An experiment was performed at the Australian National University to study the 9 Be( 6 Li, 6 Li) 9 Be * → α + α + n reaction. This experiment was designed to study the breakup of 9 Be, in an attempt to quantify the contribution played by the 5 He + α and 8 Be 2 + + n channels for the low lying excited states. This information is required in order to resolve uncertainties in the α + α + n → 9 Be reaction rate in high-energy and neutron-rich astrophysical environments such as supernovae. Angular correlation measurements have been used to deduce that the 2.429 MeV state breaks up almost exclusively via the 8 Be 2 + channel. This method of identifying the break-up channel resolves the problem of distinguishing between the 8 Be 2 + and 5 He g.s. channels which are kinetically identical at this excitation energy.

The transfer of neutrons onto 24 Ne has been measured using a reaccelerated radioactive beam of 24 Ne to study the ðd; pÞ reaction in inverse kinematics. The unusual raising of the first 3=2 þ level in 25 Ne and its significance in terms of the migration of the neutron magic number from N ¼ 20 to N ¼ 16 is put on a firm footing by confirmation of this state's identity. The raised 3=2 þ level is observed simultaneously with the intruder negative parity 7=2 À and 3=2 À levels, providing evidence for the reduction in the N ¼ 20 gap. The coincident gamma-ray decays allowed the assignment of spins as well as the transferred orbital angular momentum. The excitation energy of the 3=2 þ state shows that the established USD shell model breaks down well within the sd model space and requires a revised treatment of the proton-neutron monopole interaction. DOI: 10.1103/PhysRevLett.104.192501 PACS numbers: 21.10.Hw, 21.10.Jx, 23.20.Lv, 25.60.Je The monopole part of the nucleon-nucleon interaction is now recognized as having a major effect on nuclear shell structure far from stability [1,2]. The interaction between valence protons and neutrons is sufficient to alter the energies of single-particle levels so that different magic numbers (or shell gaps) appear, and this can substantially affect the collective [3] and magnetic [4] properties and basic quantities such as the lifetime [5]. Nucleon transfer reactions induced by light ions are an established experimental tool for studying single-particle structure [6]. Here we employ the ðd; pÞ reaction in inverse kinematics to explore the disappearance of the N ¼ 20 magic number (and its replacement by N ¼ 16) in the neutron-rich neon isotones. As will be shown, the measurement of the differential cross sections of the light ejectiles plus the coincident gamma decays of the residual nucleus brings a new power to this type of study.Recent work using other techniques has provided evidence for the emergence of N ¼ 16 as a magic number in this region, but has not identified the single-particle structure in an unambiguous manner through measurements of the spectroscopic factors and spins. In a study of the decay of 25 F [7] the increased energy of the 0d 3=2 neutron orbital was inferred. This made use of a preliminary analysis of the present work [8] and concluded that the energy shift was consistent with the monopole effect [7]. In a study of 27 Ne using the ðd; pÞ reaction but without detecting the protons [9], a reduced gap between the 0d 3=2 and higher negative parity orbitals was deduced. This agreed with nucleon removal studies [10]. Finally, in recent studies of 23 O by transfer [11] and 25 O by proton removal [12] the 0d 3=2 state was found to have an increased excitation energy, but the required modifications to the shell-model interaction were not mutually consistent [11,12]. While an extensive review including the emergence of the N ¼ 16 magic number has recently been published [2], further quantitative data are needed in order to understand this monopole effect properly....

An experiment was performed to study the 9 Be( 6 Li, 6 Li) 9 Be * → α + α + n reaction. This experiment was designed to study the breakup of 9 Be in an attempt to quantify the breakup yield for each of the decay channels (n + 8 Be g.s , n + 8 Be 2 + , and α + 5 He g.s ) from the low-lying states. The results suggest that the population of states in 9 Be from 1.68 to 11.28 MeV can be identified. Branching ratios for each of the breakup channels have been estimated for these states. These results are compared with earlier experiments and with theoretical predictions. They confirm the theoretical claim that the n + 8 Be 2 + and α + 5 He g.s channels increase in importance at higher excitation energies.

A compact, quasi-4π position sensitive silicon array, TIARA, designed to study direct reactions induced by radioactive beams in inverse kinematics is described here. The Transfer and Inelastic All-angle Reaction Array (TIARA) consists of 8 resistive charge division detectors forming an octagonal barrel around the target and a set of double-sided silicon-strip annular detectors positioned at each end of the barrel. The detector was coupled to the γ-ray array EXOGAM and the spectrometer VAMOS at the GANIL Laboratory to demonstrate the potential of such an apparatus with radioactive beams. The reaction, well known in direct kinematics, has been carried out in inverse kinematics for that purpose. The observation of the ground state and excited states at 7.16 and 7.86 MeV is presented here as well as the comparison of the measured proton angular distributions with DWBA calculations. Transferred l-values are in very good agreement with both theoretical calculations and previous experimental results obtained in direct kinematics