Measurement of the Magnetic Moment of the One-Neutron Halo NucleusB11e

Abstract

The magnetic moment of 11 Be (T 1͞2 13.8 s) was measured by detecting nuclear magnetic resonance signals in a beryllium crystal lattice. The experimental technique applied to a 11 Be 1 ion beam from a laser ion source includes in-beam optical polarization, implantation into a metallic single crystal, and observation of rf resonances in the asymmetric angular distribution of the b decay (b-NMR). The nuclear magnetic moment m͑ 11 Be͒ 21.6816͑8͒ m N provides a stringent test for theoretical models describing the structure of the 1͞2 1 neutron halo state.

Isotope shift measurements in the 2s1/2→ 2p3/2transition of Be+and extraction of the nuclear charge radii for7, 10, 11Be

“…For the radioactive isotopes a similar procedure was used. Spectra for 7,10,11 Be are shown in figure 3. Here the voltage axis is converted to a frequency scale.…”

“…10 Be, on the other hand, is well bound and the nucleus is stiff against a variation in the distance of the α clusters. The additional neutron in 11 Be can either occupy a 1p 1/2 orbit (in the excited 1/2 − state at 320 keV) or an orbit in the 2s 1/2 shell for the 1/2 + ground state. The experimental binding energy is only 504 keV and an extended halo is expected.…”

“…This is due to the motion of the 10 Be core with respect to the total center of mass. For an improved description of 11 Be we did not only use the R pp constraint which affects mainly the 10 Be core but also varied a second many-body state in a multiconfiguration calculation for each R pp . By this procedure configurations with a 10 Be core in the 2 + state and the valence neutron occupying a d-orbit are included.…”

“…Since then, many experiments were carried out to understand the structure of these extraordinary systems. The most intensely studied halo nuclei are 6,8 He, 11 Li, 11 Be and 14 Be [8].…”

“…Collinear laser spectroscopy in combination with the β-NMR technique allowed the determination of the spin and the magnetic dipole moment of 11 Li [10] and 11 Be [11] as well as the determination of the electric quadrupole moment of 11 Li [12]. The results could be used to exclude a possible deformation of 11 Li because the spin 3/2 belongs to a spherical state, the magnetic moment lies close to the Schmidt value, and the quadrupole moment is similar to that of 9 Li. Both these values, which were improved recently [13,14], again indicate that the nucleus is nearly spherical.…”