C. Thibault

β-Decay schemes of very neutron-rich sodium isotopes and their descendants

Abstract The γ-activities from the β-decay of Na isotopes up to 34 Na, formed in high-energy fragmentation and analysed through mass-spectrometry techniques, are observed as well as those from their Mg descendants. The I γ , intensities, the β-delayed one- and two-neutron probabilities and the I β intensities are measured. Decay schemes are proposed. We confirm, from the low location of the first 2 + level of 32 Mg, the occurrence of a nuclear deformation at Z ⋍ 11, N ⋍ 20 .

Hyperfine structure and isotope shift of the D2 line of 118–145Cs and some of their isomers

Abstract High-resolution laser spectroscopy has been performed on 118–145 Cs and 119m, 121m, 122m, 130m, 134m, 135m, 136m, 138m, Cs.The Cs nuclei have been produced either by spallation of La or by fission of U by the 600 MeV proton beam, from the SC at CERN. The hyperfine structures, spins, and isotope shifts have been measured. The charge radii changes deduced from the isotope shifts exhibit shell effects at N = 82, isomeric staggering for N = 64,66,67 and a strong odd-even staggering for all isotopes with N

Hyperfine structures and isotope shifts of 207–213,220–228Fr; Possible evidence of octupolar deformation

Abstract Hyperfine structures and isotope shifts of 207–213,220–228 Fr have been measured by high-resolution laser spectroscopy. Nuclear moments and changes in the mean-square charge radii are deduced. They are compared with analogous data for radium and discussed in terms of the octupole deformation mode.

Mapping of the onset of a new region of deformation: The masses of 31Mg and 32Mg

Abstract Q β values are measured by the shape-fitting method, applied to selected γ-coincident β-energy spectra of 31 Mg and 32 Na. The deduced mass excesses of 31 Mg and 32 Mg are 5.0 ± 0.7 and − 1.9 ± 1.5 MeV , respectively. The corresponding two-neutron binding energies S 2n are in marked excess over the values extrapolated from the S 2n variation with A established for less neutron-rich nuclei. This is taken as an indication for the onset of deformation at N = 19 for Mg isotopes.

Masses of Rb, Cs and Fr isotopes

Abstract The results of the direct mass measurements of the unstable isotopes of Rb, Cs and Fr are rewritten in a form-linear combination of masses-which allows a direct analysis with other experimental data. An up-to-date least-square adjustment which takes into account new reference masses is subsequently performed. A systematic study of isomers is carried out for evaluating isomeric corrections to apply to the measured masses in order to obtain the ground-state masses.

Isotope shifts, spins and hyperfine structures of 118,146Cs and of some francium isotopes

Abstract High-resolution laser spectroscopy using thermal atomic beams has been performed on-line with the ISOLDE facility at CERN. It allowed the measurement of the spins, isotope shifts and hyperfine structures of the D2 line of 118,146Cs, and that of the hyperfine factors of the first P 1 2 level of 133,135,137,139,141,143Cs and 210,212,213,221Fr. Previous data concerning 207–213,220–228Fr have also been reanalysed. All results are discussed in terms of deformations with special attention to the possible occurrence of octupole deformations.

Isotope shifts and hyperfine structure of 38–47K by laser spectroscopy

Abstract Laser optical spectroscopy on a thermal atomic beam has been performed on the 4 2 S sol1 2 −4 2 P 1 2 D 2 line of 38,39,41–47K. Hyperfine structure constants and isotope shifts have been measured. Magnetic moments and changes in the mean square charge radii are deduced.

Delayed neutron emission from the decay of neutron-rich Rb and Cs isotopes

Abstract Using an on-line mass spectrometer the delayed neutron emission probability P n and the half-lives of the new delayed neutron precursors 97 Rb, 98 Rb, 145 Cs and 146 Cs have been measured. The P n values of the known 93–96 Rb were remeasured and an upper limit was found for the β-delayed double-neutron emission probability of 98 Rb. The experimental P n values for 92–98 Rb are discussed within a simple semi-empirical picture.

β-delayed charged particles from 9Li and 11Li

Abstract β-delayed emission of α-particles from 9Li and of both α and 6He particles from 11Li is observed. Singles energy spectra and two-dimensional energy spectra of coincident particles are measured. A time-of-flight versus energy measurement is used to identify the mass of the particle. New β-branches are observed which populate high-energy levels in the daughter nuclei. The branching ratios are measured and the β-delayed neutron emission probabilities P n for 9 Li and P 3n for 11 Li are deduced.

53K, 54K and 53Ca: Three new neutron rich isotopes

Abstract β -delayed neutron yields from 49–54 K were measured with a high-efficiency liquid scintillator neutron detector. Three new nuclides have been identified; half-lives have been determined for 50–54 K and the 53 Ca daughter, delayed neutron emission probabilities have been measured for 49–53 K.