Experiments

Study of the Borromean dripline nucleus ¹⁷Ne (S318)

Abstract

This proposal aims at a study of 17 Ne at the ALADIN-LAND/R3 B setup in Cave C. 17 Ne is a Borromean dripline nucleus (the binary subsystems p − p and 15 O−p are unbound) and the only realistic candidate to show a two-proton halo in its ground state.

Proposal

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Here we propose a continuation of our programme concentrating on one single nucleus, 17Ne. This proton dripline nucleus has a halflife of T1/2 = 109.2 ms, and can be obtained as a radioactive beam from the SIS using a primary 20 Ne beam with an energy of 500 MeV/u. The primary beam hits a Be production target placed at the entrance of the FRS and the separated secondary 17 Ne beam is then brought to the reaction target in the LAND/R3B setup in Cave C.

Our experiments will be organized as follows:

1. Nuclear break up will be studied with targets CH2 and carbon.
2. Coulomb breakup will be studied using a lead target.

Present knowledge about ¹⁷Ne

17Ne is the lightest bound isotope of neon. Its two proton separation energy is S2p = 950 keV and its binary subsystems, p − p and 16 F, are unbound. This Borromean character of 17 Ne combined with its low two-proton separation energy makes it an obvious candidate to be a two-proton halo nucleus [1, 2].

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The continuum states in 17Ne are also of interest for nuclear astrophysics. The rp reaction flow for nucleosynthesis in explosive hydrogen burning in stars is influenced by two-proton reactions on long-lived waiting point nuclei as discussed in Ref. [23]. The rate estimates in this paper were obtained in a model where the reactions were characterized by two successive proton captures; the first capture leads to an unbound isotope and the system is then stablized by a second proton capture. One such reaction discussed in [23] is 15 O(2p,γ)17 Ne. Recent calculations [24, 25] have, however, demonstrated that the continuum states (15 O +2p) plays an important role for the calculated rate. It is found [24, 25] that the rate can be enhanced by 10 orders of magnitude by taking an exact account of the three-body continuum in for example 17Ne.