D. H. Forest

Cooling and bunching of ion beams for collinear laser spectroscopy

A greatly increased sensitivity in collinear laser spectroscopy experiments has been achieved by the application of new on-line ion cooling and bunching techniques. Cooling of a low-energy ion beam to low emittance and low velocity spread is shown to increase the peak efficiency while bunching the beam results in highly efficient background suppression.

Nuclear charge radii of neutron deficient titanium isotopes 44Ti and 45Ti

Optical isotope shifts of the unstable 44,45Ti isotopes, as well as those of stable 46−50Ti, have been investigated by collinear laser spectroscopy on fast ion beams using an ion guide isotope separator with a cooler-buncher. Changes in mean square charge radii across the neutron 1f7/2 shell are deduced. The evolution of the even-N Ti nuclear radii shows a generally increasing tendency with decreasing neutron number. This behaviour is significantly different to that of the neighbouring Ca isotopes which exhibit a symmetric parabolic behaviour across the shell. The trend of the Ti nuclear radii is consistent with the predictions of the relativistic mean-field theory. The charge radius of 44Ti is also compared to predictions of a 40Ca + α cluster model.

Collinear laser spectroscopy of radioisotopes of zirconium

Isotope shifts and hyperfine structures have been measured for radioisotopes of ionic zirconium using on-line laser spectroscopy at the IGISOL facility in Jyvaskyla, where the installation of an ion beam cooler/buncher has significantly improved the experimental sensitivity. Measurements have been made on all the neutron-deficient isotopes from 87Zr to 90Zr, including the isomers 87m,89mZr, and the neutron-rich isotopes from 96Zr to 102Zr. The change in mean square charge radii between the isotopes and the nuclear moments of the odd isotopes have been extracted. The data show a sudden increase in the mean square charge radius at mass A = 100, consistent with an onset of nuclear deformation which has been observed in the gamma ray spectroscopy of isotope chains in this region of the nuclear chart.

Nuclear charge radii and electromagnetic moments of radioactive scandium isotopes and isomers

Collinear laser spectroscopy experiments with the Sc+ transition 3d4s 3D2 → 3d4p 3F3 at λ = 363.1 nm were performed on the 42–46Sc isotopic chain using an ion guide isotope separator with a cooler-buncher. Nuclear magnetic dipole and electric quadrupole moments as well as isotope shifts were determined from the hyperfine structure for five ground states and two isomers. Extensive multi-configurational Dirac–Fock calculations were performed in order to evaluate the specific mass-shift, MSMS, and field-shift, F, parameters which allowed evaluation of the charge radii trend of the Sc isotopic sequence. The charge radii obtained show systematics more like the Ti radii, which increase towards the neutron shell closure N = 20, than the symmetric parabolic curve for Ca. The changes in mean-square charge radii of the isomeric states relative to the ground states for 44Sc and 45Sc were also extracted. The charge radii difference between the ground and isomeric states of 45Sc is in agreement with the deformation effect estimated from the B(E2) measurements but is smaller than the deformation extracted from the spectroscopic quadrupole moments.

Nuclear spin determination of 100mY by collinear laser spectroscopy of optically pumped ions

The nuclear spin of the τ1/2 = 0.94 s isomer in 100Y has been determined by collinear laser spectroscopy of optically pumped yttrium fission fragments at the IGISOL facility, JYFL. The isotopes 96, 98, 99, 100Y were produced by the proton-induced fission of natural uranium, and studied on the 4d5s 3D2 (1045 cm−1) → 4d5p 3P1 (32 124 cm−1) transition at 321.67 nm. Enhancement of the population of the metastable 3D2 level was achieved by optically pumping the ground state population via the 5s2 1S0 → 4d5p 1P1 transition at 363.31 nm while the ions were stored in a linear Paul trap. These data, when combined with previous spectroscopic results, give sufficient information for the nuclear spin of 100mY to be determined unambiguously as I = 4. This spin assignment reveals that 100mY has an unexpectedly large dynamic contribution to its quadrupole deformation.

Collinear laser spectroscopy of neutron-rich cerium isotopes near the N = 88 shape transition.

Laser spectroscopy has been used to measure the isotope shifts of 146Ce and 148Ce relative to 144Ce, Z = 58. The new data, in combination with existing optical data on the stable isotopes and radioactive 144Ce isotope, permits a study of charge radii variations for the even-N Ce nuclei from N = 78 to N = 90. This range covers both the N = 82 shell closure and the N = 88 shape transition region. A marked increase in deformation occurs at N = 88 for elements with Z ≥ 60 but not for those with Z ≤ 56. The new data for Ce (Z = 58) show an intermediate behaviour, resulting in a smooth increase in deformation with Z in the N = 88, 90 region.

Nuclear moments, charge radii and spins of the ground and isomeric states in 175Yb and 177Yb

This paper reports static moments and changes in mean-square charge radii of 175, 177, 177mYb measured using collinear laser spectroscopy at the IGISOL facility. The moments are compared to predictions made using the Nilsson model to determine the purity of the multi-quasiparticle T1/2 = 11.4 s, Iπ = 8− state of 176Yb and the ground state of 177Yb. The ground-state spins of 175, 177Yb and the T1/2 = 6.41 s, E = 331.5 keV isomeric state in 177Yb, have been measured from the hyperfine structure to be 7/2, 9/2 and 1/2 respectively.

Laser spectroscopy of radioactive Ti, Zr and Hf isotopes and isomers at the JYFL laser-IGISOL facility

Abstract The recent progress at the laser-ion guide isotope separator on-line facility, JYFL, is presented. At the facility new techniques for studying short-lived radioisotopes by laser spectroscopy have been developed and applied to the study of isotopes in refractory metal elements. In particular, recent results on the spectroscopy of cooled ion beams of radioactive Ti, Zr and Hf isotopes are discussed.

Note on the analysis of optical isotope shifts: an alternative plot

An alternative approach is proposed for the analysis of optical isotope shifts. It is shown that for many elements a plot of the shift for one isotope pair against that for another pair for a series of transitions is linear. In certain circumstances the gradient of this plot gives the ratio of the change in mean square charge radii of the isotope pairs directly. Alternatively the plot is helpful in making judgements as to whether specific mass effects are likely to be negligible, with the field shift dominant, and hence assisting other methods of analysis. The possible range of validity is discussed.

Laser spectroscopy of gallium isotopes beyond N = 50

The installation of an ion–beam cooler–buncher at the ISOLDE, CERN facility has provided increased sensitivity for collinear laser spectroscopy experiments. A migration of single-particle states in gallium and in copper isotopes has been investigated through extensive measurements of ground state and isomeric state hyperfine structures. Lying beyond the N = 50 shell closure, 82Ga is the most exotic nucleus in the region to have been studied by optical methods, and is reported here for the first time.