The two-neutron halo nucleus ${}^{14}\mathrm{Be}$ has been investigated in a kinematically complete measurement of the fragments ( ${}^{12}\mathrm{Be}$ and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross sections, neutron angular distributions, and invariant mass spectra were measured, and the contributions from electromagnetic dissociation (EMD) were deduced. Comparison with three-body model calculations suggests that the halo wave function contains a large $\nu ({2s}_{1/2}{)}^2$ admixture. The EMD invariant mass spectrum exhibited enhanced strength near threshold consistent with a nonresonant soft-dipole excitation.

• Received 6 June 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.600