62
5 Halo Nuclei: Properties and Experimental Techniques
Fig. 5.4 Typical momentum distribution of fragments from breakup of a halo nucleus
longitudinal (parallel) to the beam direction. The narrow momentum distribution
of the fragments (the core or the valence neutrons) is a direct manifestation of the
Heisenberg uncertainty principle owing to the rather extended spatial structure of the
halo. Figure 5.4 represents typical two-component momentum distribution of a halo
nucleus from fragmentation experiment. For experimental data of such momentum
distribution, we refer to [44].
The condition #2 mentioned above is also easily understandable as large
centrifugal barrier would hinder the formation of nuclear halo. The valence nucleon
is preferably in an s state with respect to the central core. The significant role of the s
wave for neutron halo nucleus like
11 Li is discussed and emphasized in the three-body
theoretical analysis presented in Chap. 6. In case of proton-halo nuclei, the Coulomb
barrier hinders the spatial extension of the halo. Consequently, the proton halos are
much less pronounced (or spectacular) than the neutron halos. The well-accepted
1-proton halo nucleus is
8 B. Proton removal measurements from
8 B have revealed
narrow momentum distribution [45]. The width is narrow in comparison with stable
nuclei but wider than neutron halo nuclei. The quadrupole moment of
8 B is found
to be large suggesting a proton halo [46].
17 Ne with 2-proton separation energy of
~0.94 MeV and a relatively narrow 2-proton removal momentum distribution, has
been accepted as the lightest 2-proton halo nucleus [47]. The first excited state of
17 F is also a possible candidate for proton halo state.
Probably, the most fascinating geometrical property of a typical 2-neutron halo
nucleus, like
11 Li, is its Borromean nature. It is by now well established that
11 Li has
a compact core of
9 Li and two valence neutrons forming the halo. However, neither
the di-neutron nor
10 Li is a stable system. In other word, the three-body system of
11 Li
(core-n-n) is loosely bound but none of the binary systems (n-core or n-n) is bound.
This is akin to that of the topological problem of three rings bound together but falling
5 Halo Nuclei: Properties and Experimental Techniques
Fig. 5.4 Typical momentum distribution of fragments from breakup of a halo nucleus
longitudinal (parallel) to the beam direction. The narrow momentum distribution
of the fragments (the core or the valence neutrons) is a direct manifestation of the
Heisenberg uncertainty principle owing to the rather extended spatial structure of the
halo. Figure 5.4 represents typical two-component momentum distribution of a halo
nucleus from fragmentation experiment. For experimental data of such momentum
distribution, we refer to [44].
The condition #2 mentioned above is also easily understandable as large
centrifugal barrier would hinder the formation of nuclear halo. The valence nucleon
is preferably in an s state with respect to the central core. The significant role of the s
wave for neutron halo nucleus like
11 Li is discussed and emphasized in the three-body
theoretical analysis presented in Chap. 6. In case of proton-halo nuclei, the Coulomb
barrier hinders the spatial extension of the halo. Consequently, the proton halos are
much less pronounced (or spectacular) than the neutron halos. The well-accepted
1-proton halo nucleus is
8 B. Proton removal measurements from
8 B have revealed
narrow momentum distribution [45]. The width is narrow in comparison with stable
nuclei but wider than neutron halo nuclei. The quadrupole moment of
8 B is found
to be large suggesting a proton halo [46].
17 Ne with 2-proton separation energy of
~0.94 MeV and a relatively narrow 2-proton removal momentum distribution, has
been accepted as the lightest 2-proton halo nucleus [47]. The first excited state of
17 F is also a possible candidate for proton halo state.
Probably, the most fascinating geometrical property of a typical 2-neutron halo
nucleus, like
11 Li, is its Borromean nature. It is by now well established that
11 Li has
a compact core of
9 Li and two valence neutrons forming the halo. However, neither
the di-neutron nor
10 Li is a stable system. In other word, the three-body system of
11 Li
(core-n-n) is loosely bound but none of the binary systems (n-core or n-n) is bound.
This is akin to that of the topological problem of three rings bound together but falling