Laser spectroscopy at IGISOL IV

The IGISOL (Ion Guide Isotope Separator On-Line) facility at the University of Jyväskylä accelerator laboratory has been upgraded and relocated to a purpose built laboratory. The new laboratory includes a dedicated MCC30 proton/deuteron cyclotron, which in conjunction with beams from the K130 cyclotron, will greatly increase the beam time available at the facility. Full off-line commissioning of the laser spectroscopy beam-line was achieved in February 2013 and on-line commissioning with radioactive beams was achieved in May 2013. Optical hyperfine resonance spectra were obtained for previously studied radioactive molybdenum isotopes and used to investigate our long term stability, efficiency and ability to successfully reproduce previous results from IGISOL III. A preliminary spectrum for the previously unmeasurable $^{107}$ Mo was collected, displaying the improved capabilities of the new facility. Both data-sets show that the laser-line is ready for future experiments. The IGISOL IV beams are cleaner and have a higher radioactive content compared to similar experiments at IGISOL III.     

Collinear laser spectroscopy at the new IGISOL 4 facility

In 2011 the collinear laser spectroscopy programme at the University of Jyväskylä Accelerator Laboratory (JYFL), Finland, will move to the new IGISOL 4 facility. With its own dedicated cyclotron, this new laboratory will offer unparalleled access to beam time for both technique development and exploitation. Production of sub-millisecond states is available, including elements of a refractory nature.     

Isomer and decay studies for the rp process at IGISOL

Low-energy-particle-induced fission is a cost-effective way to produce neutron-rich nuclei for spectroscopic studies. Fission has been utilized at the IGISOL to produce isotopes for decay and nuclear structure studies, collinear laser spectroscopy and precision mass measurements. The ion guide technique is also very suitable for the fission yield measurements, which can be performed very efficiently by using the Penning trap for fission fragment identification and counting. The proton- and neutron-induced fission yield measurements at the IGISOL are reviewed, and the independent isotopic yields of Zn, Ga, Rb, Sr, Cd and In in 25MeV deuterium-induced fission are presented for the first time. Moving to a new location next to the high intensity MCC30/15 light-ion cyclotron will allow also the use of the neutron-induced fission to produce the neutron rich nuclei at the IGISOL in the future.     

Trap-assisted studies of odd, neutron-rich isotopes from Tc to Pd

We review the present and future of trap-assisted structure studies of odd, neutron-rich Tc, Ru, Rh and Pd isotopes at the limits of present experimental techniques. These nuclei of refractory elements are produced in light-particle induced fission and filtered by their mass number with the IGISOL mass separator. Further mass separation with the JYFLTRAP Penning trap system provides a clean, monoisotopic beam perfectly suited for precise nuclear spectroscopy. Connecting the IGISOL and the JYFLTRAP facilities to the recently installed MCC30/15 cyclotron opens new prospects for post-trap spectroscopy of very exotic, neutron-rich nuclei.     

Resonance ionization spectroscopy of bismuth at the IGISOL facility

A programme of research has commenced at the IGISOL facility, Jyväskylä, combining the technique of resonance ionization spectroscopy with the development of the highly selective laser ion source trap (LIST). The first element of interest is bismuth, which contains three isomers of multi-quasiparticle states in near-spherical nuclei, namely ²⁰⁷Bi (21/2⁺, 182 μs), ²⁰⁴Bi (10^?, 13 ms) and ²⁰⁴Bi (17⁺, 1.07 ms). A measurement of the optical isomer shift provides a direct comparison of the mean?square charge radii between the isomer and the nuclear ground state. Due to the short isomer lifetimes the spectroscopy will be done either within the ion guide or in a sextupole ion beam guide (SPIG), located after the ion guide and used in the development of the LIST. A mixed dye-Ti:Sapphire laser ionization scheme has been successfully tested for bismuth and first off-line results have been obtained.     

Nuclear structure studies of neutron-rich fission fragments performed at JYFLTRAP

The JYFLTRAP double Penning trap setup at the University of Jyväskylä, Finland has been used to perform a wide range of studies related to neutron-rich fission fragments that can be produced with the Ion Guide Isotope Separator On-Line (IGISOL) method. Experimental results from high-precision mass measurements and decay-spectroscopy measurements have allowed us to investigate the nuclear structure of exotic neutron-rich nuclei.     

Experimental studies at JYFLTRAP

JYFLTRAP is a Penning trap system at the accelerator laboratory in Jyväskylä, Finland that enables high-precision experiments with stored, exotic species that are produced at the IGISOL facility. On one hand, these can be performed within the trap itself, like e.g. mass spectrometry. On the other hand, the trap can be used to provide the highly purified species for further experiments, e.g. for trap-assisted nuclear decay spectroscopy. This contribution focuses on these two possible applications with the presentation of some recent results on superallowed beta decays.     

Collinear laser spectroscopy techniques at JYFL

Over the last 15 years, a collinear laser spectroscopy programme has been developed at the University of Jyväskylä Accelerator Laboratory (JYFL), Finland. Continuous technique development and exploitation has taken place to address physics cases inaccessible elsewhere. In particular, the use of ion beams from the IGISOL and the pioneering application of cooled and bunched beams to laser spectroscopy. Many of these advances have additionally now been exported to facilities worldwide.     

Overview of the JYFLTRAP mass measurements and high-precision <Emphasis Type="Italic">Q</Emphasis>-values for weak interaction studies

The JYFLTRAP Penning trap set-up at the University of Jyväskylä, Finland is a Penning trap facility that has provided high-precision atomic mass values for short-lived nuclides since 2003. Until now, masses of more than 250 short-lived nuclides have been measured. Since JYFLTRAP is coupled to the chemically insensitive IGISOL mass separator, any element can be accessed. So far, a huge mass surface extending from magnesium (Z = 12) to lead (Z = 82) has been covered.     

Status of the LASER-IGISOL collaboration at the University of Jyväskylä

Recent laser spectroscopy studies at the IGISOL facility, University of Jyväskylä have focussed on the shape transition at N?=?60. A new technique of optical pumping in the ion beam cooler has given unique access to the radioactive isotopes of niobium and yttrium. Further spectroscopy from metastable states allowed nuclear moments and charge radii to be extracted for isotopes in the chains of Mo and Nb, thus exploring the extent of nuclear deformation across the entire Z?=?36–42 region.     

Decay heat studies for nuclear energy

The energy associated with the decay of fission products plays an important role in the estimation of the amount of heat released by nuclear fuel in reactors. In this article we present results of the study of the beta decay of some refractory isotopes that were considered important contributors to the decay heat in reactors. The measurements were performed at the IGISOL facility of the University of Jyväskylä, Finland. In these studies we have combined for the first time a Penning trap (JYFLTRAP), which was used as a high resolution isobaric separator, with a total absorption spectrometer. The results of the measurements as well as their consequences for decay heat summation calculations are discussed.     

Penning trap assisted decay spectroscopy of neutron-rich 115Ru

Exotic, neutron-rich ¹¹¹Mo and ¹¹⁵Ru nuclei, produced in proton-induced fission of ²³⁸U target, were separated with the IGISOL mass separator. The separator was coupled to the JYFLTRAP Penning trap to select the ions of a single, desired element out of the isobaric IGISOL beam. Monoisotopic samples of ¹¹⁵Ru and ¹¹¹Mo ions were observed with a microchannel plate detector after the trap or were implanted on a catcher foil for gamma- and beta-ray coincidence spectroscopy. In spite of short data taking time new gamma transitions were identified in the beta decay of very neutron-rich ¹¹⁵Ru.     

Laser Ion Source Project at IGISOL

The application of laser ionisation is being developed for the IGISOL mass separator facility in Jyväskylä, Finland. The conceived laser ion source will have two independent pulsed laser systems based on all solid-state lasers and dye lasers for maximal coverage of ionisation schemes throughout the periodic table. A laser ion source trap, LIST, method will be pursued for optimal selectivity.     

Laser developments and resonance ionization spectroscopy at IGISOL

We present an overview of recent laser ion source developments at the IGISOL facility, Jyväskylä. Technological advances in the lasers have led to a considerable increase in second-harmonic laser power with the use of intra-cavity second-harmonic generation, as well as to narrow linewidth capability by applying an injection-locking technique to a Ti:sapphire laser. The use of a diffraction grating for frequency selection in a new laser resonator has dramatically improved the wide-range tunability of the laser system, resulting in an ideal tool for the development of new ionization schemes. The role of different laser bandwidths, laser intensity and environmental broadening mechanisms on the experimental width of the measured spectral line have been studied using bismuth, silver and nickel, in the gas cell and expanding gas jet. Applications of novel ion guide nozzle design has led to remarkably collimated gas jets which overcome the current limitations in the gas cell-based laser ion source trap (LIST) method. Detailed planning is under way to optimize the new laser laboratory and laser transport path in order to fully exploit the unique opportunities afforded by the new IGISOL-4 facility.     

Resonance ionization spectroscopy of radioisotopes at the IGISOL facility, JYFL

The method of resonance ionization spectroscopy for measurements of hyperfine structures and isotope shifts of heavy elements, at the IGISOL facility, Jyväskylä, is discussed. Two laser geometries are considered, with reference to the effect they have on resolution and efficiency of measurements. Results of off line resonance ionization tests on natural sodium are reported.     

An ion beam cooler for collinear laser spectroscopy

An ion beam cooler has been constructed and tested at the IGISOL mass separator facility at the University of Jyväskylä. The cooler is designed to improve the ion optical properties of radioactive ion beams produced with fission-, light-ion fusion and heavy ion fusion ion guides. The performance of the device has been tested in off- and on-line conditions. It has been shown that the emittance and energy spread of the ion beam can be decoupled from the ion guide parameters with high transmission efficiency.     

Gas purification studies at IGISOL-4

A new gas purification system has been constructed at the upgraded IGISOL facility, Jyväskylä, to meet the need for ultra-high purity helium and argon buffer gas used in the ion guide technique. The purification of helium using liquid nitrogen-cooled cold traps is investigated and compared with unpurified gas using mass spectra obtained at the focal plane of the separator. Neon, an impurity intrinsic to the in-house recycled helium, was seen to have high sensitivity to the impurity level of the gas which is expected to reach sub-parts-per-billion level.     

Investigation of the low-lying isomer in 229Th by collinear laser spectroscopy

A new ion beam of ²²⁹Th is available at the Jyväsklyä IGISOL facility, produced from the α decay of ²³³U. A small branching ratio (≈ 2%) is believed to populate the inferred low-lying (5.5 eV) isomeric state in ²²⁹Th. A laser ionization scheme is currently being developed to improve the yield of ²²⁹Th from the source. The ion source uses a novel electric field configuration for fast and efficient extraction of α-recoils and is able to provide beams of short lived (τ≥ 30 ms) radioactive nuclei. Identification of the isomeric state by collinear laser spectroscopy will reduce the lower lifetime limit of the state and provide the first direct evidence for its existence.     

Time Characteristics of the Ion Beam Cooler-Buncher at JYFL

A beam cooler for low-energy ion beams was constructed to improve the ion optical properties of radioactive ion beams produced at the IGISOL facility in Jyväskylä. The beam cooler is a buffer gas filled RF-quadrupole. The delay properties and the possibility to accumulate a continuous IGISOL beam and release it in short bunches is discussed.