Neutron halo isomers in stable nuclei and their possible application for the production of low energy, pulsed, polarized neutron beams of high intensity and high brilliance |
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Authors: | D Habs M Gross P G Thirolf and P B?ni |
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Institution: | (1) Japan Proton Accelerator Research Complex Center, Japan Atomic Energy Agency, Japan;(2) Spallation Neutron Source, Oak Ridge National Laboratory, USA |
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Abstract: | We propose to search for neutron halo isomers populated via γ-capture in stable nuclei with mass numbers of about A=140–180 or A=40–60, where the 4s
1/2 or 3s
1/2 neutron shell model state reaches zero binding energy. These halo nuclei can be produced for the first time with new γ-beams of high intensity and small band width (≤0.1%) achievable via Compton back-scattering off brilliant electron beams,
thus offering a promising perspective to selectively populate these isomers with small separation energies of 1 eV to a few keV.
Similar to single-neutron halo states for very light, extremely neutron-rich, radioactive nuclei (Hansen et al. in Annu. Rev.
Nucl. Part. Sci. 45:591–634, 1995; Tanihata in J. Phys. G., Nucl. Part. Phys. 22:158–198, 1996; Aumann et al. in Phys. Rev. Lett. 84:35, 2000), the low neutron separation energy and short-range nuclear force allow the neutron to tunnel far out into free space much
beyond the nuclear core radius. This results in prolonged half-lives of the isomers for the γ-decay back to the ground state in the 100 ps-μs range. Similar to the treatment of photodisintegration of the deuteron, the
neutron release from the neutron halo isomer via a second, low-energy, intense photon beam has a known much larger cross section
with a typical energy threshold behavior. In the second step, the neutrons can be released as a low-energy, pulsed, polarized
neutron beam of high intensity and high brilliance, possibly being much superior to presently existing beams from reactors
or spallation neutron sources. |
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