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A study of high energy (43--68 MeV/nucleon) one-neutron removal reactions on a range of neutron-rich psd-shell nuclei (Z = 5--9, A = 12--25) has been undertaken. The inclusive longitudinal and transverse momentum distributions for the core fragments, together with the cross sections have been measured for breakup on a carbon target. Momentum distributions for reactions on tantalum were also measured for a subset of nuclei. An extended version of the Glauber model incorporating second order noneikonal corrections to the JLM parametrisation of the optical potential has been used to describe the nuclear breakup, whilst the Coulomb dissociation is treated within first order perturbation theory. The projectile structure has been taken into account via shell model calculations employing the psd-interaction of Warburton and Brown. Both the longitudinal and transverse momentum distributions, together with the integrated cross sections were well reproduced by these calculations and spin-parity assignments are thus proposed for $^{15}$B, $^{17}$C, $^{19-21}$N, $^{21,23}$O, $^{23-25}$F. In addition to the large spectroscopic amplitudes for the $\nu2$s$_{1/2}$ intruder configuration in the N=9 isotones,$^{14}$B and $^{15}$C, significant $\nu2$s$_{1/2}^2$ admixtures appear to occur in the ground state of the neighbouring N=10 nuclei $^{15}$B and $^{16}$C. Similarly, crossing the N=14 subshell, the occupation of the $\nu2$s$_{1/2}$ orbital is observed for $^{23}$O, $^{24,25}$F. Analysis of the longitudinal and transverse momentum distributions reveals that both carry spectroscopic information, often of a complementary nature. The general utility of high energy nucleon removal reactions as a spectroscopic tool is also examined.Comment: 50 pages, 19 figures, submitted to Phys. Rev.

The unbound nucleus ^{26}O has been investigated using invariant-mass spectroscopy following one-proton removal reaction from a ^{27}F beam at 201  MeV/nucleon. The decay products, ^{24}O and two neutrons, were detected in coincidence using the newly commissioned SAMURAI spectrometer at the RIKEN Radioactive Isotope Beam Factory. The ^{26}O ground-state resonance was found to lie only 18±3(stat)±4(syst)  keV above threshold. In addition, a higher lying level, which is most likely the first 2^{+} state, was observed for the first time at 1.28_{-0.08}^{+0.11}  MeV above threshold. Comparison with theoretical predictions suggests that three-nucleon forces, pf-shell intruder configurations, and the continuum are key elements to understanding the structure of the most neutron-rich oxygen isotopes beyond the drip line.

A new approach to the production and detection of bound neutron clusters is presented. The technique is based on the breakup of beams of very neutron-rich nuclei and the subsequent detection of the recoiling proton in a liquid scintillator. The method has been tested in the breakup of 11 Li, 14 Be and 15 B beams by a C target. Some 6 events were observed that exhibit the characteristics of a multineutron cluster liberated in the breakup of 14 Be, most probably in the channel 10 Be+ 4 n. The various backgrounds that may mimic such a signal are discussed in detail.

The breakup of 12 Be into 6 He 1 6 He and 4 He 1 8 He has been studied using a 378 MeV 12 Be beam inelastically excited by 12 C and ͑CH 2 ͒ n targets. The measurements indicate that breakup occurs from rotational states in the 10 to 25 MeV excitation energy interval, with spins in the range of 4h to 8h. The inferred moment of inertia is consistent with the cluster decay of an exotic molecular structure in 12 Be, which may be associated with an a-4n-a cluster configuration. [S0031-9007(99)08451-3]

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A systematic study of high energy, one-neutron removal reactions on 23 neutronrich, psd-shell nuclei (Z = 5−9, A = 12−25) has been carried out. The longitudinal momentum distributions of the core fragments and corresponding single-neutron removal cross sections are reported for reactions on a carbon target. Extended Glauber model calculations, weighted by the spectroscopic factors obtained from shell model calculations, are compared to the experimental results. Conclusions are drawn regarding the use of such reactions as a spectroscopic tool and spin-parity assignments are proposed for 15 B, 17 C, 19−21 N, 21,23 O, 23−25 F. The nature of the weakly bound systems 14 B and 15,17 C is discussed. 25.60.Gc, 27.20.+n, 27.30.+t KEYWORDS: one-neutron removal, momentum distributions, σ −1n , Glauber model. PACS Preprint submitted to Elsevier Preprint 15 November 2017Fragment momentum distributions have long been recognised as signatures of the large spatial extent of the valence nucleons in halo nuclei [1]. Recently measurements of one-nucleon removal reactions on light targets have been proposed as a spectroscopic tool for high-energy radioactive beams [2,3]. This approach has arisen from the development of reaction calculations in which the strong absorption limit [4] and core excited states are accounted for [3]. More specifically, the integrated cross sections are related to spectroscopic factors using an extended version [3,5] of the spectator core model [6], whilst the momentum distributions are derived in the opaque limit of the Serber model [7,8]. To date, this approach has been applied to a few near dripline and halo nuclei [2,[9][10][11].In this Letter the results of an investigation of high-energy one-neutron removal reactions over a broad range of light, neutron-rich psd-shell nuclei are reported. The goals of the work were twofold. Firstly, to explore the evolution in structure, and the manner in which it is manifested in the core fragment observables, from near stability to dripline and halo systems. Secondly, for many of the near stable nuclei the ground state structure is well established and, consequently, it has been possible to test the validity of one-neutron removal reactions as a spectroscopic tool.In the following, measurements of the core fragment longitudinal momentum distributions and integrated cross sections resulting from reactions on a C target are presented. Comparison is made for both observables to the results of extended Glauber type calculations incorporating second order noneikonal corrections to the JLM parameterisation of the optical potential [12]. In the case of those systems with unknown, or poorly defined ground state structures, probable spin-parity assignments have been made.The secondary beams were produced via the fragmentation on a 490 mg/cm 2 thick C target of an intense (∼1µAe) 70 MeV/nucleon 40 Ar 17+ beam provided by the GANIL coupled cyclotron facility. The reaction products were collected and selected according to magnetic rigidity using the SISSI device coupl...

The low-lying level structure of the unbound neutron-rich nucleus 13 Be has been investigated via breakup on a carbon target of secondary beams of 14 B was found to populate a broad lowlying structure some 0.7 MeV above the neutron-decay threshold in addition to a less prominent feature at around 2.4 MeV. Based on the selectivity of the reaction and a comparison with (0-3) ω shell-model calculations, the low-lying structure is concluded to arise from closely spaced J π =1/2 + and 5/2 + resonances (Er=0.40±0.03 and 0.85−0.11 MeV), whilst the broad higher-lying feature is a second 5/2 + level (Er=2.35±0.14 MeV). Taken in conjunction with earlier studies, it would appear that the lowest 1/2 + and 1/2 − levels lie relatively close together below 1 MeV.