Measurement ofE2transition strengths inMg32,34

Abstract

The degree of collectivity in the neutron-rich nuclei 32 Mg and 34 Mg has been determined via intermediateenergy Coulomb excitation in inverse kinematics. Measured energies of the first excited 2 + states and reduced electric quadrupole transition probabilities B(E2; 0 + g.s. → 2 + 1 ) are presented for 32 Mg and 34 Mg. The results agree with previous measurements and confirm the placement of both nuclei within the "island of inversion."

In-beamγ-ray spectroscopy ofMg35and

“…To put the predicted deformation into perspective, for the N = 22 isotone 34 Mg, the MCSM calculates B(E2; 0 + → 2 + 1 ) = 552 e 2 fm 4 (in agreement with experiment [7,9]) and Q(2 The level scheme predicted by the conventional shell model calculations based on the SDPF-U effective interaction, which does not allow for neutron intruder configurations, has the levels in the same order but predicts the 5/2 + first excited state to be within 123 keV of the 3/2 + ground state (see Fig. 5).…”

“…The cross sections for the production of these nuclei from 38 Si were measured to be σ( 36 Mg) = 0.10(1) mb [13], σ( 35 Mg) > ∼ 0.05 mb and σ( 33 Na) > ∼ 0.03 mb. The secondary 9 Be target was surrounded by SeGA, an array of 32-fold segmented high-purity germanium detectors [29]. The high degree of segmentation was used to event-by-event Doppler reconstruct the γ rays emitted by the reaction residues in flight.…”

“…The 38 Si secondary beam was produced by fragmentation of 140 MeV/nucleon 48 Ca primary beam delivered by the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory onto a 752 mg/cm 2 primary 9 Be fragmentation target. The isotope of interest was selected in the A1900 fragment separator [25], using a 750 mg/cm 2 Al wedge degrader for purification.…”

“…In this region, driven largely by the spin-isospin parts of the nuclear force [3], neutron np-nh "intruder" configurations of ν(sd) −n (f p) +n character (labeled nhω) gain "correlation energy" [4] with respect to the normal-order configurations and dominate the wave functions of low-lying states including the ground states -signaling the breakdown of N = 20 as a magic number in these nuclei. The resulting onset of collectivity was quantified with inelastic scattering experiments [5][6][7][8][9][10] and inferred from measurements of the 2 + 1 excitation energies [11][12][13][14] on even-even nuclei out to 32 Ne and 36 Mg at Z = 10 and Z = 12, respectively. These collective properties of even-even nuclei are rather well described by state-of-the-art Monte Carlo Shell-Model (MCSM) calculations (SDPF-M effective interaction) that allow for unrestricted mixing of neutron particle-hole configurations across the N = 20 shell gap.…”

Production cross sections from82Se fragmentation as indications of shell effects in neutron-rich isotopes close to the drip-line

“…[11][12][13][14][15]. This region around 31 Na, where the neutron fp shell contributes significantly to the ground-state structure, is now known as the "Island of Inversion".…”