Laser traps for radioactive isotopes

The techniques of laser cooling and trapping now make it possible to observe large samples of stable atoms in a small volume at low temperature. This capability was recently extended to radioactive isotopes. This opens up new opportunities for the investigation of fundamental symmetries through measurements using radioactive atoms. In this paper we will discuss several fundamental measurements in atomic systems and how the ability to trap radioactive atoms will play an important role in improving the precision of such measurements. Measurements of the effects of the weak interaction are of particular note since they are becoming quite precise. In particular, we will describe in detail the system developed at Stony Brook to trap radioactive alkali atoms and measure weak interaction effects in francium isotopes.     

Laser spectroscopy of radioactive isotopes

The experimental conditions for laser spectroscopy of shortlived isotopes is discussed with respect to nuclear lifetime, reaction rates and samples preparation by on-line mass-separator techniques. The method of collinear laser spectroscopy is presented with results for medium mass elements near the closed proton shell Z=50. An interpretation of magnetic moments, spectroscopic quadrupole moments and the parabolic shape of the isotope shift in this region of nuclei is given.     

Laser spectroscopy of radioactive lead and thallium isotopes

By collincar fast beam laser spectroscopy hyperfine structure and isotope shift have been measured of neutron deficient radioactive isotopes of lead (¹⁹⁰Pb,¹⁹¹Pb,¹⁹²Pb,¹⁹³Pb,¹⁹⁴Pb,¹⁹⁵Pb,¹⁹⁶Pb,¹⁹⁷Pb) and thallium (¹⁸⁸Tl¹⁹⁰Tl,¹⁹¹Tl,¹⁹²Tl,¹⁹⁴Tl,¹⁹⁶Tl). Therefrom nuclear magnetic dipole moments, electric quadrupole moments, changes of the mean square charge radii and deformation parameters are deduced and compared with predictions from theory.     

Photoluminescence analysis of semiconductors using radioactive isotopes

The combination of photoluminescence spectroscopy with the radioactive isotopes ⁷Be, ⁷¹As, ¹¹¹Ag, ¹¹¹In, ¹⁹¹Pt, ¹⁹³Au and ¹⁹⁷Hg is shown to provide definitive proof of the chemical identity of impurities producing photoluminescence spectra in all classes of semiconductors. The isotope ⁷¹As is used to show that radioactive isotopes can provide a powerful means of producing and studying a fundamental crystal defect such as an anti-site. Factors governing the luminescence intensities which can lead to apparently anomalous results are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Trapped radioactive isotopes for fundamental symmetry investigations

Discrete symmetries tested in high precision atomic physics experiments provide guidance to model building beyond the Standard Model (SM). Here experimental opportunities arise for searches for permanent electric dipole moments (EDMs) and measurements of atomic parity violation (APV). Heavy atoms are favorable for such experiments since symmetry violating effects in atoms increase faster than the third power of the nuclear charge Z. Of special interest are isotopes of the heavy alkaline earth element radium (Z=88) since they offer large enhancement factors for EDMs and provide a new experimental road towards high precision measurements of atomic parity violation. These opportunities are exploited at the TRIμP facility at KVI, Groningen.     

Charge state breeding of radioactive isotopes for ISAC

For the acceleration of radioactive isotopes with a mass greater than 30 amu charge breeding with an electron cyclotron resonance ion source (ECRIS) is being used at ISAC. Singly charged ions from the target ion source combination are injected into a 14.5 GHz ECRIS from PANTECHNIK and charge bred to highly charged ions with a mass to charge ratio around 6. Efficiencies from 1 to 8 % could be reached for different isotopes. The article describes the set- up of the system and reports on results obtained for efficiency as well as purity of the beam. Methods to improve the purity are discussed.     

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.     

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.     

Integrated target-ion source unit for on-line production of radioactive short-lived isotopes

A new version of integrated target-ion source unit (ionising target) has been developed for the on-line production of radioactive single-charged ions. The target is able to withstand temperatures up to 2500 ^°C and acts also as an ion source of the surface and laser ionisation. Off-line and on-line experiments with the ionising target, housing tantalum foils as a target material, have been carried out at the IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) facility. The off-line surface ionisation efficiency measured for stable atoms of Li, Rb and Cs was correspondingly 6% , 40% and 55% at the target temperature of 2000 ^°C and 3-10% for atoms of rare-earth elements Sm, Eu, Tm and Yb at a temperature of 2200 ^°C. The off-line measured values of the ionisation efficiency for stable Gd and Eu atoms by the laser beam ionisation inside the target were 1% and 7%, respectively. The radioactive beam intensities of neutron-deficient rare-earth nuclides from Eu to Lu produced by the integrated target-ion source unit have been measured at a temperature of 2500 ^°C. The results of the integrated target-ion source unit use for on-line laser resonance ionisation spectroscopy study of neutron-deficient Gd isotopes have been also presented.     

Atomic beam,optogalvanic and stored ion spectroscopy for radioactive isotopes

Systematic studies of the optical isotope shift and the hyperfine splitting of long chains of stable and radioactive isotopes were performed. The method applied was laser induced resonance absorption; the experimental techniques were the atomic beam method with fluorescence detection and the optogalvanic method. The theory of hyperfine splitting and isotope shift of atoms is reviewed in short with emphasis on the aspects interesting for nuclear physics and on the evaluation problem. The experimental methods are described and their key parameters sensitivity and resolution are discussed. Preliminary results on stored thorium ions are given. Sample results for the nuclear quantity δ<r ²> derived from atomic beam experiments with tin and strontium are presented.     

Sn激光共振电离质谱分析中电离通道理论探讨

Sn激光共振电离质谱同位素分析中电离通道的选择非常关键.采用Dirac–Hartree–Fock(MCDHF)方法和相对论组态相互作用的Grasp VU原子结构计算程序,计算了Sn、Te原子的低激发态能级结构、光谱跃迁几率.通过对Sn质谱分析用灯丝样品进行热蒸发实验,确定了Sn原子在蒸发条件下基态能级粒子布局.结合理论计算跃迁数据和布局数据,从选择性电离角度出发,推荐了Sn激光共振电离质谱分析中Sn电离光谱通道.     

Sn激光共振电离质谱分析中电离通道理论探讨

Sn激光共振电离质谱同位素分析中电离通道的选择非常关键。采用Dirac–Hartree–Fock（MCDHF）方法和相对论组态相互作用的GraspVU原子结构计算程序,计算了Sn、Te原子的低激发态能级结构、光谱跃迁几率。通过对Sn质谱分析用灯丝样品进行热蒸发实验,确定了Sn原子在蒸发条件下基态能级粒子布局。结合理论计算跃迁数据和布局数据,从选择性电离角度出发,推荐了Sn激光共振电离质谱分析中Sn电离光谱通道。     

ISOLTRAP: A tandem penning trap mass spectrometer for radioactive isotopes

The masses of over sixty short-lived Rb, Sr, Cs, Ba, Fr and Ra isotopes have been measured at the on-line mass separator ISOLDE at CERN/Geneva by determination of their cyclotron frequency in the tandem Penning trap system ISOLTRAP. Resolving powers exceedingm/m(FWHM)=10⁶ and accuracies of typically m/m=10^–7 could be achieved. ISOLTRAP can also act as an isomer separator, as proven for the cases of⁸⁴Rb and⁷⁸Rb.     

Laser spectroscopy and mass measurements on alkali isotopes

Isotope shifts, spins, hyperfine structures and masses have been measured for the series of the alkali isotopes including the nuclei far from stability. The method of laser spectroscopy and its combinations with rf excitation are described. Some results are discussed, namely the first observation of the red doublet D₁-D₂ of francium, and the study of shell effects and changes of shape with mass and δ〈r ²〉 measurements for Rb and Na isotopes.     

Selective ultratrace analysis of 41Ca by laser resonance ionization

A compact resonance ionization mass spectrometer is presented. It is presently applied for sensitive and highly selective ultratrace determination of the long-lived radioisotope ⁴¹Ca for environmental, biological, and fundamental investigations. The development of coherent multistep resonance ionization enables the realization of experimental detection limits as low as10⁶ atoms per sample and very high isotopic selectivity above 10¹². This revised version was published online in August 2006 with corrections to the Cover Date.