Combined high-resolution laser spectroscopy and nuclear decay spectroscopy for the study of the low-lying states inFr206,At202, and

K. M. Lynch

¹

,

T. E. Cocolios

²

,

J. Billowes

³

et al.

Abstract

High-resolution laser spectroscopy was performed on 206 Fr with the collinear resonance ionization spectroscopy (CRIS) experiment at CERN-ISOLDE. The hyperfine structure and isotope shift of the ground, first isomeric and second isomeric states were measured. The hyperfine components were unambiguously assigned to each nuclear state by means of laser-assisted nuclear decay spectroscopy. The branching ratios in the α decay of 206 Fr and 202 At were also measured for the first time with isomerically purified beams. The extracted hindrance factors allow determination of the spin of the ground, first isomeric, and second isomeric states in 202 At and 198 Bi.

Quadrupole moment of Fr203

“…See text for details. This scaling factor agrees perfectly with the experimentally determined ratio B(7p 2 P 3/2 )/B(8p 2 P 3/2 ) = 3.08(6) [11][12][13]34]. The shaded area on the 87 Fr data represents the error on the quadrupole-moment ratios due to the error of the 213 Fr reference quadrupole moment.…”

“…This suggested an onset of deformation in the 87 Fr chain closer to stability than the departures found in the 83 Bi and 84 Po isotope chains, where they occur at N = 110 and N = 114, respectively [20][21][22]. High-resolution laser spectroscopy studies of 87 Fr isotopes have been performed down to 204 Fr [11,12,19], but no firm conclusions on the possible onset of static deformation in the ground states have been reported.…”

“…High-precision quadrupole moments have been measured in the 87 Fr isotopes [11][12][13][14], which have been the subject of recent low-and high-resolution laser spectroscopic experiments [15][16][17][18][19]. Earlier relative charge-radii measurements on neutron-deficient 87 Fr isotopes down to N = 120 showed no departure from the lead isotonic radii, despite the presence of five valence protons in the π 1h 9/2 orbital [13].…”

Collinear laser spectroscopy at ISOLDE: new methods and highlights

“…The rapid change in sign of the ground state quadrupole moments in the odd-A isotopes 219 225 -Fr is consistent with the change in bands from K 1 2 = -in 219,221 Fr to K 3 2 = -in 223,225 Fr, and the associated change in coupling strength to the deformation axis. The combination of high-resolution CRIS and α-decay spectroscopy was able to unambiguously assign all hyperfine structure components for the ground and two isomeric states in 206 Fr [108]. The branching ratios of the isomeric states could be studied in complete isolation from one another for the first time.…”

Achieving sensitive, high-resolution laser spectroscopy at CRIS

“…The ions produced from resonant ionization are detected with a positive-ion multichannel plate (MCPi) held at −2.4 kV, or impinged on a copper dynode and the emitted secondary electrons detected with MCPe, biased at +2.4 kV. Alternatively, the ions can be deflected to the Decay Spectroscopy Station (DSS) for alpha-tagging of hyperfine components and laser-assisted nuclear decay spectroscopy, utilizing the silicon PIPS detectors [6,7]. …”