Cologne FN-tandem Research Articles

The first (53Mn/55Mn) isotopic ratio measurements at the Cologne FN-Tandem Accelerator

A new accelerator mass spectrometer was successfully designed for the Cologne FN accelerator to enlarge the measurement capability of CologneAMS to medium mass radionuclides. With this AMS-system (53Mn/55Mn) isotopic ratios are measurable at a 10 MV tandem accelerator in the range of 10-9 to 10-10 for the first time, with a detection limit of CL=5.0×10-12. A high 53Cr suppression in the (53Mn/55Mn) isotopic ratio measurement was achieved by using the optimal silicon nitride degrader foil thickness in combination with an electrostatic analyzer (ESA). The new system opens the field of research for CologneAMS users to the medium mass region of cosmogenic nuclides, like 53Mn for geological applications of long term erosion, exposure and burial dating and 60Fe for nuclear astrophysical models. The presented definition of an error normalized sensitivity Sx allows an inter laboratory comparison of isotopic ratio measurements.

Different collectivity in the two signatures of the i13/2 stemming band in 167Yb

Six lifetimes have been determined in the 5/2+ [642] band from vi13/2 parentage in 167Yb by means of Recoil distance Doppler-shift (RDDS) measurements carried out at the Cologne FN tandem. The deduced transition strengths and the level scheme are reasonably described by Particle plus triaxial rotor model (PTRM) calculations except for the behavior of the quadrupole collectivity in the two signatures of the 5/2+[642] band. In that band, the quadrupole collectivity of the favored signature is appreciably larger than this of the unfavored signature. The effect increases with increasing the spin. Naturally, the rigid PTRM cannot explain these features, but the structure of its wave functions suggests a possible solution. It is associated with the enhanced contribution of low-Ω orbitals from vi13/2 parentage in the favored signature compared to the unfavored one. This could selectively increase the deformation of the favored signature band members and give rise to a dynamic shape coexistence taking place between the two signatures which needs quantitative explanation by future theoretical work.

Study of vibrational signatures in 102Ru

Abstract A Mo 100 ( α , 2 n ) Ru 102 fusion evaporation experiment, performed at the HORUS cube spectrometer at the Cologne FN-Tandem accelerator, is presented and discussed. Via the analysis of γγ coincidences, it was possible to extend the level scheme with 40 new levels and 81 decays. Several new spins and multipole mixing ratios were determined using the γγ angular correlation technique. In addition, a DSAM analysis was performed and 14 new effective lifetimes were determined in the femtosecond range. Thus, several effective transition strengths were determined. Investigating the phononic structure, candidates for the quadrupole–octupole phonon multiplet 2 1 + ⊗ 3 1 − were found. The data is compared to calculations within the Interacting Boson Model (IBM-1) in the U(5) limit, the O(6) limit as well as a transitional class U(5)–O(6). The low spin level energies show characteristics of multiphonon excitations and point towards 102Ru resembling an anharmonic vibrational nucleus. The B ( E 2 ) transition strengths do not exactly match this picture, and are described in a better way using the U(5)–O(6) calculation.

Plunger lifetimes and electromagnetic transition strengths in odd 167Yb

Abstract Nine lifetimes have been determined for the first time in the 5 / 2 − [ 523 ] and 5 / 2 + [ 642 ] bands of 167Yb by means of Recoil distance Doppler-shift measurements carried out at the Cologne FN tandem. For the data analysis, a dedicated version of the Differential decay curve method was used. The newly deduced transition strengths and the level scheme are reasonably described by the Particle plus triaxial rotor model (PTRM) calculations except for the behavior of the quadrupole collectivity in the two signatures of the 5 / 2 + [ 642 ] band. The stretched B(E2)ʼs in the favored signature are appreciably larger than those in the unfavored signature. The effect increases with spin. In the PTRM calculations, the wave functions of the favored signature levels contain larger contribution of low-Ω orbitals from ν i 13 / 2 parentage than those of the unfavored levels. This could selectively increase the deformation of the favored signature band members. If so, rotation and Coriolis interaction would give rise to a dynamic shape coexistence taking place between the two signatures.

Transition probabilities and isospin structure in theN=Znucleus46V

Picosecond lifetimes in ${}^{46}\mathrm{V}$ and ${}^{46}\mathrm{Ti}$ were determined using the recoil distance Doppler-shift technique with a plunger device coupled to a setup of five HP Ge detectors enhanced by one EUROBALL CLUSTER detector. The experiment was carried out using the ${}^{32}\mathrm{S}{(}^{16}\mathrm{O},pn)$ reaction at 38 MeV at the Cologne FN TANDEM facility. The differential decay curve method in coincidence mode was employed to derive lifetimes for five excited states in each nucleus. The resulting $E2$ transition probabilities are compared with existing shell model calculations and a comparison within the $T=1$ isospin triplet is given. Absolute $E1$ strengths of the ${2}^{\ensuremath{-}}$ decay in ${}^{46}\mathrm{V}$ are discussed.

New states and $ \boldsymbol{\gamma}$ -transitions in Bi observed in the (He, d $ \boldsymbol{\gamma\gamma}$ )-subcoulomb-reaction

Single-particle states as well as collective states in the natural Bismuth isotope 209Bi were investigatedusing two Euroball Cluster detectors at the Cologne FN-tandem accelerator. The states were populated by the subcoulomb proton stripping reaction 208Pb(3He,d*γγ)209Bi at 20.5 MeV beam-energy. Forty-eight γ-transitions and 33 levels were observedfor the first time. Gamma-transitions up to an energy of 6.0 MeV were detected. The energy of the observed states were determined to an accuracy of about 0.3 keV.

Non-yrast states of 132Ce polutated in β-decay

Non-yrast low spin states of the nucleus 132Ce were studied by means of γ-spectroscopy following the β-decay of the ground and medium spin isomeric states of 132Pr. The activity was produced with the reaction 117Sn( 19F,4n) 132Pr at the Cologne FN TANDEM accelerator. The γγ coincidences and singles spectra were measured with the OSIRIS cube spectrometer. The β-decay of 132Pr populates states with spins up to 6ħ and excitation energies up to 4.4 MeV in 132Ce. Besides ground and quasi-gamma bands, an excited band based on the 0 2 + state and many other low-lying states were observed. The γγ angular correlations were analyzed to assign spins and parities to the excited states, and to determine the multipolarities of the γ-transitions. We found dominant E2 transitions in the quasi-gamma band and from the quasi-gamma band to the ground band. The experimental data are compared with calculations using the Interacting Boson Model (IBM). Good agreement is reached in the vicinity of the O(6) limit.

The γ-decay of single-particle states in 205Pb and 207Pb using an Euroball Cluster detector

Single-particle states in the odd lead isotopes 205Pb and 207Pb were investigated using an Euroball Cluster detector and five usual Ge detectors at the Osiris cube spectrometer of the Cologne FN-Tandem accelerator. The states were populated by the subCoulomb neutron stripping reaction ( d, pγ) at 10 MeV. About 102 γ-transitions could be observed for the first time. The energy of most of the observed states could be determined to an accuracy of about 0.2 keV. The ground state wave function of 206Pb could be determined to contain: 66(5) % ν3 p 1 2 −2 , 19(3) % ν2 f 5 2 −2 , 10(3) % ν3 p 3 2 −2 , and 2(1) % ν2 f 7 2 −2 .

Coincidence and correlation analysis for low spin states in 128Xe

Abstract Using the fusion evaporation reaction 125Te(α,n) 128Xe, low spin states of 128Xe have been investigated. The alpha beam at a beam energy of 16 MeV was supplied by the Cologne FN-tandem accelerator. Using the OSIRIS-6-Cube spectrometer we obtained both coincidence and singles data. We evaluated the γγ coincidence data, angular distributions and angular correlations. The technique of spin assignment by angular correlation analysis is discussed in some detail. We present an extended level scheme with 154 levels in the energy range up to 4 MeV and a spin range up to 10h. Two collective bands build up upon bandheads with spin I = 0 and I = 4, respectively, are established. Level energies and B(E2) values are compared to predictions of the IBM-1 near the O(6) dynamical symmetry and interpreted in the framework of the new Q phonon scheme.

Non-yrast states in 132Ba

Abstract The low spin structure of 132 Ba has been investigated following the β + -decay of ground and medium spin isomeric states of 132 La. The lanthanum nuclei were produced at the Cologne FN-tandem accelerator using the reaction 122 Sn( 14 N, 4n) 132 La. γγ-coincidence data was taken by means of the OSIRIS 6-cube spectrometer. Many new low lying levels were established. We report the level and transition energies, spins, parities and relative branching ratios obtained in this measurement. The low lying states of positive parity are discussed within the framework of the IBA-1 model and compared with results for the F-spin partner 128 Xe. A good description is obtained in terms of the Consistent-Q formalism near the dynamical O(6)-symmetry.

Low spin states in 130Ba

Abstract The low spin structure of 130 Ba has been investigated following the β + -decay of ground and medium spin isomeric states of 130 La. The lanthanum nuclei were produced at the Cologne FN-tandem accelerator using the reaction 120 Sn( 14 N,4n) 130 La. γγ-coincidence data was taken by means of the OSIRIS 6-cube spectrometer. Many new low lying levels were established. Of special interest are new “ K = 0”- and “K = 4”- bands . We give the level and transition energies, spins and parities, multipole mixing ratios and B (E2)-ratios obtained from this measurement. The low lying states of positive parity are discussed in the framework of the IBA-1 model and compared with results for the F-spin partner 126 Xe. The description is given in terms of a consistent-Q formalism near the dynamical O(6)-symmetry. A new scheme which gives analytical expressions for the O(6)-wave functions is presented. The scheme is still valid approximately in vicinity of O(6).

Performance of the Cologne FN tandem with a combination of Dowlish and HVEC tubes

In May 1991 the HVEC tubes at the low energy (LE) end of the Cologne FN tandem were replaced by Dowlish spiral inclined tubes with titanium electrodes

Band structures in 126Xe

Excited states of 126Xe have been investigated with the (α, n) and the ( 13C, 3n) reactions by means of the OSIRIS-12 spectrometer at the Cologne FN-tandem accelerator. With the ( 13C, 3n) reaction 13 bands were established and the yrast band was extended up to a tentative (20 +) state. With both reactions in total 178 levels and 307 transitions were observed. The data are compared to the predictions of different models.

Evidence for variable γ deformation in 126Xe

Low spin states of 126Xe have been investigated by means of the OSIRIS-12 spectrometer at the Cologne FN-Tandem accelerator using the nonselective (α, n)-reaction. New “K=0” and “K=4” bands were established. The experimental “B(E2)” ratios are compared with the predictions of the interacting boson, asymmetric rotor-vibration model. The data rules out the asymmetric rotor model with rigid γ deformation as a description of this nucleus.