Collinear Fast-beam Laser Spectroscopy Research Articles

The Collinear Fast Beam laser Spectroscopy (Cfbs) experiment at Triumf

Laser spectroscopy experiments at radioactive ion beam facilities around the world investigate properties of exotic nuclei for scientific endeavours such as, but not limited to, the investigation of nuclear structure. Advancements in experimental sensitivity and performance are continuously needed in order to extend the reach of nuclei that can be measured. The collinear fast beam laser spectroscopy (Cfbs) setup at Triumf, coupled to an out-of-plane radio-frequency quadrupole Paul trap, enables measurements of some of the most fundamental nuclear properties for long-lived ground and isomeric states. The first comprehensive overview of the Cfbs experiment is provided along with descriptions of key developments that extend the reach of laser spectroscopy experiments. A novel data acquisition technique structured around three-dimensional spectra is presented, where the integration of a custom multi-channel-scalar provides photon counts correlated with arrival time and acceleration voltage for post-experiment analysis. In addition, new rapid light manipulation techniques are discussed that suppress undesirable hyperfine pumping effects and regain losses in experimental efficiency.

Krypton Separation from Ambient Air for Application in Collinear Fast Beam Laser Spectroscopy

A portable apparatus for the separation of krypton from environmental air samples was tested. The apparatus is based on the cryogenic trapping of gases at liquid nitrogen temperature followed by controlled releases at higher temperatures. The setup consists of a liquid nitrogen trap for the removal of H(2)O and CO(2), followed by charcoal-filled coils that sequentially collect and release krypton and other gases providing four stages of gas chromatography to achieve separation and purification of krypton from mainly N(2), O(2), and Ar. Residual reactive gases remaining after the final stage of chromatography are removed with a hot Ti sponge getter. A thermal conductivity detector is used to monitor the characteristic elution times of the various components of condensed gases in the traps during step-wise warming of the traps from liquid nitrogen temperatures to 0°C, and then to 100°C. This allows optimizing the switching times of the valves between the stages of gas chromatography so that mainly krypton is selected and loaded to the next stage while exhausting the other gases using a He carrier. A krypton separation efficiency of ~80% was determined using a quadrupole mass spectrometer.

Calibration of the ISOLDE acceleration voltage using a high-precision voltage divider and applying collinear fast beam laser spectroscopy

A high-voltage divider with accuracy at the ppm level and collinear laser spectroscopy were used to calibrate the high-voltage installation at the radioactive ion beam facility ISOLDE at CERN. The accurate knowledge of this voltage is particularly important for collinear laser spectroscopy measurements. Beam velocity measurements using frequency-comb based collinear laser spectroscopy agree with the new calibration. Applying this, one obtains consistent results for isotope shifts of stable magnesium isotopes measured using collinear spectroscopy and laser spectroscopy on laser-cooled ions in a trap. The long-term stability and the transient behavior during recovery from a voltage dropout were investigated for the different power supplies currently applied at ISOLDE.

Nuclear moments of neon isotopes in the range fromNe17at the proton drip line to neutron-richNe25

Nuclear moments of odd-A neon isotopes in the range 17 ≤ A ≤ 25 have been determined from optical hyperfine structures measured by collinear fast-beam laser spectroscopy. The magnetic dipole moments of 17 Ne, 23 Ne and 25 Ne, as well as the electric quadrupole moment of 23 Ne are either reported for the first time or improved considerably. The measurements also decide for a 1/2 + ground state of 25 Ne. The behavior of the magnetic moments of the proton drip-line nucleus 17 Ne and its mirror partner 17 N suggests isospin symmetry. Thus, no clear indication of an anomalous nuclear structure is found for 17 Ne. The magnetic moments of the investigated nuclei are discussed in a shell-model approach.

Influence of the thermal motion on the line shape and position of resonances in collinear fast beam laser spectroscopy

We derive the spectral line shape for collinear fast beam laser spectroscopy. As initial condition we take a thermally distributed ensemble into account. While the thermal velocity distribution of the fast ensemble has an asymmetric structure due to the acceleration by the electrostatic field, under typical experimental conditions the convolution with the natural line shape preserves the Lorentz profile with negligible broadening. However, the spectral line as a whole experiences a small shift depending on the temperature of the source and the acceleration .

Laser-spectroscopy measurements of 72–96Kr spins, moments and charge radii

Abstract The spins, moments and radii of krypton isotopes have been investigated by collinear fast-beam laser spectroscopy in combination with ultra-sensitive collisional ionization detection. The sequence of isotopes under study ranges from the neutron-deficient N = Z = 36 isotope 72 Kr to the neutron-rich 96 Kr ( N = 60). The mean-square charge radii in the neighbourhood of the N = 50 neutron-shell closure exhibit a pronounced shell effect which has recently been explained in the framework of relativistic mean-field theory. The results for the neutron-deficient nuclei are related to the shape coexistence of strongly prolate and near-spherical states which is known from nuclear spectroscopy. Here, an inversion of the odd-even staggering is observed below the neutron number N = 45. The neutron-rich transitional nuclei are influenced by the N = 56 subshell closure. In contrast to the N = 60 isotones 97 Rb, 98 Sr and 100 Zr, the new isotope 96 Kr is not strongly deformed.

Hyperfine structure in 5s 4d 3 D ?5snf transitions of87Sr

The hyperfine spectra of the 5s4d3D1-5s20f, 5s4d3D2-5s23f, and 5s 4d3D3-5s32f transitions of87Sr (I=9/2) have been measured by collinear fast beam laser spectroscopy. The structure in the upper configurations is highly perturbed by fine structure splitting that is of comparable size to the hyperfine interaction energy. These perturbations can be adequately treated with conventional matrix diagonalization methods, using the 5s-electron magnetic dipole interaction terma5s and the unperturbed fine structure splittings as input parameters. Additionally, hyperfine constants for the lower 5s4d3D configurations, including theA- andB-factors and a separation of the individuals- andd-electron contributions to these factors, are derived.

Isotope shift measurements on the neutron-deficient thallium isotopes

Isotope shifts of the neutron-deficient thallium isotopes were measured on-line at the UNISOR mass separator. Spectroscopy was carried out using collinear fast beam laser spectroscopy in neutral thallium. The changes of the mean square charge radii were derived from the measurements. The changes in charge radii of the I=7 isotopes, including the newly measured188Tl, are compared to the results in mercury and lead.

Nuclear moments of the neutron-deficient thallium isotopes

The nuclear moments of the neutron-deficient187,188Tl 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.

Isotope shifts and hyperfine-structure-splitting constants of the 4d-5p transition of Kr II at lambda =729 nm.

Collinear fast-beam laser spectroscopy has been used to measure the hyperfine splittings and the isotope shifts in the 4${\mathit{p}}^{4}$4d $^{4}$${\mathit{D}}_{7/2}$--4${\mathit{p}}^{4}$5p $^{4}$P${\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}_{5/2}$ (\ensuremath{\lambda}=729 nm) transition of singly ionized Kr. The measured isotope shifts are very large due to a large specific-mass effect that is caused by the strong momentum correlations of the 4d electron with the core electrons. Hartree-Fock and multiconfiguration Hartree-Fock (MCHF) calculations of the specific-mass shift were carried out and are compared to the measurements. The MCHF calculation yields excellent agreement with the experimental results.

Nuclear ground state properties of 99Sr by collinear laser spectroscopy with non-optical detection

Collinear fast-beam laser spectroscopy, with improved sensitivity for ions with hyperfine split transitions, is performed to measure the hyperfine structure and the isotope shift of the well deformed short-lived 99Sr. The new method consists in ground state depopulation by a two-step optical pumping sequence prior to state selective neutralization and fast-atom counting. A definitive nuclear spin value I = 3 2 , the change in mean square charge radius δ〈 r 2〉 98,99 and the nuclear moments are derived. These results are compared to nuclear spectroscopy information and are interpreted in the frame of the particle plus deformed core model.

Hyperfine structure studies in the 6s 6p3P2-level of barium

The hfs of the3P2 state of the 6s 6p configuration of atomic barium has been determined for137Ba, applying the collinear fast-beam laser spectroscopy. The data fill the last gap in the experimental information on low lying 6s2, 6s 6p, 6s 5d and 6p 5d configurations of this alcaline earth system. The results are analyzed in terms for the existing semi-empirical modified Breit-Wills theory (MBWT), working with two basic wave functions, as well as by an extension to six-component wave functions of inclusion of configuration interaction. The semi-empirical approaches lead to a consistent description of the different hyperfine structures; they are compared with the results from recent ab initio multi-configuration Dirac Fock calculations.

Lifetime measurement of the T=23 537 cm-1, J=9/2 odd-parity level in Nd II using time-resolved collinear fast-beam laser spectroscopy.

Time-resolved collinear fast-beam laser spectroscopy has been used to measure the lifetime of the T=23 537 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, J=9/2 odd-parity [abbreviated as (23 537)${\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}_{9/2}$] level in Nd ii. Nanosecond pulsed excitation was achieved with the Doppler switching technique. The fast ions were selectively excited from the metastable 4${\mathit{f}}^{4}$5d $^{6}$${\mathit{K}}_{9/2}$ level to the (23 537)${\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}_{9/2}$ level by the light of a cw dye laser. The decay of the resonance fluorescence photons emitted in the transition to the ground 4${\mathit{f}}^{4}$6s $^{6}$${\mathit{I}}_{7/2}$ level, as a function of the flight distance, was observed. The decay length was scaled into the decay time by the ion velocity, which was determined using the optical resonance itself. The lifetime is 27.7(9) ns.

Systematics of nuclear ground state properties in 78-100Sr by laser spectroscopy.

Hyperfine structures and isotope shifts of strontium isotopes with A=78 to A=98 and A=100 were measured by collinear fast beam laser spectroscopy. Nuclear spins, moments and changes in mean square charge radii are extracted from the data. The spins and moments of most of the odd isotopes are explained in the framework of the single particle model. The changes in mean square charge radii are compared with predictions of the droplet model and of Hartree-Fock-plus-BCS calculations. For the isotopes in the transitional regions below and above the N=50 shell closure, the inclusion of quadrupole zero point motion in the Droplet model describes part of the observed shell effect. An additional change in the surface region of the charge distribution at spherical shape is suggested by the microscopic model. Furthermore, we propose that the isotopes $^{78}\mathrm{Sr}$ and $^{80}\mathrm{Sr}$ may show an unusual shape-sharing structure, with different mean deformations in the ground and ${2}_{1}^{+}$ excited states.

Hyperfine structure and isotope shift of the neutron-rich barium isotopes139?146Ba and148Ba

The hyperfme structure and isotope shift in the 6s 2 S 1/2−6p 2P3/2 line of Ba II (455.4 nm) have been measured by collinear fast-beam laser spectroscopy for the neutron-rich isotopes139–146Ba and148Ba. Nuclear moments and mean square charge radii of these isotopes have been recalculated. The isotope shift of the isotope148Ba (T1/2=0.64 s) could be studied for the first time, yieldingδ〈r2〉138,148=1.245(3) fm2.

Mean square charge radii of radium isotopes and octupole deformation in the 220–228Ra region

The first investigation of isotope shifts in both the atomic and ionic resonance lines of radium has been carried out using the technique of on-line collinear fast-beam laser spectroscopy at the ISOLDE facility at CERN. The measurements cover 19 isotopes in the mass range 208⩽A⩽232 with half-lives between 23 ms and 1600 y. The differences in the nuclear mean square charge radii δ〈r2〉 have been evaluated and - together with earlier published spins and moments from the hyperfine structure - related to nuclear deformation. In particular the inversion of the odd-even staggering effect for the isotopes 221Ra, 223Ra and 225Ra can be interpreted by the presence of octupole instability and adds weight to the concept of near-stable octupole deformation in the odd-A isotopes which already explained their spins and magnetic moments.

Quadrupole moments of radium isotopes from the 7p 2 P 3/2 hyperfine structure in Ra II

The hyperfine structure and isotope shift of221–226Ra and212,214Ra have been measured in the ionic (Ra II) transition 7s 2 S 1/2–7p 2 P 3/2 (λ=381.4 nm). The method of on-line collinear fast-beam laser spectroscopy has been applied using frequency-doubling of cw dye laser radiation in an external ring cavity. The magnetic hyperfine fields are compared with semi-empirical and ab initio calculations. The analysis of the quadrupole splitting by the same method yields the following, improved values of spectroscopic quadrupole moments:Q s (221Ra)=1.978(7)b,Q s (223Ra)=1.254(3)b and the reanalyzed valuesQ s (209Ra)=0.40(2)b,Q s (211Ra)=0.48(2)b,Q s (227Ra)=1.58(3)b,Q s (229Ra)=3.09(4)b with an additional scaling uncertainty of ±5%. Furthermore, theJ-dependence of the isotope shift is analyzed in both Ra II transitions connecting the 7s 2 S 1/2 ground state with the first excited doublet 7p 2 P 1/2 and 7p 2 P 3/2.

Nuclear structure of light thallium isotopes as deduced from laser spectroscopy on a fast atom beam.

The neutron-deficient isotopes /sup 189-194/Tl have been studied using collinear fast atom beam laser spectroscopy with mass-separated beams of 7 x 10/sup 4/ to 4 x 10/sup 5/ atoms per second. By laser excitation of the 535 nm atomic transitions of atoms in the beam, the 6s/sup 2/7s /sup 2/S/sub 1/2/ and 6s/sup 2/6p /sup 2/P/sub 3/2/ hyperfine structures were measured, as were the isotope shifts of the 535 nm transitions. From these, the magnetic dipole moments, spectroscopic quadrupole moments, and isotopic changes in mean-square charge radii were deduced. A large isomer shift in /sup 193/Tl was observed, implying a larger deformation in the (9/2/sup -/ isomer than in the (1/2/sup +/ ground state. The /sup 189,191,193/Tl/sup m/ isotopes have deformations that increase as the mass decreases. A deformed shell model calculation indicates that this increase in deformation can account for the drop in energy of the (9/2/sup -/ bandhead in these isotopes. An increase in neutron pairing correlations, having opposite and compensating effects on the rotational moment of inertia, maintains the spacing of the levels in the (9/2/sup -/ strong-coupled band. Results for /sup 194/Tl/sup m/ differ from previously published values, but are consistent with the /sup 190,192/Tl/sup m/more » data.« less

On the hyperfine structure and isotope shift of radium

The hyperfine structure and isotope shift of the heaviest known alkaline earth element radium (Z=88) have been studied in both the atomic Ra I and ionic Ra II spectra. The measurements, carried out by on-line collinear fast-beam laser spectroscopy, yield the hyperfine constantsA andB of the 7s and 7p1/2 states in Ra II, of all states of the excited 7s 7p configuration and the 7s 7d3D3 state in Ra I. The data allow a consistent evaluation of the nuclear moments for eight odd-A radium isotopes. In particular, a complete analysis of the hyperfine structure of thesp configuration in the two-electron system provides a stringent test of the validity of the semi-empirical modified Breit-Wills theory. It is shown that the effective operator formalism is equivalent, if relativistic correction functions are used to reduce the number of parameters. The semi-empirical hyperfine fields are evaluated and found to agree generally with those from ab-initio calculations. The isotope shifts in thes−p,s2−sp,sp−sd transitions are analysed semi-empirically and compared with ab-initio calculations. The consistency of the different analyses proves their validity and classifies the spectrum of Ra I as a model case for a simple and clean two-electron spectrum.

Optical spectroscopy using mass-separated beams: Nuclear properties of unstable indium and tin isotopes

Collinear fast-beam laser-spectroscopy has been used to measure the hyperfine structure and isotope shift of several indium and tin isotopes. The related experimental techniques are described, including the preparation of mass-separated beams of neutron-deficient indium and tin isotopes at the GSI on-line mass separator following fusion-evaporation reactions. The deviation of the observed dependence of the charge radii upon the neutron number from the expected behaviour is briefly discussed.