No abstract

Bunched-beam collinear laser spectroscopy was performed on neutron-deficient 52,53 Fe prepared through in-flight separation followed by a gas stopping. This novel scheme is a major step to reach nuclides far from the stability line in laser spectroscopy. Differential mean-square charge radii δ r 2 of 52,53 Fe were determined relative to stable 56 Fe as δ r 2 56,52 = −0.034(13) fm 2 and δ r 2 56,53 = −0.218(13) fm 2 , respectively, from the isotope shift of atomic hyperfine structures. The multiconfiguration Dirac-Fock method was used to calculate atomic factors to deduce δ r 2 . The values of δ r 2 exhibit a minimum at the N = 28 neutron shell closure. Nuclear density functional theory with Fayans and Skyrme energy density functionals was used to interpret the data. The trend of δ r 2 along the Fe isotopic chain results from an interplay between single-particle shell structure, pairing, and polarization effects, and provides important data for understanding the intricate trend in the δ r 2 of closed-shell Ca isotopes. Introduction -Since the first estimate of a nuclear charge radius in 1909 [1,2], the size of a nucleus has been a central theme in nuclear structure [3][4][5][6][7]. Significant data on charge radii have been obtained at Isotope Separator On Line (ISOL) facilities, where isotopes of selective elements have been investigated. The ISOL production method, however, suffers from a serious limitation due to long release times from thick targets. This can lead to large decay losses for nuclides that have long diffusion/effusion times, and with short half-lives at the limits of the nuclear chart. In-flight production and separation [8] used in the present study can provide highenergy fast beams and enables studies on nuclides far from the stability line and elements that are difficult at ISOL facilities. Conversion of the fast beams into lowenergy beams in a gas [9] was already exploited, and was used for laser spectroscopy for the first time in the present study on transition-metal Fe known to be notoriously difficult to produce at ISOL facilities. This is a major step forward for laser spectroscopy experiments that complements such capabilities already well established at ISOL facilities.

No abstract

A technique based on selective nonresonant laser photodetachment of unwanted negative ion species has been developed for efficient suppression of isobaric contaminants in negative ion beams. A radio-frequency quadrupole ion guide is employed to cool the negative ion beam and dramatically increase the interaction time of the ions with the laser, substantially increasing the efficiency of the photodetachment process. In a proof-of-principle experiment, we achieved 95% suppression of Co−59 ions by photodetachment while under identical conditions 10% of Ni−58 ions were neutralized.

Beta decay of 86Ga was studied by means of β-neutron-γ spectroscopy. An isotopically pure ^{86}Ga beam was produced at the Holifield Radioactive Ion Beam Facility using a resonance ionization laser ion source and high-resolution electromagnetic separation. The decay of 86Ga revealed a half-life of 43(-15)(+21) ms and large β-delayed one-neutron and two-neutron branching ratios of P1n=60(10)% and P2n=20(10)%. The βγ decay of 86Ga populated a 527 keV transition that is interpreted as the deexcitation of the first 2+ state in the N=54 isotone 86Ge and suggests a quick onset of deformation in Ge isotopes beyond N=50.