Laser Spectroscopy Programme at the Jyväskylä IGISOL

This paper reviews the status of the laser spectroscopy programme being carried using the IGISOL mass separator in combination with an RFQ cooler-buncher. Measurements in the zirconium region are being extended to the yttrium isotopes. Two K = 8 isomers, in ¹⁷⁶Yb and ¹³⁰Ba, are found to have smaller mean square charge radii than their ground states, and the isotope shifts of stable osmium isotopes have been measured off-line by collinear laser spectroscopy.     

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.     

Laser method of highly selective detection of rare radioactive isotopes through multistep photoionization of accelerated atoms

A laser detection method is proposed for ultralow abundance (<10^–10) of rare radioactive isotopes based on a multistep photoionization of accelerated atoms with a selectivity up to 10⁷ on each step of a collinear laser excitation.     

Hyperfine structure and isotope shifts in the 5d6s2 a2D3/2--5d6s(a3D)6p z4F5/2 ° transition of Hf II

The hyperfine structure and isotope shifts of the transition between the 5d6s² a²D_3/2 ground state and the 5d6s(a³D)6p z⁴F_5/2 ^° excited state of singly ionized hafnium at \lambda=340 nm have been investigated by laser spectroscopy using a radio-frequency quadrupole ion trap. The magnetic dipole coupling constant A and electric quadrupole coupling constant B of the two atomic levels for both stable isotopes ¹⁷⁷Hf and ¹⁷⁹Hf are determined. The changes of mean square nuclear charge radii \delta[ r²] of the stable Hf isotopes and the radioactive isotope ¹⁷²Hf (T_1/2=1.87a) have been extracted from the data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Detection of very rare isotopes by laser collinear resonant ionization of fast atoms

Results are presented of the work on the development of a method for detecting ultra rare isotopes, based on the collinear isotope-selective laser ionization of atoms in a fast bearn. The rare isotope³He was detected at a selectivity of 10⁹ and isotope-selective ionization of krypton atoms was demonstrated. A scheme is suggested for detecting the rare radioactive isotopes⁸⁵Kr and⁸¹Kr. The technique has been exploited for the measurement of hyperfine structures and isotope shifts of unstable Yb isotopes.     

A hot cavity laser ion source at IGISOL

A development program is underway at the IGISOL (Ion Guide Isotope Separator On-Line) facility, University of Jyväskylä, to efficiently and selectively produce low-energy radioactive ion beams of silver isotopes and isomers, with a particular interest in N = Z ⁹⁴Ag . A hot cavity ion source has been installed, based on the FEBIAD (Forced Electron Beam Induced Arc Discharge) technique, combined with a titanium:sapphire laser system for selective laser ionization. The silver recoils produced via the heavy-ion fusion-evaporation reaction, ⁴⁰Ca(⁵⁸Ni, p3n)⁹⁴Ag , are stopped in a graphite catcher, diffused, extracted and subsequently ionized using a three-step laser ionization scheme. The performance of the different components of the hot cavity laser ion source is discussed and initial results using stable ^{107, 109}Ag are presented.     

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.     

Perturbed angular correlation study of a nanostructured HfO2 film

The hyperfine field at ¹⁸¹Ta lattice sites in a nanostructured HfO₂ thin film was studied by the perturbed angular correlation (PAC) technique. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The thickness was about 25 nm. The radioactive ¹⁸¹Hf ions were produced by neutron activation of the very thin film in the Portuguese research reactor by the reaction ¹⁸⁰Hf(n,γ)¹⁸¹Hf. PAC measurements were carried out at room temperature after annealing at different temperatures up to 1,473 K in air. The PAC technique allows determining the electric field gradient at the ¹⁸¹Ta probe sites. The ¹⁸¹Ta isotopes appear in the sample as disintegration product of ¹⁸¹Hf.     

Nuclear moments of the neutron-deficient thallium isotopes

The nuclear moments of the neutron-deficient^187,188Tl isotopes were determined by measuring the hyperfine structure splittings of the λ=535 nm line in neutral thallium. An optical efficiency of 2×10⁻⁴ photons per radioactive ion was achieved using collinear fast beam laser spectroscopy with a large solid angle fiber optical array detector. Most of the moments can be interpreted fairly well in the single particle model.     

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.     

Characterization of a dual-etalon Ti:sapphire laser via resonance ionization spectroscopy of stable copper isotopes

Resonance ionization spectroscopy (RIS) inside a buffer gas-filled ion guide is a very sensitive tool for a first determination of nuclear moments and charge radii of radioactive isotopes produced using the IGISOL technique. Currently employed pulsed Ti:sapphire laser systems have a typical laser linewidth of 5 GHz in the fundamental, which in many cases is the dominant line broadening effect. We present results of RIS on stable ^63,65Cu using a dual-etalon Ti:sapphire laser with a reduced linewidth of 1 GHz. Determination of hyperfine parameters of ⁶³Cu revealed discrepancies when compared to existing higher resolution data. A study of systematic uncertainties is underway using a homemade scanning Fabry-Pérot interferometer (FPI). A real-time recording of the mode structure of the multi-longitudinal mode Ti:sapphire laser during a scan of the 244.238 nm atomic ground state transition in parallel with the readout from the commercial wavemeter has identified sources of uncertainty.     

Unified approach to dispersion forces within macroscopic QED

We describe a laser spectroscopy station that has been proposed to exploit the high yields of radioactive beams at the future FAIR facility at GSI, Darmstadt. Exotic nuclei produced in the Super-Fragment-Recoil-Separator (S-FRS) are stopped in a gas cell, extracted, reaccelerated and transported to the LaSpec setup. Here, collinear spectroscopy on ions and atoms, β-NMR experiments or laser-desorbed resonance ionization can be applied to these rare isotopes.     

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.     

Physics highlights from laser spectroscopy at the IGISOL

Laser spectroscopy provides model-independent access to a variety of radioactive nuclear ground state and isomeric state properties. These include the nuclear moments, changes in mean-square charge radii, and direct measurements of the nuclear spin. At the IGISOL laboratory, the collinear laser spectroscopy programme is able to access cases, such as refractory elements and short-lived states, not available at conventional facilities. A summary of physics highlights is presented here.     

Laser spectroscopy of trapped 7Be and 10Be at a prototype slow RI-beam facility of RIKEN

A next-generation slow radioactive nuclear ion beam facility (SLOWRI) which provides slow, high-purity and small emittance ion beams of all elements is being build as one of the principal facilities at the RIKEN RI-beam factory (RIBF). High energy radioactive ion beams from the projectile fragment separator BigRIPS are thermalized in a large gas catcher cell. The thermalized ions in the gas cell are guided and extracted to a vacuum environment by a combination of dc electric fields and inhomogeneous rf fields (rf carpet ion guide). From there the slow ion beam is delivered via a mass separator and a switchyard to various devices: such as an ion trap, a collinear fast beam apparatus, and a multi-reflection time of flight mass spectrometer. In the R&D works at the present RIKEN facility, an overall efficiency of 5% for a 100A MeV ⁸Li ion beam from the present projectile fragment separator RIPS was achieved and the dependence of the efficiency on the ion beam intensity was investigated. Recently our first spectroscopy experiment at the prototype SLOWI was performed on Be isotopes. Energetic ions of ¹⁰Be and ⁷Be from the RIPS were trapped and laser cooled in a linear rf trap and the specific mass shifts of these isotopes were measured for the first time.     

Development of laser ablation assisted resonant ionization mass spectrometry for isotope analysis

Stable isotope analysis using Laser Ablation Assisted Resonant Ionization Mass Spectrometry (LA-RIMS) is discussed. For the case of the ⁸⁷Sr/⁸⁶Sr isotope ratio measurements with a single color two-photon excitation scheme, the mass discrimination effects, which occur in LA-RIMS, are analyzed and a precision of 0.6% was extracted. For preparation of LA-RIMS on Hf isotopes, a novel two-color resonant excitation scheme with subsequent non-resonant ionization has been established using a high repetition-rate Ti:Sapphire laser system.     

Laser spectroscopy of stable Os isotopes

Doppler-free isotope shift measurements of the stable even ^184–192Os and ^187,189Os odd isotopes have been performed for the first time on the 5d ⁶6s ^{2 5}D₄→5d ⁶6s6p ⁷F₄ (305.9 nm) transition in the neutral atom by atomic beam laser spectroscopy and on the ionic 5d ⁶6s ⁵D_9/2→5d ⁶6p ⁶D_7/2 (228.2 nm) transition by fast collinear ion-laser spectroscopy. The measurements were carried out in Manchester and at the IGISOL facility in Jyväskylä in Finland, respectively. The results presented are the most precise measurements to-date of the absolute isotope shifts.     

Segmented linear radiofrequency quadrupole/laser ion source project at TRIUMF

Reactions such as ²⁵Al(p,γ)²⁶Si are the key to understand the production of ^26g Al and ^26m Al in our galaxy. Experimental results could provide important constraints on nova nucleosynthesis and modelling where ²⁶Al is believed to be produced. To achieve such measurements, high-intensity and high-purity radioactive beams are required. However, production targets at ISOL-type facilities such as ISAC at TRIUMF produce high-intensity alkali beams by surface ionization on hot transfer tubes hampering the measurement of isotopes of interest. To overcome this issue, an ion source combining a segmented linear radiofrequency quadrupole (RFQ) to a laser ion source is being built. Its main function is to suppress alkali impurities whilst allowing for fast-release of short-lived isotopes. The beam production method, the RFQ/laser ion source and the removal of alkali contaminants are discussed in this paper.     

First results from laser spectroscopy on bunched radioactive beams from the JYFL ion-beam cooler

A new RFQ ion-beam cooler and buncher, installed after the mass-separating magnet of the ion guide isotope separator, IGISOL, JYFL, has dramatically increased the scope of on-line laser spectroscopy at this facility. The device, operated in a bunching mode, has permitted new measurements on short-lived radionuclei in the Ti, Zr and Hf chains at a sensitivity two orders of magnitude greater than that previously achieved. The device has also opened new prospects for laser-based nuclear spectroscopy at the facility, particularly collinear resonance ionisation spectroscopy. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: pc@mags.ph.man.ac.uk     

Beta decay of very neutron-rich110Mo studied at the new IGISOL facility

The decay of the new activity¹¹⁰Mo (t_1/2=0.30(4).s) has been observed at the new IGISOL separator. Multiscaled singles,--t and -y-t coincidences were recorded. The decay scheme suggests I=2⁺ for the ground state of the daughter nucleus¹¹⁰Tc. Three 1⁺ levels are fed with logft values below 5, indicating no drastic change among Mo and Ru decays at the middle of the neutron shell. This experiment confirms the expectation that the new IGISOL facility will allow the identification of one or two new more neutron-rich isotopes per element in this region.Supported by the Academy of Finland.