Ar16+ and Ar18+ ions in a dense, cold electron target

Recombination of multiply charged ions with electrons at very low relative energies has become a major topic of interest, due to the observation of rates which are enhanced beyond the expectations for radiative recombination. We present results for Ar¹⁶⁺ and Ar¹⁸⁺ ions from systematic measurements along the argon isonuclear sequence using a high density cold electron beam target (n_e = 7 × 10⁹ cm^-3) at the UNILAC of GSI. The transverse and longitudinal temperatures of the electron beam were determined from DR resonance features observed with metastable Ar¹⁶⁺ (2³S) ions. The rate at E_rel = 0 for radiative recombination of completely stripped Ar¹⁸⁺ calculated with electron beam temperatures kT_∥ = 0.002 eV, kT_⊥ = 0.2 eV amounts to α = 10^-9 cm³ s^-1. This is exceeded by nearly a factor of 10 by the rate measured in experiments with Ar¹⁸⁺ ions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Investigation of new neutron-rich gold isotopes203Au and205Au

Using a²⁰⁸Pb beam of the UNILAC accelerator at GSI we produced the new isotopes²⁰³Au and²⁰⁵Au and identified them by measuring their-decay properties. Their half-lives were found to be 60(6)s and 31(2)s, respectively, and theQ-value of²⁰³Au was determined to beQ =2040(60)keV. Nuclear structure information of^203,205Hg was derived from this measurement. Furthermore, production cross-sections of^203,205Au are given and compared to those obtained in other experiments.This work has been supported by the Federal Ministry for Research and Technology (BMFT) under contract number 06 Gö 451-1/2     

Evidence of new isotopes:169, 170Ir,166, 167, 168Re

At the Darmstadt UNILAC newα-emitting nuclei were produced in the bombardment of⁸⁹Y and⁹³Nb targets using⁸⁴Kr ions with energies in the range of 5.1 to 5.5 MeV/u, and 5.8 to 6.4 MeV/u, and using⁸⁶Kr ions with energies in the range of 5.6 to 6.0 MeV/u. Reaction recoils emitted from the targets were stopped and transported with argon to a collection site. Using three alpha detectors and spectrum multiscaling, energies and half-lives were measured. Ir and Re isotopes were identified by cross bombardments, excitation function data andα-systematics. The decay characteristics of the new species are as follows: Estimates onα-branching ratios have been obtained for^{169, 170}Os and^{166, 167, 168}Re.     

HEAVY ION TRACK DIAMETERS IN MICA STUDIED WITH SCANNING FORCE MICROSCOPE

In the present study, the scanning force microscope (SFM) was employed to measure the heavy ion track diameters in mica and was operated in the lateral-force mode with different loading forces. The mica samples were irradiated with Se, Au, Pb and Zn ions with a kinetic energy of 11.4 MeV/u at the UNILAC of GSI. The measured average track diameter increased slowly with increasing loading force between the SFM tip and sample. The experimental data pointed out that the track diameter versus loading force could be fitted by a linear function both for Se and Au ion species and the slopes of the fitted lines were nearly the same. By extrapolating to zero loading force, the intrinsic diameters of the ion tracks were obtained. A possible mechanism for the observations was discussed.     

Measurements ofK-shell ionization with132Xe and208Pb projectiles in the energy range of 1.4–5.9 MeV/u

Projectile and targetK-shell ionization cross sections induced by 3.6-, 4.7-, and 5.9 MeV/u¹³²Xe ions and 1.4-, 3.6-, 4.7-, and 5.9 MeV/u²⁰⁸Pb ions from the UNILAC in thin solid targets between C and U are measured. The cross sections are discussed in terms of the molecular model of innershell vacancy production in heavy ion-atom collisions. The sharing of 2p _1/2σ vacancies between theK shells of the two collision partners in these very heavy ion-atom collisions is found to deviate from the Meyerhof-Demkov formula forR≦10^?2. The measured ionization cross sections are compared with theoretical calculations for 1sσ and 2p _1/2σ excitation cross sections. AZ _UA=Z₁+Z ₂ dependence is found independent ofZ ₁/Z ₂. Outer-shell vacancy configurations measured in these close encounters are reported.     

Photon migration at multiple frequencies in YLiF4:Nd crystal

A spatially resolved microluminescence technique was used to measure the spatial distribution of emitted light and photon propagation in Nd³⁺-doped YLiF₄ crystal excited at 514 nm. The spatial distribution of the luminescence was studied and the energy transfer processes among neodymium ions were discussed. We measured the photon diffusion length for specific wavelengths. It was found that re-absorption by ground and excited states plays a crucial role to the propagation. With this information, the microluminescence technique has played a useful role in the investigation of energy transfer processes in rare-earth doped systems.     

Sub-barrier fusion of 6He with 206Pb

Cross-sections for the production of ²¹⁰Po nuclei in ⁶He + ²⁰⁶Pb collisions over the incident energy range 14-18MeV were measured by means of the activation technique and a radiochemical analysis. The elastic scattering at 18.0MeV was also measured providing a precise value for the ²¹⁰Po production cross-section at this energy. The results are at variance with the earlier experimental data and rather in accord with the predictions of a density-dependent barrier penetration model for the fusion process. A proper treatment of beam energy distribution for the evaluation of the activation data is discussed.     

Mass and kinetic energy distribution in cold fission of233U,235U and239Pu induced by thermal neutrons

The time-of-flight technique was used to measure the mass and kinetic energy distribution of fragments from fission of²³³U,²³⁵U and²³⁹Pu, induced by thermal neutrons at the Grenoble High Flux Reactor. The data array is presented as equal probability lines in the high kinetic energy regions. The fluctuations observed in those experimental lines are explained by a static scission configuration model, in which the most important influence comes from the Coulomb interaction energy between the two fragments. The highest values of total kinetic energy are obtained for fragmentations with heavy fragmentsZ=50–52,N=80–82 and light fragmentsZ=40–42,N=60–64.     

Determination of deep electron traps in GaAs by time-resolved capacitance measurement

A useful technique of determining the energy levels and the spatial density distributions of multiple electron traps in semi-conductor has been developed using the time-resolved measurement of the Schottky barrier junction capacitance, and this technique has been applied to characterize the electron traps inn-GaAs. In the present technique, the energy levels are determined from single scan of temperature, and the density distributions are calculated from a set of capacitance-voltage relationships. Four traps which lay at 0.39, 0.73, 0.79, and 0.58 eV below the conduction band edge were observed in boat grown or vapor phase epitaxially grown crystals. Many layers which were obtained by a vapor phase epitaxial growth system with N₂ carrier gas were measured and it was found that almost all of them include the 0.73 eV and the 0.79 eV trap with the density between 1×10¹³ and 2×10¹⁵ cm⁻³.     

Measurement of total angular momentum values of high-lying even-parity atomic states of samarium by spectrally resolved laser-induced fluorescence technique

Spectrally resolved laser-induced fluorescence technique was used to uniquely assign total angular momentum (J) values to high-lying even-parity energy levels of atomic samarium. Unique J value assignment was done for seven energy levels in the energy region 34,800–36,200 cm⁻¹, recently observed and reported in the literature.